Diff: rfc9729.md.original - rfc9729.md

	rfc9729.md.original		rfc9729.md
	---		---
	title: The Concealed HTTP Authentication Scheme		title: The Concealed HTTP Authentication Scheme
	docname: draft-ietf-httpbis-unprompted-auth-latest		docname: draft-ietf-httpbis-unprompted-auth-latest
	submissiontype: IETF		submissiontype: IETF

	number:		number: 9729
	date:		date: 2025-02
	consensus: true		consensus: true
	v: 3		v: 3
	category: std		category: std
	wg: HTTPBIS		wg: HTTPBIS
	area: "Web and Internet Transport"		area: "Web and Internet Transport"

	venue:
	group: HTTP
	type: Working Group
	home: https://httpwg.org/
	mail: ietf-http-wg@w3.org
	arch: https://lists.w3.org/Archives/Public/ietf-http-wg/
	repo: https://github.com/httpwg/http-extensions/labels/unprompted-auth
	latest: "https://httpwg.org/http-extensions/draft-ietf-httpbis-unprompted-auth
	.html"
	github-issue-label: unprompted-auth
	keyword:		keyword:
	- secure		- secure
	- tunnels		- tunnels
	- masque		- masque
	- http-ng		- http-ng
	author:		author:
	-		-
	ins: D. Schinazi		ins: D. Schinazi
	name: David Schinazi		name: David Schinazi
	org: Google LLC		org: Google LLC

	skipping to change at line 52 ¶		skipping to change at line 43 ¶
	uri: https://guardianproject.info		uri: https://guardianproject.info
	-		-
	ins: J. Hoyland		ins: J. Hoyland
	name: Jonathan Hoyland		name: Jonathan Hoyland
	org: Cloudflare Inc.		org: Cloudflare Inc.
	email: jonathan.hoyland@gmail.com		email: jonathan.hoyland@gmail.com

	normative:		normative:
	RFC8792:		RFC8792:
	X.690:		X.690:

			target: https://www.itu.int/rec/T-REC-X.690
	title: "Information technology - ASN.1 encoding Rules: Specification of Basi c Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encodin g Rules (DER)"		title: "Information technology - ASN.1 encoding Rules: Specification of Basi c Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encodin g Rules (DER)"
	date: 2021-02		date: 2021-02
	author:		author:
	org: ITU-T		org: ITU-T
	seriesinfo:		seriesinfo:

	ISO/IEC 8824-1:2021		ITU-T: Recommendation X690
			ISO/IEC: 8825-1:2021

	informative:		informative:
	H2:		H2:
	=: RFC9113		=: RFC9113
	display: HTTP/2		display: HTTP/2
	H3:		H3:
	=: RFC9114		=: RFC9114
	display: HTTP/3		display: HTTP/3
	SEEMS-LEGIT:		SEEMS-LEGIT:
	title: "Seems Legit: Automated Analysis of Subtle Attacks on Protocols That Use Signatures"		title: "Seems Legit: Automated Analysis of Subtle Attacks on Protocols That Use Signatures"

	skipping to change at line 85 ¶		skipping to change at line 78 ¶
	surname: Cremers		surname: Cremers
	name: Cas Cremers		name: Cas Cremers
	-		-
	initials: K.		initials: K.
	surname: Cohn-Gordon		surname: Cohn-Gordon
	name: Katriel Cohn-Gordon		name: Katriel Cohn-Gordon
	-		-
	initials: R.		initials: R.
	surname: Sasse		surname: Sasse
	name: Ralf Sasse		name: Ralf Sasse

	date: 2019		date: 2019-11
	refcontent:		refcontent:
	- "CCS '19: Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security"		- "CCS '19: Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security"

	- "pp. 2165–2180"		- "pp. 2165-2180"
	seriesinfo:		seriesinfo:
	DOI: 10.1145/3319535.3339813		DOI: 10.1145/3319535.3339813

	--- abstract		--- abstract

	Most HTTP authentication schemes are probeable in the sense that it is possible		Most HTTP authentication schemes are probeable in the sense that it is possible
	for an unauthenticated client to probe whether an origin serves resources that		for an unauthenticated client to probe whether an origin serves resources that
	require authentication. It is possible for an origin to hide the fact that it		require authentication. It is possible for an origin to hide the fact that it

	requires authentication by not generating Unauthorized status codes, however		requires authentication by not generating Unauthorized status codes; however,
	that only works with non-cryptographic authentication schemes: cryptographic		that only works with non-cryptographic authentication schemes: cryptographic
	signatures require a fresh nonce to be signed. Prior to this document, there		signatures require a fresh nonce to be signed. Prior to this document, there
	was no existing way for the origin to share such a nonce without exposing the		was no existing way for the origin to share such a nonce without exposing the
	fact that it serves resources that require authentication. This document		fact that it serves resources that require authentication. This document
	defines a new non-probeable cryptographic authentication scheme.		defines a new non-probeable cryptographic authentication scheme.

