rfc9162.original   rfc9162.txt 
TRANS (Public Notary Transparency) B. Laurie Internet Engineering Task Force (IETF) B. Laurie
Internet-Draft A. Langley Request for Comments: 9162 E. Messeri
Obsoletes: 6962 (if approved) E. Kasper Obsoletes: 6962 Google
Intended status: Experimental E. Messeri Category: Experimental R. Stradling
Expires: 4 March 2022 Google ISSN: 2070-1721 Sectigo
R. Stradling November 2021
Sectigo
31 August 2021
Certificate Transparency Version 2.0 Certificate Transparency Version 2.0
draft-ietf-trans-rfc6962-bis-42
Abstract Abstract
This document describes version 2.0 of the Certificate Transparency This document describes version 2.0 of the Certificate Transparency
(CT) protocol for publicly logging the existence of Transport Layer (CT) protocol for publicly logging the existence of Transport Layer
Security (TLS) server certificates as they are issued or observed, in Security (TLS) server certificates as they are issued or observed, in
a manner that allows anyone to audit certification authority (CA) a manner that allows anyone to audit certification authority (CA)
activity and notice the issuance of suspect certificates as well as activity and notice the issuance of suspect certificates as well as
to audit the certificate logs themselves. The intent is that to audit the certificate logs themselves. The intent is that
eventually clients would refuse to honor certificates that do not eventually clients would refuse to honor certificates that do not
appear in a log, effectively forcing CAs to add all issued appear in a log, effectively forcing CAs to add all issued
certificates to the logs. certificates to the logs.
This document obsoletes RFC 6962. It also specifies a new TLS This document obsoletes RFC 6962. It also specifies a new TLS
extension that is used to send various CT log artifacts. extension that is used to send various CT log artifacts.
Logs are network services that implement the protocol operations for Logs are network services that implement the protocol operations for
submissions and queries that are defined in this document. submissions and queries that are defined in this document.
[RFC Editor: please update 'RFCXXXX' to refer to this document, once
its RFC number is known, through the document. Also, the OID
assigned below must also appear in the appendix as indicated. ]
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for examination, experimental implementation, and
evaluation.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document defines an Experimental Protocol for the Internet
and may be updated, replaced, or obsoleted by other documents at any community. This document is a product of the Internet Engineering
time. It is inappropriate to use Internet-Drafts as reference Task Force (IETF). It represents the consensus of the IETF
material or to cite them other than as "work in progress." community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
This Internet-Draft will expire on 4 March 2022. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9162.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents
license-info) in effect on the date of publication of this document. (https://trustee.ietf.org/license-info) in effect on the date of
Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
and restrictions with respect to this document. Code Components carefully, as they describe your rights and restrictions with respect
extracted from this document must include Simplified BSD License text to this document. Code Components extracted from this document must
as described in Section 4.e of the Trust Legal Provisions and are include Revised BSD License text as described in Section 4.e of the
provided without warranty as described in the Simplified BSD License. Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.1. Requirements Language
1.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 5 1.2. Data Structures
1.3. Major Differences from CT 1.0 . . . . . . . . . . . . . . 6 1.3. Major Differences from CT 1.0
2. Cryptographic Components . . . . . . . . . . . . . . . . . . 7 2. Cryptographic Components
2.1. Merkle Hash Trees . . . . . . . . . . . . . . . . . . . . 7 2.1. Merkle Trees
2.1.1. Definition of the Merkle Tree . . . . . . . . . . . . 7 2.1.1. Definition of the Merkle Tree
2.1.2. Verifying a Tree Head Given Entries . . . . . . . . . 8 2.1.2. Verifying a Tree Head Given Entries
2.1.3. Merkle Inclusion Proofs . . . . . . . . . . . . . . . 9 2.1.3. Merkle Inclusion Proofs
2.1.4. Merkle Consistency Proofs . . . . . . . . . . . . . . 11 2.1.4. Merkle Consistency Proofs
2.1.5. Example . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.5. Example
2.2. Signatures . . . . . . . . . . . . . . . . . . . . . . . 14 2.2. Signatures
3. Submitters . . . . . . . . . . . . . . . . . . . . . . . . . 15 3. Submitters
3.1. Certificates . . . . . . . . . . . . . . . . . . . . . . 15 3.1. Certificates
3.2. Precertificates . . . . . . . . . . . . . . . . . . . . . 15 3.2. Precertificates
3.2.1. Binding Intent to Issue . . . . . . . . . . . . . . . 17 3.2.1. Binding Intent to Issue
4. Log Format and Operation . . . . . . . . . . . . . . . . . . 17 4. Log Format and Operation
4.1. Log Parameters . . . . . . . . . . . . . . . . . . . . . 18 4.1. Log Parameters
4.2. Evaluating Submissions . . . . . . . . . . . . . . . . . 19 4.2. Evaluating Submissions
4.2.1. Minimum Acceptance Criteria . . . . . . . . . . . . . 19 4.2.1. Minimum Acceptance Criteria
4.2.2. Discretionary Acceptance Criteria . . . . . . . . . . 20 4.2.2. Discretionary Acceptance Criteria
4.3. Log Entries . . . . . . . . . . . . . . . . . . . . . . . 20 4.3. Log Entries
4.4. Log ID . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.4. Log ID
4.5. TransItem Structure . . . . . . . . . . . . . . . . . . . 21 4.5. TransItem Structure
4.6. Log Artifact Extensions . . . . . . . . . . . . . . . . . 22 4.6. Log Artifact Extensions
4.7. Merkle Tree Leaves . . . . . . . . . . . . . . . . . . . 23 4.7. Merkle Tree Leaves
4.8. Signed Certificate Timestamp (SCT) . . . . . . . . . . . 24 4.8. Signed Certificate Timestamp (SCT)
4.9. Merkle Tree Head . . . . . . . . . . . . . . . . . . . . 25 4.9. Merkle Tree Head
4.10. Signed Tree Head (STH) . . . . . . . . . . . . . . . . . 26 4.10. Signed Tree Head (STH)
4.11. Merkle Consistency Proofs . . . . . . . . . . . . . . . . 26 4.11. Merkle Consistency Proofs
4.12. Merkle Inclusion Proofs . . . . . . . . . . . . . . . . . 27 4.12. Merkle Inclusion Proofs
4.13. Shutting down a log . . . . . . . . . . . . . . . . . . . 28 4.13. Shutting Down a Log
5. Log Client Messages . . . . . . . . . . . . . . . . . . . . . 28 5. Log Client Messages
5.1. Submit Entry to Log . . . . . . . . . . . . . . . . . . . 30 5.1. Submit Entry to Log
5.2. Retrieve Latest STH . . . . . . . . . . . . . . . . . . . 32 5.2. Retrieve Latest STH
5.3. Retrieve Merkle Consistency Proof between Two STHs . . . 32 5.3. Retrieve Merkle Consistency Proof between Two STHs
5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash . . 33 5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash
5.5. Retrieve Merkle Inclusion Proof, STH and Consistency Proof 5.5. Retrieve Merkle Inclusion Proof, STH, and Consistency Proof
by Leaf Hash . . . . . . . . . . . . . . . . . . . . . . 34 by Leaf Hash
5.6. Retrieve Entries and STH from Log . . . . . . . . . . . . 35 5.6. Retrieve Entries and STH from Log
5.7. Retrieve Accepted Trust Anchors . . . . . . . . . . . . . 37 5.7. Retrieve Accepted Trust Anchors
6. TLS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 38 6. TLS Servers
6.1. TLS Client Authentication . . . . . . . . . . . . . . . . 38 6.1. TLS Client Authentication
6.2. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . . 39 6.2. Multiple SCTs
6.3. TransItemList Structure . . . . . . . . . . . . . . . . . 39 6.3. TransItemList Structure
6.4. Presenting SCTs, inclusions proofs and STHs . . . . . . . 40 6.4. Presenting SCTs, Inclusions Proofs, and STHs
6.5. transparency_info TLS Extension . . . . . . . . . . . . . 40 6.5. transparency_info TLS Extension
7. Certification Authorities . . . . . . . . . . . . . . . . . . 41 7. Certification Authorities
7.1. Transparency Information X.509v3 Extension . . . . . . . 41 7.1. Transparency Information X.509v3 Extension
7.1.1. OCSP Response Extension . . . . . . . . . . . . . . . 41 7.1.1. OCSP Response Extension
7.1.2. Certificate Extension . . . . . . . . . . . . . . . . 41 7.1.2. Certificate Extension
7.2. TLS Feature X.509v3 Extension . . . . . . . . . . . . . . 41 7.2. TLS Feature X.509v3 Extension
8. Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 8. Clients
8.1. TLS Client . . . . . . . . . . . . . . . . . . . . . . . 42 8.1. TLS Client
8.1.1. Receiving SCTs and inclusion proofs . . . . . . . . . 42 8.1.1. Receiving SCTs and Inclusion Proofs
8.1.2. Reconstructing the TBSCertificate . . . . . . . . . . 42 8.1.2. Reconstructing the TBSCertificate
8.1.3. Validating SCTs . . . . . . . . . . . . . . . . . . . 42 8.1.3. Validating SCTs
8.1.4. Fetching inclusion proofs . . . . . . . . . . . . . . 43 8.1.4. Fetching Inclusion Proofs
8.1.5. Validating inclusion proofs . . . . . . . . . . . . . 43 8.1.5. Validating Inclusion Proofs
8.1.6. Evaluating compliance . . . . . . . . . . . . . . . . 44 8.1.6. Evaluating Compliance
8.2. Monitor . . . . . . . . . . . . . . . . . . . . . . . . . 44 8.2. Monitor
8.3. Auditing . . . . . . . . . . . . . . . . . . . . . . . . 45 8.3. Auditing
9. Algorithm Agility . . . . . . . . . . . . . . . . . . . . . . 46 9. Algorithm Agility
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47 10. IANA Considerations
10.1. Additions to existing registries . . . . . . . . . . . . 47 10.1. Additions to Existing Registries
10.1.1. New Entry to the TLS ExtensionType Registry . . . . 47 10.1.1. New Entry to the TLS ExtensionType Registry
10.1.2. URN Sub-namespace for TRANS 10.1.2. URN Sub-namespace for TRANS (urn:ietf:params:trans)
(urn:ietf:params:trans) . . . . . . . . . . . . . . . 47 10.2. New CT-Related Registries
10.2. New CT-Related registries . . . . . . . . . . . . . . . 47 10.2.1. Hash Algorithms
10.2.1. Hash Algorithms . . . . . . . . . . . . . . . . . . 48 10.2.2. Signature Algorithms
10.2.2. Signature Algorithms . . . . . . . . . . . . . . . . 48 10.2.3. VersionedTransTypes
10.2.3. VersionedTransTypes . . . . . . . . . . . . . . . . 49 10.2.4. Log Artifact Extensions
10.2.4. Log Artifact Extension Registry . . . . . . . . . . 50 10.2.5. Log IDs
10.2.5. Log IDs Registry . . . . . . . . . . . . . . . . . . 51 10.2.6. Error Types
10.2.6. Error Types Registry . . . . . . . . . . . . . . . . 52 10.3. OID Assignment
10.3. OID Assignment . . . . . . . . . . . . . . . . . . . . . 54 11. Security Considerations
11. Security Considerations . . . . . . . . . . . . . . . . . . . 54 11.1. Misissued Certificates
11.1. Misissued Certificates . . . . . . . . . . . . . . . . . 55 11.2. Detection of Misissue
11.2. Detection of Misissue . . . . . . . . . . . . . . . . . 55 11.3. Misbehaving Logs
11.3. Misbehaving Logs . . . . . . . . . . . . . . . . . . . . 55 11.4. Multiple SCTs
11.4. Multiple SCTs . . . . . . . . . . . . . . . . . . . . . 56 11.5. Leakage of DNS Information
11.5. Leakage of DNS Information . . . . . . . . . . . . . . . 56 12. References
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 56 12.1. Normative References
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 12.2. Informative References
13.1. Normative References . . . . . . . . . . . . . . . . . . 56 Appendix A. Supporting v1 and v2 Simultaneously (Informative)
13.2. Informative References . . . . . . . . . . . . . . . . . 59 Appendix B. An ASN.1 Module (Informative)
Appendix A. Supporting v1 and v2 simultaneously (Informative) . 60 Acknowledgements
Appendix B. An ASN.1 Module (Informative) . . . . . . . . . . . 60 Authors' Addresses
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 62
1. Introduction 1. Introduction
Certificate Transparency aims to mitigate the problem of misissued Certificate Transparency aims to mitigate the problem of misissued
certificates by providing append-only logs of issued certificates. certificates by providing append-only logs of issued certificates.
The logs do not themselves prevent misissuance, but they ensure that The logs do not themselves prevent misissuance, but they ensure that
interested parties (particularly those named in certificates) can interested parties (particularly those named in certificates) can
detect such misissuance. Note that this is a general mechanism that detect such misissuance. Note that this is a general mechanism that
could be used for transparently logging any form of binary data, could be used for transparently logging any form of binary data,
subject to some kind of inclusion criteria. In this document, we subject to some kind of inclusion criteria. In this document, we
skipping to change at page 5, line 9 skipping to change at line 189
they accept as valid are accompanied by signed timestamps. they accept as valid are accompanied by signed timestamps.
Those who are concerned about misissuance can monitor the logs, Those who are concerned about misissuance can monitor the logs,
asking them regularly for all new entries, and can thus check whether asking them regularly for all new entries, and can thus check whether
domains for which they are responsible have had certificates issued domains for which they are responsible have had certificates issued
that they did not expect. What they do with this information, that they did not expect. What they do with this information,
particularly when they find that a misissuance has happened, is particularly when they find that a misissuance has happened, is
beyond the scope of this document. However, broadly speaking, they beyond the scope of this document. However, broadly speaking, they
can invoke existing business mechanisms for dealing with misissued can invoke existing business mechanisms for dealing with misissued
certificates, such as working with the CA to get the certificate certificates, such as working with the CA to get the certificate
revoked, or with maintainers of trust anchor lists to get the CA revoked or with maintainers of trust anchor lists to get the CA
removed. Of course, anyone who wants can monitor the logs and, if removed. Of course, anyone who wants can monitor the logs and, if
they believe a certificate is incorrectly issued, take action as they they believe a certificate is incorrectly issued, take action as they
see fit. see fit.
Similarly, those who have seen signed timestamps from a particular Similarly, those who have seen signed timestamps from a particular
log can later demand a proof of inclusion from that log. If the log log can later demand a proof of inclusion from that log. If the log
is unable to provide this (or, indeed, if the corresponding is unable to provide this (or, indeed, if the corresponding
certificate is absent from monitors' copies of that log), that is certificate is absent from monitors' copies of that log), that is
evidence of the incorrect operation of the log. The checking evidence of the incorrect operation of the log. The checking
operation is asynchronous to allow clients to proceed without delay, operation is asynchronous to allow clients to proceed without delay,
despite possible issues such as network connectivity and the vagaries despite possible issues, such as network connectivity and the
of firewalls. vagaries of firewalls.
The append-only property of each log is achieved using Merkle Trees, The append-only property of each log is achieved using Merkle Trees,
which can be used to efficiently prove that any particular instance which can be used to efficiently prove that any particular instance
of the log is a superset of any particular previous instance and to of the log is a superset of any particular previous instance and to
efficiently detect various misbehaviors of the log (e.g., issuing a efficiently detect various misbehaviors of the log (e.g., issuing a
signed timestamp for a certificate that is not subsequently logged). signed timestamp for a certificate that is not subsequently logged).
It is necessary to treat each log as a trusted third party, because The log auditing mechanisms described in this document can be
the log auditing mechanisms described in this document can be
circumvented by a misbehaving log that shows different, inconsistent circumvented by a misbehaving log that shows different, inconsistent
views of itself to different clients. While mechanisms are being views of itself to different clients. Therefore, it is necessary to
treat each log as a trusted third party. While mechanisms are being
developed to address these shortcomings and thereby avoid the need to developed to address these shortcomings and thereby avoid the need to
blindly trust logs, such mechanisms are outside the scope of this blindly trust logs, such mechanisms are outside the scope of this
document. document.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Data Structures 1.2. Data Structures
Data structures are defined and encoded according to the conventions Data structures are defined and encoded according to the conventions
laid out in Section 3 of [RFC8446]. laid out in Section 3 of [RFC8446].
This document uses object identifiers (OIDs) to identify Log IDs (see This document uses object identifiers (OIDs) to identify Log IDs (see
Section 4.4), the precertificate CMS "eContentType" (see Section 4.4), the precertificate Cryptographic Message Syntax (CMS)
Section 3.2), and X.509v3 extensions in certificates (see eContentType (see Section 3.2), X.509v3 extensions in certificates
Section 7.1.2) and OCSP responses (see Section 7.1.1). The OIDs are (see Section 7.1.2), and Online Certificate Status Protocol (OCSP)
defined in an arc that was selected due to its short encoding. responses (see Section 7.1.1). The OIDs are defined in an arc that
was selected due to its short encoding.
1.3. Major Differences from CT 1.0 1.3. Major Differences from CT 1.0
This document revises and obsoletes the CT 1.0 [RFC6962] protocol, This document revises and obsoletes the CT 1.0 protocol [RFC6962],
drawing on insights gained from CT 1.0 deployments and on feedback drawing on insights gained from CT 1.0 deployments and on feedback
from the community. The major changes are: from the community. The major changes are:
* Hash and signature algorithm agility: permitted algorithms are now * Hash and signature algorithm agility: Permitted algorithms are now
specified in IANA registries. specified in IANA registries.
* Precertificate format: precertificates are now CMS objects rather * Precertificate format: Precertificates are now CMS objects rather
than X.509 certificates, which avoids violating the certificate than X.509 certificates, which avoids violating the certificate
serial number uniqueness requirement in Section 4.1.2.2 of serial number uniqueness requirement in Section 4.1.2.2 of
[RFC5280]. [RFC5280].
* Removed precertificate signing certificates and the precertificate * Removal of precertificate signing certificates and the
poison extension: the change of precertificate format means that precertificate poison extension: The change of precertificate
these are no longer needed. format means that these are no longer needed.
* Logs IDs: each log is now identified by an OID rather than by the * Logs IDs: Each log is now identified by an OID rather than by the
hash of its public key. OID allocations are managed by an IANA hash of its public key. OID allocations are available from an
registry. IANA registry.
* "TransItem" structure: this new data structure is used to * TransItem structure: This new data structure is used to
encapsulate most types of CT data. A "TransItemList", consisting encapsulate most types of CT data. A TransItemList, consisting of
of one or more "TransItem" structures, can be used anywhere that one or more TransItem structures, can be used anywhere that
"SignedCertificateTimestampList" was used in [RFC6962]. SignedCertificateTimestampList was used in [RFC6962].
* Merkle tree leaves: the "MerkleTreeLeaf" structure has been * Merkle Tree leaves: The MerkleTreeLeaf structure has been replaced
replaced by the "TransItem" structure, which eases extensibility by the TransItem structure, which eases extensibility and
and simplifies the leaf structure by removing one layer of simplifies the leaf structure by removing one layer of
abstraction. abstraction.
* Unified leaf format: the structure for both certificate and * Unified leaf format: The structure for both certificate and
precertificate entries now includes only the TBSCertificate precertificate entries now includes only the TBSCertificate
(whereas certificate entries in [RFC6962] included the entire (whereas certificate entries in [RFC6962] included the entire
certificate). certificate).
* Log Artifact Extensions: these are now typed and managed by an * Log artifact extensions: These are now typed and managed by an
IANA registry, and they can now appear not only in SCTs but also IANA registry, and they can now appear not only in Signed
in STHs. Certificate Timestamps (SCTs) but also in Signed Tree Heads
(STHs).
* API outputs: complete "TransItem" structures are returned, rather * API outputs: Complete TransItem structures are returned rather
than the constituent parts of each structure. than the constituent parts of each structure.
* get-all-by-hash: new client API for obtaining an inclusion proof * get-all-by-hash: This is a new client API for obtaining an
and the corresponding consistency proof at the same time. inclusion proof and the corresponding consistency proof at the
same time.
* submit-entry: new client API, replacing add-chain and add-pre- * submit-entry: This is a new client API, replacing add-chain and
chain. add-pre-chain.
* Presenting SCTs with proofs: TLS servers may present SCTs together * Presenting SCTs with proofs: TLS servers may present SCTs together
with the corresponding inclusion proofs using any of the with the corresponding inclusion proofs, using any of the
mechanisms that [RFC6962] defined for presenting SCTs only. mechanisms that [RFC6962] defined for presenting SCTs only.
(Presenting SCTs only is still supported). (Presenting SCTs only is still supported).
* CT TLS extension: the "signed_certificate_timestamp" TLS extension * CT TLS extension: The signed_certificate_timestamp TLS extension
has been replaced by the "transparency_info" TLS extension. has been replaced by the transparency_info TLS extension.
* Verification algorithms: added detailed algorithms for verifying * Verification algorithms: Detailed algorithms for verifying
inclusion proofs, for verifying consistency between two STHs, and inclusion proofs, for verifying consistency between two STHs, and
for verifying a root hash given a complete list of the relevant for verifying a root hash given a complete list of the relevant
leaf input entries. leaf input entries have been added.
* Extensive clarifications and editorial work. * Extensive clarifications and editorial work.
2. Cryptographic Components 2. Cryptographic Components
2.1. Merkle Hash Trees 2.1. Merkle Trees
A full description of Merkle Hash Tree is beyond the scope of this A full description of the Merkle Tree is beyond the scope of this
document. Briefly, it is a binary tree where each non-leaf node is a document. Briefly, it is a binary tree where each non-leaf node is a
hash of its children. For CT, the number of children is at most two. hash of its children. For CT, the number of children is at most two.
Additional information can be found in the Introduction and Reference Additional information can be found in the Introduction and Reference
section of [RFC8391]. sections of [RFC8391].
2.1.1. Definition of the Merkle Tree 2.1.1. Definition of the Merkle Tree
The log uses a binary Merkle Hash Tree for efficient auditing. The The log uses a binary Merkle Tree for efficient auditing. The hash
hash algorithm used is one of the log's parameters (see Section 4.1). algorithm used is one of the log's parameters (see Section 4.1).
