HTTP Message Signatures
draft-ietf-httpbis-message-signatures-09
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9421.
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|---|---|---|---|
| Authors | Annabelle Backman , Justin Richer , Manu Sporny | ||
| Last updated | 2022-03-06 (Latest revision 2022-01-28) | ||
| Replaces | draft-richanna-http-message-signatures, draft-cavage-http-signatures | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-httpbis-message-signatures-09
HTTP A. Backman, Ed.
Internet-Draft Amazon
Intended status: Standards Track J. Richer
Expires: 7 September 2022 Bespoke Engineering
M. Sporny
Digital Bazaar
6 March 2022
HTTP Message Signatures
draft-ietf-httpbis-message-signatures-09
Abstract
This document describes a mechanism for creating, encoding, and
verifying digital signatures or message authentication codes over
components of an HTTP message. This mechanism supports use cases
where the full HTTP message may not be known to the signer, and where
the message may be transformed (e.g., by intermediaries) before
reaching the verifier. This document also describes a means for
requesting that a signature be applied to a subsequent HTTP message
in an ongoing HTTP exchange.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-message-
signatures/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/signatures.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 7 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Discussion . . . . . . . . . . . . . . . . . 5
1.2. HTTP Message Transformations . . . . . . . . . . . . . . 6
1.3. Safe Transformations . . . . . . . . . . . . . . . . . . 7
1.4. Conventions and Terminology . . . . . . . . . . . . . . . 7
1.5. Application of HTTP Message Signatures . . . . . . . . . 10
2. HTTP Message Components . . . . . . . . . . . . . . . . . . . 11
2.1. HTTP Fields . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.1. Canonicalized Structured HTTP Fields . . . . . . . . 14
2.1.2. Dictionary Structured Field Members . . . . . . . . . 14
2.2. Derived Components . . . . . . . . . . . . . . . . . . . 15
2.2.1. Signature Parameters . . . . . . . . . . . . . . . . 16
2.2.2. Method . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.3. Target URI . . . . . . . . . . . . . . . . . . . . . 19
2.2.4. Authority . . . . . . . . . . . . . . . . . . . . . . 19
2.2.5. Scheme . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.6. Request Target . . . . . . . . . . . . . . . . . . . 20
2.2.7. Path . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.8. Query . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.9. Query Parameters . . . . . . . . . . . . . . . . . . 23
2.2.10. Status Code . . . . . . . . . . . . . . . . . . . . . 24
2.2.11. Request-Response Signature Binding . . . . . . . . . 24
2.3. Creating the Signature Base . . . . . . . . . . . . . . . 27
3. HTTP Message Signatures . . . . . . . . . . . . . . . . . . . 30
3.1. Creating a Signature . . . . . . . . . . . . . . . . . . 30
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3.2. Verifying a Signature . . . . . . . . . . . . . . . . . . 32
3.2.1. Enforcing Application Requirements . . . . . . . . . 34
3.3. Signature Algorithm Methods . . . . . . . . . . . . . . . 35
3.3.1. RSASSA-PSS using SHA-512 . . . . . . . . . . . . . . 36
3.3.2. RSASSA-PKCS1-v1_5 using SHA-256 . . . . . . . . . . . 36
3.3.3. HMAC using SHA-256 . . . . . . . . . . . . . . . . . 37
3.3.4. ECDSA using curve P-256 DSS and SHA-256 . . . . . . . 37
3.3.5. EdDSA using curve edwards25519 . . . . . . . . . . . 38
3.3.6. JSON Web Signature (JWS) algorithms . . . . . . . . . 39
4. Including a Message Signature in a Message . . . . . . . . . 39
4.1. The 'Signature-Input' HTTP Field . . . . . . . . . . . . 40
4.2. The 'Signature' HTTP Field . . . . . . . . . . . . . . . 40
4.3. Multiple Signatures . . . . . . . . . . . . . . . . . . . 41
5. Requesting Signatures . . . . . . . . . . . . . . . . . . . . 44
5.1. The Accept-Signature Field . . . . . . . . . . . . . . . 45
5.2. Processing an Accept-Signature . . . . . . . . . . . . . 46
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
6.1. HTTP Signature Algorithms Registry . . . . . . . . . . . 47
6.1.1. Registration Template . . . . . . . . . . . . . . . . 47
6.1.2. Initial Contents . . . . . . . . . . . . . . . . . . 48
6.2. HTTP Signature Metadata Parameters Registry . . . . . . . 48
6.2.1. Registration Template . . . . . . . . . . . . . . . . 48
6.2.2. Initial Contents . . . . . . . . . . . . . . . . . . 49
6.3. HTTP Signature Derived Component Identifiers Registry . . 50
6.3.1. Registration Template . . . . . . . . . . . . . . . . 50
6.3.2. Initial Contents . . . . . . . . . . . . . . . . . . 51
7. Security Considerations . . . . . . . . . . . . . . . . . . . 52
7.1. Signature Verification Skipping . . . . . . . . . . . . . 52
7.2. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . 52
7.3. Signature Replay . . . . . . . . . . . . . . . . . . . . 53
7.4. Insufficient Coverage . . . . . . . . . . . . . . . . . . 53
7.5. Cryptography and Signature Collision . . . . . . . . . . 54
7.6. Key Theft . . . . . . . . . . . . . . . . . . . . . . . . 54
7.7. Modification of Required Message Parameters . . . . . . . 55
7.8. Mismatch of Signature Parameters from Message . . . . . . 55
7.9. Multiple Signature Confusion . . . . . . . . . . . . . . 55
7.10. Signature Labels . . . . . . . . . . . . . . . . . . . . 56
7.11. Symmetric Cryptography . . . . . . . . . . . . . . . . . 56
7.12. Canonicalization Attacks . . . . . . . . . . . . . . . . 57
7.13. Key Specification Mix-Up . . . . . . . . . . . . . . . . 57
7.14. HTTP Versions and Component Ambiguity . . . . . . . . . . 57
7.15. Key and Algorithm Specification Downgrades . . . . . . . 58
7.16. Parsing Structured Field Values . . . . . . . . . . . . . 58
7.17. Choosing Message Components . . . . . . . . . . . . . . . 59
7.18. Confusing HTTP Field Names for Derived Component
Identifiers . . . . . . . . . . . . . . . . . . . . . . 59
7.19. Non-deterministic Signature Primitives . . . . . . . . . 60
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7.20. Choosing Signature Parameters and Derived Components over
HTTP Fields . . . . . . . . . . . . . . . . . . . . . . 60
7.21. Semantically Equivalent Field Values . . . . . . . . . . 61
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 61
8.1. Identification through Keys . . . . . . . . . . . . . . . 62
8.2. Signatures do not provide confidentiality . . . . . . . . 62
8.3. Oracles . . . . . . . . . . . . . . . . . . . . . . . . . 62