	--- middle		--- middle

	# Introduction {#introduction}		# Introduction {#introduction}

	HTTP authentication schemes (see {{Section 11 of !HTTP=RFC9110}}) allow origins		HTTP authentication schemes (see {{Section 11 of !HTTP=RFC9110}}) allow origins
	to restrict access for some resources to only authenticated requests. While		to restrict access for some resources to only authenticated requests. While
	these schemes commonly involve a challenge where the origin asks the client to		these schemes commonly involve a challenge where the origin asks the client to
	provide authentication information, it is possible for clients to send such		provide authentication information, it is possible for clients to send such
	information unprompted. This is particularly useful in cases where an origin		information unprompted. This is particularly useful in cases where an origin

	wants to offer a service or capability only to "those who know" while all		wants to offer a service or capability only to "those who know", while all
	others are given no indication the service or capability exists. Such designs		others are given no indication the service or capability exists. Such designs

	rely on an externally-defined mechanism by which keys are distributed. For		rely on an externally defined mechanism by which keys are distributed. For
	example, a company might offer remote employee access to company services		example, a company might offer remote employee access to company services

	directly via its website using their employee credentials, or offer access to		directly via its website using their employee credentials or offer access to
	limited special capabilities for specific employees, while making discovering		limited special capabilities for specific employees while making discovering
	(or probing for) such capabilities difficult. As another example, members of		(or probing for) such capabilities difficult. As another example, members of
	less well-defined communities might use more ephemeral keys to acquire access		less well-defined communities might use more ephemeral keys to acquire access
	to geography- or capability-specific resources, as issued by an entity whose		to geography- or capability-specific resources, as issued by an entity whose
	user base is larger than the available resources can support (by having that		user base is larger than the available resources can support (by having that
	entity metering the availability of keys temporally or geographically).		entity metering the availability of keys temporally or geographically).

	While digital-signature-based HTTP authentication schemes already exist (e.g.,		While digital-signature-based HTTP authentication schemes already exist (e.g.,
	{{?HOBA=RFC7486}}), they rely on the origin explicitly sending a fresh		{{?HOBA=RFC7486}}), they rely on the origin explicitly sending a fresh
	challenge to the client, to ensure that the signature input is fresh. That		challenge to the client, to ensure that the signature input is fresh. That
	makes the origin probeable as it sends the challenge to unauthenticated		makes the origin probeable as it sends the challenge to unauthenticated
	clients. This document defines a new signature-based authentication scheme that		clients. This document defines a new signature-based authentication scheme that
	is not probeable.		is not probeable.

	## Conventions and Definitions {#conventions}		## Conventions and Definitions {#conventions}

	{::boilerplate bcp14-tagged}		{::boilerplate bcp14-tagged}

	This document uses the notation from {{Section 1.3 of !QUIC=RFC9000}}.		This document uses the notation from {{Section 1.3 of !QUIC=RFC9000}}.


	# The Concealed Authentication Scheme		Various examples in this document contain long lines that may be folded,
			as described in [RFC8792].

			# The Concealed HTTP Authentication Scheme

	This document defines the "Concealed" HTTP authentication scheme. It uses		This document defines the "Concealed" HTTP authentication scheme. It uses
	asymmetric cryptography. Clients possess a key ID and a public/private key		asymmetric cryptography. Clients possess a key ID and a public/private key
	pair, and origin servers maintain a mapping of authorized key IDs to associated		pair, and origin servers maintain a mapping of authorized key IDs to associated
	public keys.		public keys.

	The client uses a TLS keying material exporter to generate data to be signed		The client uses a TLS keying material exporter to generate data to be signed
	(see {{client}}) then sends the signature using the Authorization (or		(see {{client}}) then sends the signature using the Authorization (or
	Proxy-Authorization) header field (see {{Section 11 of HTTP}}). The signature		Proxy-Authorization) header field (see {{Section 11 of HTTP}}). The signature
	and additional information are exchanged using authentication parameters (see		and additional information are exchanged using authentication parameters (see
	{{auth-params}}). Once the server receives these, it can check whether the		{{auth-params}}). Once the server receives these, it can check whether the
	signature validates against an entry in its database of known keys. The server		signature validates against an entry in its database of known keys. The server
	can then use the validation result to influence its response to the client, for		can then use the validation result to influence its response to the client, for

	example by restricting access to certain resources.		example, by restricting access to certain resources.

	# Client Handling {#client}		# Client Handling {#client}

	When a client wishes to use the Concealed HTTP authentication scheme with a		When a client wishes to use the Concealed HTTP authentication scheme with a
	request, it SHALL compute the authentication proof using a TLS keying material		request, it SHALL compute the authentication proof using a TLS keying material
	exporter with the following parameters:		exporter with the following parameters:


	* the label is set to "EXPORTER-HTTP-Concealed-Authentication"		* The label is set to "EXPORTER-HTTP-Concealed-Authentication".


	* the context is set to the structure described in {{context}}		* The context is set to the structure described in {{context}}.


	* the exporter output length is set to 48 bytes (see {{output}})		* The exporter output length is set to 48 bytes (see {{output}}).

	Note that TLS 1.3 keying material exporters are defined in {{Section 7.5 of		Note that TLS 1.3 keying material exporters are defined in {{Section 7.5 of
	TLS}}, while TLS 1.2 keying material exporters are defined in		TLS}}, while TLS 1.2 keying material exporters are defined in
	{{!KEY-EXPORT=RFC5705}}.		{{!KEY-EXPORT=RFC5705}}.