This document establishes a registry of acceptable hash algorithms This document establishes a registry of acceptable hash algorithms
(see Section 10.2.1). Throughout this document, the hash algorithm (see Section 10.2.1). Throughout this document, the hash algorithm
in use is referred to as HASH and the size of its output in bytes as in use is referred to as HASH and the size of its output in bytes is
HASH_SIZE. The input to the Merkle Tree Hash is a list of data referred to as HASH_SIZE. The input to the Merkle Tree Hash is a
entries; these entries will be hashed to form the leaves of the list of data entries; these entries will be hashed to form the leaves
Merkle Hash Tree. The output is a single HASH_SIZE Merkle Tree Hash. of the Merkle Tree. The output is a single HASH_SIZE Merkle Tree
Given an ordered list of n inputs, D_n = {d[0], d[1], ..., d[n-1]}, Hash. Given an ordered list of n inputs, D_n = {d[0], d[1], ...,
the Merkle Tree Hash (MTH) is thus defined as follows: d[n-1]}, the Merkle Tree Hash (MTH) is thus defined as follows:
The hash of an empty list is the hash of an empty string: The hash of an empty list is the hash of an empty string:
MTH({}) = HASH(). MTH({}) = HASH().
The hash of a list with one entry (also known as a leaf hash) is: The hash of a list with one entry (also known as a leaf hash) is:
MTH({d[0]}) = HASH(0x00 || d[0]). MTH({d[0]}) = HASH(0x00 || d[0]).
For n > 1, let k be the largest power of two smaller than n (i.e., k For n > 1, let k be the largest power of two smaller than n (i.e., k
< n <= 2k). The Merkle Tree Hash of an n-element list D_n is then < n <= 2k). The Merkle Tree Hash of an n-element list D_n is then
defined recursively as defined recursively as:
MTH(D_n) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])), MTH(D_n) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])),
where: where:
* || denotes concatenation * || denotes concatenation
* : denotes concatenation of lists * : denotes concatenation of lists
* D[k1:k2] = D'_(k2-k1) denotes the list {d'[0] = d[k1], d'[1] = * D[k1:k2] = D'_(k2-k1) denotes the list {d'[0] = d[k1], d'[1] =
d[k1+1], ..., d'[k2-k1-1] = d[k2-1]} of length (k2 - k1). d[k1+1], ..., d'[k2-k1-1] = d[k2-1]} of length (k2 - k1).
Note that the hash calculations for leaves and nodes differ; this Note that the hash calculations for leaves and nodes differ; this
domain separation is required to give second preimage resistance. domain separation is required to give second preimage resistance.
Note that we do not require the length of the input list to be a Note that we do not require the length of the input list to be a
power of two. The resulting Merkle Tree may thus not be balanced; power of two. The resulting Merkle Tree may thus not be balanced;
however, its shape is uniquely determined by the number of leaves. however, its shape is uniquely determined by the number of leaves.
(Note: This Merkle Tree is essentially the same as the history tree (Note: This Merkle Tree is essentially the same as the history tree
[CrosbyWallach] proposal, except our definition handles non-full proposed by [CrosbyWallach], except our definition handles non-full
trees differently). trees differently.)
2.1.2. Verifying a Tree Head Given Entries 2.1.2. Verifying a Tree Head Given Entries
When a client has a complete list of "entries" from "0" up to When a client has a complete list of entries from 0 up to tree_size -
"tree_size - 1" and wishes to verify this list against a tree head 1 and wishes to verify this list against a tree head root_hash
"root_hash" returned by the log for the same "tree_size", the returned by the log for the same tree_size, the following algorithm
following algorithm may be used: may be used:
1. Set "stack" to an empty stack. 1. Set stack to an empty stack.
2. For each "i" from "0" up to "tree_size - 1": 2. For each i from 0 up to tree_size - 1:
1. Push "HASH(0x00 || entries[i])" to "stack". a. Push HASH(0x00 || entries[i]) to stack.
2. Set "merge_count" to the lowest value ("0" included) such b. Set merge_count to the lowest value (0 included) such that
that "LSB(i >> merge_count)" is not set, where "LSB" means LSB(i >> merge_count) is not set, where LSB means the least
the least significant bit. In other words, set "merge_count" significant bit. In other words, set merge_count to the
to the number of consecutive "1"s found starting at the least number of consecutive 1s found starting at the least
significant bit of "i". significant bit of i.
3. Repeat "merge_count" times: c. Repeat merge_count times:
1. Pop "right" from "stack". i. Pop right from stack.
2. Pop "left" from "stack". ii. Pop left from stack.
3. Push "HASH(0x01 || left || right)" to "stack". iii. Push HASH(0x01 || left || right) to stack.
3. If there is more than one element in the "stack", repeat the same 3. If there is more than one element in the stack, repeat the same
merge procedure (the sub-items of Step 2.3 above) until only a merge procedure (the sub-items of Step 2(c) above) until only a
single element remains. single element remains.
4. The remaining element in "stack" is the Merkle Tree hash for the 4. The remaining element in stack is the Merkle Tree Hash for the
given "tree_size" and should be compared by equality against the given tree_size and should be compared by equality against the
supplied "root_hash". supplied root_hash.
2.1.3. Merkle Inclusion Proofs 2.1.3. Merkle Inclusion Proofs
A Merkle inclusion proof for a leaf in a Merkle Hash Tree is the A Merkle inclusion proof for a leaf in a Merkle Tree is the shortest
shortest list of additional nodes in the Merkle Tree required to list of additional nodes in the Merkle Tree required to compute the
compute the Merkle Tree Hash for that tree. Each node in the tree is Merkle Tree Hash for that tree. Each node in the tree is either a
either a leaf node or is computed from the two nodes immediately leaf node or is computed from the two nodes immediately below it
below it (i.e., towards the leaves). At each step up the tree (i.e., towards the leaves). At each step up the tree (towards the
(towards the root), a node from the inclusion proof is combined with root), a node from the inclusion proof is combined with the node
the node computed so far. In other words, the inclusion proof computed so far. In other words, the inclusion proof consists of the
consists of the list of missing nodes required to compute the nodes list of missing nodes required to compute the nodes leading from a
leading from a leaf to the root of the tree. If the root computed leaf to the root of the tree. If the root computed from the
from the inclusion proof matches the true root, then the inclusion inclusion proof matches the true root, then the inclusion proof
proof proves that the leaf exists in the tree. proves that the leaf exists in the tree.
2.1.3.1. Generating an Inclusion Proof 2.1.3.1. Generating an Inclusion Proof
Given an ordered list of n inputs to the tree, D_n = {d[0], d[1], Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],
..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th ..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th
input d[m], 0 <= m < n, is defined as follows: input d[m], 0 <= m < n, is defined as follows:
The proof for the single leaf in a tree with a one-element input list The proof for the single leaf in a tree with a one-element input list
D[1] = {d[0]} is empty: D[1] = {d[0]} is empty:
skipping to change at page 10, line 4 skipping to change at line 419
2.1.3.1. Generating an Inclusion Proof 2.1.3.1. Generating an Inclusion Proof
Given an ordered list of n inputs to the tree, D_n = {d[0], d[1], Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],
..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th ..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th
input d[m], 0 <= m < n, is defined as follows: input d[m], 0 <= m < n, is defined as follows:
The proof for the single leaf in a tree with a one-element input list The proof for the single leaf in a tree with a one-element input list
D[1] = {d[0]} is empty: D[1] = {d[0]} is empty:
PATH(0, {d[0]}) = {} PATH(0, {d[0]}) = {}
For n > 1, let k be the largest power of two smaller than n. The For n > 1, let k be the largest power of two smaller than n. The
proof for the (m+1)th element d[m] in a list of n > m elements is proof for the (m+1)th element d[m] in a list of n > m elements is
then defined recursively as then defined recursively as:
PATH(m, D_n) = PATH(m, D[0:k]) : MTH(D[k:n]) for m < k; and PATH(m, D_n) = PATH(m, D[0:k]) : MTH(D[k:n]) for m < k; and
PATH(m, D_n) = PATH(m - k, D[k:n]) : MTH(D[0:k]) for m >= k, PATH(m, D_n) = PATH(m - k, D[k:n]) : MTH(D[0:k]) for m >= k,
The : operator and D[k1:k2] are defined the same as in Section 2.1.1. The : operator and D[k1:k2] are defined the same as in Section 2.1.1.
2.1.3.2. Verifying an Inclusion Proof 2.1.3.2. Verifying an Inclusion Proof
When a client has received an inclusion proof (e.g., in a "TransItem" When a client has received an inclusion proof (e.g., in a TransItem
of type "inclusion_proof_v2") and wishes to verify inclusion of an of type inclusion_proof_v2) and wishes to verify inclusion of an
input "hash" for a given "tree_size" and "root_hash", the following input hash for a given tree_size and root_hash, the following
algorithm may be used to prove the "hash" was included in the algorithm may be used to prove the hash was included in the
"root_hash": root_hash:
1. Compare "leaf_index" from the "inclusion_proof_v2" structure 1. Compare leaf_index from the inclusion_proof_v2 structure against
against "tree_size". If "leaf_index" is greater than or equal to tree_size. If leaf_index is greater than or equal to tree_size,
"tree_size" then fail the proof verification. then fail the proof verification.
2. Set "fn" to "leaf_index" and "sn" to "tree_size - 1". 2. Set fn to leaf_index and sn to tree_size - 1.
3. Set "r" to "hash". 3. Set r to hash.
4. For each value "p" in the "inclusion_path" array: 4. For each value p in the inclusion_path array:
If "sn" is 0, stop the iteration and fail the proof verification. a. If sn is 0, then stop the iteration and fail the proof
verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then: b. If LSB(fn) is set, or if fn is equal to sn, then:
1. Set "r" to "HASH(0x01 || p || r)" i. Set r to HASH(0x01 || p || r).
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn" ii. If LSB(fn) is not set, then right-shift both fn and sn
equally until either "LSB(fn)" is set or "fn" is "0". equally until either LSB(fn) is set or fn is 0.
Otherwise: Otherwise:
1. Set "r" to "HASH(0x01 || r || p)" i. Set r to HASH(0x01 || r || p).
Finally, right-shift both "fn" and "sn" one time. c. Finally, right-shift both fn and sn one time.
5. Compare "sn" to 0. Compare "r" against the "root_hash". If "sn" 5. Compare sn to 0. Compare r against the root_hash. If sn is
is equal to 0, and "r" and the "root_hash" are equal, then the equal to 0 and r and the root_hash are equal, then the log has
log has proven the inclusion of "hash". Otherwise, fail the proven the inclusion of hash. Otherwise, fail the proof
proof verification. verification.
2.1.4. Merkle Consistency Proofs 2.1.4. Merkle Consistency Proofs
Merkle consistency proofs prove the append-only property of the tree. Merkle consistency proofs prove the append-only property of the tree.
A Merkle consistency proof for a Merkle Tree Hash MTH(D_n) and a A Merkle consistency proof for a Merkle Tree Hash MTH(D_n) and a
previously advertised hash MTH(D[0:m]) of the first m leaves, m <= n, previously advertised hash MTH(D[0:m]) of the first m leaves, m <= n,
is the list of nodes in the Merkle Tree required to verify that the is the list of nodes in the Merkle Tree required to verify that the
first m inputs D[0:m] are equal in both trees. Thus, a consistency first m inputs D[0:m] are equal in both trees. Thus, a consistency
proof must contain a set of intermediate nodes (i.e., commitments to proof must contain a set of intermediate nodes (i.e., commitments to
inputs) sufficient to verify MTH(D_n), such that (a subset of) the inputs) sufficient to verify MTH(D_n), such that (a subset of) the
skipping to change at page 11, line 26 skipping to change at line 490
2.1.4.1. Generating a Consistency Proof 2.1.4.1. Generating a Consistency Proof
Given an ordered list of n inputs to the tree, D_n = {d[0], d[1], Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],
..., d[n-1]}, the Merkle consistency proof PROOF(m, D_n) for a ..., d[n-1]}, the Merkle consistency proof PROOF(m, D_n) for a
previous Merkle Tree Hash MTH(D[0:m]), 0 < m < n, is defined as: previous Merkle Tree Hash MTH(D[0:m]), 0 < m < n, is defined as:
PROOF(m, D_n) = SUBPROOF(m, D_n, true) PROOF(m, D_n) = SUBPROOF(m, D_n, true)
In SUBPROOF, the boolean value represents whether the subtree created In SUBPROOF, the boolean value represents whether the subtree created
from D[0:m] is a complete subtree of the Merkle Tree created from from D[0:m] is a complete subtree of the Merkle Tree created from D_n
D_n, and, consequently, whether the subtree Merkle Tree Hash and, consequently, whether the subtree Merkle Tree Hash MTH(D[0:m])
MTH(D[0:m]) is known. The initial call to SUBPROOF sets this to be is known. The initial call to SUBPROOF sets this to be true, and
true, and SUBPROOF is then defined as follows: SUBPROOF is then defined as follows:
The subproof for m = n is empty if m is the value for which PROOF was The subproof for m = n is empty if m is the value for which PROOF was
originally requested (meaning that the subtree created from D[0:m] is originally requested (meaning that the subtree created from D[0:m] is
a complete subtree of the Merkle Tree created from the original D_n a complete subtree of the Merkle Tree created from the original D_n
for which PROOF was requested, and the subtree Merkle Tree Hash for which PROOF was requested and the subtree Merkle Tree Hash
MTH(D[0:m]) is known): MTH(D[0:m]) is known):
SUBPROOF(m, D_m, true) = {} SUBPROOF(m, D_m, true) = {}
Otherwise, the subproof for m = n is the Merkle Tree Hash committing Otherwise, the subproof for m = n is the Merkle Tree Hash committing
inputs D[0:m]: inputs D[0:m]:
SUBPROOF(m, D_m, false) = {MTH(D_m)} SUBPROOF(m, D_m, false) = {MTH(D_m)}
For m < n, let k be the largest power of two smaller than n. The For m < n, let k be the largest power of two smaller than n. The
skipping to change at page 12, line 4 skipping to change at line 517
For m < n, let k be the largest power of two smaller than n. The For m < n, let k be the largest power of two smaller than n. The
subproof is then defined recursively, using the appropriate step subproof is then defined recursively, using the appropriate step
below: below:
If m <= k, the right subtree entries D[k:n] only exist in the current If m <= k, the right subtree entries D[k:n] only exist in the current
tree. We prove that the left subtree entries D[0:k] are consistent tree. We prove that the left subtree entries D[0:k] are consistent
and add a commitment to D[k:n]: and add a commitment to D[k:n]:
SUBPROOF(m, D_n, b) = SUBPROOF(m, D[0:k], b) : MTH(D[k:n]) SUBPROOF(m, D_n, b) = SUBPROOF(m, D[0:k], b) : MTH(D[k:n])
If m > k, the left subtree entries D[0:k] are identical in both If m > k, the left subtree entries D[0:k] are identical in both
trees. We prove that the right subtree entries D[k:n] are consistent trees. We prove that the right subtree entries D[k:n] are consistent
and add a commitment to D[0:k]. and add a commitment to D[0:k]:
SUBPROOF(m, D_n, b) = SUBPROOF(m - k, D[k:n], false) : MTH(D[0:k]) SUBPROOF(m, D_n, b) = SUBPROOF(m - k, D[k:n], false) : MTH(D[0:k])
The number of nodes in the resulting proof is bounded above by The number of nodes in the resulting proof is bounded above by
ceil(log2(n)) + 1. ceil(log2(n)) + 1.
The : operator and D[k1:k2] are defined the same as in Section 2.1.1. The : operator and D[k1:k2] are defined the same as in Section 2.1.1.
2.1.4.2. Verifying Consistency between Two Tree Heads 2.1.4.2. Verifying Consistency between Two Tree Heads
When a client has a tree head "first_hash" for tree size "first", a When a client has a tree head first_hash for tree size first, has a
tree head "second_hash" for tree size "second" where "0 < first < tree head second_hash for tree size second where 0 < first < second,
second", and has received a consistency proof between the two (e.g., and has received a consistency proof between the two (e.g., in a
in a "TransItem" of type "consistency_proof_v2"), the following TransItem of type consistency_proof_v2), the following algorithm may
algorithm may be used to verify the consistency proof: be used to verify the consistency proof:
1. If "consistency_path" is an empty array, stop and fail the proof 1. If consistency_path is an empty array, stop and fail the proof
verification. verification.
2. If "first" is an exact power of 2, then prepend "first_hash" to 2. If first is an exact power of 2, then prepend first_hash to the
the "consistency_path" array. consistency_path array.
3. Set "fn" to "first - 1" and "sn" to "second - 1". 3. Set fn to first - 1 and sn to second - 1.
4. If "LSB(fn)" is set, then right-shift both "fn" and "sn" equally 4. If LSB(fn) is set, then right-shift both fn and sn equally until
until "LSB(fn)" is not set. LSB(fn) is not set.
5. Set both "fr" and "sr" to the first value in the 5. Set both fr and sr to the first value in the consistency_path
"consistency_path" array. array.
6. For each subsequent value "c" in the "consistency_path" array: 6. For each subsequent value c in the consistency_path array:
If "sn" is 0, stop the iteration and fail the proof verification. a. If sn is 0, then stop the iteration and fail the proof
verification.
If "LSB(fn)" is set, or if "fn" is equal to "sn", then: b. If LSB(fn) is set, or if fn is equal to sn, then:
1. Set "fr" to "HASH(0x01 || c || fr)" i. Set fr to HASH(0x01 || c || fr).
Set "sr" to "HASH(0x01 || c || sr)" ii. Set sr to HASH(0x01 || c || sr).
2. If "LSB(fn)" is not set, then right-shift both "fn" and "sn" iii. If LSB(fn) is not set, then right-shift both fn and sn
equally until either "LSB(fn)" is set or "fn" is "0". equally until either LSB(fn) is set or fn is 0.
Otherwise: Otherwise:
1. Set "sr" to "HASH(0x01 || sr || c)" i. Set sr to HASH(0x01 || sr || c).
Finally, right-shift both "fn" and "sn" one time. c. Finally, right-shift both fn and sn one time.
7. After completing iterating through the "consistency_path" array 7. After completing iterating through the consistency_path array as
as described above, verify that the "fr" calculated is equal to described above, verify that the fr calculated is equal to the
the "first_hash" supplied, that the "sr" calculated is equal to first_hash supplied, that the sr calculated is equal to the
the "second_hash" supplied and that "sn" is 0. second_hash supplied, and that sn is 0.
2.1.5. Example 2.1.5. Example
The binary Merkle Tree with 7 leaves: The following is a binary Merkle Tree with 7 leaves:
hash hash
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
k l k l
/ \ / \ / \ / \
/ \ / \ / \ / \
skipping to change at page 14, line 32 skipping to change at line 633
/ \ / \ / \ / \ / \ / \ / \ / \
/ \ e f / \ / \ / \ e f / \ / \
/ \ | | / \ / \ / \ | | / \ / \
g h d4 d5 g h i j g h d4 d5 g h i j
/ \ / \ / \ / \ / \ | / \ / \ / \ / \ / \ |
a b c d a b c d e f d6 a b c d a b c d e f d6
| | | | | | | | | | | | | | | | | | | |
d0 d1 d2 d3 d0 d1 d2 d3 d4 d5 d0 d1 d2 d3 d0 d1 d2 d3 d4 d5
The consistency proof between hash0 and hash is PROOF(3, D[7]) = [c, The consistency proof between hash0 and hash is PROOF(3, D[7]) = [c,
d, g, l]. c, g are used to verify hash0, and d, l are additionally d, g, l]. Non-leaf nodes c, g are used to verify hash0, and non-leaf
used to show hash is consistent with hash0. nodes d, l are additionally used to show hash is consistent with
hash0.
The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l]. The consistency proof between hash1 and hash is PROOF(4, D[7]) = [l].
hash can be verified using hash1=k and l. hash can be verified using hash1=k and l.
The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i, The consistency proof between hash2 and hash is PROOF(6, D[7]) = [i,
j, k]. k, i are used to verify hash2, and j is additionally used to j, k]. Non-leaf nodes k, i are used to verify hash2, and non-leaf
show hash is consistent with hash2. node j is additionally used to show hash is consistent with hash2.
2.2. Signatures 2.2. Signatures
When signing data structures, a log MUST use one of the signature When signing data structures, a log MUST use one of the signature
algorithms from the IANA CT Signature Algorithms registry, described algorithms from the IANA "Signature Algorithms" registry, described
in Section 10.2.2. in Section 10.2.2.
3. Submitters 3. Submitters
Submitters submit certificates or preannouncements of certificates Submitters submit certificates or preannouncements of certificates
prior to issuance (precertificates) to logs for public auditing, as prior to issuance (precertificates) to logs for public auditing, as
described below. In order to enable attribution of each logged described below. In order to enable attribution of each logged
certificate or precertificate to its issuer, each submission MUST be certificate or precertificate to its issuer, each submission MUST be
accompanied by all additional certificates required to verify the accompanied by all additional certificates required to verify the
chain up to an accepted trust anchor (Section 5.7). The trust anchor chain up to an accepted trust anchor (Section 5.7). The trust anchor
(a root or intermediate CA certificate) MAY be omitted from the (a root or intermediate CA certificate) MAY be omitted from the
submission. submission.
If a log accepts a submission, it will return a Signed Certificate If a log accepts a submission, it will return a Signed Certificate
Timestamp (SCT) (see Section 4.8). The submitter SHOULD validate the Timestamp (SCT) (see Section 4.8). The submitter SHOULD validate the
returned SCT as described in Section 8.1 if they understand its returned SCT, as described in Section 8.1, if they understand its
format and they intend to use it directly in a TLS handshake or to format and they intend to use it directly in a TLS handshake or to
construct a certificate. If the submitter does not need the SCT (for construct a certificate. If the submitter does not need the SCT (for
example, the certificate is being submitted simply to make it example, the certificate is being submitted simply to make it
available in the log), it MAY validate the SCT. available in the log), it MAY validate the SCT.
3.1. Certificates 3.1. Certificates
Any entity can submit a certificate (Section 5.1) to a log. Since it Any entity can submit a certificate (Section 5.1) to a log. Since it
is anticipated that TLS clients will reject certificates that are not is anticipated that TLS clients will reject certificates that are not
logged, it is expected that certificate issuers and subjects will be logged, it is expected that certificate issuers and subjects will be
strongly motivated to submit them. strongly motivated to submit them.
3.2. Precertificates 3.2. Precertificates
CAs may preannounce a certificate prior to issuance by submitting a CAs may preannounce a certificate prior to issuance by submitting a
precertificate (Section 5.1) that the log can use to create an entry precertificate (Section 5.1) that the log can use to create an entry
that will be valid against the issued certificate. The CA MAY that will be valid against the issued certificate. The CA MAY
incorporate the returned SCT in the issued certificate. One example incorporate the returned SCT in the issued certificate. One example
of where the returned SCT is not incorporated in the issued of where the returned SCT is not incorporated in the issued
certificate is when a CA sends the precertificate to multiple logs, certificate is when a CA sends the precertificate to multiple logs
but only incorporates the SCTs that are returned first. but only incorporates the SCTs that are returned first.
