Network Working Group M. Miller Internet-Draft Cisco Systems, Inc. Intended status: Standards Track July 13, 2012 Expires: January 14, 2013 End-to-End Object Encryption for the Extensible Messaging and Presence Protocol (XMPP) draft-miller-xmpp-e2e-02 Abstract This document defines a method of end-to-end object encryption for the Extensible Messaging and Presence Protocol (XMPP). Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 14, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Miller Expires January 14, 2013 [Page 1] Internet-Draft XMPP E2E July 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Determining Support . . . . . . . . . . . . . . . . . . . . . 3 4. Encrypting XMPP Stanzas . . . . . . . . . . . . . . . . . . . 4 4.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Process . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3. Example - Securing a Message . . . . . . . . . . . . . . . 6 5. Decrypting XMPP Stanzas . . . . . . . . . . . . . . . . . . . 9 5.1. Protocol Not Understood . . . . . . . . . . . . . . . . . 9 5.2. Process . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3. Insufficient Information . . . . . . . . . . . . . . . . . 10 5.4. Failed Decryption . . . . . . . . . . . . . . . . . . . . 11 5.5. Timestamp Not Acceptable . . . . . . . . . . . . . . . . . 12 5.6. Successful Decryption . . . . . . . . . . . . . . . . . . 12 6. Requesting Session Keys . . . . . . . . . . . . . . . . . . . 12 6.1. Request Process . . . . . . . . . . . . . . . . . . . . . 13 6.2. Accept Process . . . . . . . . . . . . . . . . . . . . . . 13 6.3. Error Conditions . . . . . . . . . . . . . . . . . . . . . 14 6.4. Example of Successful Key Request . . . . . . . . . . . . 14 7. Inclusion and Checking of Timestamps . . . . . . . . . . . . . 17 8. Interaction with Stanza Semantics . . . . . . . . . . . . . . 18 9. Mandatory-to-Implement Cryptographic Algorithms . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 19 10.1. Storage of Encrypted Stanzas . . . . . . . . . . . . . . . 19 10.2. Re-use of Session Master Keys . . . . . . . . . . . . . . 19 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 11.1. XML Namespace Name for e2e Data in XMPP . . . . . . . . . 19 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 12.1. Normative References . . . . . . . . . . . . . . . . . . . 20 12.2. Informative References . . . . . . . . . . . . . . . . . . 21 Appendix A. Schema for urn:ietf:params:xml:ns:xmpp-e2e:3 . . . . 21 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23 Miller Expires January 14, 2013 [Page 2] Internet-Draft XMPP E2E July 2012 1. Introduction End-to-end encryption of traffic sent over the Extensible Messaging and Presence Protocol [RFC6120] is a desirable goal. Requirements and a threat analysis for XMPP encryption are provided in [E2E-REQ]. Many possible approaches to meet those (or similar) requirements have been proposed over the years, including methods based on PGP, S/MIME, SIGMA, and TLS. Most proposals have not been able to support multiple end-points for a given recipient. As more devices support XMPP, it becomes more desirable to allow an entity to communicate with another in a more secure manner, regardless of the number of agents the entity is employing. This document specifies an approach for encrypting communications between two entities which each might have multiple end-points. 