	## Key Exporter Context {#context}		## Key Exporter Context {#context}

	The TLS key exporter context is described in {{fig-context}}, using the		The TLS key exporter context is described in {{fig-context}}, using the
	notation from {{Section 1.3 of QUIC}}:		notation from {{Section 1.3 of QUIC}}:


	~~		~~~
	Signature Algorithm (16),		Signature Algorithm (16),
	Key ID Length (i),		Key ID Length (i),
	Key ID (..),		Key ID (..),
	Public Key Length (i),		Public Key Length (i),
	Public Key (..),		Public Key (..),
	Scheme Length (i),		Scheme Length (i),
	Scheme (..),		Scheme (..),
	Host Length (i),		Host Length (i),
	Host (..),		Host (..),
	Port (16),		Port (16),
	Realm Length (i),		Realm Length (i),
	Realm (..),		Realm (..),

	~~		~~~
	{: #fig-context title="Key Exporter Context Format"}		{: #fig-context title="Key Exporter Context Format"}

	The key exporter context contains the following fields:		The key exporter context contains the following fields:

	Signature Algorithm:		Signature Algorithm:

	: The signature scheme sent in the `s` Parameter (see {{parameter-s}}).		: The signature scheme sent in the `s` Parameter (see {{parameter-s}}).

	Key ID:		Key ID:


	skipping to change at line 219 ¶		skipping to change at line 215 ¶
	of a URI as defined in {{Section 3.1 of !URI=RFC3986}}.		of a URI as defined in {{Section 3.1 of !URI=RFC3986}}.

	Host:		Host:

	: The host for this request, encoded using the format of the host portion of a		: The host for this request, encoded using the format of the host portion of a
	URI as defined in {{Section 3.2.2 of URI}}.		URI as defined in {{Section 3.2.2 of URI}}.

	Port:		Port:

	: The port for this request, encoded in network byte order. Note that the port		: The port for this request, encoded in network byte order. Note that the port

	is either included in the URI, or is the default port for the scheme in use;		is either included in the URI or is the default port for the scheme in use;
	see {{Section 3.2.3 of URI}}.		see {{Section 3.2.3 of URI}}.

	Realm:		Realm:

	: The realm of authentication that is sent in the realm authentication		: The realm of authentication that is sent in the realm authentication

	parameter ({{Section 11.5 of HTTP}}). If the realm authentication parameter is		parameter (see {{Section 11.5 of HTTP}}). If the realm authentication parameter is
	not present, this SHALL be empty. This document does not define a means for the		not present, this SHALL be empty. This document does not define a means for the
	origin to communicate a realm to the client. If a client is not configured to		origin to communicate a realm to the client. If a client is not configured to
	use a specific realm, it SHALL use an empty realm and SHALL NOT send the realm		use a specific realm, it SHALL use an empty realm and SHALL NOT send the realm
	authentication parameter.		authentication parameter.

	The Signature Algorithm and Port fields are encoded as unsigned 16-bit integers		The Signature Algorithm and Port fields are encoded as unsigned 16-bit integers
	in network byte order. The Key ID, Public Key, Scheme, Host, and Realm fields		in network byte order. The Key ID, Public Key, Scheme, Host, and Realm fields

	are length prefixed strings; they are preceded by a Length field that		are length-prefixed strings; they are preceded by a Length field that
	represents their length in bytes. These length fields are encoded using the		represents their length in bytes. These length fields are encoded using the
	variable-length integer encoding from {{Section 16 of QUIC}} and MUST be		variable-length integer encoding from {{Section 16 of QUIC}} and MUST be
	encoded in the minimum number of bytes necessary.		encoded in the minimum number of bytes necessary.

	### Public Key Encoding {#public-key-encoding}		### Public Key Encoding {#public-key-encoding}

	Both the "Public Key" field of the TLS key exporter context (see above) and the		Both the "Public Key" field of the TLS key exporter context (see above) and the
	`a` Parameter (see {{parameter-a}}) carry the same public key. The encoding of		`a` Parameter (see {{parameter-a}}) carry the same public key. The encoding of

	the public key is determined by the Signature Algorithm in use as follows:		the public key is determined by the signature algorithm in use as follows:

	RSASSA-PSS algorithms:		RSASSA-PSS algorithms:

	: The public key is an RSAPublicKey structure {{!PKCS1=RFC8017}} encoded in DER		: The public key is an RSAPublicKey structure {{!PKCS1=RFC8017}} encoded in DER

	{{X.690}}. BER encodings which are not DER MUST be rejected.		{{X.690}}. BER encodings that are not DER MUST be rejected.

	ECDSA algorithms:		ECDSA algorithms:


	: The public key is a UncompressedPointRepresentation structure defined in		: The public key is an UncompressedPointRepresentation structure defined in
	{{Section 4.2.8.2 of TLS}}, using the curve specified by the SignatureScheme.		{{Section 4.2.8.2 of TLS}}, using the curve specified by the SignatureScheme.

	EdDSA algorithms:		EdDSA algorithms:

	: The public key is the byte string encoding defined in {{!EdDSA=RFC8032}}.		: The public key is the byte string encoding defined in {{!EdDSA=RFC8032}}.

	This document does not define the public key encodings for other algorithms. In		This document does not define the public key encodings for other algorithms. In
	order for a SignatureScheme to be usable with the Concealed HTTP authentication		order for a SignatureScheme to be usable with the Concealed HTTP authentication
	scheme, its public key encoding needs to be defined in a corresponding document.		scheme, its public key encoding needs to be defined in a corresponding document.