A precertificate is a CMS [RFC5652] "signed-data" object that A precertificate is a CMS [RFC5652] signed-data object that conforms
conforms to the following profile: to the following profile:
* It MUST be DER encoded as described in [X690]. * It MUST be DER encoded, as described in [X690].
* "SignedData.version" MUST be v3(3). * SignedData.version MUST be v3(3).
* "SignedData.digestAlgorithms" MUST be the same as the * SignedData.digestAlgorithms MUST be the same as the
"SignerInfo.digestAlgorithm" OID value (see below). SignerInfo.digestAlgorithm OID value (see below).
* "SignedData.encapContentInfo": * SignedData.encapContentInfo:
- "eContentType" MUST be the OID 1.3.101.78. - eContentType MUST be the OID 1.3.101.78.
- "eContent" MUST contain a TBSCertificate [RFC5280] that will be - eContent MUST contain a TBSCertificate [RFC5280] that will be
identical to the TBSCertificate in the issued certificate, identical to the TBSCertificate in the issued certificate,
except that the Transparency Information (Section 7.1) except that the Transparency Information (Section 7.1)
extension MUST be omitted. extension MUST be omitted.
* "SignedData.certificates" MUST be omitted. * SignedData.certificates MUST be omitted.
* "SignedData.crls" MUST be omitted. * SignedData.crls MUST be omitted.
* "SignedData.signerInfos" MUST contain one "SignerInfo": * SignedData.signerInfos MUST contain one SignerInfo:
- "version" MUST be v3(3). - version MUST be v3(3).
- "sid" MUST use the "subjectKeyIdentifier" option. - sid MUST use the subjectKeyIdentifier option.
- "digestAlgorithm" MUST be one of the hash algorithm OIDs listed - digestAlgorithm MUST be one of the hash algorithm OIDs listed
in the IANA CT Hash Algorithms Registry, described in in the IANA "Hash Algorithms" registry, described in
Section 10.2.1. Section 10.2.1.
- "signedAttrs" MUST be present and MUST contain two attributes: - signedAttrs MUST be present and MUST contain two attributes:
o A content-type attribute whose value is the same as o a content-type attribute whose value is the same as
"SignedData.encapContentInfo.eContentType". SignedData.encapContentInfo.eContentType and
o A message-digest attribute whose value is the message digest o a message-digest attribute whose value is the message digest
of "SignedData.encapContentInfo.eContent". of SignedData.encapContentInfo.eContent.
- "signatureAlgorithm" MUST be the same OID as - signatureAlgorithm MUST be the same OID as
"TBSCertificate.signature". TBSCertificate.signature.
- "signature" MUST be from the same (root or intermediate) CA - signature MUST be from the same (root or intermediate) CA that
that intends to issue the corresponding certificate (see intends to issue the corresponding certificate (see
Section 3.2.1). Section 3.2.1).
- "unsignedAttrs" MUST be omitted. - unsignedAttrs MUST be omitted.
"SignerInfo.signedAttrs" is included in the message digest SignerInfo.signedAttrs is included in the message digest calculation
calculation process (see Section 5.4 of [RFC5652]), which ensures process (see Section 5.4 of [RFC5652]), which ensures that the
that the "SignerInfo.signature" value will not be a valid X.509v3 SignerInfo.signature value will not be a valid X.509v3 signature that
signature that could be used in conjunction with the TBSCertificate could be used in conjunction with the TBSCertificate (from
(from "SignedData.encapContentInfo.eContent") to construct a valid SignedData.encapContentInfo.eContent) to construct a valid
certificate. certificate.
3.2.1. Binding Intent to Issue 3.2.1. Binding Intent to Issue
Under normal circumstances, there will be a short delay between Under normal circumstances, there will be a short delay between
precertificate submission and issuance of the corresponding precertificate submission and issuance of the corresponding
certificate. Longer delays are to be expected occasionally (e.g., certificate. Longer delays are to be expected occasionally (e.g.,
due to log server downtime), and in some cases the CA might not due to log server downtime); in some cases, the CA might not actually
actually issue the corresponding certificate. Nevertheless, a issue the corresponding certificate. Nevertheless, a
precertificate's "signature" indicates the CA's binding intent to precertificate's signature indicates the CA's binding intent to issue
issue the corresponding certificate, which means that: the corresponding certificate, which means that:
* Misissuance of a precertificate is considered equivalent to * Misissuance of a precertificate is considered equivalent to
misissuance of the corresponding certificate. The CA should misissuance of the corresponding certificate. The CA should
expect to be held to account, even if the corresponding expect to be held accountable, even if the corresponding
certificate has not actually been issued. certificate has not actually been issued.
* Upon observing a precertificate, a client can reasonably presume * Upon observing a precertificate, a client can reasonably presume
that the corresponding certificate has been issued. A client may that the corresponding certificate has been issued. A client may
wish to obtain status information (e.g., by using the Online wish to obtain status information (e.g., by using the Online
Certificate Status Protocol [RFC6960] or by checking a Certificate Certificate Status Protocol [RFC6960] or by checking a Certificate
Revocation List [RFC5280]) about a certificate that is presumed to Revocation List [RFC5280]) about a certificate that is presumed to
exist, especially if there is evidence or suspicion that the exist, especially if there is evidence or suspicion that the
corresponding precertificate was misissued. corresponding precertificate was misissued.
* TLS clients may have policies that require CAs to be able to * TLS clients may have policies that require CAs to be able to
revoke, and to provide certificate status services for, each revoke and to provide certificate status services for each
certificate that is presumed to exist based on the existence of a certificate that is presumed to exist based on the existence of a
corresponding precertificate. corresponding precertificate.
4. Log Format and Operation 4. Log Format and Operation
A log is a single, append-only Merkle Tree of submitted certificate A log is a single, append-only Merkle Tree of submitted certificate
and precertificate entries. and precertificate entries.
When it receives and accepts a valid submission, the log MUST return When it receives and accepts a valid submission, the log MUST return
an SCT that corresponds to the submitted certificate or an SCT that corresponds to the submitted certificate or
precertificate. If the log has previously seen this valid precertificate. If the log has previously seen this valid
submission, it SHOULD return the same SCT as it returned before, as submission, it SHOULD return the same SCT as it returned before, as
discussed in Section 11.3. If different SCTs are produced for the discussed in Section 11.3. If different SCTs are produced for the
same submission, multiple log entries will have to be created, one same submission, multiple log entries will have to be created, one
for each SCT (as the timestamp is a part of the leaf structure). for each SCT (as the timestamp is a part of the leaf structure).
Note that if a certificate was previously logged as a precertificate, Note that if a certificate was previously logged as a precertificate,
then the precertificate's SCT of type "precert_sct_v2" would not be then the precertificate's SCT of type precert_sct_v2 would not be
appropriate; instead, a fresh SCT of type "x509_sct_v2" should be appropriate; instead, a fresh SCT of type x509_sct_v2 should be
generated. generated.
An SCT is the log's promise to append to its Merkle Tree an entry for An SCT is the log's promise to append to its Merkle Tree an entry for
the accepted submission. Upon producing an SCT, the log MUST fulfil the accepted submission. Upon producing an SCT, the log MUST fulfill
this promise by performing the following actions within a fixed this promise by performing the following actions within a fixed
amount of time known as the Maximum Merge Delay (MMD), which is one amount of time known as the Maximum Merge Delay (MMD), which is one
of the log's parameters (see Section 4.1): of the log's parameters (see Section 4.1):
* Allocate a tree index to the entry representing the accepted * Allocate a tree index to the entry representing the accepted
submission. submission.
* Calculate the root of the tree. * Calculate the root of the tree.
* Sign the root of the tree (see Section 4.10). * Sign the root of the tree (see Section 4.10).
skipping to change at page 18, line 28 skipping to change at line 811
The log may append multiple entries before signing the root of the The log may append multiple entries before signing the root of the
tree. tree.
Log operators SHOULD NOT impose any conditions on retrieving or Log operators SHOULD NOT impose any conditions on retrieving or
sharing data from the log. sharing data from the log.
4.1. Log Parameters 4.1. Log Parameters
A log is defined by a collection of immutable parameters, which are A log is defined by a collection of immutable parameters, which are
used by clients to communicate with the log and to verify log used by clients to communicate with the log and to verify log
artifacts. Except for the Final Signed Tree Head (STH), each of artifacts. Except for the Final STH, each of these parameters MUST
these parameters MUST be established before the log operator begins be established before the log operator begins to operate the log.
to operate the log.
Base URL: The prefix used to construct URLs ([RFC3986]) for client Base URL: The prefix used to construct URLs [RFC3986] for client
messages (see Section 5). The base URL MUST be an "https" URL, messages (see Section 5). The base URL MUST be an "https" URL,
MAY contain a port, MAY contain a path with any number of path MAY contain a port, and MAY contain a path with any number of path
segments, but MUST NOT contain a query string, fragment, or segments but MUST NOT contain a query string, fragment, or
trailing "/". Example: https://ct.example.org/blue trailing "/". Example: https://ct.example.org/blue.
Hash Algorithm: The hash algorithm used for the Merkle Tree (see Hash Algorithm: The hash algorithm used for the Merkle Tree (see
Section 10.2.1). Section 10.2.1).
Signature Algorithm: The signature algorithm used (see Section 2.2). Signature Algorithm: The signature algorithm used (see Section 2.2).
Public Key: The public key used to verify signatures generated by Public Key: The public key used to verify signatures generated by
the log. A log MUST NOT use the same keypair as any other log. the log. A log MUST NOT use the same keypair as any other log.
Log ID: The OID that uniquely identifies the log. Log ID: The OID that uniquely identifies the log.
Maximum Merge Delay: The MMD the log has committed to. This Maximum Merge Delay: The MMD the log has committed to. This
document deliberately does not specify any limits on the value, to document deliberately does not specify any limits on the value to
allow for experimentation. allow for experimentation.
Version: The version of the protocol supported by the log (currently Version: The version of the protocol supported by the log (currently
1 or 2). 1 or 2).
Maximum Chain Length: The longest certificate chain submission the Maximum Chain Length: The longest certificate chain submission the
log is willing to accept, if the log imposes any limit. log is willing to accept, if the log imposes any limit.
STH Frequency Count: The maximum number of STHs the log may produce STH Frequency Count: The maximum number of STHs the log may produce
in any period equal to the "Maximum Merge Delay" (see in any period equal to the Maximum Merge Delay (see Section 4.10).
Section 4.10).
Final STH: If a log has been closed down (i.e., no longer accepts Final STH: If a log has been closed down (i.e., no longer accepts
new entries), existing entries may still be valid. In this case, new entries), existing entries may still be valid. In this case,
the client should know the final valid STH in the log to ensure no the client should know the final valid STH in the log to ensure no
new entries can be added without detection. This value MUST be new entries can be added without detection. This value MUST be
provided in the form of a TransItem of type "signed_tree_head_v2". provided in the form of a TransItem of type signed_tree_head_v2.
If a log is still accepting entries, this value should not be If a log is still accepting entries, this value should not be
provided. provided.
[JSON.Metadata] is an example of a metadata format which includes the [JSON.Metadata] is an example of a metadata format that includes the
above elements. above elements.
4.2. Evaluating Submissions 4.2. Evaluating Submissions
A log determines whether to accept or reject a submission by A log determines whether to accept or reject a submission by
evaluating it against the minimum acceptance criteria (see evaluating it against the minimum acceptance criteria (see
Section 4.2.1) and against the log's discretionary acceptance Section 4.2.1) and against the log's discretionary acceptance
criteria (see Section 4.2.2). criteria (see Section 4.2.2).
If the acceptance criteria are met, the log SHOULD accept the If the acceptance criteria are met, the log SHOULD accept the
submission. (A log may decide, for example, to temporarily reject submission. (A log may decide, for example, to temporarily reject
acceptable submissions to protect itself against denial-of-service acceptable submissions to protect itself against denial-of-service
attacks). attacks.)
The log SHALL allow retrieval of its list of accepted trust anchors The log SHALL allow retrieval of its list of accepted trust anchors
(see Section 5.7), each of which is a root or intermediate CA (see Section 5.7), each of which is a root or intermediate CA
certificate. This list might usefully be the union of root certificate. This list might usefully be the union of root
certificates trusted by major browser vendors. certificates trusted by major browser vendors.
4.2.1. Minimum Acceptance Criteria 4.2.1. Minimum Acceptance Criteria
To ensure that logged certificates and precertificates are To ensure that logged certificates and precertificates are
attributable to an accepted trust anchor, to set clear expectations attributable to an accepted trust anchor, to set clear expectations
for what monitors would find in the log, and to avoid being for what monitors would find in the log, and to avoid being
overloaded by invalid submissions, the log MUST reject a submission overloaded by invalid submissions, the log MUST reject a submission
if any of the following conditions are not met: if any of the following conditions are not met:
* The "submission", "type" and "chain" inputs MUST be set as * The submission, type, and chain inputs MUST be set as described in
described in Section 5.1. The log MUST NOT accommodate misordered Section 5.1. The log MUST NOT accommodate misordered CA
CA certificates or use any other source of intermediate CA certificates or use any other source of intermediate CA
certificates to attempt certification path construction. certificates to attempt certification path construction.
* Each of the zero or more intermediate CA certificates in the chain * Each of the zero or more intermediate CA certificates in the chain
MUST have one or both of the following features: MUST have one or both of the following features:
- The Basic Constraints extension with the cA boolean asserted. - The Basic Constraints extension with the cA boolean asserted.
- The Key Usage extension with the keyCertSign bit asserted. - The Key Usage extension with the keyCertSign bit asserted.
* Each certificate in the chain MUST fall within the limits imposed * Each certificate in the chain MUST fall within the limits imposed
skipping to change at page 20, line 30 skipping to change at line 904
* Precertificate submissions MUST conform to all of the requirements * Precertificate submissions MUST conform to all of the requirements
in Section 3.2. in Section 3.2.
4.2.2. Discretionary Acceptance Criteria 4.2.2. Discretionary Acceptance Criteria
If the minimum acceptance criteria are met but the submission is not If the minimum acceptance criteria are met but the submission is not
fully valid according to [RFC5280] verification rules (e.g., the fully valid according to [RFC5280] verification rules (e.g., the
certificate or precertificate has expired, is not yet valid, has been certificate or precertificate has expired, is not yet valid, has been
revoked, exhibits ASN.1 DER encoding errors but the log can still revoked, exhibits ASN.1 DER encoding errors but the log can still
parse it, etc), then the acceptability of the submission is left to parse it, etc.), then the acceptability of the submission is left to
the log's discretion. It is useful for logs to accept such the log's discretion. It is useful for logs to accept such
submissions in order to accommodate quirks of CA certificate-issuing submissions in order to accommodate quirks of CA certificate-issuing
software and to facilitate monitoring of CA compliance with software and to facilitate monitoring of CA compliance with
applicable policies and technical standards. However, it is applicable policies and technical standards. However, it is
impractical for this document to enumerate, and for logs to consider, impractical for this document to enumerate, and for logs to consider,
all of the ways that a submission might fail to comply with all of the ways that a submission might fail to comply with
[RFC5280]. [RFC5280].
Logs SHOULD limit the length of chain they will accept. The maximum Logs SHOULD limit the length of chain they will accept. The maximum
chain length is one of the log's parameters (see Section 4.1). chain length is one of the log's parameters (see Section 4.1).
4.3. Log Entries 4.3. Log Entries
If a submission is accepted and an SCT issued, the accepting log MUST If a submission is accepted and an SCT is issued, the accepting log
store the entire chain used for verification. This chain MUST MUST store the entire chain used for verification. This chain MUST
include the certificate or precertificate itself, the zero or more include the certificate or precertificate itself, the zero or more
intermediate CA certificates provided by the submitter, and the trust intermediate CA certificates provided by the submitter, and the trust
anchor used to verify the chain (even if it was omitted from the anchor used to verify the chain (even if it was omitted from the
submission). The log MUST provide this chain for auditing upon submission). The log MUST provide this chain for auditing upon
request (see Section 5.6) so that the CA cannot avoid blame by request (see Section 5.6) so that the CA cannot avoid blame by
logging a partial or empty chain. Each log entry is a "TransItem" logging a partial or empty chain. Each log entry is a TransItem
structure of type "x509_entry_v2" or "precert_entry_v2". However, a structure of type x509_entry_v2 or precert_entry_v2. However, a log
log may store its entries in any format. If a log does not store may store its entries in any format. If a log does not store this
this "TransItem" in full, it must store the "timestamp" and TransItem in full, it must store the timestamp and sct_extensions of
"sct_extensions" of the corresponding the corresponding TimestampedCertificateEntryDataV2 structure. The
"TimestampedCertificateEntryDataV2" structure. The "TransItem" can TransItem can be reconstructed from these fields and the entire chain
be reconstructed from these fields and the entire chain that the log that the log used to verify the submission.
used to verify the submission.
4.4. Log ID 4.4. Log ID
Each log is identified by an OID, which is one of the log's Each log is identified by an OID, which is one of the log's
parameters (see Section 4.1) and which MUST NOT be used to identify parameters (see Section 4.1) and which MUST NOT be used to identify
any other log. A log's operator MUST either allocate the OID any other log. A log's operator MUST either allocate the OID
themselves or request an OID from the Log ID registry (see themselves or request an OID from the Log ID registry (see
Section 10.2.5). One way to get an OID arc, from which OIDs can be Section 10.2.5). One way to get an OID arc, from which OIDs can be
allocated, is to request a Private Enterprise Number from IANA, by allocated, is to request a Private Enterprise Number from IANA by
completing the registration form (https://pen.iana.org/pen/ completing the registration form (https://pen.iana.org/pen/
PenApplication.page). The only advantage of the registry is that the PenApplication.page). The only advantage of the registry is that the
DER encoding can be small. (Recall that OID allocations do not DER encoding can be small. (Recall that OID allocations do not
require a central registration, although logs will most likely want require a central registration, although logs will most likely want
to make themselves known to potential clients through out of band to make themselves known to potential clients through out-of-band
means.) Various data structures include the DER encoding of this means.) Various data structures include the DER encoding of this
OID, excluding the ASN.1 tag and length bytes, in an opaque vector: OID, excluding the ASN.1 tag and length bytes, in an opaque vector:
opaque LogID<2..127>; opaque LogID<2..127>;
Note that the ASN.1 length and the opaque vector length are identical Note that the ASN.1 length and the opaque vector length are identical
in size (1 byte) and value, so the full DER encoding (including the in size (1 byte) and value, so the full DER encoding (including the
tag and length) of the OID can be reproduced simply by prepending an tag and length) of the OID can be reproduced simply by prepending an
OBJECT IDENTIFIER tag (0x06) to the opaque vector length and OBJECT IDENTIFIER tag (0x06) to the opaque vector length and
contents. contents.
The OID used to identify a log is limited such that the DER encoding The OID used to identify a log is limited such that the DER encoding
of its value, excluding the tag and length, MUST be no longer than of its value, excluding the tag and length, MUST be no longer than
127 octets. 127 octets.
4.5. TransItem Structure 4.5. TransItem Structure
Various data structures are encapsulated in the "TransItem" structure Various data structures are encapsulated in the TransItem structure
to ensure that the type and version of each one is identified in a to ensure that the type and version of each one is identified in a
common fashion: common fashion:
enum { enum {
x509_entry_v2(0x0100), precert_entry_v2(0x0101), x509_entry_v2(0x0100), precert_entry_v2(0x0101),
x509_sct_v2(0x0102), precert_sct_v2(0x0103), x509_sct_v2(0x0102), precert_sct_v2(0x0103),
signed_tree_head_v2(0x0104), consistency_proof_v2(0x0105), signed_tree_head_v2(0x0104), consistency_proof_v2(0x0105),
inclusion_proof_v2(0x0106), inclusion_proof_v2(0x0106),
/* Reserved Code Points */ /* Reserved Code Points */
skipping to change at page 22, line 31 skipping to change at line 993
case x509_entry_v2: TimestampedCertificateEntryDataV2; case x509_entry_v2: TimestampedCertificateEntryDataV2;
case precert_entry_v2: TimestampedCertificateEntryDataV2; case precert_entry_v2: TimestampedCertificateEntryDataV2;
case x509_sct_v2: SignedCertificateTimestampDataV2; case x509_sct_v2: SignedCertificateTimestampDataV2;
case precert_sct_v2: SignedCertificateTimestampDataV2; case precert_sct_v2: SignedCertificateTimestampDataV2;
case signed_tree_head_v2: SignedTreeHeadDataV2; case signed_tree_head_v2: SignedTreeHeadDataV2;
case consistency_proof_v2: ConsistencyProofDataV2; case consistency_proof_v2: ConsistencyProofDataV2;
case inclusion_proof_v2: InclusionProofDataV2; case inclusion_proof_v2: InclusionProofDataV2;
} data; } data;
} TransItem; } TransItem;
"versioned_type" is a value from the IANA registry in Section 10.2.3 versioned_type is a value from the IANA registry in Section 10.2.3
that identifies the type of the encapsulated data structure and the that identifies the type of the encapsulated data structure and the
earliest version of this protocol to which it conforms. This earliest version of this protocol to which it conforms. This
document is v2. document is v2.
"data" is the encapsulated data structure. The various structures data is the encapsulated data structure. The various structures
named with the "DataV2" suffix are defined in later sections of this named with the DataV2 suffix are defined in later sections of this
document. document.
Note that "VersionedTransType" combines the v1 [RFC6962] type Note that VersionedTransType combines the v1 type enumerations
enumerations "Version", "LogEntryType", "SignatureType" and Version, LogEntryType, SignatureType, and MerkleLeafType [RFC6962].
"MerkleLeafType". Note also that v1 did not define "TransItem", but Note also that v1 did not define TransItem, but this document
this document provides guidelines (see Appendix A) on how v2 provides guidelines (see Appendix A) on how v2 implementations can
implementations can co-exist with v1 implementations. coexist with v1 implementations.
Future versions of this protocol may reuse "VersionedTransType" Future versions of this protocol may reuse VersionedTransType values
values defined in this document as long as the corresponding data defined in this document as long as the corresponding data structures
structures are not modified, and may add new "VersionedTransType" are not modified and may add new VersionedTransType values for new or
values for new or modified data structures. modified data structures.