8.4. Required Content . . . . . . . . . . . . . . . . . . . . 63
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 63
9.1. Normative References . . . . . . . . . . . . . . . . . . 63
9.2. Informative References . . . . . . . . . . . . . . . . . 65
Appendix A. Detecting HTTP Message Signatures . . . . . . . . . 65
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 66
B.1. Example Keys . . . . . . . . . . . . . . . . . . . . . . 66
B.1.1. Example Key RSA test . . . . . . . . . . . . . . . . 66
B.1.2. Example RSA PSS Key . . . . . . . . . . . . . . . . . 67
B.1.3. Example ECC P-256 Test Key . . . . . . . . . . . . . 68
B.1.4. Example Ed25519 Test Key . . . . . . . . . . . . . . 69
B.1.5. Example Shared Secret . . . . . . . . . . . . . . . . 69
B.2. Test Cases . . . . . . . . . . . . . . . . . . . . . . . 69
B.2.1. Minimal Signature Using rsa-pss-sha512 . . . . . . . 70
B.2.2. Selective Covered Components using rsa-pss-sha512 . . 71
B.2.3. Full Coverage using rsa-pss-sha512 . . . . . . . . . 72
B.2.4. Signing a Response using ecdsa-p256-sha256 . . . . . 73
B.2.5. Signing a Request using hmac-sha256 . . . . . . . . . 74
B.2.6. Signing a Request using ed25519 . . . . . . . . . . . 74
B.3. TLS-Terminating Proxies . . . . . . . . . . . . . . . . . 75
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 77
Document History . . . . . . . . . . . . . . . . . . . . . . . . 78
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 82
1. Introduction
Message integrity and authenticity are important security properties
that are critical to the secure operation of many HTTP applications.
Application developers typically rely on the transport layer to
provide these properties, by operating their application over [TLS].
However, TLS only guarantees these properties over a single TLS
connection, and the path between client and application may be
composed of multiple independent TLS connections (for example, if the
application is hosted behind a TLS-terminating gateway or if the
client is behind a TLS Inspection appliance). In such cases, TLS
cannot guarantee end-to-end message integrity or authenticity between
the client and application. Additionally, some operating
environments present obstacles that make it impractical to use TLS,
or to use features necessary to provide message authenticity.
Furthermore, some applications require the binding of an application-
level key to the HTTP message, separate from any TLS certificates in
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use. Consequently, while TLS can meet message integrity and
authenticity needs for many HTTP-based applications, it is not a
universal solution.
This document defines a mechanism for providing end-to-end integrity
and authenticity for components of an HTTP message. The mechanism
allows applications to create digital signatures or message
authentication codes (MACs) over only the components of the message
that are meaningful and appropriate for the application. Strict
canonicalization rules ensure that the verifier can verify the
signature even if the message has been transformed in any of the many
ways permitted by HTTP.
The signing mechanism described in this document consists of three
parts:
* A common nomenclature and canonicalization rule set for the
different protocol elements and other components of HTTP messages,
used to create the signature base.
* Algorithms for generating and verifying signatures over HTTP
message components using this signature base through application
of cryptographic primitives.
* A mechanism for attaching a signature and related metadata to an
HTTP message, and for parsing attached signatures and metadata
from HTTP messages.
This document also provides a mechanism for a potential verifier to
signal to a potential signer that a signature is desired in one or
more subsequent messages. This optional negotiation mechanism can be
used along with opportunistic or application-driven message
signatures by either party.
1.1. Requirements Discussion
HTTP permits and sometimes requires intermediaries to transform
messages in a variety of ways. This may result in a recipient
receiving a message that is not bitwise equivalent to the message
that was originally sent. In such a case, the recipient will be
unable to verify a signature over the raw bytes of the sender's HTTP
message, as verifying digital signatures or MACs requires both signer
and verifier to have the exact same signature base. Since the exact
raw bytes of the message cannot be relied upon as a reliable source
for a signature base, the signer and verifier must independently
create the signature base from their respective versions of the
message, via a mechanism that is resilient to safe changes that do
not alter the meaning of the message.
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For a variety of reasons, it is impractical to strictly define what
constitutes a safe change versus an unsafe one. Applications use
HTTP in a wide variety of ways, and may disagree on whether a
particular piece of information in a message (e.g., the body, or the
Date header field) is relevant. Thus a general purpose solution must
provide signers with some degree of control over which message
components are signed.
HTTP applications may be running in environments that do not provide
complete access to or control over HTTP messages (such as a web
browser's JavaScript environment), or may be using libraries that
abstract away the details of the protocol (such as the Java
HTTPClient library (https://openjdk.java.net/groups/net/httpclient/
intro.html)). These applications need to be able to generate and
verify signatures despite incomplete knowledge of the HTTP message.
1.2. HTTP Message Transformations
As mentioned earlier, HTTP explicitly permits and in some cases
requires implementations to transform messages in a variety of ways.
Implementations are required to tolerate many of these
transformations. What follows is a non-normative and non-exhaustive
list of transformations that may occur under HTTP, provided as
context:
* Re-ordering of header fields with different header field names
(Section 3.2.2 of [MESSAGING]).
* Combination of header fields with the same field name
(Section 3.2.2 of [MESSAGING]).
* Removal of header fields listed in the Connection header field
(Section 6.1 of [MESSAGING]).
* Addition of header fields that indicate control options
(Section 6.1 of [MESSAGING]).
* Addition or removal of a transfer coding (Section 5.7.2 of
[MESSAGING]).
* Addition of header fields such as Via (Section 5.7.1 of
[MESSAGING]) and Forwarded (Section 4 of [RFC7239]).