	## Key Exporter Output {#output}		## Key Exporter Output {#output}

	The key exporter output is 48 bytes long. Of those, the first 32 bytes are part		The key exporter output is 48 bytes long. Of those, the first 32 bytes are part
	of the input to the signature and the next 16 bytes are sent alongside the		of the input to the signature and the next 16 bytes are sent alongside the
	signature. This allows the recipient to confirm that the exporter produces the		signature. This allows the recipient to confirm that the exporter produces the
	right values. This is described in {{fig-output}}, using the notation from		right values. This is described in {{fig-output}}, using the notation from
	{{Section 1.3 of QUIC}}:		{{Section 1.3 of QUIC}}:


	~~		~~~
	Signature Input (256),		Signature Input (256),
	Verification (128),		Verification (128),

	~~		~~~
	{: #fig-output title="Key Exporter Output Format"}		{: #fig-output title="Key Exporter Output Format"}

	The key exporter output contains the following fields:		The key exporter output contains the following fields:

	Signature Input:		Signature Input:

	: This is part of the data signed using the client's chosen asymmetric private		: This is part of the data signed using the client's chosen asymmetric private
	key (see {{computation}}).		key (see {{computation}}).

	Verification:		Verification:

	skipping to change at line 298 ¶		skipping to change at line 294 ¶
	## Signature Computation {#computation}		## Signature Computation {#computation}

	Once the Signature Input has been extracted from the key exporter output (see		Once the Signature Input has been extracted from the key exporter output (see
	{{output}}), it is prefixed with static data before being signed. The signature		{{output}}), it is prefixed with static data before being signed. The signature
	is computed over the concatenation of:		is computed over the concatenation of:

	* A string that consists of octet 32 (0x20) repeated 64 times		* A string that consists of octet 32 (0x20) repeated 64 times

	* The context string "HTTP Concealed Authentication"		* The context string "HTTP Concealed Authentication"


	* A single 0 byte which serves as a separator		* A single 0 byte that serves as a separator

	* The Signature Input extracted from the key exporter output (see {{output}})		* The Signature Input extracted from the key exporter output (see {{output}})

	For example, if the Signature Input has all its 32 bytes set to 01, the content		For example, if the Signature Input has all its 32 bytes set to 01, the content
	covered by the signature (in hexadecimal format) would be:		covered by the signature (in hexadecimal format) would be:


	~~		~~~
	2020202020202020202020202020202020202020202020202020202020202020		2020202020202020202020202020202020202020202020202020202020202020
	2020202020202020202020202020202020202020202020202020202020202020		2020202020202020202020202020202020202020202020202020202020202020
	48545450205369676E61747572652041757468656E7469636174696F6E		48545450205369676E61747572652041757468656E7469636174696F6E
	00		00
	0101010101010101010101010101010101010101010101010101010101010101		0101010101010101010101010101010101010101010101010101010101010101

	~~		~~~
	{: #fig-sig-example title="Example Content Covered by Signature"}		{: #fig-sig-example title="Example Content Covered by Signature"}

	The purpose of this static prefix is to mitigate issues that could arise if		The purpose of this static prefix is to mitigate issues that could arise if
	authentication asymmetric keys were accidentally reused across protocols (even		authentication asymmetric keys were accidentally reused across protocols (even
	though this is forbidden, see {{security}}). This construction mirrors that of		though this is forbidden, see {{security}}). This construction mirrors that of
	the TLS 1.3 CertificateVerify message defined in {{Section 4.4.3 of TLS}}.		the TLS 1.3 CertificateVerify message defined in {{Section 4.4.3 of TLS}}.

	The resulting signature is then transmitted to the server using the `p`		The resulting signature is then transmitted to the server using the `p`
	Parameter (see {{parameter-p}}).		Parameter (see {{parameter-p}}).

	# Authentication Parameters {#auth-params}		# Authentication Parameters {#auth-params}

	This specification defines the following authentication parameters.		This specification defines the following authentication parameters.

	All of the byte sequences below are encoded using base64url (see {{Section 5 of		All of the byte sequences below are encoded using base64url (see {{Section 5 of
	!BASE64=RFC4648}}) without quotes and without padding. In other words, the		!BASE64=RFC4648}}) without quotes and without padding. In other words, the
	values of these byte-sequence authentication parameters MUST NOT include any		values of these byte-sequence authentication parameters MUST NOT include any

	characters other than ASCII letters, digits, dash and underscore.		characters other than ASCII letters, digits, dash, and underscore.

	The integer below is encoded without a minus and without leading zeroes. In		The integer below is encoded without a minus and without leading zeroes. In
	other words, the value of this integer authentication parameter MUST NOT		other words, the value of this integer authentication parameter MUST NOT

	include any characters other than digits, and MUST NOT start with a zero unless		include any characters other than digits and MUST NOT start with a zero unless
	the full value is "0".		the full value is "0".