2. Terminology This document inherits XMPP-related terminology from [RFC6120], JSON Web Algorithms (JWA)-related terminology from [JOSE-JWA], JSON Web Encryption (JWE)-related terminology from [JOSE-JWE], and JSON Web Key (JWK)-related terminology from [JOSE-JWK]. Security-related terms are to be understood in the sense defined in [RFC4949]. The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Determining Support If an agent supports end-to-end object encryption, it MUST advertiset that fact in its responses to [XEP-0030] information ("disco#info") requests by returning a feature of "urn:ietf:params:xml:ns:xmpp-e2e:3:encrypt". ... ... Miller Expires January 14, 2013 [Page 3] Internet-Draft XMPP E2E July 2012 To help facilitate discovery, an agent SHOULD also include [XEP-0115] information in any directed or broadcast presence updates. 4. Encrypting XMPP Stanzas The process that a sending agent follows for securing stanzas is the same regardless of the form of stanza (i.e., , , or ). 4.1. Prerequisites First, the sending agent prepares and retains the following: o The JID of the sender (i.e. its own JID). This SHOULD be the bare JID (localpart@domainpart). o The JID of the recipient. This SHOULD be the bare JID (localpart@domainpart). o A Session Master Key (SMK). The SMK MUST have a length at least equal to that required by the key wrapping algorithm in use and MUST be generated randomly. See [RFC4086] for considerations on generating random values. o A SMK identifier (SID). The SID MUST be unique for a given (sender, recipient, SMK) tuple, and MUST NOT be derived from SMK itself. 4.2. Process For a given plaintext stanza (S), the sending agent performs the following: 1. Ensures the plaintext stanza is fully qualified, including the proper namespace declarations (e.g. contains the attribute 'xmlns' set to the value "jabber:client" for 'jabber:client' stanzas defined in [RFC6120]). 2. Notes the current UTC date and time N when this stanza is constructed, formatted as described under Section 7. 3. Constructs a forwarding envelope M using a element qualified by the "urn:xmpp:forward:0" namespace (as defined in [XEP-0297]) as follows: Miller Expires January 14, 2013 [Page 4] Internet-Draft XMPP E2E July 2012 * The child element qualified by the "urn:xmpp:delay" namespace (as defined in [XEP-0203]) with the attribute 'stamp' set to the UTC date and time value N * The plaintext stanza S 4. Convert the forwarding envelope M to a UTF-8 encoded string (M'), optionallly removing line breaks and other insignificant whitespace between elements and attributes, i.e. M' = UTF8- encode(M). We call M' a "stanza-string" because for purposes of encryption and decryption it is treated not as XML but as an opaque string (this avoids the need for complex canonicalization of the XML input). 5. Generates a Content Master Key (CMK). The CMK MUST have a length at least equal to that required by the content encryption algorithm in use and MUST be generated randomly. See [RFC4086] for considerations on generating random values. 6. Generates any additional unprotected block cipher factors (IV); e.g. initialization vector/nonce. A sending agent MUST ensure that no two sets of factors are used with the same CMK, and SHOULD NOT reuse such factors for other stanzas. 7. Performs the message encryption steps from [JOSE-JWE] to generate the JWE Header H, JWE Encrypted Key E, JWE Ciphertext C, and JWE Integrity Value I; using the following inputs: * The 'alg' property is set to an appropriate key wrapping algorithm (e.g. "A256KW" or "A128KW"); recipients use 'keyreq' in Section 6 to obtain the SMK. * The 'enc' property is set to the intended content encryption algorithm. * SMK as the key for CMK Encryption. * CMK as the Content Master Key. * M' as the plaintext content to encrypt. 8. Constructs an element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace as follows: * The attribute 'id' set to the identifier value SID. Miller Expires January 14, 2013 [Page 5] Internet-Draft XMPP E2E July 2012 * The child element
qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character data as H, encoded base64url as per [RFC4684]. * The child element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character as E, encoded base64url as per [RFC4684]. * The child element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character data as C, encoded base64url as per [RFC4684]. * The child element qualified by the "urn"ietf:params: xml:ns:xmpp-e2e:3" namespace and with XML character data as I, encoded base64url as per [RFC4684]. 9. Sends the element as the payload of a stanza that SHOULD match the stanza from step 1 in kind (e.g., ), type (e.g., "chat"), and addressing (e.g. to="romeo@montague.net" from="juliet@capulet.net/balcony"). If the original stanza (S) has a value for the "id" attribute, this stanza MUST NOT use the same value for its "id" attribute. 4.3. Example - Securing a Message NOTE: unless otherwise indicated, all line breaks are included for readability. The sending agent begins with the plaintext version of the stanza 'S': 35740be5-b5a4-4c4e-962a-a03b14ed92f4 But to be frank, and give it thee again. And yet I wish but for the thing I have. My bounty is as boundless as the sea, My love as deep; the more I give to thee, The more I have, for both are infinite. and the following prerequisites: Miller Expires January 14, 2013 [Page 6] Internet-Draft XMPP E2E July 2012 o Sender JID as "juliet@capulet.lit/balcony" o Recipient JID as "romeo@montegue.lit" o Session Master Key 'SMK' as (base64 encoded) "xWtdjhYsH4Va_9SfYSefsJfZu03m5RrbXo_UavxxeU8=" o CMK identifier SID as "835c92a8-94cd-4e96-b3f3-b2e75a438f92" The sending agent performs steps 1, 2, and 3 to generate the envelope: 35740be5-b5a4-4c4e-962a-a03b14ed92f4 But to be frank, and give it thee again. And yet I wish but for the thing I have. My bounty is as boundless as the sea, My love as deep; the more I give to thee, The more I have, for both are infinite. Then the sending agent performs steps 4 through 7 (with Content Master Key as "-ElMo6FndEkMxWP3TIkp1dDfVKqmqAAgrlcvVnUVpOc=", base64 encoded) to generate the [JOSE-JWE] outputs: JWE Header { "alg":"A256KW", "enc":"A256CCM", "iv":"B7waCj2vF_sLaJfe-1GHrA==" } JWE Content Encryption Key XvySjpkqv6m-hUrG2VSEwIM9wZqVcdP037trOMpqFbK_i2AvHLqiNA== Miller Expires January 14, 2013 [Page 7] Internet-Draft XMPP E2E July 2012 JWE Ciphertext 7LlMXd-qqPAQ_LZm6u9AR2csyDgT09z5DWdn8K5GLr_qbWRDKw2ufZrmO9YZ-jHl 1IDeXeQ9azbNNViv8gpa-prDYkXOo3QoqYOJiA0RAkPU-UjN41wqqVvV62gad_OB Dd9q2xsNnK1PI5frIGTCZSexOIeSD3EcP0cDI_0MzMEKqpVnPbYQDkWQNrtxPs2b lE15KcQXbHVxA9rEz7y0a-ITXruV_fOXGftkRVDuiF1yVh2xNRPa-TQxDegZh1D_ u_c2mwPLO6ED_1ZlvL7075_VL0DT01YGtDDQeyzrQWnQNEBJ4G5jFpCyqtCszbgx 9kjWjxLYNLLGxbMOtwF45OLCd8JFUIQAHoLeKp4aIWr5yp7aATX8dKvQm5_TFICt nLonaM1e5mRPnRgg5zNeMErx6FFkqowOI1h7hVl_QHF8Ofoy99CmWKiVT3Nq5ngL 74Xm4CtiJMHnAEn2Q-10-fWuIHIEA0u4GwBaXo0ToBw4uCM4ZhG1SFSKyCKkjXmr 7TL-5jwSuuQHX6efS8Hhi7fujmqw9VXekeubsY2btl5put0SWT8_0S8ZBDMjrkXj y7iI5NUOhQMms3ou1r01NZdzNVKcqiX5q3z1eB1FLWmGymnnj_gE_HalWUL0HoqL 93Fr1nfFLNhXLCZYhZ7By6T9NN8omp4ZYE92HMpPzgo-eCGP NOTE: For CCM [RFC3610], the integrity value is encoded as part of the ciphertext, therefore the resulting Integrity Value is an octet string of length 0. Then the sending agent performs steps 8 and 9, and sends the following: Miller Expires January 14, 2013 [Page 8] Internet-Draft XMPP E2E July 2012