4.6. Log Artifact Extensions 4.6. Log Artifact Extensions
enum { enum {
reserved(65535) reserved(65535)
} ExtensionType; } ExtensionType;
struct { struct {
ExtensionType extension_type; ExtensionType extension_type;
opaque extension_data<0..2^16-1>; opaque extension_data<0..2^16-1>;
} Extension; } Extension;
The "Extension" structure provides a generic extensibility for log The Extension structure provides a generic extensibility for log
artifacts, including SCTs (Section 4.8) and STHs (Section 4.10). The artifacts, including SCTs (Section 4.8) and STHs (Section 4.10). The
interpretation of the "extension_data" field is determined solely by interpretation of the extension_data field is determined solely by
the value of the "extension_type" field. the value of the extension_type field.
This document does not define any extensions, but it does establish a This document does not define any extensions, but it does establish a
registry for future "ExtensionType" values (see Section 10.2.4). registry for future ExtensionType values (see Section 10.2.4). Each
Each document that registers a new "ExtensionType" must specify the document that registers a new ExtensionType must specify the context
context in which it may be used (e.g., SCT, STH, or both) and in which it may be used (e.g., SCT, STH, or both) and describe how to
describe how to interpret the corresponding "extension_data". interpret the corresponding extension_data.
4.7. Merkle Tree Leaves 4.7. Merkle Tree Leaves
The leaves of a log's Merkle Tree correspond to the log's entries The leaves of a log's Merkle Tree correspond to the log's entries
(see Section 4.3). Each leaf is the leaf hash (Section 2.1) of a (see Section 4.3). Each leaf is the leaf hash (Section 2.1) of a
"TransItem" structure of type "x509_entry_v2" or "precert_entry_v2", TransItem structure of type x509_entry_v2 or precert_entry_v2, which
which encapsulates a "TimestampedCertificateEntryDataV2" structure. encapsulates a TimestampedCertificateEntryDataV2 structure. Note
Note that leaf hashes are calculated as HASH(0x00 || TransItem), that leaf hashes are calculated as HASH(0x00 || TransItem), where the
where the hash algorithm is one of the log's parameters. hash algorithm is one of the log's parameters.
opaque TBSCertificate<1..2^24-1>; opaque TBSCertificate<1..2^24-1>;
struct { struct {
uint64 timestamp; uint64 timestamp;
opaque issuer_key_hash<32..2^8-1>; opaque issuer_key_hash<32..2^8-1>;
TBSCertificate tbs_certificate; TBSCertificate tbs_certificate;
Extension sct_extensions<0..2^16-1>; Extension sct_extensions<0..2^16-1>;
} TimestampedCertificateEntryDataV2; } TimestampedCertificateEntryDataV2;
"timestamp" is the date and time at which the certificate or timestamp is the date and time at which the certificate or
precertificate was accepted by the log, in the form of a 64-bit precertificate was accepted by the log, in the form of a 64-bit
unsigned number of milliseconds elapsed since the Unix Epoch (1 unsigned number of milliseconds elapsed since the Unix Epoch (1
January 1970 00:00:00 UTC - see [UNIXTIME]), ignoring leap seconds, January 1970 00:00:00 UTC -- see [UNIXTIME]), ignoring leap seconds,
in network byte order. Note that the leaves of a log's Merkle Tree in network byte order. Note that the leaves of a log's Merkle Tree
are not required to be in strict chronological order. are not required to be in strict chronological order.
"issuer_key_hash" is the HASH of the public key of the CA that issued issuer_key_hash is the HASH of the public key of the CA that issued
the certificate or precertificate, calculated over the DER encoding the certificate or precertificate, calculated over the DER encoding
of the key represented as SubjectPublicKeyInfo [RFC5280]. This is of the key represented as SubjectPublicKeyInfo [RFC5280]. This is
needed to bind the CA to the certificate or precertificate, making it needed to bind the CA to the certificate or precertificate, making it
impossible for the corresponding SCT to be valid for any other impossible for the corresponding SCT to be valid for any other
certificate or precertificate whose TBSCertificate matches certificate or precertificate whose TBSCertificate matches
"tbs_certificate". The length of the "issuer_key_hash" MUST match tbs_certificate. The length of the issuer_key_hash MUST match
HASH_SIZE. HASH_SIZE.
"tbs_certificate" is the DER encoded TBSCertificate from the tbs_certificate is the DER-encoded TBSCertificate from the
submission. (Note that a precertificate's TBSCertificate can be submission. (Note that a precertificate's TBSCertificate can be
reconstructed from the corresponding certificate as described in reconstructed from the corresponding certificate, as described in
Section 8.1.2). Section 8.1.2).
"sct_extensions" is byte-for-byte identical to the SCT extensions of sct_extensions is byte-for-byte identical to the SCT extensions of
the corresponding SCT. the corresponding SCT.
The type of the "TransItem" corresponds to the value of the "type" The type of the TransItem corresponds to the value of the type
parameter supplied in the Section 5.1 call. parameter supplied in the Section 5.1 call.
4.8. Signed Certificate Timestamp (SCT) 4.8. Signed Certificate Timestamp (SCT)
An SCT is a "TransItem" structure of type "x509_sct_v2" or An SCT is a TransItem structure of type x509_sct_v2 or
"precert_sct_v2", which encapsulates a precert_sct_v2, which encapsulates a SignedCertificateTimestampDataV2
"SignedCertificateTimestampDataV2" structure: structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 timestamp; uint64 timestamp;
Extension sct_extensions<0..2^16-1>; Extension sct_extensions<0..2^16-1>;
opaque signature<1..2^16-1>; opaque signature<1..2^16-1>;
} SignedCertificateTimestampDataV2; } SignedCertificateTimestampDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as log_id is this log's unique ID, encoded in an opaque vector, as
described in Section 4.4. described in Section 4.4.
"timestamp" is equal to the timestamp from the corresponding timestamp is equal to the timestamp from the corresponding
"TimestampedCertificateEntryDataV2" structure. TimestampedCertificateEntryDataV2 structure.
"sct_extensions" is a vector of 0 or more SCT extensions. This sct_extensions is a vector of 0 or more SCT extensions. This vector
vector MUST NOT include more than one extension with the same MUST NOT include more than one extension with the same
"extension_type". The extensions in the vector MUST be ordered by extension_type. The extensions in the vector MUST be ordered by the
the value of the "extension_type" field, smallest value first. All value of the extension_type field, smallest value first. All SCT
SCT extensions are similar to non-critical X.509v3 extensions (i.e., extensions are similar to noncritical X.509v3 extensions (i.e., the
the "mustUnderstand" field is not set), and a recipient SHOULD ignore mustUnderstand field is not set), and a recipient SHOULD ignore any
any extension it does not understand. Furthermore, an implementation extension it does not understand. Furthermore, an implementation MAY
MAY choose to ignore any extension(s) that it does understand. choose to ignore any extension(s) that it does understand.
"signature" is computed over a "TransItem" structure of type signature is computed over a TransItem structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 4.7) using the x509_entry_v2 or precert_entry_v2 (see Section 4.7) using the
signature algorithm declared in the log's parameters (see signature algorithm declared in the log's parameters (see
Section 4.1). Section 4.1).
4.9. Merkle Tree Head 4.9. Merkle Tree Head
The log stores information about its Merkle Tree in a The log stores information about its Merkle Tree in a TreeHeadDataV2:
"TreeHeadDataV2":
opaque NodeHash<32..2^8-1>; opaque NodeHash<32..2^8-1>;
struct { struct {
uint64 timestamp; uint64 timestamp;
uint64 tree_size; uint64 tree_size;
NodeHash root_hash; NodeHash root_hash;
Extension sth_extensions<0..2^16-1>; Extension sth_extensions<0..2^16-1>;
} TreeHeadDataV2; } TreeHeadDataV2;
The length of NodeHash MUST match HASH_SIZE of the log. The length of NodeHash MUST match HASH_SIZE of the log.
"timestamp" is the current date and time, using the format defined in timestamp is the current date and time, using the format defined in
Section 4.7. Section 4.7.
"tree_size" is the number of entries currently in the log's Merkle tree_size is the number of entries currently in the log's Merkle
Tree. Tree.
"root_hash" is the root of the Merkle Hash Tree. root_hash is the root of the Merkle Tree.
"sth_extensions" is a vector of 0 or more STH extensions. This sth_extensions is a vector of 0 or more STH extensions. This vector
vector MUST NOT include more than one extension with the same MUST NOT include more than one extension with the same
"extension_type". The extensions in the vector MUST be ordered by extension_type. The extensions in the vector MUST be ordered by the
the value of the "extension_type" field, smallest value first. If an value of the extension_type field, smallest value first. If an
implementation sees an extension that it does not understand, it implementation sees an extension that it does not understand, it
SHOULD ignore that extension. Furthermore, an implementation MAY SHOULD ignore that extension. Furthermore, an implementation MAY
choose to ignore any extension(s) that it does understand. choose to ignore any extension(s) that it does understand.
4.10. Signed Tree Head (STH) 4.10. Signed Tree Head (STH)
Periodically each log SHOULD sign its current tree head information Periodically, each log SHOULD sign its current tree head information
(see Section 4.9) to produce an STH. When a client requests a log's (see Section 4.9) to produce an STH. When a client requests a log's
latest STH (see Section 5.2), the log MUST return an STH that is no latest STH (see Section 5.2), the log MUST return an STH that is no
older than the log's MMD. However, since STHs could be used to mark older than the log's MMD. However, since STHs could be used to mark
individual clients (by producing a new STH for each query), a log individual clients (by producing a new STH for each query), a log
MUST NOT produce STHs more frequently than its parameters declare MUST NOT produce STHs more frequently than its parameters declare
(see Section 4.1). In general, there is no need to produce a new STH (see Section 4.1). In general, there is no need to produce a new STH
unless there are new entries in the log; however, in the event that a unless there are new entries in the log; however, in the event that a
log does not accept any submissions during an MMD period, the log log does not accept any submissions during an MMD period, the log
MUST sign the same Merkle Tree Hash with a fresh timestamp. MUST sign the same Merkle Tree Hash with a fresh timestamp.
An STH is a "TransItem" structure of type "signed_tree_head_v2", An STH is a TransItem structure of type signed_tree_head_v2, which
which encapsulates a "SignedTreeHeadDataV2" structure: encapsulates a SignedTreeHeadDataV2 structure:
struct { struct {
LogID log_id; LogID log_id;
TreeHeadDataV2 tree_head; TreeHeadDataV2 tree_head;
opaque signature<1..2^16-1>; opaque signature<1..2^16-1>;
} SignedTreeHeadDataV2; } SignedTreeHeadDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as log_id is this log's unique ID encoded in an opaque vector, as
described in Section 4.4. described in Section 4.4.
The "timestamp" in "tree_head" MUST be at least as recent as the most The timestamp in tree_head MUST be at least as recent as the most
recent SCT timestamp in the tree. Each subsequent timestamp MUST be recent SCT timestamp in the tree. Each subsequent timestamp MUST be
more recent than the timestamp of the previous update. more recent than the timestamp of the previous update.
"tree_head" contains the latest tree head information (see tree_head contains the latest tree head information (see
Section 4.9). Section 4.9).
"signature" is computed over the "tree_head" field using the signature is computed over the tree_head field using the signature
signature algorithm declared in the log's parameters (see algorithm declared in the log's parameters (see Section 4.1).
Section 4.1).
4.11. Merkle Consistency Proofs 4.11. Merkle Consistency Proofs
To prepare a Merkle Consistency Proof for distribution to clients, To prepare a Merkle consistency proof for distribution to clients,
the log produces a "TransItem" structure of type the log produces a TransItem structure of type consistency_proof_v2,
"consistency_proof_v2", which encapsulates a "ConsistencyProofDataV2" which encapsulates a ConsistencyProofDataV2 structure:
structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size_1; uint64 tree_size_1;
uint64 tree_size_2; uint64 tree_size_2;
NodeHash consistency_path<0..2^16-1>; NodeHash consistency_path<0..2^16-1>;
} ConsistencyProofDataV2; } ConsistencyProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as log_id is this log's unique ID encoded in an opaque vector, as
described in Section 4.4. described in Section 4.4.
"tree_size_1" is the size of the older tree. tree_size_1 is the size of the older tree.
"tree_size_2" is the size of the newer tree. tree_size_2 is the size of the newer tree.
"consistency_path" is a vector of Merkle Tree nodes proving the consistency_path is a vector of Merkle Tree nodes proving the
consistency of two STHs as described in Section 2.1.4. consistency of two STHs, as described in Section 2.1.4.
4.12. Merkle Inclusion Proofs 4.12. Merkle Inclusion Proofs
To prepare a Merkle Inclusion Proof for distribution to clients, the To prepare a Merkle inclusion proof for distribution to clients, the
log produces a "TransItem" structure of type "inclusion_proof_v2", log produces a TransItem structure of type inclusion_proof_v2, which
which encapsulates an "InclusionProofDataV2" structure: encapsulates an InclusionProofDataV2 structure:
struct { struct {
LogID log_id; LogID log_id;
uint64 tree_size; uint64 tree_size;
uint64 leaf_index; uint64 leaf_index;
NodeHash inclusion_path<0..2^16-1>; NodeHash inclusion_path<0..2^16-1>;
} InclusionProofDataV2; } InclusionProofDataV2;
"log_id" is this log's unique ID, encoded in an opaque vector as log_id is this log's unique ID encoded in an opaque vector, as
described in Section 4.4. described in Section 4.4.
"tree_size" is the size of the tree on which this inclusion proof is tree_size is the size of the tree on which this inclusion proof is
based. based.
"leaf_index" is the 0-based index of the log entry corresponding to leaf_index is the 0-based index of the log entry corresponding to
this inclusion proof. this inclusion proof.
"inclusion_path" is a vector of Merkle Tree nodes proving the inclusion_path is a vector of Merkle Tree nodes proving the inclusion
inclusion of the chosen certificate or precertificate as described in of the chosen certificate or precertificate, as described in
Section 2.1.3. Section 2.1.3.
4.13. Shutting down a log 4.13. Shutting Down a Log
Log operators may decide to shut down a log for various reasons, such Log operators may decide to shut down a log for various reasons, such
as deprecation of the signature algorithm. If there are entries in as deprecation of the signature algorithm. If there are entries in
the log for certificates that have not yet expired, simply making TLS the log for certificates that have not yet expired, simply making TLS
clients stop recognizing that log will have the effect of clients stop recognizing that log will have the effect of
invalidating SCTs from that log. In order to avoid that, the invalidating SCTs from that log. In order to avoid that, the
following actions SHOULD be taken: following actions SHOULD be taken:
* Make it known to clients and monitors that the log will be frozen. * Make it known to clients and monitors that the log will be frozen.
This is not part of the API, so it will have to be done via a This is not part of the API, so it will have to be done via a
relevant out-of-band mechanism. relevant out-of-band mechanism.
* Stop accepting new submissions (the error code "shutdown" should * Stop accepting new submissions (the error code "shutdown" should
be returned for such requests). be returned for such requests).
* Once MMD from the last accepted submission has passed and all * Once MMD from the last accepted submission has passed and all
pending submissions are incorporated, issue a final STH and pending submissions are incorporated, issue a final STH and
publish it as one of the log's parameters. Having an STH with a publish it as one of the log's parameters. Having an STH with a
timestamp that is after the MMD has passed from the last SCT timestamp that is after the MMD has passed from the last SCT
issuance allows clients to audit this log regularly without issuance allows clients to audit this log regularly without
special handling for the final STH. At this point the log's special handling for the final STH. At this point, the log's
private key is no longer needed and can be destroyed. private key is no longer needed and can be destroyed.
* Keep the log running until the certificates in all of its entries * Keep the log running until the certificates in all of its entries
have expired or exist in other logs (this can be determined by have expired or exist in other logs (this can be determined by
scanning other logs or connecting to domains mentioned in the scanning other logs or connecting to domains mentioned in the
certificates and inspecting the SCTs served). certificates and inspecting the SCTs served).
5. Log Client Messages 5. Log Client Messages
Messages are sent as HTTPS GET or POST requests. Parameters for Messages are sent as HTTPS GET or POST requests. Parameters for
POSTs and all responses are encoded as JavaScript Object Notation POSTs and all responses are encoded as JavaScript Object Notation
(JSON) objects [RFC8259]. Parameters for GETs are encoded as order- (JSON) objects [RFC8259]. Parameters for GETs are encoded as order-
independent key/value URL parameters, using the "application/x-www- independent key/value URL parameters, using the "application/x-www-
form-urlencoded" format described in the "HTML 4.01 Specification" form-urlencoded" format described in the "HTML 4.01 Specification"
[HTML401]. Binary data is base64 encoded according to section 4 of [HTML401]. Binary data is base64 encoded according to Section 4 of
[RFC4648] as specified in the individual messages. [RFC4648], as specified in the individual messages.
Clients are configured with a log's base URL, which is one of the Clients are configured with a log's base URL, which is one of the
log's parameters. Clients construct URLs for requests by appending log's parameters. Clients construct URLs for requests by appending
suffixes to this base URL. This structure places some degree of suffixes to this base URL. This structure places some degree of
restriction on how log operators can deploy these services, as noted restriction on how log operators can deploy these services, as noted
in [RFC8820]. However, operational experience with version 1 of this in [RFC8820]. However, operational experience with version 1 of this
protocol has not indicated that these restrictions are a problem in protocol has not indicated that these restrictions are a problem in
practice. practice.
Note that JSON objects and URL parameters may contain fields not Note that JSON objects and URL parameters may contain fields not
specified here, to allow for experimentation. Any fields that are specified here to allow for experimentation. Any fields that are not
not understood SHOULD be ignored. understood SHOULD be ignored.
In practice, log servers may include multiple front-end machines. In practice, log servers may include multiple front-end machines.
Since it is impractical to keep these machines in perfect sync, Since it is impractical to keep these machines in perfect sync,
errors may occur that are caused by skew between the machines. Where errors that are caused by skew between the machines may occur. Where
such errors are possible, the front-end will return additional such errors are possible, the front end will return additional
information (as specified below) making it possible for clients to information (as specified below), making it possible for clients to
make progress, if progress is possible. Front-ends MUST only serve make progress, if progress is possible. Front ends MUST only serve
data that is free of gaps (that is, for example, no front-end will data that is free of gaps (that is, for example, no front end will
respond with an STH unless it is also able to prove consistency from respond with an STH unless it is also able to prove consistency from
all log entries logged within that STH). all log entries logged within that STH).
For example, when a consistency proof between two STHs is requested, For example, when a consistency proof between two STHs is requested,
the front-end reached may not yet be aware of one or both STHs. In the front end reached may not yet be aware of one or both STHs. In
the case where it is unaware of both, it will return the latest STH the case where it is unaware of both, it will return the latest STH
it is aware of. Where it is aware of the first but not the second, it is aware of. Where it is aware of the first but not the second,
it will return the latest STH it is aware of and a consistency proof it will return the latest STH it is aware of and a consistency proof
from the first STH to the returned STH. The case where it knows the from the first STH to the returned STH. The case where it knows the
second but not the first should not arise (see the "no gaps" second but not the first should not arise (see the "no gaps"
requirement above). requirement above).
If the log is unable to process a client's request, it MUST return an If the log is unable to process a client's request, it MUST return an
HTTP response code of 4xx/5xx (see [RFC7231]), and, in place of the HTTP response code of 4xx/5xx (see [RFC7231]), and, in place of the
responses outlined in the subsections below, the body SHOULD be a responses outlined in the subsections below, the body SHOULD be a
JSON Problem Details Object (see [RFC7807] Section 3), containing: JSON problem details object (see Section 3 of [RFC7807]) containing:
type: A URN reference identifying the problem. To facilitate type: A URN reference identifying the problem. To facilitate
automated response to errors, this document defines a set of automated response to errors, this document defines a set of
standard tokens for use in the "type" field, within the URN standard tokens for use in the type field within the URN namespace
namespace of: "urn:ietf:params:trans:error:". of: "urn:ietf:params:trans:error:".
detail: A human-readable string describing the error that prevented detail: A human-readable string describing the error that prevented
the log from processing the request, ideally with sufficient the log from processing the request, ideally with sufficient
detail to enable the error to be rectified. detail to enable the error to be rectified.
e.g., In response to a request of "<Base URL>/ct/v2/get- For example, in response to a request of <Base URL>/ct/v2/get-
entries?start=100&end=99", the log would return a "400 Bad Request" entries?start=100&end=99, the log would return a 400 Bad Request
response code with a body similar to the following: response code with a body similar to the following:
{ {
"type": "urn:ietf:params:trans:error:endBeforeStart", "type": "urn:ietf:params:trans:error:endBeforeStart",
"detail": "'start' cannot be greater than 'end'" "detail": "'start' cannot be greater than 'end'"
} }
Most error types are specific to the type of request and are defined Most error types are specific to the type of request and are defined
in the respective subsections below. The one exception is the in the respective subsections below. The one exception is the
"malformed" error type, which indicates that the log server could not "malformed" error type, which indicates that the log server could not
skipping to change at page 30, line 19 skipping to change at line 1335
document: document:
+===========+==================================+ +===========+==================================+
| type | detail | | type | detail |
+===========+==================================+ +===========+==================================+
| malformed | The request could not be parsed. | | malformed | The request could not be parsed. |
+-----------+----------------------------------+ +-----------+----------------------------------+
Table 1 Table 1
Clients SHOULD treat "500 Internal Server Error" and "503 Service Clients SHOULD treat 500 Internal Server Error and 503 Service
Unavailable" responses as transient failures and MAY retry the same Unavailable responses as transient failures and MAY retry the same
request without modification at a later date. Note that as per request without modification at a later date. Note that in the case
[RFC7231], in the case of a 503 response the log MAY include a of a 503 response, the log MAY include a Retry-After header field per
"Retry-After:" header field in order to request a minimum time for [RFC7231] in order to request a minimum time for the client to wait
the client to wait before retrying the request. In the absence of before retrying the request. In the absence of this header field,
this header field, this document does not specify a minimum. this document does not specify a minimum.
Clients SHOULD treat any 4xx error as a problem with the request and Clients SHOULD treat any 4xx error as a problem with the request and
not attempt to resubmit without some modification to the request. not attempt to resubmit without some modification to the request.
The full status code MAY provide additional details. The full status code MAY provide additional details.
This document deliberately does not provide more specific guidance on This document deliberately does not provide more specific guidance on
the use of HTTP status codes. the use of HTTP status codes.