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1.3. Safe Transformations
Based on the definition of HTTP and the requirements described above,
we can identify certain types of transformations that should not
prevent signature verification, even when performed on message
components covered by the signature. The following list describes
those transformations:
* Combination of header fields with the same field name.
* Reordering of header fields with different names.
* Conversion between different versions of the HTTP protocol (e.g.,
HTTP/1.x to HTTP/2, or vice-versa).
* Changes in casing (e.g., "Origin" to "origin") of any case-
insensitive components such as header field names, request URI
scheme, or host.
* Addition or removal of leading or trailing whitespace to a header
field value.
* Addition or removal of obs-folds.
* Changes to the request-target and Host header field that when
applied together do not result in a change to the message's
effective request URI, as defined in Section 5.5 of [MESSAGING].
Additionally, all changes to components not covered by the signature
are considered safe.
1.4. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The terms "HTTP message", "HTTP request", "HTTP response", absolute-
form, absolute-path, "effective request URI", "gateway", "header
field", "intermediary", request-target, "sender", and "recipient" are
used as defined in [MESSAGING].
The term "method" is to be interpreted as defined in Section 4 of
[SEMANTICS].
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For brevity, the term "signature" on its own is used in this document
to refer to both digital signatures (which use asymmetric
cryptography) and keyed MACs (which use symmetric cryptography).
Similarly, the verb "sign" refers to the generation of either a
digital signature or keyed MAC over a given input string. The
qualified term "digital signature" refers specifically to the output
of an asymmetric cryptographic signing operation.
In addition to those listed above, this document uses the following
terms:
HTTP Message Signature:
A digital signature or keyed MAC that covers one or more portions
of an HTTP message. Note that a given HTTP Message can contain
multiple HTTP Message Signatures.
Signer:
The entity that is generating or has generated an HTTP Message
Signature. Note that multiple entities can act as signers and
apply separate HTTP Message Signatures to a given HTTP Message.
Verifier:
An entity that is verifying or has verified an HTTP Message
Signature against an HTTP Message. Note that an HTTP Message
Signature may be verified multiple times, potentially by different
entities.
HTTP Message Component:
A portion of an HTTP message that is capable of being covered by
an HTTP Message Signature.
HTTP Message Component Identifier:
A value that uniquely identifies a specific HTTP Message Component
in respect to a particular HTTP Message Signature and the HTTP
Message it applies to.
HTTP Message Component Value:
The value associated with a given component identifier within the
context of a particular HTTP Message. Component values are
derived from the HTTP Message and are usually subject to a
canonicalization process.
Covered Components:
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An ordered set of HTTP message component identifiers for fields
(Section 2.1) and derived components (Section 2.2) that indicates
the set of message components covered by the signature, never
including the @signature-params identifier itself. The order of
this set is preserved and communicated between the signer and
verifier to facilitate reconstruction of the signature base.
Signature Base:
The sequence of bytes processed by the cryptographic algorithm to
produce or verify the HTTP Message Signature. The signature base
is generated by the signer and verifier using the covered
components set and the HTTP Message.
HTTP Message Signature Algorithm:
A cryptographic algorithm that describes the signing and
verification process for the signature, defined in terms of the
HTTP_SIGN and HTTP_VERIFY primitives described in Section 3.3.
Key Material:
The key material required to create or verify the signature. The
key material is often identified with an explicit key identifier,
allowing the signer to indicate to the verifier which key was
used.
Creation Time:
A timestamp representing the point in time that the signature was
generated, as asserted by the signer.
Expiration Time:
A timestamp representing the point in time after which the
signature should no longer be accepted by the verifier, as
asserted by the signer.
The term "Unix time" is defined by [POSIX.1], Section 4.16
(http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
V1_chap04.html#tag_04_16).
This document contains non-normative examples of partial and complete
HTTP messages. Some examples use a single trailing backslash '' to
indicate line wrapping for long values, as per [RFC8792]. The \
character and leading spaces on wrapped lines are not part of the
value.
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1.5. Application of HTTP Message Signatures
HTTP Message Signatures are designed to be a general-purpose security
mechanism applicable in a wide variety of circumstances and
applications. In order to properly and safely apply HTTP Message
Signatures, an application or profile of this specification MUST
specify all of the following items:
* The set of component identifiers (Section 2) that are expected and
required. For example, an authorization protocol could mandate
that the Authorization header be covered to protect the
authorization credentials and mandate the signature parameters
contain a created parameter, while an API expecting HTTP message
bodies could require the Digest header to be present and covered.
* A means of retrieving the key material used to verify the
signature. An application will usually use the keyid parameter of
the signature parameters (Section 2.2.1) and define rules for
resolving a key from there, though the appropriate key could be
known from other means.
* A means of determining the signature algorithm used to verify the
signature is appropriate for the key material. For example, the
process could use the alg parameter of the signature parameters
(Section 2.2.1) to state the algorithm explicitly, derive the
algorithm from the key material, or use some pre-configured
algorithm agreed upon by the signer and verifier.
* A means of determining that a given key and algorithm presented in
the request are appropriate for the request being made. For
example, a server expecting only ECDSA signatures should know to
reject any RSA signatures, or a server expecting asymmetric
cryptography should know to reject any symmetric cryptography.
An application using signatures also has to ensure that the verifier
will have access to all required information to re-create the
signature base. For example, a server behind a reverse proxy would
need to know the original request URI to make use of identifiers like
@target-uri. Additionally, an application using signatures in
responses would need to ensure that clients receiving signed
responses have access to all the signed portions, including any
portions of the request that were signed by the server.
The details of this kind of profiling are the purview of the
application and outside the scope of this specification, however some
additional considerations are discussed in Section 7.
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2. HTTP Message Components
In order to allow signers and verifiers to establish which components
are covered by a signature, this document defines component
identifiers for components covered by an HTTP Message Signature, a
set of rules for deriving and canonicalizing the values associated
with these component identifiers from the HTTP Message, and the means
for combining these canonicalized values into a signature base. The
values for these items MUST be accessible to both the signer and the
verifier of the message, which means these are usually derived from
aspects of the HTTP message or signature itself.