	Using the syntax from {{!ABNF=RFC5234}}:		Using the syntax from {{!ABNF=RFC5234}}:


	~~		~~~ abnf
	concealed-byte-sequence-param-value = *( ALPHA / DIGIT / "-" / "_" )		concealed-byte-sequence-param-value = *( ALPHA / DIGIT / "-" / "_" )
	concealed-integer-param-value = %x31-39 1*4( DIGIT ) / "0"		concealed-integer-param-value = %x31-39 1*4( DIGIT ) / "0"

	~~		~~~
	{: #fig-param title="Authentication Parameter Value ABNF"}		{: #fig-param title="Authentication Parameter Value ABNF"}

	## The k Parameter {#parameter-k}		## The k Parameter {#parameter-k}

	The REQUIRED "k" (key ID) Parameter is a byte sequence that identifies which		The REQUIRED "k" (key ID) Parameter is a byte sequence that identifies which
	key the client wishes to use to authenticate. This is used by the backend to		key the client wishes to use to authenticate. This is used by the backend to

	point to an entry in a server-side database of known keys, see {{backend}}.		point to an entry in a server-side database of known keys (see {{backend}}).

	## The a Parameter {#parameter-a}		## The a Parameter {#parameter-a}

	The REQUIRED "a" (public key) Parameter is a byte sequence that specifies the		The REQUIRED "a" (public key) Parameter is a byte sequence that specifies the
	public key used by the server to validate the signature provided by the client.		public key used by the server to validate the signature provided by the client.
	This avoids key confusion issues (see {{SEEMS-LEGIT}}). The encoding of the		This avoids key confusion issues (see {{SEEMS-LEGIT}}). The encoding of the
	public key is described in {{public-key-encoding}}.		public key is described in {{public-key-encoding}}.

	## The p Parameter {#parameter-p}		## The p Parameter {#parameter-p}

	The REQUIRED "p" (proof) Parameter is a byte sequence that specifies the proof		The REQUIRED "p" (proof) Parameter is a byte sequence that specifies the proof
	that the client provides to attest to possessing the credential that matches		that the client provides to attest to possessing the credential that matches
	its key ID.		its key ID.

	## The s Parameter {#parameter-s}		## The s Parameter {#parameter-s}


	The REQUIRED "s" (signature) Parameter is an integer that specifies the		The REQUIRED "s" (signature scheme) Parameter is an integer that specifies the
	signature scheme used to compute the proof transmitted in the `p` Parameter.		signature scheme used to compute the proof transmitted in the `p` Parameter.
	Its value is an integer between 0 and 65535 inclusive from the IANA "TLS		Its value is an integer between 0 and 65535 inclusive from the IANA "TLS
	SignatureScheme" registry maintained at		SignatureScheme" registry maintained at
	<[](https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-sig naturescheme)>.		<[](https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-sig naturescheme)>.

	## The v Parameter {#parameter-v}		## The v Parameter {#parameter-v}

	The REQUIRED "v" (verification) Parameter is a byte sequence that specifies the		The REQUIRED "v" (verification) Parameter is a byte sequence that specifies the
	verification that the client provides to attest to possessing the key exporter		verification that the client provides to attest to possessing the key exporter
	output (see {{output}} for details). This avoids issues with signature schemes		output (see {{output}} for details). This avoids issues with signature schemes
	where certain keys can generate signatures that are valid for multiple inputs		where certain keys can generate signatures that are valid for multiple inputs
	(see {{SEEMS-LEGIT}}).		(see {{SEEMS-LEGIT}}).

	# Example {#example}		# Example {#example}


	For example, the key ID "basement" authenticating using Ed25519		For example, a client using the key ID "basement" and the signature algorithm
	{{?ED25519=RFC8410}} could produce the following header field:		Ed25519 {{?ED25519=RFC8410}} could produce the following header field:


	~~ http-message		~~~ http-message
	NOTE: '\' line wrapping per RFC 8792		NOTE: '\' line wrapping per RFC 8792

	Authorization: Concealed \		Authorization: Concealed \
	k=YmFzZW1lbnQ, \		k=YmFzZW1lbnQ, \
	a=VGhpcyBpcyBh-HB1YmxpYyBrZXkgaW4gdXNl_GhlcmU, \		a=VGhpcyBpcyBh-HB1YmxpYyBrZXkgaW4gdXNl_GhlcmU, \
	s=2055, \		s=2055, \
	v=dmVyaWZpY2F0aW9u_zE2Qg, \		v=dmVyaWZpY2F0aW9u_zE2Qg, \
	p=QzpcV2luZG93c_xTeXN0ZW0zMlxkcml2ZXJz-ENyb3dkU\		p=QzpcV2luZG93c_xTeXN0ZW0zMlxkcml2ZXJz-ENyb3dkU\
	3RyaWtlXEMtMDAwMDAwMDAyOTEtMD-wMC0w_DAwLnN5cw		3RyaWtlXEMtMDAwMDAwMDAyOTEtMD-wMC0w_DAwLnN5cw

	~~		~~~
	{: #fig-hdr-example title="Example Header Field"}		{: #fig-hdr-example title="Example Header Field"}

	# Server Handling		# Server Handling

	In this section, we subdivide the server role in two:		In this section, we subdivide the server role in two:


	* the "frontend" runs in the HTTP server that terminates the TLS or QUIC		* The "frontend" runs in the HTTP server that terminates the TLS or QUIC
	connection created by the client.		connection created by the client.


	* the "backend" runs in the HTTP server that has access to the database of		* The "backend" runs in the HTTP server that has access to the database of
	accepted key identifiers and public keys.		accepted key identifiers and public keys.