5.1. Submit Entry to Log 5.1. Submit Entry to Log
POST <Base URL>/ct/v2/submit-entry POST <Base URL>/ct/v2/submit-entry
Inputs: submission: The base64 encoded certificate or Inputs:
precertificate. submission: The base64-encoded certificate or precertificate.
type: The "VersionedTransType" integer value that indicates type: The VersionedTransType integer value that indicates the
the type of the "submission": 1 for "x509_entry_v2", or 2 for type of the submission: 1 for x509_entry_v2 or 2 for
"precert_entry_v2". precert_entry_v2.
chain: An array of zero or more JSON strings, each of which chain: An array of zero or more JSON strings, each of which is a
is a base64 encoded CA certificate. The first element is the base64-encoded CA certificate. The first element is the
certifier of the "submission"; the second certifies the first; certifier of the submission, the second certifies the first,
etc. The last element of "chain" (or, if "chain" is an empty etc. The last element of chain (or, if chain is an empty
array, the "submission") is certified by an accepted trust array, the submission) is certified by an accepted trust
anchor. anchor.
Outputs: sct: A base64 encoded "TransItem" of type "x509_sct_v2" or Outputs:
"precert_sct_v2", signed by this log, that corresponds to the sct: A base64-encoded TransItem of type x509_sct_v2 or
"submission". precert_sct_v2, signed by this log, that corresponds to the
submission.
If the submitted entry is immediately appended to (or already If the submitted entry is immediately appended to (or already
exists in) this log's tree, then the log SHOULD also output: exists in) this log's tree, then the log SHOULD also output:
sth: A base64 encoded "TransItem" of type "signed_tree_head_v2", sth: A base64-encoded TransItem of type signed_tree_head_v2
signed by this log. signed by this log.
inclusion: A base64 encoded "TransItem" of type inclusion: A base64-encoded TransItem of type inclusion_proof_v2
"inclusion_proof_v2" whose "inclusion_path" array of Merkle whose inclusion_path array of Merkle Tree nodes proves the
Tree nodes proves the inclusion of the "submission" in the inclusion of the submission in the returned sth.
returned "sth".
Error codes: Error codes:
+================+==============================================+ +================+===============================================+
| type | detail | | type | detail |
+================+==============================================+ +================+===============================================+
| badSubmission | "submission" is neither a valid certificate | | badSubmission | submission is neither a valid certificate nor |
| | nor a valid precertificate. | | | a valid precertificate. |
+----------------+----------------------------------------------+ +----------------+-----------------------------------------------+
| badType | "type" is neither 1 nor 2. | | badType | type is neither 1 nor 2. |
+----------------+----------------------------------------------+ +----------------+-----------------------------------------------+
| badChain | The first element of "chain" is not the | | badChain | The first element of chain is not the |
| | certifier of the "submission", or the second | | | certifier of the submission, or the second |
| | element does not certify the first, etc. | | | element does not certify the first, etc. |
+----------------+----------------------------------------------+ +----------------+-----------------------------------------------+
| badCertificate | One or more certificates in the "chain" are | | badCertificate | One or more certificates in chain are not |
| | not valid (e.g., not properly encoded). | | | valid (e.g., not properly encoded). |
+----------------+----------------------------------------------+ +----------------+-----------------------------------------------+
| unknownAnchor | The last element of "chain" (or, if "chain" | | unknownAnchor | The last element of chain (or, if chain is an |
| | is an empty array, the "submission") both is | | | empty array, the submission) is not, nor is |
| | not, and is not certified by, an accepted | | | it certified by, an accepted trust anchor. |
| | trust anchor. | +----------------+-----------------------------------------------+
+----------------+----------------------------------------------+ | shutdown | The log is no longer accepting submissions. |
| shutdown | The log is no longer accepting submissions. | +----------------+-----------------------------------------------+
+----------------+----------------------------------------------+
Table 2 Table 2
If the version of "sct" is not v2, then a v2 client may be unable to If the version of sct is not v2, then a v2 client may be unable to
verify the signature. It MUST NOT construe this as an error. This verify the signature. It MUST NOT construe this as an error. This
is to avoid forcing an upgrade of compliant v2 clients that do not is to avoid forcing an upgrade of compliant v2 clients that do not
use the returned SCTs. use the returned SCTs.
If a log detects bad encoding in a chain that otherwise verifies If a log detects bad encoding in a chain that otherwise verifies
correctly then the log MUST either log the certificate or return the correctly, then the log MUST either log the certificate or return the
"bad certificate" error. If the certificate is logged, an SCT MUST "badCertificate" error. If the certificate is logged, an SCT MUST be
be issued. Logging the certificate is useful, because monitors issued. Logging the certificate is useful, because monitors
(Section 8.2) can then detect these encoding errors, which may be (Section 8.2) can then detect these encoding errors, which may be
accepted by some TLS clients. accepted by some TLS clients.
If "submission" is an accepted trust anchor whose certifier is If submission is an accepted trust anchor whose certifier is neither
neither an accepted trust anchor nor the first element of "chain", an accepted trust anchor nor the first element of chain, then the log
then the log MUST return the "unknown anchor" error. A log is not MUST return the "unknownAnchor" error. A log is not able to generate
able to generate an SCT for a submission if it does not have access an SCT for a submission if it does not have access to the issuer's
to the issuer's public key. public key.
If the returned "sct" is intended to be provided to TLS clients, then If the returned sct is intended to be provided to TLS clients, then
"sth" and "inclusion" (if returned) SHOULD also be provided to TLS sth and inclusion (if returned) SHOULD also be provided to TLS
clients. For example, if "type" was 2 (indicating "precert_sct_v2") clients. For example, if type was 2 (indicating precert_sct_v2),
then all three "TransItem"s could be embedded in the certificate. then all three TransItems could be embedded in the certificate.
5.2. Retrieve Latest STH 5.2. Retrieve Latest STH
GET <Base URL>/ct/v2/get-sth GET <Base URL>/ct/v2/get-sth
No inputs. No inputs.
Outputs: sth: A base64 encoded "TransItem" of type Outputs:
"signed_tree_head_v2", signed by this log, that is no older sth: A base64-encoded TransItem of type signed_tree_head_v2
than the log's MMD. signed by this log that is no older than the log's MMD.
5.3. Retrieve Merkle Consistency Proof between Two STHs 5.3. Retrieve Merkle Consistency Proof between Two STHs
GET <Base URL>/ct/v2/get-sth-consistency GET <Base URL>/ct/v2/get-sth-consistency
Inputs: first: The tree_size of the older tree, in decimal. Inputs:
first: The tree_size of the older tree, in decimal.
second: The tree_size of the newer tree, in decimal second: The tree_size of the newer tree, in decimal (optional).
(optional).
Both tree sizes must be from existing v2 STHs. However, because Both tree sizes must be from existing v2 STHs. However, because
of skew, the receiving front-end may not know one or both of the of skew, the receiving front end may not know one or both of the
existing STHs. If both are known, then only the "consistency" existing STHs. If both are known, then only the consistency
output is returned. If the first is known but the second is not output is returned. If the first is known but the second is not
(or has been omitted), then the latest known STH is returned, (or has been omitted), then the latest known STH is returned,
along with a consistency proof between the first STH and the along with a consistency proof between the first STH and the
latest. If neither are known, then the latest known STH is latest. If neither are known, then the latest known STH is
returned without a consistency proof. returned without a consistency proof.
Outputs: consistency: A base64 encoded "TransItem" of type Outputs:
"consistency_proof_v2", whose "tree_size_1" MUST match the consistency: A base64-encoded TransItem of type
"first" input. If the "sth" output is omitted, then consistency_proof_v2 whose tree_size_1 MUST match the first
"tree_size_2" MUST match the "second" input. If "first" and input. If the sth output is omitted, then tree_size_2 MUST
"second" are equal and correspond to a known STH, the returned match the second input. If first and second are equal and
consistency proof MUST be empty (a "consistency_path" array correspond to a known STH, the returned consistency proof MUST
with zero elements). be empty (a consistency_path array with zero elements).
sth: A base64 encoded "TransItem" of type sth: A base64-encoded TransItem of type signed_tree_head_v2,
"signed_tree_head_v2", signed by this log. signed by this log.
Note that no signature is required for the "consistency" output as Note that no signature is required for the consistency output, as
it is used to verify the consistency between two STHs, which are it is used to verify the consistency between two signed STHs.
signed.
Error codes: Error codes:
+===================+======================================+ +===================+======================================+
| type | detail | | type | detail |
+===================+======================================+ +===================+======================================+
| firstUnknown | "first" is before the latest known | | firstUnknown | first is before the latest known STH |
| | STH but is not from an existing STH. | | | but is not from an existing STH. |
+-------------------+--------------------------------------+ +-------------------+--------------------------------------+
| secondUnknown | "second" is before the latest known | | secondUnknown | second is before the latest known |
| | STH but is not from an existing STH. | | | STH but is not from an existing STH. |
+-------------------+--------------------------------------+ +-------------------+--------------------------------------+
| secondBeforeFirst | "second" is smaller than "first". | | secondBeforeFirst | second is smaller than first. |
+-------------------+--------------------------------------+ +-------------------+--------------------------------------+
Table 3 Table 3
See Section 2.1.4.2 for an outline of how to use the "consistency" See Section 2.1.4.2 for an outline of how to use the consistency
output. output.
5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash 5.4. Retrieve Merkle Inclusion Proof from Log by Leaf Hash
GET <Base URL>/ct/v2/get-proof-by-hash GET <Base URL>/ct/v2/get-proof-by-hash
Inputs: hash: A base64 encoded v2 leaf hash. Inputs:
hash: A base64-encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the tree_size: The tree_size of the tree on which to base the proof,
proof, in decimal. in decimal.
The "hash" must be calculated as defined in Section 4.7. A v2 STH The hash must be calculated as defined in Section 4.7. A v2 STH
must exist for the "tree_size". Because of skew, the front-end must exist for the tree_size. Because of skew, the front end may
may not know the requested tree head. In that case, it will not know the requested tree head. In that case, it will return
return the latest STH it knows, along with an inclusion proof to the latest STH it knows, along with an inclusion proof to that
that STH. If the front-end knows the requested tree head then STH. If the front end knows the requested tree head, then only
only "inclusion" is returned. inclusion is returned.
Outputs: inclusion: A base64 encoded "TransItem" of type Outputs:
"inclusion_proof_v2" whose "inclusion_path" array of Merkle inclusion: A base64-encoded TransItem of type inclusion_proof_v2
Tree nodes proves the inclusion of the certificate (as whose inclusion_path array of Merkle Tree nodes proves the
specified by the "hash" parameter) in the selected STH. inclusion of the certificate (as specified by the hash
parameter) in the selected STH.
sth: A base64 encoded "TransItem" of type sth: A base64-encoded TransItem of type signed_tree_head_v2,
"signed_tree_head_v2", signed by this log. signed by this log.
Note that no signature is required for the "inclusion" output as Note that no signature is required for the inclusion output, as it
it is used to verify inclusion in the selected STH, which is is used to verify inclusion in the selected STH, which is signed.
signed.
Error codes: Error codes:
+=================+=====================================+ +=================+=====================================+
| type | detail | | type | detail |
+=================+=====================================+ +=================+=====================================+
| hashUnknown | "hash" is not the hash of a known | | hashUnknown | hash is not the hash of a known |
| | leaf (may be caused by skew or by a | | | leaf (may be caused by skew or by a |
| | known certificate not yet merged). | | | known certificate not yet merged). |
+-----------------+-------------------------------------+ +-----------------+-------------------------------------+
| treeSizeUnknown | "hash" is before the latest known | | treeSizeUnknown | hash is before the latest known STH |
| | STH but is not from an existing | | | but is not from an existing STH. |
| | STH. |
+-----------------+-------------------------------------+ +-----------------+-------------------------------------+
Table 4 Table 4
See Section 2.1.3.2 for an outline of how to use the "inclusion" See Section 2.1.3.2 for an outline of how to use the inclusion
output. output.
5.5. Retrieve Merkle Inclusion Proof, STH and Consistency Proof by Leaf 5.5. Retrieve Merkle Inclusion Proof, STH, and Consistency Proof by
Hash Leaf Hash
GET <Base URL>/ct/v2/get-all-by-hash GET <Base URL>/ct/v2/get-all-by-hash
Inputs: hash: A base64 encoded v2 leaf hash. Inputs:
hash: A base64-encoded v2 leaf hash.
tree_size: The tree_size of the tree on which to base the tree_size: The tree_size of the tree on which to base the proofs,
proofs, in decimal. in decimal.
The "hash" must be calculated as defined in Section 4.7. A v2 STH The hash must be calculated as defined in Section 4.7. A v2 STH
must exist for the "tree_size". must exist for the tree_size.
Because of skew, the front-end may not know the requested tree head Because of skew, the front end may not know the requested tree head
or the requested hash, which leads to a number of cases: or the requested hash, which leads to a number of cases:
+=====================+=====================================+ +=====================+=====================================+
| Case | Response | | Case | Response |
+=====================+=====================================+ +=====================+=====================================+
| latest STH < | Return latest STH | | latest STH < | Return latest STH. |
| requested tree head | | | requested tree head | |
+---------------------+-------------------------------------+ +---------------------+-------------------------------------+
| latest STH > | Return latest STH and a consistency | | latest STH > | Return latest STH and a consistency |
| requested tree head | proof between it and the requested | | requested tree head | proof between it and the requested |
| | tree head (see Section 5.3) | | | tree head (see Section 5.3). |
+---------------------+-------------------------------------+ +---------------------+-------------------------------------+
| index of requested | Return "inclusion" | | index of requested | Return inclusion. |
| hash < latest STH | | | hash < latest STH | |
+---------------------+-------------------------------------+ +---------------------+-------------------------------------+
Table 5 Table 5
Note that more than one case can be true, in which case the returned Note that more than one case can be true; in which case, the returned
data is their union. It is also possible for none to be true, in data is their union. It is also possible for none to be true; in
which case the front-end MUST return an empty response. which case, the front end MUST return an empty response.
Outputs: inclusion: A base64 encoded "TransItem" of type Outputs:
"inclusion_proof_v2" whose "inclusion_path" array of Merkle inclusion: A base64-encoded TransItem of type inclusion_proof_v2
Tree nodes proves the inclusion of the certificate (as whose inclusion_path array of Merkle Tree nodes proves the
specified by the "hash" parameter) in the selected STH. inclusion of the certificate (as specified by the hash
parameter) in the selected STH.
sth: A base64 encoded "TransItem" of type sth: A base64-encoded TransItem of type signed_tree_head_v2,
"signed_tree_head_v2", signed by this log. signed by this log.
consistency: A base64 encoded "TransItem" of type consistency: A base64-encoded TransItem of type
"consistency_proof_v2" that proves the consistency of the consistency_proof_v2 that proves the consistency of the
requested tree head and the returned STH. requested tree head and the returned STH.
Note that no signature is required for the "inclusion" or Note that no signature is required for the inclusion or
"consistency" outputs as they are used to verify inclusion in and consistency outputs, as they are used to verify inclusion in and
consistency of STHs, which are signed. consistency of signed STHs.
Errors are the same as in Section 5.4. Errors are the same as in Section 5.4.
See Section 2.1.3.2 for an outline of how to use the "inclusion" See Section 2.1.3.2 for an outline of how to use the inclusion
output, and see Section 2.1.4.2 for an outline of how to use the output, and see Section 2.1.4.2 for an outline of how to use the
"consistency" output. consistency output.
5.6. Retrieve Entries and STH from Log 5.6. Retrieve Entries and STH from Log
GET <Base URL>/ct/v2/get-entries GET <Base URL>/ct/v2/get-entries
Inputs: start: 0-based index of first entry to retrieve, in Inputs:
decimal. start: 0-based index of first entry to retrieve, in decimal.
end: 0-based index of last entry to retrieve, in decimal. end: 0-based index of last entry to retrieve, in decimal.
Outputs: entries: An array of objects, each consisting of Outputs:
entries: An array of objects, each consisting of:
log_entry: The base64 encoded "TransItem" structure of type log_entry: The base64-encoded TransItem structure of type
"x509_entry_v2" or "precert_entry_v2" (see Section 4.3). x509_entry_v2 or precert_entry_v2 (see Section 4.3).
submitted_entry: JSON object equivalent to inputs that were submitted_entry: JSON object equivalent to inputs that were
submitted to "submit-entry", with the addition of the trust submitted to submit-entry, with the addition of the trust
anchor to the "chain" field if the submission did not anchor to the chain field if the submission did not include
include it. it.
sct: The base64 encoded "TransItem" of type "x509_sct_v2" or sct: The base64-encoded TransItem of type x509_sct_v2 or
"precert_sct_v2" corresponding to this log entry. precert_sct_v2, corresponding to this log entry.
sth: A base64 encoded "TransItem" of type sth: A base64-encoded TransItem of type signed_tree_head_v2,
"signed_tree_head_v2", signed by this log. signed by this log.
Note that this message is not signed -- the "entries" data can be Note that this message is not signed -- the entries data can be
verified by constructing the Merkle Tree Hash corresponding to a verified by constructing the Merkle Tree Hash corresponding to a
retrieved STH. All leaves MUST be v2. However, a compliant v2 retrieved STH. All leaves MUST be v2. However, a compliant v2
client MUST NOT construe an unrecognized TransItem type as an error. client MUST NOT construe an unrecognized TransItem type as an error.
This means it may be unable to parse some entries, but note that each This means it may be unable to parse some entries, but note that each
client can inspect the entries it does recognize as well as verify client can inspect the entries it does recognize as well as verify
the integrity of the data by treating unrecognized leaves as opaque the integrity of the data by treating unrecognized leaves as opaque
input to the tree. input to the tree.
The "start" and "end" parameters SHOULD be within the range 0 <= x < The start and end parameters SHOULD be within the range 0 <= x <
"tree_size" as returned by "get-sth" in Section 5.2. tree_size, as returned by get-sth in Section 5.2.
The "start" parameter MUST be less than or equal to the "end" The start parameter MUST be less than or equal to the end parameter.
parameter.
Each "submitted_entry" output parameter MUST include the trust anchor Each submitted_entry output parameter MUST include the trust anchor
that the log used to verify the "submission", even if that trust that the log used to verify the submission, even if that trust anchor
anchor was not provided to "submit-entry" (see Section 5.1). If the was not provided to submit-entry (see Section 5.1). If the
"submission" does not certify itself, then the first element of submission does not certify itself, then the first element of chain
"chain" MUST be present and MUST certify the "submission". MUST be present and MUST certify the submission.
Log servers MUST honor requests where 0 <= "start" < "tree_size" and Log servers MUST honor requests where 0 <= start < tree_size and end
"end" >= "tree_size" by returning a partial response covering only >= tree_size by returning a partial response covering only the valid
the valid entries in the specified range. "end" >= "tree_size" could entries in the specified range. end >= tree_size could be caused by
be caused by skew. Note that the following restriction may also skew. Note that the following restriction may also apply:
apply:
Logs MAY restrict the number of entries that can be retrieved per Logs MAY restrict the number of entries that can be retrieved per
"get-entries" request. If a client requests more than the permitted get-entries request. If a client requests more than the permitted
number of entries, the log SHALL return the maximum number of entries number of entries, the log SHALL return the maximum number of entries
permissible. These entries SHALL be sequential beginning with the permissible. These entries SHALL be sequential beginning with the
entry specified by "start". Note that limit on the number of entries entry specified by start. Note that a limit on the number of entries
is not immutable and therefore the restriction may be changed or is not immutable, and therefore the restriction may be changed or
lifted at any time and is not listed with the other Log Parameters in lifted at any time and is not listed with the other Log Parameters in
Section 4.1. Section 4.1.
Because of skew, it is possible the log server will not have any Because of skew, it is possible the log server will not have any
entries between "start" and "end". In this case it MUST return an entries between start and end. In this case, it MUST return an empty
empty "entries" array. entries array.
In any case, the log server MUST return the latest STH it knows In any case, the log server MUST return the latest STH it knows
about. about.
See Section 2.1.2 for an outline of how to use a complete list of See Section 2.1.2 for an outline of how to use a complete list of
"log_entry" entries to verify the "root_hash". log_entry entries to verify the root_hash.
Error codes: Error codes:
+================+====================================+ +================+==================================+
| type | detail | | type | detail |
+================+====================================+ +================+==================================+
| startUnknown | "start" is greater than the number | | startUnknown | start is greater than the number |
| | of entries in the Merkle tree. | | | of entries in the Merkle Tree. |
+----------------+------------------------------------+ +----------------+----------------------------------+
| endBeforeStart | "start" cannot be greater than | | endBeforeStart | start cannot be greater than |
| | "end". | | | end. |
+----------------+------------------------------------+ +----------------+----------------------------------+
Table 6 Table 6
5.7. Retrieve Accepted Trust Anchors 5.7. Retrieve Accepted Trust Anchors
GET <Base URL>/ct/v2/get-anchors GET <Base URL>/ct/v2/get-anchors
No inputs. No inputs.
Outputs: certificates: An array of JSON strings, each of which is a Outputs:
base64 encoded CA certificate that is acceptable to the log. certificates: An array of JSON strings, each of which is a
base64-encoded CA certificate that is acceptable to the log.
max_chain_length: If the server has chosen to limit the max_chain_length: If the server has chosen to limit the length of
length of chains it accepts, this is the maximum number of chains it accepts, this is the maximum number of certificates
certificates in the chain, in decimal. If there is no limit, in the chain, in decimal. If there is no limit, this is
this is omitted. omitted.
This data is not signed and the protocol depends on the security This data is not signed, and the protocol depends on the security
guarantees of TLS to ensure correctness. guarantees of TLS to ensure correctness.
6. TLS Servers 6. TLS Servers
CT-using TLS servers MUST use at least one of the mechanisms CT-using TLS servers MUST use at least one of the mechanisms
described below to present one or more SCTs from one or more logs to described below to present one or more SCTs from one or more logs to
each TLS client during full TLS handshakes, when requested by the each TLS client during full TLS handshakes, when requested by the
client, where each SCT corresponds to the server certificate. (Of client, where each SCT corresponds to the server certificate. (Of
course, a server can only send a TLS extension if the client has course, a server can only send a TLS extension if the client has
specified it first.) Servers SHOULD also present corresponding specified it first.) Servers SHOULD also present corresponding
inclusion proofs and STHs. inclusion proofs and STHs.
A server can provide SCTs using a TLS 1.3 extension (Section 4.2 of A server can provide SCTs using a TLS 1.3 extension (Section 4.2 of
[RFC8446]) with type "transparency_info" (see Section 6.5). This [RFC8446]) with type transparency_info (see Section 6.5). This
mechanism allows TLS servers to participate in CT without the mechanism allows TLS servers to participate in CT without the
cooperation of CAs, unlike the other two mechanisms. It also allows cooperation of CAs, unlike the other two mechanisms. It also allows
SCTs and inclusion proofs to be updated on the fly. SCTs and inclusion proofs to be updated on the fly.