Some HTTP message components can undergo transformations that change
the bitwise value without altering meaning of the component's value
(for example, the merging together of header fields with the same
name). Message component values must therefore be canonicalized
before it is signed, to ensure that a signature can be verified
despite such intermediary transformations. This document defines
rules for each component identifier that transform the identifier's
associated component value into such a canonical form.
Component identifiers are serialized using the production grammar
defined by [RFC8941], Section 4. The component identifier itself is
an sf-string value and MAY define parameters which are included using
the parameters rule.
component-identifier = sf-string parameters
Note that this means the serialization of the component identifier
itself is encased in double quotes, with parameters following as a
semicolon-separated list, such as "cache-control", "date", or
"@signature-params".
Component identifiers, including component identifiers with
parameters, MUST NOT be repeated within a single list of covered
components. Component identifiers with different parameter values
MAY be repeated within a single list of covered components.
The component value associated with a component identifier is defined
by the identifier itself. Component values MUST NOT contain newline
(\n) characters.
The following sections define component identifier types, their
parameters, their associated values, and the canonicalization rules
for their values. The method for combining component identifiers
into the signature base is defined in Section 2.3.
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2.1. HTTP Fields
The component identifier for an HTTP field is the lowercased form of
its field name. While HTTP field names are case-insensitive,
implementations MUST use lowercased field names (e.g., content-type,
date, etag) when using them as component identifiers.
Unless overridden by additional parameters and rules, the HTTP field
value MUST be canonicalized as a single combined value as defined in
Section 5.2 of [SEMANTICS].
If the combined value is not available for a given header, the
following algorithm will produce canonicalized results for an
implementation:
1. Create an ordered list of the field values of each instance of
the field in the message, in the order that they occur (or will
occur) in the message.
2. Strip leading and trailing whitespace from each item in the list.
Note that since HTTP field values are not allowed to contain
leading and trailing whitespace, this will be a no-op in a
compliant implementation.
3. Remove any obsolete line-folding within the line and replace it
with a single space (" "), as discussed in Section 5.2 of
[MESSAGING]. Note that this behavior is specific to [MESSAGING]
and does not apply to other versions of the HTTP specification.
4. Concatenate the list of values together with a single comma (",")
and a single space (" ") between each item.
The resulting string is the canonicalized component value.
Note that some HTTP fields have values with multiple valid
serializations that have equivalent semantics. Applications signing
and processing such fields MUST consider how to handle the values of
such fields to ensure that the signer and verifier can derive the
same value, as discussed in Section 7.21.
Following are non-normative examples of canonicalized values for
header fields, given the following example HTTP message fragment:
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Host: www.example.com
Date: Tue, 20 Apr 2021 02:07:56 GMT
X-OWS-Header: Leading and trailing whitespace.
X-Obs-Fold-Header: Obsolete
line folding.
Cache-Control: max-age=60
Cache-Control: must-revalidate
Example-Dict: a=1, b=2;x=1;y=2, c=(a b c)
The following example shows canonicalized values for these example
header fields, presented using the signature base format discussed in
Section 2.3:
"host": www.example.com
"date": Tue, 20 Apr 2021 02:07:56 GMT
"x-ows-header": Leading and trailing whitespace.
"x-obs-fold-header": Obsolete line folding.
"cache-control": max-age=60, must-revalidate
"example-dict": a=1, b=2;x=1;y=2, c=(a b c)
Since empty HTTP header fields are allowed, they are also able to be
signed when present in a message. The canonicalized value is the
empty string. This means that the following empty header:
NOTE: '\' line wrapping per RFC 8792
X-Empty-Header: \
Is serialized by the signature base generation algorithm
(Section 2.3) with an empty string value following the colon and
space added after the content identifier.
NOTE: '\' line wrapping per RFC 8792
"x-empty-header": \
Note: these are shown here using the line wrapping algorithm in
[RFC8792] due to limitations in the document format that strips
trailing spaces from diagrams.
Any HTTP field component identifiers MAY have the following
parameters in specific circumstances.
sf A boolean flag indicating that the field value is to be
canonicalized using strict encoding of the structured field value.
Section 2.1.1
key A string parameter used to select a single member value from a
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dictionary structured field. Section 2.1.2
2.1.1. Canonicalized Structured HTTP Fields
If value of the the HTTP field in question is a structured field
([RFC8941]), the component identifier MAY include the sf parameter to
indicate it is a known structured field. If this parameter is
included with a component identifier, the HTTP field value MUST be
serialized using the rules specified in Section 4 of [RFC8941]
applicable to the type of the HTTP field. Note that this process
will replace any optional internal whitespace with a single space
character, among other potential transformations of the value.
For example, the following dictionary field is a valid serialization:
Example-Dict: a=1, b=2;x=1;y=2, c=(a b c)
If included in the input string as-is, it would be:
"example-dict": a=1, b=2;x=1;y=2, c=(a b c)
However, if the sf parameter is added, the value is re-serialized as
follows:
"example-dict";sf: a=1, b=2;x=1;y=2, c=(a b c)
The resulting string is used as the component value in Section 2.1.
2.1.2. Dictionary Structured Field Members
An individual member in the value of a Dictionary Structured Field is
identified by using the parameter key to indicate the member key as
an sf-string value.
An individual member in the value of a Dictionary Structured Field is
canonicalized by applying the serialization algorithm described in
Section 4.1.2 of [RFC8941] on the member value and its parameters,
without the dictionary key.
Each parameterized key for a given field MUST NOT appear more than
once in the signature base. Parameterized keys MAY appear in any
order.
If a dictionary key is named as a covered component but it does not
occur in the dictionary, this MUST cause an error in the signature
base generation.
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Following are non-normative examples of canonicalized values for
Dictionary Structured Field Members given the following example
header field, whose value is known to be a Dictionary:
Example-Dict: a=1, b=2;x=1;y=2, c=(a b c)
The following example shows canonicalized values for different
component identifiers of this field, presented using the signature
base format discussed in Section 2.3:
"example-dict";key="a": 1
"example-dict";key="b": 2;x=1;y=2
"example-dict";key="c": (a b c)
Note that the value for key="c" has been re-serialized.
2.2. Derived Components
In addition to HTTP fields, there are a number of different
components that can be derived from the control data, processing
context, or other aspects of the HTTP message being signed. Such
derived components can be included in the signature base by defining
a component identifier and the derivation method for its component
value.