eyJlbmMiOiJBMjU2Q0NNIiwiaXYiOiJCN3dhQ2oydkZfc0xhSmZlLTFHS HJBPT0iLCJhZGF0YSI6IjQ5Mi0wNS0xMlQyMDowNzozNy4wMTJaIiwibX NpemUiOiIxNiJ9
7LlMXd-qqPAQ_LZm6u9AR2csyDgT09z5DWdn8K5GLr_qbWRDKw2ufZrmO 9YZ-jHl1IDeXeQ9azbNNViv8gpa-prDYkXOo3QoqYOJiA0RAkPU-UjN41 wqqVvV62gad_OBDd9q2xsNnK1PI5frIGTCZSexOIeSD3EcP0cDI_0MzME KqpVnPbYQDkWQNrtxPs2blE15KcQXbHVxA9rEz7y0a-ITXruV_fOXGftk RVDuiF1yVh2xNRPa-TQxDegZh1D_u_c2mwPLO6ED_1ZlvL7075_VL0DT0 1YGtDDQeyzrQWnQNEBJ4G5jFpCyqtCszbgx9kjWjxLYNLLGxbMOtwF45O LCd8JFUIQAHoLeKp4aIWr5yp7aATX8dKvQm5_TFICtnLonaM1e5mRPnRg g5zNeMErx6FFkqowOI1h7hVl_QHF8Ofoy99CmWKiVT3Nq5ngL74Xm4Cti JMHnAEn2Q-10-fWuIHIEA0u4GwBaXo0ToBw4uCM4ZhG1SFSKyCKkjXmr7 TL-5jwSuuQHX6efS8Hhi7fujmqw9VXekeubsY2btl5put0SWT8_0S8ZBD MjrkXjy7iI5NUOhQMms3ou1r01NZdzNVKcqiX5q3z1eB1FLWmGymnnj_g E_HalWUL0HoqL93Fr1nfFLNhXLCZYhZ7By6T9NN8omp4ZYE92HMpPzgo- eCGP 5. Decrypting XMPP Stanzas 5.1. Protocol Not Understood If the receiving agent does not understand the protocol, it MUST do one and only one of the following: (1) ignore the extension, (2) ignore the entire stanza, or (3) return a error to the sender, as described in [RFC6120]. NOTE: If the inbound stanza is an , the receiving agent MUST return an error to the sending agent, to comply with the exchanging of IQ stanzas in [RFC6121]. Miller Expires January 14, 2013 [Page 9] Internet-Draft XMPP E2E July 2012 5.2. Process Upon receipt of an encrypted stanza, the receiving agent performs the following: 1. Determines if a valid SMK is available, associated with the SID specified by the 'id' attribute value of the element's character data content. * The JWE Content Encryption Key from the element's character data content. * The JWE Ciphertext C from the element's character data content. * The JWE Integrity Value I from the element's character data content. 3. Converts the forwarding envelope UTF-8 ecoded string M' into XML element M. 4. Obtains the UTC date and time N from the child element, and verifies it is within the accepted range, as specified in Section 7. 5. Obtains the plaintext stanza S, which is a child element node of M; the stanza MUST be fully qualified with proper namespace declarations for XMPP stanzas, to help distinguish it from other content within M. . 5.3. Insufficient Information At step 1, if the receiving agent is unable to obtain the CMK, or the receiving agent could not otherwise determine the additional information, it MAY return a error to the sending agent (as described in [RFC6120]), optionally supplemented by an application-specific error condition element of : Miller Expires January 14, 2013 [Page 10] Internet-Draft XMPP E2E July 2012
[XML character data]
[XML character data]
 In addition to returning an error, the receiving agent SHOULD NOT present the stanza to the intended recipient (human or application) and SHOULD provide some explicit alternate processing of the stanza (which MAY be to display a message informing the recipient that it has received a stanza that cannot be decrypted). 5.4. Failed Decryption At step 2, if the receiving agent is unable to successfully decrypt the stanza, the receiving agent SHOULD return a error to the sending agent (as described in [RFC6120]), optionally supplemented by an application-specific error condition element of (previously defined in [RFC3923]):
[XML character data]