The server may also use an Online Certificate Status Protocol (OCSP) The server may also use an Online Certificate Status Protocol (OCSP)
[RFC6960] response extension (see Section 7.1.1), providing the OCSP [RFC6960] response extension (see Section 7.1.1), providing the OCSP
response as part of the TLS handshake. Providing a response during a response as part of the TLS handshake. Providing a response during a
TLS handshake is popularly known as "OCSP stapling." For TLS 1.3, TLS handshake is popularly known as "OCSP stapling". For TLS 1.3,
the information is encoded as an extension in the "status_request" the information is encoded as an extension in the status_request
extension data; see Section 4.4.2.1 of [RFC8446]. For TLS 1.2 extension data; see Section 4.4.2.1 of [RFC8446]. For TLS 1.2
([RFC5246]), the information is encoded in the "CertificateStatus" [RFC5246], the information is encoded in the CertificateStatus
message; see Section 8 of [RFC6066]. Using stapling also allows SCTs message; see Section 8 of [RFC6066]. Using stapling also allows SCTs
and inclusion proofs to be updated on the fly. and inclusion proofs to be updated on the fly.
CT information can also be encoded as an extension in the X.509v3 CT information can also be encoded as an extension in the X.509v3
certificate (see Section 7.1.2). This mechanism allows the use of certificate (see Section 7.1.2). This mechanism allows the use of
unmodified TLS servers, but the SCTs and inclusion proofs cannot be unmodified TLS servers, but the SCTs and inclusion proofs cannot be
updated on the fly. Since the logs from which the SCTs and inclusion updated on the fly. Since the logs from which the SCTs and inclusion
proofs originated won't necessarily be accepted by TLS clients for proofs originated won't necessarily be accepted by TLS clients for
the full lifetime of the certificate, there is a risk that TLS the full lifetime of the certificate, there is a risk that TLS
clients may subsequently consider the certificate to be non-compliant clients may subsequently consider the certificate to be noncompliant.
and in need of re-issuance or the use of one of the other two methods In such an event, one of the other two mechanisms will need to be
for delivering CT information. used to deliver CT information, or, if this is not possible, the
certificate will need to be reissued.
6.1. TLS Client Authentication 6.1. TLS Client Authentication
This specification includes no description of how a TLS server can This specification includes no description of how a TLS server can
use CT for TLS client certificates. While this may be useful, it is use CT for TLS client certificates. While this may be useful, it is
not documented here for the following reasons: not documented here for the following reasons:
* The greater security exposure is for clients to end up interacting * The greater security exposure is for clients to end up interacting
with an illegitimate server. with an illegitimate server.
* In general, TLS client certificates are not expected to be * In general, TLS client certificates are not expected to be
submitted to CT logs, particularly those intended for general submitted to CT logs, particularly those intended for general
public use. public use.
A future version could include such information. A future version could include such information.
6.2. Multiple SCTs 6.2. Multiple SCTs
CT-using TLS servers SHOULD send SCTs from multiple logs, because: CT-using TLS servers SHOULD send SCTs from multiple logs because:
* One or more logs may not have become acceptable to all CT-using * The set of logs trusted by TLS clients is neither unified nor
TLS clients. Note that client discovery, trust, and distrust of static; each client vendor may maintain an independent list of
logs is expected to be handled out-of-band and is out of scope of trusted logs, and, over time, new logs may become trusted and
this document. current logs may become distrusted. Note that client discovery,
trust, and distrust of logs are expected to be handled out of band
and are out of scope of this document.
* If a CA and a log collude, it is possible to temporarily hide * If a CA and a log collude, it is possible to temporarily hide
misissuance from clients. When a TLS client requires SCTs from misissuance from clients. When a TLS client requires SCTs from
multiple logs to be provided, it is more difficult to mount this multiple logs to be provided, it is more difficult to mount this
attack. attack.
* If a log misbehaves or suffers a key compromise, a consequence may * If a log misbehaves or suffers a key compromise, a consequence may
be that clients cease to trust it. Since the time an SCT may be be that clients cease to trust it. Since the time an SCT may be
in use can be considerable (several years is common in current in use can be considerable (several years is common in current
practice when embedded in a certificate), including SCTs from practice when embedded in a certificate), including SCTs from
multiple logs reduces the probability of the certificate being multiple logs reduces the probability of the certificate being
rejected by TLS clients. rejected by TLS clients.
* TLS clients may have policies related to the above risks requiring * TLS clients may have policies related to the above risks requiring
TLS servers to present multiple SCTs. For example, at the time of TLS servers to present multiple SCTs. For example, at the time of
writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to writing, Chromium [Chromium.Log.Policy] requires multiple SCTs to
be presented with EV certificates in order for the EV indicator to be presented with Extended Validation (EV) certificates in order
be shown. for the EV indicator to be shown.
To select the logs from which to obtain SCTs, a TLS server can, for To select the logs from which to obtain SCTs, a TLS server can, for
example, examine the set of logs popular TLS clients accept and example, examine the set of logs popular TLS clients accept and
recognize. recognize.
6.3. TransItemList Structure 6.3. TransItemList Structure
Multiple SCTs, inclusion proofs, and indeed "TransItem" structures of Multiple SCTs, inclusion proofs, and indeed TransItem structures of
any type, are combined into a list as follows: any type are combined into a list as follows:
opaque SerializedTransItem<1..2^16-1>; opaque SerializedTransItem<1..2^16-1>;
struct { struct {
SerializedTransItem trans_item_list<1..2^16-1>; SerializedTransItem trans_item_list<1..2^16-1>;
} TransItemList; } TransItemList;
Here, "SerializedTransItem" is an opaque byte string that contains Here, SerializedTransItem is an opaque byte string that contains the
the serialized "TransItem" structure. This encoding ensures that TLS serialized TransItem structure. This encoding ensures that TLS
clients can decode each "TransItem" individually (so, for example, if clients can decode each TransItem individually (so, for example, if
there is a version upgrade, out-of-date clients can still parse old there is a version upgrade, out-of-date clients can still parse old
"TransItem" structures while skipping over new "TransItem" structures TransItem structures while skipping over new TransItem structures
whose versions they don't understand). whose versions they don't understand).
6.4. Presenting SCTs, inclusions proofs and STHs 6.4. Presenting SCTs, Inclusions Proofs, and STHs
In each "TransItemList" that is sent during a TLS handshake, the TLS In each TransItemList that is sent during a TLS handshake, the TLS
server MUST include a "TransItem" structure of type "x509_sct_v2" or server MUST include a TransItem structure of type x509_sct_v2 or
"precert_sct_v2". precert_sct_v2.
Presenting inclusion proofs and STHs in the TLS handshake helps to Presenting inclusion proofs and STHs in the TLS handshake helps to
protect the client's privacy (see Section 8.1.4) and reduces load on protect the client's privacy (see Section 8.1.4) and reduces load on
log servers. Therefore, if the TLS server can obtain them, it SHOULD log servers. Therefore, if the TLS server can obtain them, it SHOULD
also include "TransItem"s of type "inclusion_proof_v2" and also include TransItems of type inclusion_proof_v2 and
"signed_tree_head_v2" in the "TransItemList". signed_tree_head_v2 in the TransItemList.
6.5. transparency_info TLS Extension 6.5. transparency_info TLS Extension
Provided that a TLS client includes the "transparency_info" extension Provided that a TLS client includes the transparency_info extension
type in the ClientHello and the TLS server supports the type in the ClientHello and the TLS server supports the
"transparency_info" extension: transparency_info extension:
* The TLS server MUST verify that the received "extension_data" is * The TLS server MUST verify that the received extension_data is
empty. empty.
* The TLS server MUST construct a "TransItemList" of relevant * The TLS server MUST construct a TransItemList of relevant
"TransItem"s (see Section 6.4), which SHOULD omit any "TransItem"s TransItems (see Section 6.4), which SHOULD omit any TransItems
that are already embedded in the server certificate or the stapled that are already embedded in the server certificate or the stapled
OCSP response (see Section 7.1). If the constructed OCSP response (see Section 7.1). If the constructed TransItemList
"TransItemList" is not empty, then the TLS server MUST include the is not empty, then the TLS server MUST include the
"transparency_info" extension with the "extension_data" set to transparency_info extension with the extension_data set to this
this "TransItemList". If the list is empty then the server SHOULD TransItemList. If the list is empty, then the server SHOULD omit
omit the "extension_data" element, but MAY send it with an empty the extension_data element but MAY send it with an empty array.
array.
TLS servers MUST only include this extension in the following TLS servers MUST only include this extension in the following
messages: messages:
* the ServerHello message (for TLS 1.2 or earlier). * the ServerHello message (for TLS 1.2 or earlier)
* the Certificate or CertificateRequest message (for TLS 1.3). * the Certificate or CertificateRequest message (for TLS 1.3)
TLS servers MUST NOT process or include this extension when a TLS TLS servers MUST NOT process or include this extension when a TLS
session is resumed, since session resumption uses the original session is resumed, since session resumption uses the original
session information. session information.
7. Certification Authorities 7. Certification Authorities
7.1. Transparency Information X.509v3 Extension 7.1. Transparency Information X.509v3 Extension
The Transparency Information X.509v3 extension, which has OID The Transparency Information X.509v3 extension, which has OID
1.3.101.75 and SHOULD be non-critical, contains one or more 1.3.101.75 and SHOULD be noncritical, contains one or more TransItem
"TransItem" structures in a "TransItemList". This extension MAY be structures in a TransItemList. This extension MAY be included in
included in OCSP responses (see Section 7.1.1) and certificates (see OCSP responses (see Section 7.1.1) and certificates (see
Section 7.1.2). Since RFC5280 requires the "extnValue" field (an Section 7.1.2). Since [RFC5280] requires the extnValue field (an
OCTET STRING) of each X.509v3 extension to include the DER encoding OCTET STRING) of each X.509v3 extension to include the DER encoding
of an ASN.1 value, a "TransItemList" MUST NOT be included directly. of an ASN.1 value, a TransItemList MUST NOT be included directly.
Instead, it MUST be wrapped inside an additional OCTET STRING, which Instead, it MUST be wrapped inside an additional OCTET STRING, which
is then put into the "extnValue" field: is then put into the extnValue field:
TransparencyInformationSyntax ::= OCTET STRING TransparencyInformationSyntax ::= OCTET STRING
"TransparencyInformationSyntax" contains a "TransItemList". TransparencyInformationSyntax contains a TransItemList.
7.1.1. OCSP Response Extension 7.1.1. OCSP Response Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in the "singleExtensions" of a "SingleResponse" in X.509v3 extension in the singleExtensions of a SingleResponse in an
an OCSP response. All included SCTs and inclusion proofs MUST be for OCSP response. All included SCTs and inclusion proofs MUST be for
the certificate identified by the "certID" of that "SingleResponse", the certificate identified by the certID of that SingleResponse or
or for a precertificate that corresponds to that certificate. for a precertificate that corresponds to that certificate.
7.1.2. Certificate Extension 7.1.2. Certificate Extension
A certification authority MAY include a Transparency Information A certification authority MAY include a Transparency Information
X.509v3 extension in a certificate. All included SCTs and inclusion X.509v3 extension in a certificate. All included SCTs and inclusion
proofs MUST be for a precertificate that corresponds to this proofs MUST be for a precertificate that corresponds to this
certificate. certificate.
7.2. TLS Feature X.509v3 Extension 7.2. TLS Feature X.509v3 Extension
A certification authority SHOULD NOT issue any certificate that A certification authority SHOULD NOT issue any certificate that
identifies the "transparency_info" TLS extension in a TLS feature identifies the transparency_info TLS extension in a TLS feature
extension [RFC7633], because TLS servers are not required to support extension [RFC7633], because TLS servers are not required to support
the "transparency_info" TLS extension in order to participate in CT the transparency_info TLS extension in order to participate in CT
(see Section 6). (see Section 6).
8. Clients 8. Clients
There are various different functions clients of logs might perform. There are various different functions clients of logs might perform.
We describe here some typical clients and how they should function. We describe here some typical clients and how they should function.
Any inconsistency may be used as evidence that a log has not behaved Any inconsistency may be used as evidence that a log has not behaved
correctly, and the signatures on the data structures prevent the log correctly, and the signatures on the data structures prevent the log
from denying that misbehavior. from denying that misbehavior.
All clients need various parameters in order to communicate with logs All clients need various parameters in order to communicate with logs
and verify their responses. These parameters are described in and verify their responses. These parameters are described in
Section 4.1, but note that this document does not describe how the Section 4.1, but note that this document does not describe how the
parameters are obtained, which is implementation-dependent (see, for parameters are obtained, which is implementation dependent (for
example, [Chromium.Policy]). example, see [Chromium.Policy]).
8.1. TLS Client 8.1. TLS Client
8.1.1. Receiving SCTs and inclusion proofs 8.1.1. Receiving SCTs and Inclusion Proofs
TLS clients receive SCTs and inclusion proofs alongside or in TLS clients receive SCTs and inclusion proofs alongside or in
certificates. CT-using TLS clients MUST implement all of the three certificates. CT-using TLS clients MUST implement all of the three
mechanisms by which TLS servers may present SCTs (see Section 6). mechanisms by which TLS servers may present SCTs (see Section 6).
TLS clients that support the "transparency_info" TLS extension (see TLS clients that support the transparency_info TLS extension (see
Section 6.5) SHOULD include it in ClientHello messages, with empty Section 6.5) SHOULD include it in ClientHello messages, with empty
"extension_data". If a TLS server includes the "transparency_info" extension_data. If a TLS server includes the transparency_info TLS
TLS extension when resuming a TLS session, the TLS client MUST abort extension when resuming a TLS session, the TLS client MUST abort the
the handshake. handshake.
8.1.2. Reconstructing the TBSCertificate 8.1.2. Reconstructing the TBSCertificate
Validation of an SCT for a certificate (where the "type" of the Validation of an SCT for a certificate (where the type of the
"TransItem" is "x509_sct_v2") uses the unmodified TBSCertificate TransItem is x509_sct_v2) uses the unmodified TBSCertificate
component of the certificate. component of the certificate.
Before an SCT for a precertificate (where the "type" of the Before an SCT for a precertificate (where the type of the TransItem
"TransItem" is "precert_sct_v2") can be validated, the TBSCertificate is precert_sct_v2) can be validated, the TBSCertificate component of
component of the precertificate needs to be reconstructed from the the precertificate needs to be reconstructed from the TBSCertificate
TBSCertificate component of the certificate as follows: component of the certificate as follows:
* Remove the Transparency Information extension (see Section 7.1). * Remove the Transparency Information extension (see Section 7.1).
* Remove embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 * Remove embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2
(see section 3.3 of [RFC6962]). This allows embedded v1 and v2 (see Section 3.3 of [RFC6962]). This allows embedded v1 and v2
SCTs to co-exist in a certificate (see Appendix A). SCTs to co-exist in a certificate (see Appendix A).
8.1.3. Validating SCTs 8.1.3. Validating SCTs
In order to make use of a received SCT, the TLS client MUST first In order to make use of a received SCT, the TLS client MUST first
validate it as follows: validate it as follows:
* Compute the signature input by constructing a "TransItem" of type * Compute the signature input by constructing a TransItem of type
"x509_entry_v2" or "precert_entry_v2", depending on the SCT's x509_entry_v2 or precert_entry_v2, depending on the SCT's
"TransItem" type. The "TimestampedCertificateEntryDataV2" TransItem type. The TimestampedCertificateEntryDataV2 structure
structure is constructed in the following manner: is constructed in the following manner:
- "timestamp" is copied from the SCT. - timestamp is copied from the SCT.
- "tbs_certificate" is the reconstructed TBSCertificate portion - tbs_certificate is the reconstructed TBSCertificate portion of
of the server certificate, as described in Section 8.1.2. the server certificate, as described in Section 8.1.2.
- "issuer_key_hash" is computed as described in Section 4.7. - issuer_key_hash is computed as described in Section 4.7.
- "sct_extensions" is copied from the SCT. - sct_extensions is copied from the SCT.
* Verify the SCT's "signature" against the computed signature input * Verify the SCT's signature against the computed signature input
using the public key of the corresponding log, which is identified using the public key of the corresponding log, which is identified
by the "log_id". The required signature algorithm is one of the by the log_id. The required signature algorithm is one of the
log's parameters. log's parameters.
If the TLS client does not have the corresponding log's parameters, If the TLS client does not have the corresponding log's parameters,
it cannot attempt to validate the SCT. When evaluating compliance it cannot attempt to validate the SCT. When evaluating compliance
(see Section 8.1.6), the TLS client will consider only those SCTs (see Section 8.1.6), the TLS client will consider only those SCTs
that it was able to validate. that it was able to validate.
Note that SCT validation is not a substitute for the normal Note that SCT validation is not a substitute for the normal
validation of the server certificate and its chain. validation of the server certificate and its chain.
8.1.4. Fetching inclusion proofs 8.1.4. Fetching Inclusion Proofs
When a TLS client has validated a received SCT but does not yet When a TLS client has validated a received SCT but does not yet
possess a corresponding inclusion proof, the TLS client MAY request possess a corresponding inclusion proof, the TLS client MAY request
the inclusion proof directly from a log using "get-proof-by-hash" the inclusion proof directly from a log using get-proof-by-hash
(Section 5.4) or "get-all-by-hash" (Section 5.5). (Section 5.4) or get-all-by-hash (Section 5.5).
Note that fetching inclusion proofs directly from a log will disclose Note that fetching inclusion proofs directly from a log will disclose
to the log which TLS server the client has been communicating with. to the log which TLS server the client has been communicating with.
This may be regarded as a significant privacy concern, and so it is This may be regarded as a significant privacy concern, and so it is
preferable for the TLS server to send the inclusion proofs (see preferable for the TLS server to send the inclusion proofs (see
Section 6.4). Section 6.4).
8.1.5. Validating inclusion proofs 8.1.5. Validating Inclusion Proofs
When a TLS client has received, or fetched, an inclusion proof (and When a TLS client has received, or fetched, an inclusion proof (and
an STH), it SHOULD proceed to verifying the inclusion proof to the an STH), it SHOULD proceed to verify the inclusion proof to the
provided STH. The TLS client SHOULD also verify consistency between provided STH. The TLS client SHOULD also verify consistency between
the provided STH and an STH it knows about. the provided STH and an STH it knows about.
If the TLS client holds an STH that predates the SCT, it MAY, in the If the TLS client holds an STH that predates the SCT, it MAY, in the
process of auditing, request a new STH from the log (Section 5.2), process of auditing, request a new STH from the log (Section 5.2) and
then verify it by requesting a consistency proof (Section 5.3). Note then verify it by requesting a consistency proof (Section 5.3). Note
that if the TLS client uses "get-all-by-hash", then it will already that if the TLS client uses get-all-by-hash, then it will already
have the new STH. have the new STH.
8.1.6. Evaluating compliance 8.1.6. Evaluating Compliance
It is up to a client's local policy to specify the quantity and form It is up to a client's local policy to specify the quantity and form
of evidence (SCTs, inclusion proofs or a combination) needed to of evidence (SCTs, inclusion proofs, or a combination) needed to
achieve compliance and how to handle non-compliance. achieve compliance and how to handle noncompliance.
A TLS client can only evaluate compliance if it has given the TLS A TLS client can only evaluate compliance if it has given the TLS
server the opportunity to send SCTs and inclusion proofs by any of server the opportunity to send SCTs and inclusion proofs by any of
the three mechanisms that are mandatory to implement for CT-using TLS the three mechanisms that are mandatory to implement for CT-using TLS
clients (see Section 8.1.1). Therefore, a TLS client MUST NOT clients (see Section 8.1.1). Therefore, a TLS client MUST NOT
evaluate compliance if it did not include both the evaluate compliance if it did not include both the transparency_info
"transparency_info" and "status_request" TLS extensions in the and status_request TLS extensions in the ClientHello.
ClientHello.
8.2. Monitor 8.2. Monitor
Monitors watch logs to check that they behave correctly, for Monitors watch logs to check for correct behavior, for certificates
certificates of interest, or both. For example, a monitor may be of interest, or for both. For example, a monitor may be configured
configured to report on all certificates that apply to a specific to report on all certificates that apply to a specific domain name
domain name when fetching new entries for consistency validation. when fetching new entries for consistency validation.
A monitor MUST at least inspect every new entry in every log it A monitor MUST at least inspect every new entry in every log it
watches, and it MAY also choose to keep copies of entire logs. watches, and it MAY also choose to keep copies of entire logs.
To inspect all of the existing entries, the monitor SHOULD follow To inspect all of the existing entries, the monitor SHOULD follow
these steps once for each log: these steps once for each log:
1. Fetch the current STH (Section 5.2). 1. Fetch the current STH (Section 5.2).
2. Verify the STH signature. 2. Verify the STH signature.
skipping to change at page 44, line 49 skipping to change at line 2033
4. If applicable, check each entry to see if it's a certificate of 4. If applicable, check each entry to see if it's a certificate of
interest. interest.
5. Confirm that the tree made from the fetched entries produces the 5. Confirm that the tree made from the fetched entries produces the
same hash as that in the STH. same hash as that in the STH.
To inspect new entries, the monitor SHOULD follow these steps To inspect new entries, the monitor SHOULD follow these steps
repeatedly for each log: repeatedly for each log:
1. Fetch the current STH (Section 5.2). Repeat until the STH 1. Fetch the current STH (Section 5.2). Repeat until the STH
changes. This document does not specify the polling frequency, changes. To allow for experimentation, this document does not
to allow for experimentation. specify the polling frequency.
2. Verify the STH signature. 2. Verify the STH signature.
3. Fetch all the new entries in the tree corresponding to the STH 3. Fetch all the new entries in the tree corresponding to the STH
(Section 5.6). If they remain unavailable for an extended (Section 5.6). If they remain unavailable for an extended
period, then this should be viewed as misbehavior on the part of period, then this should be viewed as misbehavior on the part of
the log. the log.
4. If applicable, check each entry to see if it's a certificate of 4. If applicable, check each entry to see if it's a certificate of
interest. interest.
5. Either: 5. Either:
1. Verify that the updated list of all entries generates a tree a. Verify that the updated list of all entries generates a tree
with the same hash as the new STH. with the same hash as the new STH.
Or, if it is not keeping all log entries: Or, if it is not keeping all log entries:
1. Fetch a consistency proof for the new STH with the previous a. Fetch a consistency proof for the new STH with the previous
STH (Section 5.3). STH (Section 5.3).