Derived component identifiers MUST start with the "at" @ character.
This differentiates derived component identifiers from HTTP field
names, which cannot contain the @ character as per Section 5.1 of
[SEMANTICS]. Processors of HTTP Message Signatures MUST treat
derived component identifiers separately from field names, as
discussed in Section 7.18.
This specification defines the following derived component
identifiers:
@signature-params The signature metadata parameters for this
signature. (Section 2.2.1)
@method The method used for a request. (Section 2.2.2)
@target-uri The full target URI for a request. (Section 2.2.3)
@authority The authority of the target URI for a request.
(Section 2.2.4)
@scheme The scheme of the target URI for a request. (Section 2.2.5)
@request-target The request target. (Section 2.2.6)
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@path The absolute path portion of the target URI for a request.
(Section 2.2.7)
@query The query portion of the target URI for a request.
(Section 2.2.8)
@query-params The parsed query parameters of the target URI for a
request. (Section 2.2.9)
@status The status code for a response. (Section 2.2.10).
@request-response A signature from a request message that resulted
in this response message. (Section 2.2.11)
Additional derived component identifiers MAY be defined and
registered in the HTTP Signatures Derived Component Identifier
Registry. (Section 6.3)
Derived components can be applied in one or more of three targets:
request: Values derived from and results applied to an HTTP request
message as described in {{Section 3.4 of SEMANTICS.
response: Values derived from and results applied to an HTTP
response message as described in Section 3.4 of [SEMANTICS].
related-response: Values derived from an HTTP request message and
results applied to the HTTP response message that is responding to
that specific request.
A component identifier definition MUST define all targets to which it
can be applied.
The component value MUST be derived from the HTTP message being
signed or the context in which the derivation occurs. The derived
component value MUST be of the following form:
derived-component-value = *VCHAR
2.2.1. Signature Parameters
HTTP Message Signatures have metadata properties that provide
information regarding the signature's generation and verification,
such as the set of covered components, a timestamp, identifiers for
verification key material, and other utilities.
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The signature parameters component identifier is @signature-params.
This message component's value is REQUIRED as part of the signature
base (Section 2.3) but the component identifier MUST NOT be
enumerated within the set of covered components itself.
The signature parameters component value is the serialization of the
signature parameters for this signature, including the covered
components set with all associated parameters. These parameters
include any of the following:
* created: Creation time as an sf-integer UNIX timestamp value.
Sub-second precision is not supported. Inclusion of this
parameter is RECOMMENDED.
* expires: Expiration time as an sf-integer UNIX timestamp value.
Sub-second precision is not supported.
* nonce: A random unique value generated for this signature as an
sf-string value.
* alg: The HTTP message signature algorithm from the HTTP Message
Signature Algorithm Registry, as an sf-string value.
* keyid: The identifier for the key material as an sf-string value.
Additional parameters can be defined in the HTTP Signature Parameters
Registry (Section 6.2.2).
The signature parameters component value is serialized as a
parameterized inner list using the rules in Section 4 of [RFC8941] as
follows:
1. Let the output be an empty string.
2. Determine an order for the component identifiers of the covered
components, not including the @signature-params component
identifier itself. Once this order is chosen, it cannot be
changed. This order MUST be the same order as used in creating
the signature base (Section 2.3).
3. Serialize the component identifiers of the covered components,
including all parameters, as an ordered inner-list according to
Section 4.1.1.1 of [RFC8941] and append this to the output.
4. Determine an order for any signature parameters. Once this order
is chosen, it cannot be changed.
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5. Append the parameters to the inner-list in the chosen order
according to Section 4.1.1.2 of [RFC8941], skipping parameters
that are not available or not used for this message signature.
6. The output contains the signature parameters component value.
Note that the inner-list serialization is used for the covered
component value instead of the sf-list serialization in order to
facilitate this value's inclusion in message fields such as the
Signature-Input field's dictionary, as discussed in Section 4.1.
This example shows a canonicalized value for the parameters of a
given signature:
NOTE: '\' line wrapping per RFC 8792
("@target-uri" "@authority" "date" "cache-control")\
;keyid="test-key-rsa-pss";alg="rsa-pss-sha512";\
created=1618884475;expires=1618884775
Note that an HTTP message could contain multiple signatures
(Section 4.3), but only the signature parameters used for a single
signature are included in an entry.
2.2.2. Method
The @method component identifier refers to the HTTP method of a
request message. The component value of is canonicalized by taking
the value of the method as a string. Note that the method name is
case-sensitive as per [SEMANTICS], Section 9.1, and conventionally
standardized method names are uppercase US-ASCII. If used, the
@method component identifier MUST occur only once in the covered
components.
For example, the following request message:
POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @method value:
"@method": POST
If used in a related-response, the @method component identifier
refers to the associated component value of the request that
triggered the response message being signed.
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2.2.3. Target URI
The @target-uri component identifier refers to the target URI of a
request message. The component value is the full absolute target URI
of the request, potentially assembled from all available parts
including the authority and request target as described in
[SEMANTICS], Section 7.1. If used, the @target-uri component
identifier MUST occur only once in the covered components.
For example, the following message sent over HTTPS:
POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @target-uri value:
"@target-uri": https://www.example.com/path?param=value
If used in a related-response, the @target-uri component identifier
refers to the associated component value of the request that
triggered the response message being signed.
2.2.4. Authority
The @authority component identifier refers to the authority component
of the target URI of the HTTP request message, as defined in
[SEMANTICS], Section 7.2. In HTTP 1.1, this is usually conveyed
using the Host header, while in HTTP 2 and HTTP 3 it is conveyed
using the :authority pseudo-header. The value is the fully-qualified
authority component of the request, comprised of the host and,
optionally, port of the request target, as a string. The component
value MUST be normalized according to the rules in [SEMANTICS],
Section 4.2.3. Namely, the host name is normalized to lowercase and
the default port is omitted. If used, the @authority component
identifier MUST occur only once in the covered components.
For example, the following request message:
POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @authority component value:
"@authority": www.example.com
If used in a related-response, the @authority component identifier
refers to the associated component value of the request that
triggered the response message being signed.