[XML character data] Miller Expires January 14, 2013 [Page 11] Internet-Draft XMPP E2E July 2012 In addition to returning an error, the receiving agent SHOULD NOT present the stanza to the intended recipient (human or application) and SHOULD provide some explicit alternate processing of the stanza (which MAY be to display a message informing the recipient that it has received a stanza that cannot be decrypted). 5.5. Timestamp Not Acceptable At step 4, if the stanza is successfully decrypted but the timestamp fails the checks outlined in Section 7, the receiving agent MAY return a error to the sender (as described in [RFC6120]), optionally supplemented by an application-specific error condition element of (previously defined in [RFC3923]):
[XML character data]
[XML character data] 5.6. Successful Decryption If the receiving agent successfully decrypted the payload, it MUST NOT return a stanza error. If the payload is an of type "get" or "set", and the response to this is of type "error", the receiving agent MUST send the encrypted response wrapped in an of type "result", to prevent exposing information about the payload. 6. Requesting Session Keys Because of the dynamic nature of XMPP stanza routing, the protocol does not exchange session keys as part of the encrypted stanza. Instead, a separate protocol is used by receiving agents to request a particular session key from the sending agent. Miller Expires January 14, 2013 [Page 12] Internet-Draft XMPP E2E July 2012 6.1. Request Process Before a SMK can be requested, the receiving agent MUST have at least one public key for which it also has the private key. To request a SMK, the receiving agent performs the following: 1. Constructs a [JOSE-JWK] JWK Set (KS), containing information about each public key the requesting agent wishes to use. Each key SHOULD include a value for the property 'kid' which uniquely identifies it within the context of all provided keys. Each key MUST include a value for the property 'kid' if any two keys use the same algorithm. 2. Constructs a element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace as follows: * The attribute 'id' set to the SMK identifier value SID. * The child element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character data as KS, encoded base64url as pre [RFC4684]. 3. Sends the element as the payload of an stanza with the attribute 'type' set to "get", the attribute 'to' set to the full JID of the original encrypted stanza's sender, and the attribute 'id' set to an opaque string value the receiving agent uses to track the response. 6.2. Accept Process If the sending agent approves the request, it performs the following: 1. Chooses a key (PK) from the keys provided via KS, and notes its identifier value 'kid'. 2. Constructs a parial [JOSE-JWE] header (H) as follows: * The property 'alg' set to the cryptographic algorithm for PK, which is used to secure the content master key SMK. * The property 'kid' set to the identifier matching PK. 3. Encrypts the content master key SMK using the key PK, i.e. SMK' = pki-encrypt(PK, SMK). Miller Expires January 14, 2013 [Page 13] Internet-Draft XMPP E2E July 2012 4. Constructs a element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace as follows: * The attribute 'id' set to the SMK identifier SID. * The child element
qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character data as H, encoded base64url as per [RFC4684]. * The child element qualified by the "urn:ietf:params:xml:ns:xmpp-e2e:3" namespace and with XML character data as SMK', encoded base64url as per [RFC4684]. 5. Sends the element as the payload of an stanza with the attribute 'type' set to "result", the attribute 'to' set to the full JID from the request 's 'from' attribute, and the attribute 'id' set to the value of the request 's 'id' attribute. 6.3. Error Conditions If the sending agent does not approve the request, it sends an stanza of type "error" and containing the reason for denying the request: o : the key request is made by an entity that is not authorized to decrypt stanzas from the sending agent and/or for the indicated SID. o : the requested SID is no longer valid. o : the key request did not contain any keys the sending agent understands. 6.4. Example of Successful Key Request NOTE: unless otherwise indicated, all line breaks are included for readability. To begin a key request, the receiving agent performs step 1 from Section 6.1 to generate the [JOSE-JWK]: Miller Expires January 14, 2013 [Page 14] Internet-Draft XMPP E2E July 2012 { "keys": [{ "alg":"RSA-OAEP", "mod":"vtqejkMF01h8oKEaHfHEYO0C2jM7eISbbSvNs0SNItYWO6GbjpJf N4ldXw2vpVRdysnwU3zk6o2_SD0YCH1WgeuI0QK1knMTDdNSXx52e1c4BTw hlA8iHuutTWmpBqesn1GNZmqB3jYsJOkVBYwCJtkB9APaBvk0itlRtizjCf 1HHnau7nGStyshgu8-srxi_d8rC5TTLSB_zT1i6fP8fwDloemXOtC0U65by 5P-1ZHxaf_bD8fpjps6gwSgdkZKMJAI0bOWZWuMpp2ntqa0wLB7Ndxb2Ijr eog_s5ssAoSiXDVdoswSbp36ZP-1lnCk2j-vZ4qbhaFg5bZtgt-gwQ==", "exp":"AQAB", "kid":"romeo@montegue.lit/garden" }] } Then the receiving agent performs step 2 to generate the : W3siYWxnIjoiUlNBIiwibW9kIjoiQUw3YW5vNURCZE5ZZktDaEdoM3h4R0R 0QXRvek8zaUVtMjByemJORWpTTFdGanVobTQ2U1h6ZUpYVjhOcjZWVVhjck o4Rk44NU9xTnYwZzlHQWg5Vm9IcmlORUN0Wkp6RXczVFVsOGVkbnRYT0FVO ElaUVBJaDdyclUxcHFRYW5ySjlSaldacWdkNDJMQ1RwRlFXTUFpYlpBZlFE MmdiNU5JclpVYllzNHduOVJ4NTJydTV4a3JjcklZTHZQcks4WXYzZkt3dVU weTBnZjgwOVl1bnpfSDhBNWFIcGx6clF0Rk91Vzh1VF90V1I4V25fMndfSD ZZNmJPb01Fb0haR1NqQ1FDTkd6bG1WcmpLYWRwN2FtdE1Dd2V6WGNXOWlJN jNxSVA3T2JMQUtFb2x3MVhhTE1FbTZkLW1UX3RaWndwTm9fcjJlS200V2hZ T1cyYllMZm9NRT0iLCJleHAiOiJBUUFCIiwia2lkIjoicm9tZW9AbW9udGV ndWUubGl0L2dhcmRlbiJ9XQ== Then the receiving agent performs step 3 and sends the following: Miller Expires January 14, 2013 [Page 15] Internet-Draft XMPP E2E July 2012 W3siYWxnIjoiUlNBIiwibW9kIjoiQUw3YW5vNURCZE5ZZktDaEdoM3h4R 0R0QXRvek8zaUVtMjByemJORWpTTFdGanVobTQ2U1h6ZUpYVjhOcjZWVV hjcko4Rk44NU9xTnYwZzlHQWg5Vm9IcmlORUN0Wkp6RXczVFVsOGVkbnR YT0FVOElaUVBJaDdyclUxcHFRYW5ySjlSaldacWdkNDJMQ1RwRlFXTUFp YlpBZlFEMmdiNU5JclpVYllzNHduOVJ4NTJydTV4a3JjcklZTHZQcks4W XYzZkt3dVUweTBnZjgwOVl1bnpfSDhBNWFIcGx6clF0Rk91Vzh1VF90V1 I4V25fMndfSDZZNmJPb01Fb0haR1NqQ1FDTkd6bG1WcmpLYWRwN2FtdE1 Dd2V6WGNXOWlJNjNxSVA3T2JMQUtFb2x3MVhhTE1FbTZkLW1UX3RaWndw Tm9fcjJlS200V2hZT1cyYllMZm9NRT0iLCJleHAiOiJBUUFCIiwia2lkI joicm9tZW9AbW9udGVndWUubGl0L2dhcmRlbiJ9XQ== If the sending agent accepts this key request, it performs steps 1 and 2 from Section 6.2 to generate the partial [JOSE-JWE] header: { "alg":"RSA-OAEP", "kid":"romeo@montegue.lit/garden" } Then the sending agent performs step 3 to generate the encrypted SMK: DsLfaD3ZPtE4k1wnhsHNsYyFi3spey8NNNMeYQ6L-sdLJrcWIwfOYNPK-Sb oLvsSiXB7yw1MLtKhhrAiRovEmMnTgoLvcuzX8PIBcDbSP3ie0aMynXqStb Rk-LwijdSY7NqD_WB1tP4dhqo3OwlXf4bSWlBnUDEzGh8giF6KYeRzw181m vMIJ6BCjwnvqTKBNlMDUX3cTfXSAFi9j8MkkS3wLbc2MM4RzP4ESyiZZQJn z_zkg1enjAbJ_fpwJ-E4a14EyWhwYpCNW3Tb5IhyhhgBsiLB6kulm9RMYwc TCGIDCUsfTo5vzDOKX7DBF6KtwSY8bF1AiOiGlsGo2SlrSg== Then the sending agent performs step 4 to generate the response: Miller Expires January 14, 2013 [Page 16] Internet-Draft XMPP E2E July 2012
eyJhbGciOiJSU0EtT0VBUCIsImtpZCI6InJvbWVvQG1vbnRlZ3VlLmxpc3Q vZ2FyZGVuIn0=