2. Verify the consistency proof. b. Verify the consistency proof.
3. Verify that the new entries generate the corresponding c. Verify that the new entries generate the corresponding
elements in the consistency proof. elements in the consistency proof.
6. Repeat from step 1. 6. Repeat from Step 1.
8.3. Auditing 8.3. Auditing
Auditing ensures that the current published state of a log is Auditing ensures that the current published state of a log is
reachable from previously published states that are known to be good, reachable from previously published states that are known to be good
and that the promises made by the log in the form of SCTs have been and that the promises made by the log, in the form of SCTs, have been
kept. Audits are performed by monitors or TLS clients. kept. Audits are performed by monitors or TLS clients.
In particular, there are four log behavior properties that should be In particular, there are four properties of log behavior that should
checked: be checked:
* The Maximum Merge Delay (MMD). * the Maximum Merge Delay (MMD)
* The STH Frequency Count. * the STH Frequency Count
* The append-only property. * the append-only property
* The consistency of the log view presented to all query sources. * the consistency of the log view presented to all query sources
A benign, conformant log publishes a series of STHs over time, each A benign, conformant log publishes a series of STHs over time, each
derived from the previous STH and the submitted entries incorporated derived from the previous STH and the submitted entries incorporated
into the log since publication of the previous STH. This can be into the log since publication of the previous STH. This can be
proven through auditing of STHs. SCTs returned to TLS clients can be proven through auditing of STHs. SCTs returned to TLS clients can be
audited by verifying against the accompanying certificate, and using audited by verifying against the accompanying certificate and using
Merkle Inclusion Proofs, against the log's Merkle tree. Merkle inclusion proofs against the log's Merkle Tree.
The action taken by the auditor if an audit fails is not specified, The action taken by the auditor, if an audit fails, is not specified,
but note that in general if audit fails, the auditor is in possession but note that in general, if an audit fails, the auditor is in
of signed proof of the log's misbehavior. possession of signed proof of the log's misbehavior.
A monitor (Section 8.2) can audit by verifying the consistency of A monitor (Section 8.2) can audit by verifying the consistency of
STHs it receives, ensure that each entry can be fetched and that the STHs it receives, ensuring that each entry can be fetched and that
STH is indeed the result of making a tree from all fetched entries. the STH is indeed the result of making a tree from all fetched
entries.
A TLS client (Section 8.1) can audit by verifying an SCT against any A TLS client (Section 8.1) can audit by verifying an SCT against any
STH dated after the SCT timestamp + the Maximum Merge Delay by STH dated after the SCT timestamp + the Maximum Merge Delay by
requesting a Merkle inclusion proof (Section 5.4). It can also requesting a Merkle inclusion proof (Section 5.4). It can also
verify that the SCT corresponds to the server certificate it arrived verify that the SCT corresponds to the server certificate it arrived
with (i.e., the log entry is that certificate, or is a precertificate with (i.e., the log entry is that certificate or is a precertificate
corresponding to that certificate). corresponding to that certificate).
Checking of the consistency of the log view presented to all entities Checking of the consistency of the log view presented to all entities
is more difficult to perform because it requires a way to share log is more difficult to perform because it requires a way to share log
responses among a set of CT-using entities, and is discussed in responses among a set of CT-using entities and is discussed in
Section 11.3. Section 11.3.
9. Algorithm Agility 9. Algorithm Agility
It is not possible for a log to change any of its algorithms part way It is not possible for a log to change either of its algorithms part
through its lifetime: way through its lifetime:
Signature algorithm: SCT signatures must remain valid so signature Signature algorithm: SCT signatures must remain valid so signature
algorithms can only be added, not removed. algorithms can only be added, not removed.
Hash algorithm: A log would have to support the old and new hash Hash algorithm: A log would have to support the old and new hash
algorithms to allow backwards-compatibility with clients that are algorithms to allow backwards compatibility with clients that are
not aware of a hash algorithm change. not aware of a hash algorithm change.
Allowing multiple signature or hash algorithms for a log would Allowing multiple signature or hash algorithms for a log would
require that all data structures support it and would significantly require that all data structures support it and would significantly
complicate client implementation, which is why it is not supported by complicate client implementation, which is why it is not supported by
this document. this document.
If it should become necessary to deprecate an algorithm used by a If it should become necessary to deprecate an algorithm used by a
live log, then the log MUST be frozen as specified in Section 4.13 live log, then the log MUST be frozen, as specified in Section 4.13,
and a new log SHOULD be started. Certificates in the frozen log that and a new log SHOULD be started. Certificates in the frozen log that
have not yet expired and require new SCTs SHOULD be submitted to the have not yet expired and require new SCTs SHOULD be submitted to the
new log and the SCTs from that log used instead. new log and the SCTs from that log used instead.
10. IANA Considerations 10. IANA Considerations
The assignment policy criteria mentioned in this section refer to the The assignment policy criteria mentioned in this section refer to the
policies outlined in [RFC8126]. policies outlined in [RFC8126].
10.1. Additions to existing registries 10.1. Additions to Existing Registries
This sub-section defines additions to existing registries. This subsection defines additions to existing registries.
10.1.1. New Entry to the TLS ExtensionType Registry 10.1.1. New Entry to the TLS ExtensionType Registry
IANA is asked to add the following entry to the "TLS ExtensionType IANA has added the following entry to the "TLS ExtensionType Values"
Values" registry defined in [RFC8446], with an assigned Value: registry defined in [RFC8446], with an assigned Value:
+=======+===================+============+=============+===========+ +=====+===================+===+===========+=============+===========+
| Value | Extension Name | TLS 1.3 | Recommended | Reference | |Value| Extension Name |TLS| DTLS-Only | Recommended | Reference |
+=======+===================+============+=============+===========+ | | |1.3| | | |
| TBD | transparency_info | CH, CR, CT | Y | RFCXXXX | +=====+===================+===+===========+=============+===========+
+-------+-------------------+------------+-------------+-----------+ |52 | transparency_info |CH,| N | Y | RFC 9162 |
| | |CR,| | | |
| | |CT | | | |
+-----+-------------------+---+-----------+-------------+-----------+
Table 7 Table 7
10.1.2. URN Sub-namespace for TRANS (urn:ietf:params:trans) 10.1.2. URN Sub-namespace for TRANS (urn:ietf:params:trans)
IANA is requested to add a new entry in the "IETF URN Sub-namespace IANA has added a new entry in the "IETF URN Sub-namespace for
for Registered Protocol Parameter Identifiers" registry, following Registered Protocol Parameter Identifiers" registry, following the
the template in [RFC3553]: template in [RFC3553]:
Registry name: trans Registry name: trans
Specification: RFC 9162
Repository: <https://www.iana.org/assignments/trans>
Index value: No transformation needed.
Specification: RFCXXXX 10.2. New CT-Related Registries
Repository: https://www.iana.org/assignments/trans IANA has added a new protocol registry, "Public Notary Transparency",
to the list that appears at <https://www.iana.org/assignments/>
Index value: No transformation needed. The rest of this section defines the subregistries that have been
created within the new "Public Notary Transparency" registry.
10.2. New CT-Related registries 10.2.1. Hash Algorithms
IANA is requested to add a new protocol registry, "Public Notary IANA has established a registry of hash algorithm values, named "Hash
Transparency", to the list that appears at https://www.iana.org/ Algorithms", with the following registration procedures:
assignments/
The rest of this section defines sub-registries to be created within
the new Public Notary Transparency registry.
10.2.1. Hash Algorithms +===========+=========================+
| Range | Registration Procedures |
+===========+=========================+
| 0x00-0xDF | Specification Required |
+-----------+-------------------------+
| 0xE0-0xEF | Experimental Use |
+-----------+-------------------------+
| 0xF0-0xFF | Private Use |
+-----------+-------------------------+
IANA is asked to establish a registry of hash algorithm values, named Table 8
"Hash Algorithms", that initially consists of:
+========+============+========================+===================+ The "Hash Algorithms" registry initially consists of:
| Value | Hash | OID | Reference / |
| | Algorithm | | Assignment Policy |
+========+============+========================+===================+
| 0x00 | SHA-256 | 2.16.840.1.101.3.4.2.1 | [RFC6234] |
+--------+------------+------------------------+-------------------+
| 0x01 - | Unassigned | | Specification |
| 0xDF | | | Required |
+--------+------------+------------------------+-------------------+
| 0xE0 - | Reserved | | Experimental Use |
| 0xEF | | | |
+--------+------------+------------------------+-------------------+
| 0xF0 - | Reserved | | Private Use |
| 0xFF | | | |
+--------+------------+------------------------+-------------------+
Table 8 +========+==================+========================+===========+
| Value | Hash Algorithm | OID | Reference |
+========+==================+========================+===========+
| 0x00 | SHA-256 | 2.16.840.1.101.3.4.2.1 | [RFC6234] |
+--------+------------------+------------------------+-----------+
| 0x01 - | Unassigned | | RFC 9162 |
| 0xDF | | | |
+--------+------------------+------------------------+-----------+
| 0xE0 - | Reserved for | | RFC 9162 |
| 0xEF | Experimental Use | | |
+--------+------------------+------------------------+-----------+
| 0xF0 - | Reserved for | | RFC 9162 |
| 0xFF | Private Use | | |
+--------+------------------+------------------------+-----------+
The Designated Expert(s) should ensure that the proposed algorithm Table 9
The designated expert(s) should ensure that the proposed algorithm
has a public specification and is suitable for use as a cryptographic has a public specification and is suitable for use as a cryptographic
hash algorithm with no known preimage or collision attacks. These hash algorithm with no known preimage or collision attacks. These
attacks can damage the integrity of the log. attacks can damage the integrity of the log.
10.2.2. Signature Algorithms 10.2.2. Signature Algorithms
IANA is asked to establish a registry of signature algorithm values, IANA has established a registry of signature algorithm values, named
named "Signature Algorithms". "Signature Algorithms".
The following notes should be added: The following notes have been added to the registry:
* This is a subset of the TLS SignatureScheme Registry, limited to | *Note:*
those algorithms that are appropriate for CT. A major advantage | This is a subset of the "TLS SignatureScheme" registry, limited
of this is leveraging the expertise of the TLS working group and | to those algorithms that are appropriate for CT. A major
its Designated Expert(s). | advantage of this is leveraging the expertise of the TLS
| Working Group and its designated expert(s).
* The value "0x0403" appears twice. While this may be confusing, it | *Note:*
is okay because the verification process is the same for both | The value 0x0403 appears twice. While this may be confusing,
algorithms, and the choice of which to use when generating a | it is okay because the verification process is the same for
signature is purely internal to the log server. | both algorithms, and the choice of which to use when generating
| a signature is purely internal to the log server.
The registry should initially consist of: The "Signature Algorithms" registry has the following registration
procedures:
+================================+==================+===============+ +===============+=========================+
| SignatureScheme Value | Signature | Reference / | | Range | Registration Procedures |
| | Algorithm | Assignment | +===============+=========================+
| | | Policy | | 0x0000-0x0807 | Specification Required |
+================================+==================+===============+ +---------------+-------------------------+
| 0x0000 - 0x0402 | Unassigned | Specification | | 0x0808-0xFDFF | Expert Review |
| | | Required | +---------------+-------------------------+
+--------------------------------+------------------+---------------+ | 0xFE00-0xFEFF | Experimental Use |
| ecdsa_secp256r1_sha256(0x0403) | ECDSA (NIST | [FIPS186-4] | +---------------+-------------------------+
| | P-256) with | | | 0xFF00-0xFFFF | Private Use |
| | SHA-256 | | +---------------+-------------------------+
+--------------------------------+------------------+---------------+
| ecdsa_secp256r1_sha256(0x0403) | Deterministic | [RFC6979] |
| | ECDSA (NIST | |
| | P-256) with | |
| | HMAC-SHA256 | |
+--------------------------------+------------------+---------------+
| 0x0404 - 0x0806 | Unassigned | Specification |
| | | Required |
+--------------------------------+------------------+---------------+
| ed25519(0x0807) | Ed25519 | [RFC8032] |
| | (PureEdDSA | |
| | with the | |
| | edwards25519 | |
| | curve) | |
+--------------------------------+------------------+---------------+
| 0x0808 - 0xFDFF | Unassigned | Expert Review |
+--------------------------------+------------------+---------------+
| 0xFE00 - 0xFEFF | Reserved | Experimental |
| | | Use |
+--------------------------------+------------------+---------------+
| 0xFF00 - 0xFFFF | Reserved | Private Use |
+--------------------------------+------------------+---------------+
Table 9 Table 10
The Designated Expert(s) should ensure that the proposed algorithm The "Signature Algorithms" registry initially consists of:
has a public specification, has a value assigned to it in the TLS
SignatureScheme Registry (that IANA was asked to establish in +========================+===========================+=============+
[RFC8446]), and is suitable for use as a cryptographic signature | SignatureScheme Value | Signature Algorithm | Reference |
algorithm. +========================+===========================+=============+
| 0x0000 - 0x0402 | Unassigned | |
+------------------------+---------------------------+-------------+
| ecdsa_secp256r1_sha256 | ECDSA (NIST P-256) with | [FIPS186-4] |
| (0x0403) | SHA-256 | |
+------------------------+---------------------------+-------------+
| ecdsa_secp256r1_sha256 | Deterministic ECDSA (NIST | [RFC6979] |
| (0x0403) | P-256) with HMAC-SHA256 | |
+------------------------+---------------------------+-------------+
| 0x0404 - 0x0806 | Unassigned | |
+------------------------+---------------------------+-------------+
| ed25519 (0x0807) | Ed25519 (PureEdDSA with | [RFC8032] |
| | the edwards25519 curve) | |
+------------------------+---------------------------+-------------+
| 0x0808 - 0xFDFF | Unassigned | |
+------------------------+---------------------------+-------------+
| 0xFE00 - 0xFEFF | Reserved for Experimental | RFC 9162 |
| | Use | |
+------------------------+---------------------------+-------------+
| 0xFF00 - 0xFFFF | Reserved for Private Use | RFC 9162 |
+------------------------+---------------------------+-------------+
Table 11
The designated expert(s) should ensure that the proposed algorithm
has a public specification, has a value assigned to it in the "TLS
SignatureScheme" registry (which was established by [RFC8446]), and
is suitable for use as a cryptographic signature algorithm.
10.2.3. VersionedTransTypes 10.2.3. VersionedTransTypes
IANA is asked to establish a registry of "VersionedTransType" values, IANA has established a registry of VersionedTransType values, named
named "VersionedTransTypes". "VersionedTransTypes".
The following note should be added: The following note has been added:
* The range 0x0000..0x00FF is reserved so that v1 SCTs are | *Note:*
distinguishable from v2 SCTs and other "TransItem" structures. | The range 0x0000..0x00FF is reserved so that v1 SCTs are
| distinguishable from v2 SCTs and other TransItem structures.
The registry should initially consist of: The registration procedures for the "VersionedTransTypes" registry
are the following:
+==========+======================+===============================+ +===============+=========================+
| Value | Type and Version | Reference / Assignment Policy | | Range | Registration Procedures |
+==========+======================+===============================+ +===============+=========================+
| 0x0000 - | Reserved | [RFC6962] | | 0x0100-0xDFFF | Specification Required |
| 0x00FF | | | +---------------+-------------------------+
+----------+----------------------+-------------------------------+ | 0xE000-0xEFFF | Experimental Use |
| 0x0100 | x509_entry_v2 | RFCXXXX | +---------------+-------------------------+
+----------+----------------------+-------------------------------+ | 0xF000-0xFFFF | Private Use |
| 0x0101 | precert_entry_v2 | RFCXXXX | +---------------+-------------------------+
+----------+----------------------+-------------------------------+
| 0x0102 | x509_sct_v2 | RFCXXXX |
+----------+----------------------+-------------------------------+
| 0x0103 | precert_sct_v2 | RFCXXXX |
+----------+----------------------+-------------------------------+
| 0x0104 | signed_tree_head_v2 | RFCXXXX |
+----------+----------------------+-------------------------------+
| 0x0105 | consistency_proof_v2 | RFCXXXX |
+----------+----------------------+-------------------------------+
| 0x0106 | inclusion_proof_v2 | RFCXXXX |
+----------+----------------------+-------------------------------+
| 0x0107 - | Unassigned | Specification Required |
| 0xDFFF | | |
+----------+----------------------+-------------------------------+
| 0xE000 - | Reserved | Experimental Use |
| 0xEFFF | | |
+----------+----------------------+-------------------------------+
| 0xF000 - | Reserved | Private Use |
| 0xFFFF | | |
+----------+----------------------+-------------------------------+
Table 10 Table 12
The Designated Expert(s) should review the public specification to The "VersionedTransTypes" registry initially consists of:
+=================+===============================+===========+
| Value | Type and Version | Reference |
+=================+===============================+===========+
| 0x0000 - 0x00FF | Reserved | [RFC6962] |
+-----------------+-------------------------------+-----------+
| 0x0100 | x509_entry_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0101 | precert_entry_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0102 | x509_sct_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0103 | precert_sct_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0104 | signed_tree_head_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0105 | consistency_proof_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0106 | inclusion_proof_v2 | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0x0107 - 0xDFFF | Unassigned | |
+-----------------+-------------------------------+-----------+
| 0xE000 - 0xEFFF | Reserved for Experimental Use | RFC 9162 |
+-----------------+-------------------------------+-----------+
| 0xF000 - 0xFFFF | Reserved for Private Use | RFC 9162 |
+-----------------+-------------------------------+-----------+
Table 13
The designated expert(s) should review the public specification to
ensure that it is detailed enough to ensure implementation ensure that it is detailed enough to ensure implementation
interoperability. interoperability.
10.2.4. Log Artifact Extension Registry 10.2.4. Log Artifact Extensions
IANA is asked to establish a registry of "ExtensionType" values, IANA has established a registry of ExtensionType values, named "Log
named "Log Artifact Extensions", that initially consists of: Artifact Extensions".
+===============+============+=====+===============================+ The registration procedures for the "Log Artifact Extensions"
| ExtensionType | Status | Use | Reference / Assignment Policy | registry are the following:
+===============+============+=====+===============================+
| 0x0000 - | Unassigned | n/a | Specification Required |
| 0xDFFF | | | |
+---------------+------------+-----+-------------------------------+
| 0xE000 - | Reserved | n/a | Experimental Use |
| 0xEFFF | | | |
+---------------+------------+-----+-------------------------------+
| 0xF000 - | Reserved | n/a | Private Use |
| 0xFFFF | | | |
+---------------+------------+-----+-------------------------------+
Table 11 +===============+=========================+
| Range | Registration Procedures |
+===============+=========================+
| 0x0000-0xDFFF | Specification Required |
+---------------+-------------------------+
| 0xE000-0xEFFF | Experimental Use |
+---------------+-------------------------+
| 0xF000-0xFFFF | Private Use |
+---------------+-------------------------+
Table 14
The "Log Artifact Extensions" registry initially consists of:
+=================+===============================+=====+===========+
| ExtensionType | Status | Use | Reference |
+=================+===============================+=====+===========+
| 0x0000 - 0xDFFF | Unassigned | n/a | |
+-----------------+-------------------------------+-----+-----------+
| 0xE000 - 0xEFFF | Reserved for | n/a | RFC 9162 |
| | Experimental Use | | |
+-----------------+-------------------------------+-----+-----------+
| 0xF000 - 0xFFFF | Reserved for | n/a | RFC 9162 |
| | Private Use | | |
+-----------------+-------------------------------+-----+-----------+
Table 15
The "Use" column should contain one or both of the following values: The "Use" column should contain one or both of the following values:
* "SCT", for extensions specified for use in Signed Certificate * "SCT", for extensions specified for use in Signed Certificate
Timestamps. Timestamps.
* "STH", for extensions specified for use in Signed Tree Heads. * "STH", for extensions specified for use in Signed Tree Heads.
The Designated Expert(s) should review the public specification to The designated expert(s) should review the public specification to
ensure that it is detailed enough to ensure implementation ensure that it is detailed enough to ensure implementation
interoperability. They should also verify that the extension is interoperability. They should also verify that the extension is
appropriate to the contexts in which it is specified to be used (SCT, appropriate to the contexts in which it is specified to be used (SCT,
STH, or both). STH, or both).
10.2.5. Log IDs Registry 10.2.5. Log IDs
IANA is asked to establish a registry of Log IDs, named "Log IDs", IANA has established a registry of Log IDs, named "Log IDs".
that initially consists of:
+================+==============+==============+===================+ The registry's registration procedure is First Come First Served.
| Log ID | Log Base URL | Log Operator | Reference / |
| | | | Assignment Policy |
+================+==============+==============+===================+
| 1.3.101.8192 - | Unassigned | Unassigned | First Come First |
| 1.3.101.16383 | | | Served |
+----------------+--------------+--------------+-------------------+
| 1.3.101.80.0 - | Unassigned | Unassigned | First Come First |
| 1.3.101.80.* | | | Served |
+----------------+--------------+--------------+-------------------+
Table 12 The "Log IDs" registry initially consists of:
All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been +================+==============+==============+===========+
set aside for Log IDs. This is a limited resource of 8,192 OIDs, | Log ID | Log Base URL | Log Operator | Reference |
each of which has an encoded length of 4 octets. +================+==============+==============+===========+
| 1.3.101.8192 - | Unassigned | Unassigned | |
| 1.3.101.16383 | | | |
+----------------+--------------+--------------+-----------+
| 1.3.101.80.0 - | Unassigned | Unassigned | |
| 1.3.101.80.* | | | |
+----------------+--------------+--------------+-----------+
The 1.3.101.80 arc has also been set aside for Log IDs. This is an Table 16
unlimited resource, but only the 128 OIDs from 1.3.101.80.0 to
1.3.101.80.127 have an encoded length of only 4 octets. The following notes have been added to the registry:
| *Note:*
| All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have
| been set aside for Log IDs. This is a limited resource of
| 8,192 OIDs, each of which has an encoded length of 4 octets.
| *Note:*
| The 1.3.101.80 arc has also been set aside for Log IDs. This
| is an unlimited resource, but only the 128 OIDs from
| 1.3.101.80.0 to 1.3.101.80.127 have an encoded length of only 4
| octets.
Each application for the allocation of a Log ID MUST be accompanied Each application for the allocation of a Log ID MUST be accompanied
by: by:
* the Log's Base URL (see Section 4.1). * the Log's Base URL (see Section 4.1) and
* the Log Operator's contact details. * the Log Operator's contact details.