	In most deployments, we expect the frontend and backend roles to both be		In most deployments, we expect both the frontend and backend roles to be
	implemented in a single HTTP origin server (as defined in {{Section 3.6 of		implemented in a single HTTP origin server (as defined in {{Section 3.6 of
	HTTP}}). However, these roles can be split such that the frontend is an HTTP		HTTP}}). However, these roles can be split such that the frontend is an HTTP
	gateway (as defined in {{Section 3.7 of HTTP}}) and the backend is an HTTP		gateway (as defined in {{Section 3.7 of HTTP}}) and the backend is an HTTP
	origin server.		origin server.

	## Frontend Handling		## Frontend Handling


	If a frontend is configured to check the Concealed authentication scheme, it		If a frontend is configured to check the Concealed HTTP authentication scheme, i t
	will parse the Authorization (or Proxy-Authorization) header field. If the		will parse the Authorization (or Proxy-Authorization) header field. If the
	authentication scheme is set to "Concealed", the frontend MUST validate that		authentication scheme is set to "Concealed", the frontend MUST validate that
	all the required authentication parameters are present and can be parsed		all the required authentication parameters are present and can be parsed
	correctly as defined in {{auth-params}}. If any parameter is missing or fails		correctly as defined in {{auth-params}}. If any parameter is missing or fails
	to parse, the frontend MUST ignore the entire Authorization (or		to parse, the frontend MUST ignore the entire Authorization (or
	Proxy-Authorization) header field.		Proxy-Authorization) header field.

	The frontend then uses the data from these authentication parameters to compute		The frontend then uses the data from these authentication parameters to compute
	the key exporter output, as defined in {{output}}. The frontend then shares the		the key exporter output, as defined in {{output}}. The frontend then shares the
	header field and the key exporter output with the backend.		header field and the key exporter output with the backend.


	## Communication between Frontend and Backend		## Communication Between Frontend and Backend

	If the frontend and backend roles are implemented in the same machine, this can		If the frontend and backend roles are implemented in the same machine, this can
	be handled by a simple function call.		be handled by a simple function call.

	If the roles are split between two separate HTTP servers, then the backend		If the roles are split between two separate HTTP servers, then the backend
	won't be able to directly access the TLS keying material exporter from the TLS		won't be able to directly access the TLS keying material exporter from the TLS

	connection between the client and frontend, so the frontend needs to explictly		connection between the client and frontend, so the frontend needs to explicitly
	send it. This document defines the "Concealed-Auth-Export" request header field		send it. This document defines the "Concealed-Auth-Export" request header field
	for this purpose. The Concealed-Auth-Export header field's value is a		for this purpose. The Concealed-Auth-Export header field's value is a
	Structured Field Byte Sequence (see {{Section 3.3.5 of		Structured Field Byte Sequence (see {{Section 3.3.5 of

	!STRUCTURED-FIELDS=RFC8941}}) that contains the 48-byte key exporter output		!STRUCTURED-FIELDS=RFC9651}}) that contains the 48-byte key exporter output
	(see {{output}}), without any parameters. Note that Structured Field Byte		(see {{output}}), without any parameters. Note that Structured Field Byte
	Sequences are encoded using the non-URL-safe variant of base64. For example:		Sequences are encoded using the non-URL-safe variant of base64. For example:


	~~ http-message		~~~ http-message
	NOTE: '\' line wrapping per RFC 8792		NOTE: '\' line wrapping per RFC 8792

	Concealed-Auth-Export: :VGhpc+BleGFtcGxlIFRMU/BleHBvcn\		Concealed-Auth-Export: :VGhpc+BleGFtcGxlIFRMU/BleHBvcn\
	Rlc+BvdXRwdXQ/aXMgNDggYnl0ZXMgI/+h:		Rlc+BvdXRwdXQ/aXMgNDggYnl0ZXMgI/+h:

	~~		~~~
	{: #fig-int-hdr-example title="Example Concealed-Auth-Export Header Field"}		{: #fig-int-hdr-example title="Example Concealed-Auth-Export Header Field"}

	The frontend SHALL forward the HTTP request to the backend, including the		The frontend SHALL forward the HTTP request to the backend, including the
	original unmodified Authorization (or Proxy-Authorization) header field and the		original unmodified Authorization (or Proxy-Authorization) header field and the
	newly added Concealed-Auth-Export header field.		newly added Concealed-Auth-Export header field.

	Note that, since the security of this mechanism requires the key exporter		Note that, since the security of this mechanism requires the key exporter
	output to be correct, backends need to trust frontends to send it truthfully.		output to be correct, backends need to trust frontends to send it truthfully.
	This trust relationship is common because the frontend already needs access to		This trust relationship is common because the frontend already needs access to
	the TLS certificate private key in order to respond to requests. HTTP servers		the TLS certificate private key in order to respond to requests. HTTP servers

	skipping to change at line 485 ¶		skipping to change at line 481 ¶
	* validate that the public key from the database is equal to the one in the		* validate that the public key from the database is equal to the one in the
	Authorization (or Proxy-Authorization) header field		Authorization (or Proxy-Authorization) header field

	* validate that the verification field from the Authorization (or		* validate that the verification field from the Authorization (or
	Proxy-Authorization) header field matches the one extracted from the key		Proxy-Authorization) header field matches the one extracted from the key
	exporter output		exporter output

	* verify the cryptographic signature as defined in {{computation}}		* verify the cryptographic signature as defined in {{computation}}

	If all of these checks succeed, the backend can consider the request to be		If all of these checks succeed, the backend can consider the request to be

	properly authenticated, and can reply accordingly (the backend can also forward		properly authenticated and can reply accordingly (the backend can also forward
	the request to another HTTP server).		the request to another HTTP server).