DsLfaD3ZPtE4k1wnhsHNsYyFi3spey8NNNMeYQ6L-sdLJrcWIwfOYNPK-Sb oLvsSiXB7yw1MLtKhhrAiRovEmMnTgoLvcuzX8PIBcDbSP3ie0aMynXqStb Rk-LwijdSY7NqD_WB1tP4dhqo3OwlXf4bSWlBnUDEzGh8giF6KYeRzw181m vMIJ6BCjwnvqTKBNlMDUX3cTfXSAFi9j8MkkS3wLbc2MM4RzP4ESyiZZQJn z_zkg1enjAbJ_fpwJ-E4a14EyWhwYpCNW3Tb5IhyhhgBsiLB6kulm9RMYwc TCGIDCUsfTo5vzDOKX7DBF6KtwSY8bF1AiOiGlsGo2SlrSg== Then the sending agent performs step 5 and sends the following:
eyJhbGciOiJSU0EtT0VBUCIsImtpZCI6InJvbWVvQG1vbnRlZ3VlLmxpc 3QvZ2FyZGVuIn0=
DsLfaD3ZPtE4k1wnhsHNsYyFi3spey8NNNMeYQ6L-sdLJrcWIwfOYNPK- SboLvsSiXB7yw1MLtKhhrAiRovEmMnTgoLvcuzX8PIBcDbSP3ie0aMynX qStbRk-LwijdSY7NqD_WB1tP4dhqo3OwlXf4bSWlBnUDEzGh8giF6KYeR zw181mvMIJ6BCjwnvqTKBNlMDUX3cTfXSAFi9j8MkkS3wLbc2MM4RzP4E SyiZZQJnz_zkg1enjAbJ_fpwJ-E4a14EyWhwYpCNW3Tb5IhyhhgBsiLB6 kulm9RMYwcTCGIDCUsfTo5vzDOKX7DBF6KtwSY8bF1AiOiGlsGo2SlrSg == 7. Inclusion and Checking of Timestamps Timestamps are included to help prevent replay attacks. All timestamps MUST conform to [XEP-0082] and be presented as UTC with no offset, and SHOULD include the seconds and fractions of a second to three digits. Absent a local adjustment to the sending agent's Miller Expires January 14, 2013 [Page 17] Internet-Draft XMPP E2E July 2012 perceived time or the underlying clock time, the sending agent MUST ensure that the timestamps it sends to the receiver increase monotonically (if necessary by incrementing the seconds fraction in the timestamp if the clock returns the same time for multiple requests). The following rules apply to the receiving agent: o It MUST verify that the timestamp received is within five minutes of the current time, except as described below for offline messages. o It SHOULD verify that the timestamp received is greater than any timestamp received in the last 10 minutes which passed the previous check. o If any of the foregoing checks fails, the timestamp SHOULD be presented to the receiving entity (human or application) marked as "old timestamp", "future timestamp", or "decreasing timestamp", and the receiving entity MAY return a stanza error to the sender. The foregoing timestamp checks assume that the recipient is online when the message is received. However, if the recipient is offline then the server might store the message for delivery when the recipient is next online (offline storage does not apply to or stanzas, only stanzas). As described in [XEP-0160], when sending an offline message to the recipient, the server SHOULD include delayed delivery data as specified in [XEP-0203] so that the recipient knows that this is an offline message and also knows the original time of receipt at the server. In this case, the recipient SHOULD verify that the timestamp received in the encrypted message is within five minutes of the time stamped by the recipient's server in the element. 8. Interaction with Stanza Semantics The following limitations and caveats apply: o Undirected stanzas SHOULD NOT be encrypted. Such stanzas are delivered to anyone the sender has authorized, and can generate a large volume of key requests. o Stanzas directed to multiplexing services (e.g. multi-user chat) SHOULD NOT be encrypted, unless the sender has established an acceptable trust relationship with the multiplexing service. Miller Expires January 14, 2013 [Page 18] Internet-Draft XMPP E2E July 2012 9. Mandatory-to-Implement Cryptographic Algorithms All algorithms that MUST be implemented for [JOSE-JWE] also MUST be implemented for this specification. 10. Security Considerations 10.1. Storage of Encrypted Stanzas The recipient's server might store any stanzas received until the recipient is next available; this duration could be anywhere from a few minutes to several months. 