IANA is asked to reject any request to update a Log ID or Log Base IANA is asked to reject any request to update a Log ID or Log Base
URL in this registry, because these fields are immutable (see URL in this registry because these fields are immutable (see
Section 4.1). Section 4.1).
IANA is asked to accept requests from log operators to update their IANA is asked to accept requests from log operators to update their
contact details in this registry. contact details in this registry.
Since log operators can choose to not use this registry (see Since log operators can choose to not use this registry (see
Section 4.4), it is not expected to be a global directory of all Section 4.4), it is not expected to be a global directory of all
logs. logs.
10.2.6. Error Types Registry 10.2.6. Error Types
IANA is requested to create a new registry for errors, the "Error IANA has created a new registry for errors, the "Error Types"
Types" registry. registry.
Requirements for this registry are Specification Required. The registration procedure for this registry is Specification
Required.
This registry should have the following three fields: This registry has the following three fields:
+============+========+===========+ +============+========+===========+
| Field Name | Type | Reference | | Field Name | Type | Reference |
+============+========+===========+ +============+========+===========+
| identifier | string | RFCXXXX | | Identifier | string | RFC 9162 |
+------------+--------+-----------+ +------------+--------+-----------+
| meaning | string | RFCXXXX | | Meaning | string | RFC 9162 |
+------------+--------+-----------+ +------------+--------+-----------+
| reference | string | RFCXXXX | | Reference | string | RFC 9162 |
+------------+--------+-----------+ +------------+--------+-----------+
Table 13 Table 17
The initial values are as follows, taken from the text above: The initial values of the "Error Types" registry, which are taken
from the text in Section 5, are as follows:
+===================+===============================+===========+ +===================+===================================+===========+
| Identifier | Meaning | Reference | | Identifier | Meaning | Reference |
+===================+===============================+===========+ +===================+===================================+===========+
| malformed | The request could not be | RFCXXXX | | malformed | The request could not be | RFC 9162 |
| | parsed. | | | | parsed. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| badSubmission | "submission" is neither a | RFCXXXX | | badSubmission | submission is neither a | RFC 9162 |
| | valid certificate nor a valid | | | | valid certificate nor a | |
| | precertificate | | | | valid precertificate. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| badType | "type" is neither 1 nor 2 | RFCXXXX | | badType | type is neither 1 nor 2. | RFC 9162 |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| badChain | The first element of "chain" | RFCXXXX | | badChain | The first element of chain | RFC 9162 |
| | is not the certifier of the | | | | is not the certifier of the | |
| | "submission", or the second | | | | submission, or the second | |
| | element does not certify the | | | | element does not certify the | |
| | first, etc. | | | | first, etc. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| badCertificate | One or more certificates in | RFCXXXX | | badCertificate | One or more certificates in | RFC 9162 |
| | the "chain" are not valid | | | | chain are not valid (e.g., | |
| | (e.g., not properly encoded) | | | | not properly encoded). | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| unknownAnchor | The last element of "chain" | RFCXXXX | | unknownAnchor | The last element of chain | RFC 9162 |
| | (or, if "chain" is an empty | | | | (or, if chain is an empty | |
| | array, the "submission") both | | | | array, the submission) is | |
| | is not, and is not certified | | | | not, nor is it certified by, | |
| | by, an accepted trust anchor | | | | an accepted trust anchor. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| shutdown | The log is no longer | RFCXXXX | | shutdown | The log is no longer | RFC 9162 |
| | accepting submissions | | | | accepting submissions. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| firstUnknown | "first" is before the latest | RFCXXXX | | firstUnknown | first is before the latest | RFC 9162 |
| | known STH but is not from an | | | | known STH but is not from an | |
| | existing STH. | | | | existing STH. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| secondUnknown | "second" is before the latest | RFCXXXX | | secondUnknown | second is before the latest | RFC 9162 |
| | known STH but is not from an | | | | known STH but is not from an | |
| | existing STH. | | | | existing STH. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| secondBeforeFirst | "second" is smaller than | RFCXXXX | | secondBeforeFirst | second is smaller than | RFC 9162 |
| | "first". | | | | first. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| hashUnknown | "hash" is not the hash of a | RFCXXXX | | hashUnknown | hash is not the hash of a | RFC 9162 |
| | known leaf (may be caused by | | | | known leaf (may be caused by | |
| | skew or by a known | | | | skew or by a known | |
| | certificate not yet merged). | | | | certificate not yet merged). | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| treeSizeUnknown | "hash" is before the latest | RFCXXXX | | treeSizeUnknown | hash is before the latest | RFC 9162 |
| | known STH but is not from an | | | | known STH but is not from an | |
| | existing STH. | | | | existing STH. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| startUnknown | "start" is greater than the | RFCXXXX | | startUnknown | start is greater than the | RFC 9162 |
| | number of entries in the | | | | number of entries in the | |
| | Merkle tree. | | | | Merkle Tree. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
| endBeforeStart | "start" cannot be greater | RFCXXXX | | endBeforeStart | start cannot be greater than | RFC 9162 |
| | than "end". | | | | end. | |
+-------------------+-------------------------------+-----------+ +-------------------+-----------------------------------+-----------+
Table 14 Table 18
10.3. OID Assignment 10.3. OID Assignment
IANA is asked to assign one object identifier from the "SMI Security IANA has assigned an object identifier from the "SMI Security for
for PKIX Module Identifier" registry to identify the ASN.1 module in PKIX Module Identifier" registry to identify the ASN.1 module in
Appendix B of this document with an assigned Decimal value. Appendix B of this document.
+=========+=========================+============+ +=========+=========================+============+
| Decimal | Description | References | | Decimal | Description | References |
+=========+=========================+============+ +=========+=========================+============+
| TBD | id-mod-public-notary-v2 | RFCXXXX | | 102 | id-mod-public-notary-v2 | RFC 9162 |
+---------+-------------------------+------------+ +---------+-------------------------+------------+
Table 15 Table 19
11. Security Considerations 11. Security Considerations
With CAs, logs, and servers performing the actions described here, With CAs, logs, and servers performing the actions described here,
TLS clients can use logs and signed timestamps to reduce the TLS clients can use logs and signed timestamps to reduce the
likelihood that they will accept misissued certificates. If a server likelihood that they will accept misissued certificates. If a server
presents a valid signed timestamp for a certificate, then the client presents a valid signed timestamp for a certificate, then the client
knows that a log has committed to publishing the certificate. From knows that a log has committed to publishing the certificate. From
this, the client knows that monitors acting for the subject of the this, the client knows that monitors acting for the subject of the
certificate have had some time to notice the misissuance and take certificate have had some time to notice the misissuance and take
some action, such as asking a CA to revoke a misissued certificate. some action, such as asking a CA to revoke a misissued certificate.
A signed timestamp does not guarantee this though, since appropriate A signed timestamp does not guarantee this, though, since appropriate
monitors might not have checked the logs or the CA might have refused monitors might not have checked the logs or the CA might have refused
to revoke the certificate. to revoke the certificate.
In addition, if TLS clients will not accept unlogged certificates, In addition, if TLS clients will not accept unlogged certificates,
then site owners will have a greater incentive to submit certificates then site owners will have a greater incentive to submit certificates
to logs, possibly with the assistance of their CA, increasing the to logs, possibly with the assistance of their CA, increasing the
overall transparency of the system. overall transparency of the system.
11.1. Misissued Certificates 11.1. Misissued Certificates
skipping to change at page 55, line 24 skipping to change at line 2584
is twice the MMD. is twice the MMD.
11.2. Detection of Misissue 11.2. Detection of Misissue
The logs do not themselves detect misissued certificates; they rely The logs do not themselves detect misissued certificates; they rely
instead on interested parties, such as domain owners, to monitor them instead on interested parties, such as domain owners, to monitor them
and take corrective action when a misissue is detected. and take corrective action when a misissue is detected.
11.3. Misbehaving Logs 11.3. Misbehaving Logs
A log can misbehave in several ways. Examples include: failing to A log can misbehave in several ways. Examples include the following:
incorporate a certificate with an SCT in the Merkle Tree within the failing to incorporate a certificate with an SCT in the Merkle Tree
MMD; presenting different, conflicting views of the Merkle Tree at within the MMD; presenting different, conflicting views of the Merkle
different times and/or to different parties; issuing STHs too Tree at different times and/or to different parties; issuing STHs too
frequently; mutating the signature of a logged certificate; and frequently; mutating the signature of a logged certificate; and
failing to present a chain containing the certifier of a logged failing to present a chain containing the certifier of a logged
certificate. certificate.
Violation of the MMD contract is detected by log clients requesting a Violation of the MMD contract is detected by log clients requesting a
Merkle inclusion proof (Section 5.4) for each observed SCT. These Merkle inclusion proof (Section 5.4) for each observed SCT. These
checks can be asynchronous and need only be done once per checks can be asynchronous and need only be done once per
certificate. However, note that there may be privacy concerns (see certificate. However, note that there may be privacy concerns (see
Section 8.1.4). Section 8.1.4).
Violation of the append-only property or the STH issuance rate limit Violation of the append-only property or the STH issuance rate limit
can be detected by multiple clients comparing their instances of the can be detected by multiple clients comparing their instances of the
STHs. This technique, known as "gossip," is an active area of STHs. This technique, known as "gossip", is an active area of
research and not defined here. Proof of misbehavior in such cases research and not defined here. Proof of misbehavior in such cases
would be: a series of STHs that were issued too closely together, would be either a series of STHs that were issued too closely
proving violation of the STH issuance rate limit; or an STH with a together, proving violation of the STH issuance rate limit, or an STH
root hash that does not match the one calculated from a copy of the with a root hash that does not match the one calculated from a copy
log, proving violation of the append-only property. of the log, proving violation of the append-only property.
Clients that report back SCTs can be tracked or traced if a log Clients that report back SCTs can be tracked or traced if a log
produces multiple STHs or SCTs with the same timestamp and data but produces multiple STHs or SCTs with the same timestamp and data but
different signatures. Logs SHOULD mitigate this risk by either: different signatures. Logs SHOULD mitigate this risk by either:
* Using deterministic signature schemes, or * using deterministic signature schemes or
* Producing no more than one SCT for each distinct submission and no
* producing no more than one SCT for each distinct submission and no
more than one STH for each distinct tree_size. Each of these SCTs more than one STH for each distinct tree_size. Each of these SCTs
and STHs can be stored by the log and served to other clients that and STHs can be stored by the log and served to other clients that
submit the same certificate or request the same STH. submit the same certificate or request the same STH.
11.4. Multiple SCTs 11.4. Multiple SCTs
By requiring TLS servers to offer multiple SCTs, each from a By requiring TLS servers to offer multiple SCTs, each from a
different log, TLS clients reduce the effectiveness of an attack different log, TLS clients reduce the effectiveness of an attack
where a CA and a log collude (see Section 6.2). where a CA and a log collude (see Section 6.2).
11.5. Leakage of DNS Information 11.5. Leakage of DNS Information
Malicious monitors can use logs to learn about the existence of Malicious monitors can use logs to learn about the existence of
domain names that might not otherwise be easy to discover. Some domain names that might not otherwise be easy to discover. Some
subdomain labels may reveal information about the service and subdomain labels may reveal information about the service and
software for which the subdomain is used, which in turn might software for which the subdomain is used, which in turn might
facilitate targeted attacks. facilitate targeted attacks.
12. Acknowledgements 12. References
The authors would like to thank Erwann Abelea, Robin Alden, Andrew
Ayer, Richard Barnes, Al Cutter, David Drysdale, Francis Dupont, Adam
Eijdenberg, Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad
Hill, Jeff Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce,
Stephen Kent, SM, Alexey Melnikov, Linus Nordberg, Chris Palmer,
Trevor Perrin, Pierre Phaneuf, Eric Rescorla, Rich Salz, Melinda
Shore, Ryan Sleevi, Martin Smith, Carl Wallace and Paul Wouters for
their valuable contributions.
A big thank you to Symantec for kindly donating the OIDs from the
1.3.101 arc that are used in this document.
13. References
13.1. Normative References 12.1. Normative References
[FIPS186-4] [FIPS186-4]
NIST, "FIPS PUB 186-4", 1 July 2013, National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-4, July 2013,
<http://nvlpubs.nist.gov/nistpubs/FIPS/ <http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>. NIST.FIPS.186-4.pdf>.
[HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01 [HTML401] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Recommendation Specification", W3C Recommendation SPSD-html401-20180327,
REC-html401-19991224, 24 December 1999, March 2018,
<http://www.w3.org/TR/1999/REC-html401-19991224>. <https://www.w3.org/TR/2018/SPSD-html401-20180327>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <https://www.rfc-editor.org/info/rfc3553>. 2003, <https://www.rfc-editor.org/info/rfc3553>.
skipping to change at page 59, line 5 skipping to change at line 2738
[RFC8391] Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A. [RFC8391] Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A.
Mohaisen, "XMSS: eXtended Merkle Signature Scheme", Mohaisen, "XMSS: eXtended Merkle Signature Scheme",
RFC 8391, DOI 10.17487/RFC8391, May 2018, RFC 8391, DOI 10.17487/RFC8391, May 2018,
<https://www.rfc-editor.org/info/rfc8391>. <https://www.rfc-editor.org/info/rfc8391>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[UNIXTIME] IEEE, "The Open Group Base Specifications Issue 7 IEEE Std [UNIXTIME] IEEE, "The Open Group Base Specifications Issue 7",
1003.1-2008, 2016 Edition", n.d., Section 4.16 Seconds Since the Epoch, IEEE
<http://pubs.opengroup.org/ Std 1003.1-2008, 2016, <http://pubs.opengroup.org/
onlinepubs/9699919799.2016edition/basedefs/ onlinepubs/9699919799.2016edition/basedefs/
V1_chap04.html#tag_04_16>. V1_chap04.html#tag_04_16>.
[X690] ITU-T, "Information technology - ASN.1 encoding Rules: [X690] ITU-T, "Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ISO/IEC 8825-1:2002, November 2015. (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1,
February 2021.
13.2. Informative References 12.2. Informative References
[CABBR] CA/Browser Forum, "Baseline Requirements for the Issuance [CABBR] CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates", 2020, and Management of Publicly-Trusted Certificates",
<https://cabforum.org/wp-content/uploads/CA-Browser-Forum- Version 1.7.3, October 2020, <https://cabforum.org/wp-
BR-1.7.3.pdf>. content/uploads/CA-Browser-Forum-BR-1.7.3.pdf>.
[Chromium.Log.Policy] [Chromium.Log.Policy]
The Chromium Projects, "Chromium Certificate Transparency The Chromium Projects, "Chromium Certificate Transparency
Log Policy", 2014, <http://www.chromium.org/Home/chromium- Log Policy",
security/certificate-transparency/log-policy>. <https://googlechrome.github.io/CertificateTransparency/
log_policy.html>.
[Chromium.Policy] [Chromium.Policy]
The Chromium Projects, "Chromium Certificate The Chromium Projects, "Chromium Certificate Transparency
Transparency", 2014, <http://www.chromium.org/Home/ Policy",
chromium-security/certificate-transparency>. <https://googlechrome.github.io/CertificateTransparency/
ct_policy.html>.
[CrosbyWallach] [CrosbyWallach]
Crosby, S. and D. Wallach, "Efficient Data Structures for Crosby, S. and D. Wallach, "Efficient Data Structures for
Tamper-Evident Logging", Proceedings of the 18th USENIX Tamper-Evident Logging", Proceedings of the 18th USENIX
Security Symposium, Montreal, August 2009, Security Symposium, Montreal, August 2009,
<http://static.usenix.org/event/sec09/tech/full_papers/ <http://static.usenix.org/event/sec09/tech/full_papers/
crosby.pdf>. crosby.pdf>.
[JSON.Metadata] [JSON.Metadata]
The Chromium Projects, "Chromium Log Metadata JSON The Chromium Projects, "Chromium Log Metadata JSON
Schema", 2014, <https://www.gstatic.com/ct/log_list/ Schema", <https://www.gstatic.com/ct/log_list/
log_list_schema.json>. log_list_schema.json>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/info/rfc5912>.
[RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules
for the Cryptographic Message Syntax (CMS) and the Public
Key Infrastructure Using X.509 (PKIX)", RFC 6268,
DOI 10.17487/RFC6268, July 2011,
<https://www.rfc-editor.org/info/rfc6268>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013, Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<https://www.rfc-editor.org/info/rfc6962>. <https://www.rfc-editor.org/info/rfc6962>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8820] Nottingham, M., "URI Design and Ownership", BCP 190, [RFC8820] Nottingham, M., "URI Design and Ownership", BCP 190,
RFC 8820, DOI 10.17487/RFC8820, June 2020, RFC 8820, DOI 10.17487/RFC8820, June 2020,
<https://www.rfc-editor.org/info/rfc8820>. <https://www.rfc-editor.org/info/rfc8820>.
Appendix A. Supporting v1 and v2 simultaneously (Informative) [X.680] ITU-T, "Information technology - Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ITU-T
Recommendation X.680, February 2021.
Appendix A. Supporting v1 and v2 Simultaneously (Informative)
Certificate Transparency logs have to be either v1 (conforming to Certificate Transparency logs have to be either v1 (conforming to
[RFC6962]) or v2 (conforming to this document), as the data [RFC6962]) or v2 (conforming to this document), as the data
structures are incompatible and so a v2 log could not issue a valid structures are incompatible, and so a v2 log could not issue a valid
v1 SCT. v1 SCT.
CT clients, however, can support v1 and v2 SCTs, for the same CT clients, however, can support v1 and v2 SCTs for the same
certificate, simultaneously, as v1 SCTs are delivered in different certificate simultaneously, as v1 SCTs are delivered in different
TLS, X.509 and OCSP extensions than v2 SCTs. TLS, X.509, and OCSP extensions than v2 SCTs.
v1 and v2 SCTs for X.509 certificates can be validated independently. v1 and v2 SCTs for X.509 certificates can be validated independently.
For precertificates, v2 SCTs should be embedded in the TBSCertificate For precertificates, v2 SCTs should be embedded in the TBSCertificate
before submission of the TBSCertificate (inside a v1 precertificate, before submission of the TBSCertificate (inside a v1 precertificate,
as described in Section 3.1. of [RFC6962]) to a v1 log so that TLS as described in Section 3.1 of [RFC6962]) to a v1 log so that TLS
clients conforming to [RFC6962] but not this document are oblivious clients conforming to [RFC6962] but not this document are oblivious
to the embedded v2 SCTs. An issuer can follow these steps to produce to the embedded v2 SCTs. An issuer can follow these steps to produce
an X.509 certificate with embedded v1 and v2 SCTs: an X.509 certificate with embedded v1 and v2 SCTs:
* Create a CMS precertificate as described in Section 3.2 and submit * Create a CMS precertificate, as described in Section 3.2, and
it to v2 logs. submit it to v2 logs.
* Embed the obtained v2 SCTs in the TBSCertificate, as described in * Embed the obtained v2 SCTs in the TBSCertificate, as described in
Section 7.1.2. Section 7.1.2.
* Use that TBSCertificate to create a v1 precertificate, as * Use that TBSCertificate to create a v1 precertificate, as
described in Section 3.1. of [RFC6962] and submit it to v1 logs. described in Section 3.1 of [RFC6962], and submit it to v1 logs.
* Embed the v1 SCTs in the TBSCertificate, as described in * Embed the v1 SCTs in the TBSCertificate, as described in
Section 3.3 of [RFC6962]. Section 3.3 of [RFC6962].
* Sign that TBSCertificate (which now contains v1 and v2 SCTs) to * Sign that TBSCertificate (which now contains v1 and v2 SCTs) to
issue the final X.509 certificate. issue the final X.509 certificate.
Appendix B. An ASN.1 Module (Informative) Appendix B. An ASN.1 Module (Informative)
The following ASN.1 module may be useful to implementors. The following ASN.1 [X.680] module may be useful to implementors.
This module references [RFC5912] and [RFC6268].
CertificateTransparencyV2Module-2021 CertificateTransparencyV2Module-2021
-- { id-mod-public-notary-v2 from above, in -- { id-mod-public-notary-v2 from above, in
iso(1) identified-organization(3) ... iso(1) identified-organization(3) ...
form } form }
DEFINITIONS IMPLICIT TAGS ::= BEGIN DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL -- -- EXPORTS ALL --
IMPORTS IMPORTS
EXTENSION EXTENSION
FROM PKIX-CommonTypes-2009 -- RFC 5912 FROM PKIX-CommonTypes-2009 -- RFC 5912
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) } id-mod-pkixCommon-02(57) }
CONTENT-TYPE CONTENT-TYPE
skipping to change at page 62, line 28 skipping to change at line 2926
IDENTIFIED BY id-ce-embeddedSCT-CTv1 IDENTIFIED BY id-ce-embeddedSCT-CTv1
CRITICALITY { FALSE } } CRITICALITY { FALSE } }
id-ce-embeddedSCT-CTv1 OBJECT IDENTIFIER ::= { id-ce-embeddedSCT-CTv1 OBJECT IDENTIFIER ::= {
1 3 6 1 4 1 11129 2 4 2 } 1 3 6 1 4 1 11129 2 4 2 }
SignedCertificateTimestampList ::= OCTET STRING SignedCertificateTimestampList ::= OCTET STRING
END END
Acknowledgements
The authors would like to thank Erwann Abelea, Robin Alden, Andrew
Ayer, Richard Barnes, Al Cutter, David Drysdale, Francis Dupont, Adam
Eijdenberg, Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad
Hill, Jeff Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Emilia
Kasper, Stephen Kent, Adam Langley, SM, Alexey Melnikov, Linus
Nordberg, Chris Palmer, Trevor Perrin, Pierre Phaneuf, Eric Rescorla,
Rich Salz, Melinda Shore, Ryan Sleevi, Martin Smith, Carl Wallace,
and Paul Wouters for their valuable contributions.
A big thank you to Symantec for kindly donating the OIDs from the
1.3.101 arc that are used in this document.
Authors' Addresses Authors' Addresses
Ben Laurie Ben Laurie
Google UK Ltd. Google UK Ltd.
Email: benl@google.com Email: benl@google.com
Adam Langley
Google Inc.
Email: agl@google.com
Emilia Kasper
Google Switzerland GmbH
Email: ekasper@google.com
Eran Messeri Eran Messeri
Google UK Ltd. Google UK Ltd.
Email: eranm@google.com Email: eranm@google.com
Rob Stradling Rob Stradling
Sectigo Ltd. Sectigo Ltd.
Email: rob@sectigo.com Email: rob@sectigo.com
 End of changes. 409 change blocks. 
1062 lines changed or deleted 1132 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/