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The @authority derived component SHOULD be used instead signing the
Host header directly, see Section 7.20.
2.2.5. Scheme
The @scheme component identifier refers to the scheme of the target
URL of the HTTP request message. The component value is the scheme
as a string as defined in [SEMANTICS], Section 4.2. While the scheme
itself is case-insensitive, it MUST be normalized to lowercase for
inclusion in the signature base. If used, the @scheme component
identifier MUST occur only once in the covered components.
For example, the following request message requested over plain HTTP:
POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @scheme value:
"@scheme": http
If used in a related-response, the @scheme component identifier
refers to the associated component value of the request that
triggered the response message being signed.
2.2.6. Request Target
The @request-target component identifier refers to the full request
target of the HTTP request message, as defined in [SEMANTICS],
Section 7.1. The component value of the request target can take
different forms, depending on the type of request, as described
below. If used, the @request-target component identifier MUST occur
only once in the covered components.
For HTTP 1.1, the component value is equivalent to the request target
portion of the request line. However, this value is more difficult
to reliably construct in other versions of HTTP. Therefore, it is
NOT RECOMMENDED that this identifier be used when versions of HTTP
other than 1.1 might be in use.
The origin form value is combination of the absolute path and query
components of the request URL. For example, the following request
message:
POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @request-target component value:
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"@request-target": /path?param=value
The following request to an HTTP proxy with the absolute-form value,
containing the fully qualified target URI:
GET https://www.example.com/path?param=value HTTP/1.1
Would result in the following @request-target component value:
"@request-target": https://www.example.com/path?param=value
The following CONNECT request with an authority-form value,
containing the host and port of the target:
CONNECT www.example.com:80 HTTP/1.1
Host: www.example.com
Would result in the following @request-target component value:
"@request-target": www.example.com:80
The following OPTIONS request message with the asterisk-form value,
containing a single asterisk * character:
OPTIONS * HTTP/1.1
Host: www.example.com
Would result in the following @request-target component value:
"@request-target": *
If used in a related-response, the @request-target component
identifier refers to the associated component value of the request
that triggered the response message being signed.
2.2.7. Path
The @path component identifier refers to the target path of the HTTP
request message. The component value is the absolute path of the
request target defined by [RFC3986], with no query component and no
trailing ? character. The value is normalized according to the rules
in [SEMANTICS], Section 4.2.3. Namely, an empty path string is
normalized as a single slash / character, and path components are
represented by their values after decoding any percent-encoded
octets. If used, the @path component identifier MUST occur only once
in the covered components.
For example, the following request message:
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POST /path?param=value HTTP/1.1
Host: www.example.com
Would result in the following @path value:
"@path": /path
If used in a related-response, the @path identifier refers to the
associated component value of the request that triggered the response
message being signed.
2.2.8. Query
The @query component identifier refers to the query component of the
HTTP request message. The component value is the entire normalized
query string defined by [RFC3986], including the leading ? character.
The value is normalized according to the rules in [SEMANTICS],
Section 4.2.3. Namely, percent-encoded octets are decoded. If used,
the @query component identifier MUST occur only once in the covered
components.
For example, the following request message:
POST /path?param=value&foo=bar&baz=batman HTTP/1.1
Host: www.example.com
Would result in the following @query value:
"@query": ?param=value&foo=bar&baz=batman
The following request message:
POST /path?queryString HTTP/1.1
Host: www.example.com
Would result in the following @query value:
"@query": ?queryString
If the query string is absent from the request message, the value is
the leading ? character alone:
"@query": ?
If used in a related-response, the @query component identifier refers
to the associated component value of the request that triggered the
response message being signed.
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2.2.9. Query Parameters
If a request target URI uses HTML form parameters in the query string
as defined in HTMLURL, Section 5 [HTMLURL], the @query-params
component identifier allows addressing of individual query
parameters. The query parameters MUST be parsed according to
HTMLURL, Section 5.1 [HTMLURL], resulting in a list of (nameString,
valueString) tuples. The REQUIRED name parameter of each input
identifier contains the nameString of a single query parameter as an
sf-string value. Several different named query parameters MAY be
included in the covered components. Single named parameters MAY
occur in any order in the covered components.
The component value of a single named parameter is the the
valueString of the named query parameter defined by HTMLURL,
Section 5.1 [HTMLURL], which is the value after percent-encoded
octets are decoded. Note that this value does not include any
leading ? characters, equals sign =, or separating & characters.
Named query parameters with an empty valueString are included with an
empty string as the component value.
If a query parameter is named as a covered component but it does not
occur in the query parameters, this MUST cause an error in the
signature base generation.
For example for the following request:
POST /path?param=value&foo=bar&baz=batman&qux= HTTP/1.1
Host: www.example.com
Indicating the baz, qux and param named query parameters in would
result in the following @query-param value:
"@query-params";name="baz": batman
"@query-params";name="qux":
"@query-params";name="param": value
If a parameter name occurs multiple times in a request, all parameter
values of that name MUST be included in separate signature base lines
in the order in which the parameters occur in the target URI. Note
that in some implementations, the order of parsed query parameters is
not stable, and this situation could lead to unexpected results. If
multiple parameters are common within an application, it is
RECOMMENDED to sign the entire query string using the @query
component identifier defined in Section 2.2.8.
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If used in a related-response, the @query-params component identifier
refers to the associated component value of the request that
triggered the response message being signed.
2.2.10. Status Code
The @status component identifier refers to the three-digit numeric
HTTP status code of a response message as defined in [SEMANTICS],
Section 15. The component value is the serialized three-digit
integer of the HTTP response code, with no descriptive text. If
used, the @status component identifier MUST occur only once in the
covered components.
For example, the following response message:
HTTP/1.1 200 OK
Date: Fri, 26 Mar 2010 00:05:00 GMT
Would result in the following @status value:
"@status": 200
The @status component identifier MUST NOT be used in a request
message.
2.2.11. Request-Response Signature Binding
When a signed request message results in a signed response message,
the @request-response component identifier can be used to
cryptographically link the request and the response to each other by
including the identified request signature value in the response's
signature base without copying the value of the request's signature
to the response directly. This component identifier has a single
REQUIRED parameter:
key Identifies which signature from the response to sign.