	If any of the above checks fail, the backend MUST treat it as if the		If any of the above checks fail, the backend MUST treat it as if the
	Authorization (or Proxy-Authorization) header field was missing.		Authorization (or Proxy-Authorization) header field was missing.

	## Non-Probeable Server Handling		## Non-Probeable Server Handling

	Servers that wish to introduce resources whose existence cannot be probed need		Servers that wish to introduce resources whose existence cannot be probed need
	to ensure that they do not reveal any information about those resources to		to ensure that they do not reveal any information about those resources to
	unauthenticated clients. In particular, such servers MUST respond to		unauthenticated clients. In particular, such servers MUST respond to
	authentication failures with the exact same response that they would have used		authentication failures with the exact same response that they would have used

	for non-existent resources. For example, this can mean using HTTP status code		for nonexistent resources. For example, this can mean using HTTP status code
	404 (Not Found) instead of 401 (Unauthorized).		404 (Not Found) instead of 401 (Unauthorized).

	The authentication checks described above can take time to compute, and an		The authentication checks described above can take time to compute, and an
	attacker could detect use of this mechanism if that time is observable by		attacker could detect use of this mechanism if that time is observable by

	comparing the timing of a request for a known non-existent resource to the		comparing the timing of a request for a known nonexistent resource to the
	timing of a request for a potentially authenticated resource. Servers can		timing of a request for a potentially authenticated resource. Servers can

	mitigate this observability by slightly delaying responses to some non-existent		mitigate this observability by slightly delaying responses to some nonexistent
	resources such that the timing of the authentication verification is not		resources such that the timing of the authentication verification is not
	observable. This delay needs to be carefully considered to avoid having the		observable. This delay needs to be carefully considered to avoid having the
	delay itself leak the fact that this origin uses this mechanism at all.		delay itself leak the fact that this origin uses this mechanism at all.

	Non-probeable resources also need to be non-discoverable for unauthenticated		Non-probeable resources also need to be non-discoverable for unauthenticated
	users. For example, if a server operator wishes to hide an authenticated		users. For example, if a server operator wishes to hide an authenticated
	resource by pretending it does not exist to unauthenticated users, then the		resource by pretending it does not exist to unauthenticated users, then the
	server operator needs to ensure there are no unauthenticated pages with links		server operator needs to ensure there are no unauthenticated pages with links

	to that resource, and no other out-of-band ways for unauthenticated users to		to that resource and no other out-of-band ways for unauthenticated users to
	discover this resource.		discover this resource.

	# Requirements on TLS Usage		# Requirements on TLS Usage

	This authentication scheme is only defined for uses of HTTP with TLS		This authentication scheme is only defined for uses of HTTP with TLS
	{{!TLS=RFC8446}}. This includes any use of HTTP over TLS as typically used for		{{!TLS=RFC8446}}. This includes any use of HTTP over TLS as typically used for
	HTTP/2 {{H2}}, or HTTP/3 {{H3}} where the transport protocol uses TLS as its		HTTP/2 {{H2}}, or HTTP/3 {{H3}} where the transport protocol uses TLS as its
	authentication and key exchange mechanism {{?QUIC-TLS=RFC9001}}.		authentication and key exchange mechanism {{?QUIC-TLS=RFC9001}}.

	Because the TLS keying material exporter is only secure for authentication when		Because the TLS keying material exporter is only secure for authentication when
	it is uniquely bound to the TLS session {{!RFC7627}}, the Concealed		it is uniquely bound to the TLS session {{!RFC7627}}, the Concealed
	authentication scheme requires either one of the following properties:		authentication scheme requires either one of the following properties:


	* The TLS version in use is greater or equal to 1.3 {{TLS}}.		* The TLS version in use is greater than or equal to 1.3 {{TLS}}.


	* The TLS version in use is 1.2 and the Extended Master Secret extension		* The TLS version in use is 1.2, and the extended master secret extension
	{{RFC7627}} has been negotiated.		{{RFC7627}} has been negotiated.


	Clients MUST NOT use the Concealed authentication scheme on connections that do		Clients MUST NOT use the Concealed HTTP authentication scheme on connections tha t do
	not meet one of the two properties above. If a server receives a request that		not meet one of the two properties above. If a server receives a request that
	uses this authentication scheme on a connection that meets neither of the above		uses this authentication scheme on a connection that meets neither of the above
	properties, the server MUST treat the request as if the authentication were not		properties, the server MUST treat the request as if the authentication were not
	present.		present.

	# Security Considerations {#security}		# Security Considerations {#security}

	The Concealed HTTP authentication scheme allows a client to authenticate to an		The Concealed HTTP authentication scheme allows a client to authenticate to an
	origin server while guaranteeing freshness and without the need for the server		origin server while guaranteeing freshness and without the need for the server
	to transmit a nonce to the client. This allows the server to accept		to transmit a nonce to the client. This allows the server to accept
	authenticated clients without revealing that it supports or expects		authenticated clients without revealing that it supports or expects
	authentication for some resources. It also allows authentication without the		authentication for some resources. It also allows authentication without the

	client leaking the presence of authentication to observers due to clear-text		client leaking the presence of authentication to observers due to cleartext
	TLS Client Hello extensions.		TLS Client Hello extensions.

