Diff: rfc9729.md.original

	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: 2025-01
	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 57 ¶	skipping to change at line 48 ¶
	email: jonathan.hoyland@gmail.com	email: jonathan.hoyland@gmail.com

	normative:	normative:
	RFC8792:	RFC8792:
	X.690:	X.690:
	title: "Information technology - ASN.1 encoding Rules: Specification of Basic Encoding Rules (BE R), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)"	title: "Information technology - ASN.1 encoding Rules: Specification of Basic Encoding Rules (BE R), Canonical Encoding Rules (CER) and Distinguished Encoding 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 77 ¶
	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 Secur ity"	- "CCS '19: Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Secur ity"

	- "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}}.


		<!-- [rfced] FYI, we have added the following sentence to Section 1.1
		("Conventions and Definitions") in order to include a citation for RFC 8792 in
		the text. Please let us know of any objections.

		Current:
		Various examples in this document contain long lines that may be folded,
		as described in [RFC8792].
		-->

		Various examples in this document contain long lines that may be folded,
		as described in [RFC8792].

		<!--[rfced] Throughout the text, "Concealed HTTP authentication scheme" and
		"Concealed authentication scheme" appear to be used inconsistently. Please
		review these occurrences and let us know if/how they be made consistent.
		Some examples are listed here:

		Original:
		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 exporter with the following parameters:
		...
		If a frontend is configured to check the Concealed authentication
		scheme, it will parse the Authorization (or Proxy-Authorization)
		header field.
		-->

	# The Concealed Authentication Scheme	# The Concealed 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}}:


	~~	<!-- [rfced] Please review sourcecode types within the markdown file, and
		let us know if they should be set and/or have been set correctly.

		The current list of preferred values for sourcecode types is available at
		<https://www.rfc-editor.org/rpc/wiki/doku.php?id=sourcecode-types>.
		If the current list does not contain an applicable type, feel free to
		suggest additions for consideration. Note that it is also acceptable
		to leave the sourcecode type not set.
		-->

		~~~
	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}}).


		<!-- [rfced] We see that the capitalization of "Key ID" is inconsistent. Please let how we should up
		date it.
		-->

	Key ID:	Key ID:

	: The key ID sent in the `k` Parameter (see {{parameter-k}}).	: The key ID sent in the `k` Parameter (see {{parameter-k}}).

	Public Key:	Public Key:

	: The public key used by the server to validate the signature provided by the	: The public key used by the server to validate the signature provided by the
	client. Its encoding is described in {{public-key-encoding}}.	client. Its encoding is described in {{public-key-encoding}}.

	Scheme:	Scheme:

	skipping to change at line 219 ¶	skipping to change at line 251 ¶
	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 ({{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}


		<!--[rfced] As "Signature Algorithm" is being used in a general way and not as
		a field name, may we make it lowercase in this sentence?

		Original:
		The encoding of the public key is determined by the Signature
		Algorithm in use as follows:

		Perhaps:
		The encoding of the public key is determined by the signature
		algorithm in use as follows:
		-->

	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:


		<!--[rfced] For clarity, may we update "which" to "that" here? It depends on the
		intended meaning, as noted below.

		Original:
		The public key is an RSAPublicKey structure
		[PKCS1] encoded in DER [X.690]. BER encodings which are not DER
		MUST be rejected.

		Perhaps (restrictive "that", meaning some BER encodings):
		The public key is an RSAPublicKey structure
		[PKCS1] encoded in DER [X.690]. BER encodings that are not DER
		MUST be rejected.

		Or (nonrestrictive "which", meaning all BER encodings):
		The public key is an RSAPublicKey structure
		[PKCS1] encoded in DER [X.690]. BER encodings, which are not DER,
		MUST be rejected.
		-->

	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 which 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 361 ¶
	## 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}


	skipping to change at line 381 ¶	skipping to change at line 444 ¶
	## 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}


		<!-- [rfced] We having difficulty parsing the following sentence.
		Does the key ID authenticate or does the client?

		Current:
		For example, the key ID "basement" authenticating using Ed25519
		[ED25519] could produce the following header field

		Perhaps:
		For example, a client authenticating with the key ID "basement"
		and using Ed25519 [ED25519] could produce the following header
		field
		-->

	For example, the key ID "basement" authenticating using Ed25519	For example, the key ID "basement" authenticating using Ed25519
	{{?ED25519=RFC8410}} could produce the following header field:	{{?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 authentication scheme, it
	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.


		<!-- [rfced] RFC 8941 has been obsoleted by RFC 9651. May we replace RFC
		8941 with RFC 9651?
		-->

	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=RFC8941}}) 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 565 ¶
	* 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	<!-- [rfced] Please review the "Inclusive Language" portion of the online
		Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
		and let us know if any changes are needed. Updates of this nature typically
		result in more precise language, which is helpful for readers.
		-->

		* 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 authentication scheme on connections that 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"}

	The authors would like to thank many members of the IETF community, as this	The authors would like to thank many members of the IETF community, as this
	document is the fruit of many hallway conversations. In particular, the authors	document is the fruit of many hallway conversations. In particular, the authors
	would like to thank {{{David Benjamin}}}, {{{Reese Enghardt}}}, {{{Nick	would like to thank {{{David Benjamin}}}, {{{Reese Enghardt}}}, {{{Nick
	Harper}}}, {{{Dennis Jackson}}}, {{{Ilari Liusvaara}}}, {{{François Michel}}},	Harper}}}, {{{Dennis Jackson}}}, {{{Ilari Liusvaara}}}, {{{François Michel}}},
	{{{Lucas Pardue}}}, {{{Justin Richer}}}, {{{Ben Schwartz}}}, {{{Martin	{{{Lucas Pardue}}}, {{{Justin Richer}}}, {{{Ben Schwartz}}}, {{{Martin
	Thomson}}}, and {{{Chris A. Wood}}} for their reviews and contributions. The	Thomson}}}, and {{{Chris A. Wood}}} for their reviews and contributions. The
	mechanism described in this document was originally part of the first iteration	mechanism described in this document was originally part of the first iteration
	of MASQUE {{?MASQUE-ORIGINAL=I-D.schinazi-masque-00}}.	of MASQUE {{?MASQUE-ORIGINAL=I-D.schinazi-masque-00}}.


		<!--[rfced] References. May we add the following URL to this reference for the ease of the reader?

		https://www.itu.int/rec/T-REC-X.690

		Current:

		[X.690] ITU-T, "Information technology - ASN.1 encoding Rules:
		Specification of Basic Encoding Rules (BER), Canonical
		Encoding Rules (CER) and Distinguished Encoding Rules
		(DER)", ITU-T Recommendation X690, ISO/IEC 8825-1:2021,
		February 2021.
		-->

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