The component value is the sf-binary representation of the signature
value of the referenced request identified by the key parameter.
For example, when serving this signed request:
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NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
Signature-Input: sig1=("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
{"hello": "world"}
This would result in the following unsigned response message:
HTTP/1.1 503 Service Unavailable
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Length: 62
{"busy": true, "message": "Your call is very important to us"}
To cryptographically link the response to the request, the server
signs the response with its own key and includes the signature of
sig1 from the request in the covered components of the response. The
signature base for this example is:
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NOTE: '\' line wrapping per RFC 8792
"@status": 503
"content-length": 62
"content-type": application/json
"@request-response";key="sig1": :LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJR\
GziCLuD8r5MW9S0RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVd\
wXyY/UkBIS1M8Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMT\
e0QE3IpWINTEzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuT\
Z9HdbD2Tr65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S\
1ag3LZElYyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
"@signature-params": ("@status" "content-length" "content-type" \
"@request-response";key="sig1");created=1618884479\
;keyid="test-key-ecc-p256"
The signed response message is:
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 503 Service Unavailable
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Length: 62
Signature-Input: reqres=("@status" "content-length" "content-type" \
"@request-response";key="sig1");created=1618884479\
;keyid="test-key-ecc-p256"
Signature: reqres=:JqzXLIjNd6VWVg/M7enbjWkOgsPmIK9vcoFQEkLD0SXNbFjR\
6d+olsof1dv7xC7ygF1q0YKjVrbV2QlCpDxrHg==:
{"busy": true, "message": "Your call is very important to us"}
Since the request's signature value itself is not repeated in the
response, the requester MUST keep the original signature value around
long enough to validate the signature of the response that uses this
component identifier.
Note that the ECDSA algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
The @request-response component identifier MUST NOT be used in a
request message.
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2.3. Creating the Signature Base
The signature base is a US-ASCII string containing the canonicalized
HTTP message components covered by the signature. The input to the
signature base creation algorithm is the list of covered component
identifiers and their associated values, along with any additional
signature parameters. The output is the ordered set of bytes that
form the signature base, which conforms to the following ABNF:
signature-base = *( signature-base-line LF ) signature-params-line
signature-base-line = component-identifier ":" SP
( derived-component-value / field-value )
signature-params-line = DQUOTE "@signature-params" DQUOTE ":" SP inner-list
To create the signature base, the signer or verifier concatenates
together entries for each identifier in the signature's covered
components (including their parameters) using the following
algorithm:
1. Let the output be an empty string.
2. For each message component item in the covered components set (in
order):
1. Append the component identifier for the covered component
serialized according to the component-identifier rule. Note
that this serialization places the component identifier in
double quotes and appends any parameters outside of the
quotes.
2. Append a single colon :
3. Append a single space " "
4. Determine the component value for the component identifier.
* If the component identifier starts with an "at" character
(@), derive the component's value from the message
according to the specific rules defined for the derived
component identifier, as in Section 2.2. If the derived
component identifier is unknown or the value cannot be
derived, produce an error.
* If the component identifier does not start with an "at"
character (@), canonicalize the HTTP field value as
described in Section 2.1. If the value cannot be
calculated, produce an error.
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5. Append the covered component's canonicalized component value.
6. Append a single newline \n
3. Append the signature parameters component (Section 2.2.1) as
follows:
1. Append the component identifier for the signature parameters
serialized according to the component-identifier rule, i.e.
"@signature-params"
2. Append a single colon :
3. Append a single space " "
4. Append the signature parameters' canonicalized component
value as defined in Section 2.2.1
4. Return the output string.
If covered components reference a component identifier that cannot be
resolved to a component value in the message, the implementation MUST
produce an error and not create an input string. Such situations are
included but not limited to:
* The signer or verifier does not understand the derived component
identifier.
* The component identifier identifies a field that is not present in
the message or whose value is malformed.
* The component identifier indicates that a structured field
serialization is used (via the sf parameter), but the field in
question is known to not be a structured field or the type of
structured field is not known to the implementation.
* The component identifier is a dictionary member identifier that
references a field that is not present in the message, is not a
Dictionary Structured Field, or whose value is malformed.
* The component identifier is a dictionary member identifier or a
named query parameter identifier that references a member that is
not present in the component value, or whose value is malformed.
E.g., the identifier is "example-dict";key="c" and the value of
the Example-Dict header field is a=1, b=2, which does not have the
c value.
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In the following non-normative example, the HTTP message being signed
is the following request:
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
{"hello": "world"}
The covered components consist of the @method, @path, and @authority
derived component identifiers followed by the Content-Digest,
Content-Length, and Content-Type HTTP header fields, in order. The
signature parameters consist of a creation timestamp of 1618884473
and a key identifier of test-key-rsa-pss. Note that no explicit alg
parameter is given here since the verifier is assumed by the
application to correctly use the RSA PSS algorithm based on the
identified key. The signature base for this message with these
parameters is:
NOTE: '\' line wrapping per RFC 8792
"@method": POST
"@authority": example.com
"@path": /foo
"content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
"content-length": 18
"content-type": application/json
"@signature-params": ("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884473;keyid="test-key-rsa-pss"
Figure 1: Non-normative example Signature Base
Note that the example signature base here, or anywhere else within
this specification, does not include the final newline that ends the
displayed example.
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3. HTTP Message Signatures
An HTTP Message Signature is a signature over a string generated from
a subset of the components of an HTTP message in addition to metadata
about the signature itself. When successfully verified against an
HTTP message, an HTTP Message Signature provides cryptographic proof
that the message is semantically equivalent to the message for which
the signature was generated, with respect to the subset of message
components that was signed.
3.1. Creating a Signature
Creation of an HTTP message signature is a process that takes as its
input the message and the requirements for the application. The
output is a signature value and set of signature parameters that can
be applied to the message.
In order to create a signature, a signer MUST follow the following
algorithm:
1. The signer chooses an HTTP signature algorithm and key material
for signing. The signer MUST choose key material that is
appropriate for the signature's algorithm, and that conforms to
any requirements defined by the algorithm, such as key size or
format. The mechanism by which the signer chooses the algorithm
and key material is out of scope for this document.