10.2. Re-use of Session Master Keys A sender SHOULD NOT use the same SMK for stanzas intended for different recipients, as determined by the localpart and domainpart of the recipient's JID. A sender MAY re-use a SMK for several stanzas to the same recipient. In this case, the SID remains the same, but the sending agent MUST generate a new CMK and IV for each encrypted stanza. The sender SHOULD periodically generate a new SMK; however, this specification does not mandate any specific algorithms or processes. In the case of stanzas, a sending agent might generate a new SMK each time it generates a new ThreadID, as outlined in [XEP-0201]. 11. IANA Considerations 11.1. XML Namespace Name for e2e Data in XMPP A URN sub-namespace of encrypted content for the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. URI: urn:ietf:params:xml:ns:xmpp-e2e:3 Specification: RFC XXXX Description: This is an XML namespace name of encrypted content for the Extensible Messaging and Presence Protocol as defined by RFC XXXX. Registrant Contact: IESG, 12. References Miller Expires January 14, 2013 [Page 19] Internet-Draft XMPP E2E July 2012 12.1. Normative References [E2E-REQ] Saint-Andre, P., "Requirements for End-to-End Encryption in the Extensible Messaging and Presence Protocol (XMPP)", draft-saintandre-xmpp-e2e-requirements-01 (work in progress), March 2010. [JOSE-JWA] Jones, M., "JSON Web Algorithms (JWA)", draft-ietf-jose-json-web-algorithms-03 (work in progress), July 2012. [JOSE-JWE] Jones, M., Rescola, E., and J. Hildebrand, "JSON Web Encryption (JWE)", draft-ietf-jose-json-web-encryption-03 (work in progress), July 2012. [JOSE-JWK] Jones, M., "JSON Web Key (JWK)", draft-ietf-jose-json-web-key-03 (work in progress), July 2012. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4684] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC 4949, August 2007. [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, March 2011. [RFC6121] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", RFC 6121, March 2011. [XEP-0030] Eatmon, R., Hildebrand, J., Millard, P., and P. Saint- Andre, "Service Discovery", XSF XEP 0030, June 2006. [XEP-0082] Saint-Andre, P., "XMPP Date and Time Profiles", XSF XEP 0082, May 2003. [XEP-0115] Hildebrand, J., Troncon, R., and P. Saint-Andre, "Entity Miller Expires January 14, 2013 [Page 20] Internet-Draft XMPP E2E July 2012 Capabilities", XSF XEP 0115, February 2008. [XEP-0203] Saint-Andre, P., "Delayed Delivery", XSF XEP 0203, September 2009. [XEP-0297] Wild, M. and K. Smith, "Stanza Forwarding", XSF XEP 0297, July 2012. 12.2. Informative References [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-MAC (CCM)", RFC 3923, September 2003. [RFC3923] Saint-Andre, P., "End-to-End Signing and Object Encryption for the Extensible Messaging and Presence Protocol (XMPP)", RFC 3923, October 2004. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", RFC 4086, June 2005. [XEP-0160] Saint-Andre, P., "Best Practices for Handling Offline Messages", XSF XEP 0160, January 2006. [XEP-0201] Saint-Andre, P., Paterson, I., and K. Smith, "Best Practices for Message Threads", XSF XEP 0203, November 2010. Appendix A. Schema for urn:ietf:params:xml:ns:xmpp-e2e:3 The following XML schema is descriptive, not normative. Miller Expires January 14, 2013 [Page 21] Internet-Draft XMPP E2E July 2012 Miller Expires January 14, 2013 [Page 22] Internet-Draft XMPP E2E July 2012 Miller Expires January 14, 2013 [Page 23] Internet-Draft XMPP E2E July 2012 Author's Address Matthew Miller Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3204 Email: mamille2@cisco.com Miller Expires January 14, 2013 [Page 24]