	Since the freshness described above is provided by a TLS key exporter, it can		Since the freshness described above is provided by a TLS key exporter, it can
	be as old as the underlying TLS connection. Servers can require better		be as old as the underlying TLS connection. Servers can require better
	freshness by forcing clients to create new connections using mechanisms such as		freshness by forcing clients to create new connections using mechanisms such as
	the GOAWAY frame (see {{Section 5.2 of H3}}).		the GOAWAY frame (see {{Section 5.2 of H3}}).

	The authentication proofs described in this document are not bound to		The authentication proofs described in this document are not bound to
	individual HTTP requests; if the key is used for authentication proofs on		individual HTTP requests; if the key is used for authentication proofs on
	multiple requests on the same connection, they will all be identical. This		multiple requests on the same connection, they will all be identical. This

	allows for better compression when sending over the wire, but implies that		allows for better compression when sending over the wire, but it implies that
	client implementations that multiplex different security contexts over a single		client implementations that multiplex different security contexts over a single
	HTTP connection need to ensure that those contexts cannot read each other's		HTTP connection need to ensure that those contexts cannot read each other's
	header fields. Otherwise, one context would be able to replay the Authorization		header fields. Otherwise, one context would be able to replay the Authorization

	header field of another. This constraint is met by modern Web browsers. If an		header field of another. This constraint is met by modern web browsers. If an
	attacker were to compromise the browser such that it could access another		attacker were to compromise the browser such that it could access another
	context's memory, the attacker might also be able to access the corresponding		context's memory, the attacker might also be able to access the corresponding
	key, so binding authentication to requests would not provide much benefit in		key, so binding authentication to requests would not provide much benefit in
	practice.		practice.

	Authentication asymmetric keys used for the Concealed HTTP authentication		Authentication asymmetric keys used for the Concealed HTTP authentication
	scheme MUST NOT be reused in other protocols. Even though we attempt to		scheme MUST NOT be reused in other protocols. Even though we attempt to
	mitigate these issues by adding a static prefix to the signed data (see		mitigate these issues by adding a static prefix to the signed data (see
	{{computation}}), reusing keys could undermine the security guarantees of the		{{computation}}), reusing keys could undermine the security guarantees of the
	authentication.		authentication.

	Origins offering this scheme can link requests that use the same key.		Origins offering this scheme can link requests that use the same key.
	However, requests are not linkable across origins if the keys used are specific		However, requests are not linkable across origins if the keys used are specific
	to the individual origins using this scheme.		to the individual origins using this scheme.

	# IANA Considerations {#iana}		# IANA Considerations {#iana}

	## HTTP Authentication Schemes Registry {#iana-schemes}		## HTTP Authentication Schemes Registry {#iana-schemes}


	This document, if approved, requests IANA to register the following entry in		IANA has registered the following entry in
	the "HTTP Authentication Schemes" Registry maintained at		the "HTTP Authentication Schemes" registry maintained at
	<[](https://www.iana.org/assignments/http-authschemes)>:		<[](https://www.iana.org/assignments/http-authschemes)>:

	Authentication Scheme Name:		Authentication Scheme Name:

	: Concealed		: Concealed

	Reference:		Reference:


	: This document		: RFC 9729

	Notes:		Notes:

	: None		: None
	{: spacing="compact"}		{: spacing="compact"}

	## TLS Keying Material Exporter Labels {#iana-exporter-label}		## TLS Keying Material Exporter Labels {#iana-exporter-label}


	This document, if approved, requests IANA to register the following entry in		IANA has registered the following entry in
	the "TLS Exporter Labels" registry maintained at		the "TLS Exporter Labels" registry maintained at
	<[](https://www.iana.org/assignments/tls-parameters#exporter-labels)>:		<[](https://www.iana.org/assignments/tls-parameters#exporter-labels)>:

	Value:		Value:

	: EXPORTER-HTTP-Concealed-Authentication		: EXPORTER-HTTP-Concealed-Authentication

	DTLS-OK:		DTLS-OK:

	: N		: N

	Recommended:		Recommended:

	: Y		: Y

	Reference:		Reference:


	: This document		: RFC 9729
	{: spacing="compact"}		{: spacing="compact"}

	## HTTP Field Name		## HTTP Field Name


	This document, if approved, requests IANA to register the following entry in		IANA has registered the following entry in
	the "Hypertext Transfer Protocol (HTTP) Field Name" registry maintained at		the "Hypertext Transfer Protocol (HTTP) Field Name Registry" maintained at
	<[](https://www.iana.org/assignments/http-fields/http-fields.xhtml)>:		<[](https://www.iana.org/assignments/http-fields/http-fields.xhtml)>:

	Field Name:		Field Name:

	: Concealed-Auth-Export		: Concealed-Auth-Export

	Status:		Status:

	: permanent		: permanent

	Structured Type:		Structured Type:

	: Item		: Item

	Reference:		Reference:


	: This document		: RFC 9729

	Comments:		Comments:

	: None		: None
	{: spacing="compact"}		{: spacing="compact"}

	--- back		--- back

	# Acknowledgments {#acknowledgments}		# Acknowledgments {#acknowledgments}
	{:numbered="false"}		{:numbered="false"}

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