2. The signer sets the signature's creation time to the current
time.
3. If applicable, the signer sets the signature's expiration time
property to the time at which the signature is to expire. The
expiration is a hint to the verifier, expressing the time at
which the signer is no longer willing to vouch for the safety of
the signature.
4. The signer creates an ordered set of component identifiers
representing the message components to be covered by the
signature, and attaches signature metadata parameters to this
set. The serialized value of this is later used as the value of
the Signature-Input field as described in Section 4.1.
* Once an order of covered components is chosen, the order MUST
NOT change for the life of the signature.
* Each covered component identifier MUST be either an HTTP field
in the message Section 2.1 or a derived component identifier
listed in Section 2.2 or its associated registry.
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* Signers of a request SHOULD include some or all of the message
control data in the covered components, such as the @method,
@authority, @target-uri, or some combination thereof.
* Signers SHOULD include the created signature metadata
parameter to indicate when the signature was created.
* The @signature-params derived component identifier is not
explicitly listed in the list of covered component
identifiers, because it is required to always be present as
the last line in the signature base. This ensures that a
signature always covers its own metadata.
* Further guidance on what to include in this set and in what
order is out of scope for this document.
5. The signer creates the signature base using these parameters and
the signature base creation algorithm. (Section 2.3)
6. The signer uses the HTTP_SIGN primitive function to sign the
signature base with the chosen signing algorithm using the key
material chosen by the signer. The HTTP_SIGN primitive and
several concrete applications of signing algorithms are defined
in in Section 3.3.
7. The byte array output of the signature function is the HTTP
message signature output value to be included in the Signature
field as defined in Section 4.2.
For example, given the HTTP message and signature parameters in the
example in Section 2.3, the example signature base is signed with the
test-key-rsa-pss key in Appendix B.1.2 and the RSA PSS algorithm
described in Section 3.3.1, giving the following message signature
output value, encoded in Base64:
NOTE: '\' line wrapping per RFC 8792
HIbjHC5rS0BYaa9v4QfD4193TORw7u9edguPh0AW3dMq9WImrlFrCGUDih47vAxi4L2\
YRZ3XMJc1uOKk/J0ZmZ+wcta4nKIgBkKq0rM9hs3CQyxXGxHLMCy8uqK488o+9jrptQ\
+xFPHK7a9sRL1IXNaagCNN3ZxJsYapFj+JXbmaI5rtAdSfSvzPuBCh+ARHBmWuNo1Uz\
VVdHXrl8ePL4cccqlazIJdC4QEjrF+Sn4IxBQzTZsL9y9TP5FsZYzHvDqbInkTNigBc\
E9cKOYNFCn4D/WM7F6TNuZO9EgtzepLWcjTymlHzK7aXq6Am6sfOrpIC49yXjj3ae6H\
RalVc/g==
Figure 2: Non-normative example signature value
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Note that the RSA PSS algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
3.2. Verifying a Signature
Verification of an HTTP message signature is a process that takes as
its input the message (including Signature and Signature-Input
fields) and the requirements for the application. The output of the
verification is either a positive verification or an error.
In order to verify a signature, a verifier MUST follow the following
algorithm:
1. Parse the Signature and Signature-Input fields as described in
Section 4.1 and Section 4.2, and extract the signatures to be
verified.
1. If there is more than one signature value present, determine
which signature should be processed for this message based on
the policy and configuration of the verifier. If an
applicable signature is not found, produce an error.
2. If the chosen Signature value does not have a corresponding
Signature-Input value, produce an error.
2. Parse the values of the chosen Signature-Input field as a
parameterized structured field inner list item (inner-list) to
get the signature parameters for the signature to be verified.
3. Parse the value of the corresponding Signature field to get the
byte array value of the signature to be verified.
4. Examine the signature parameters to confirm that the signature
meets the requirements described in this document, as well as any
additional requirements defined by the application such as which
message components are required to be covered by the signature.
(Section 3.2.1)
5. Determine the verification key material for this signature. If
the key material is known through external means such as static
configuration or external protocol negotiation, the verifier will
use that. If the key is identified in the signature parameters,
the verifier will dereference this to appropriate key material to
use with the signature. The verifier has to determine the
trustworthiness of the key material for the context in which the
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signature is presented. If a key is identified that the verifier
does not know, does not trust for this request, or does not match
something preconfigured, the verification MUST fail.
6. Determine the algorithm to apply for verification:
1. If the algorithm is known through external means such as
static configuration or external protocol negotiation, the
verifier will use this algorithm.
2. If the algorithm is explicitly stated in the signature
parameters using a value from the HTTP Message Signatures
registry, the verifier will use the referenced algorithm.
3. If the algorithm can be determined from the keying material,
such as through an algorithm field on the key value itself,
the verifier will use this algorithm.
4. If the algorithm is specified in more that one location, such
as through static configuration and the algorithm signature
parameter, or the algorithm signature parameter and from the
key material itself, the resolved algorithms MUST be the
same. If the algorithms are not the same, the verifier MUST
vail the verification.
7. Use the received HTTP message and the signature's metadata to
recreate the signature base, using the algorithm defined in
Section 2.3. The value of the @signature-params input is the
value of the Signature-Input field for this signature serialized
according to the rules described in Section 2.2.1, not including
the signature's label from the Signature-Input field.
8. If the key material is appropriate for the algorithm, apply the
appropriate HTTP_VERIFY cryptographic verification algorithm to
the signature, recalculated signature base, key material,
signature value. The HTTP_VERIFY primitive and several concrete
algorithms are defined in Section 3.3.
9. The results of the verification algorithm function are the final
results of the cryptographic verification function.
If any of the above steps fail or produce an error, the signature
validation fails.
For example, verifying the signature with the key sig1 of the
following message with the test-key-rsa-pss key in Appendix B.1.2 and
the RSA PSS algorithm described in Section 3.3.1:
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NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
Signature-Input: sig1=("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884473;keyid="test-key-rsa-pss"
Signature: sig1=:HIbjHC5rS0BYaa9v4QfD4193TORw7u9edguPh0AW3dMq9WImrl\
FrCGUDih47vAxi4L2YRZ3XMJc1uOKk/J0ZmZ+wcta4nKIgBkKq0rM9hs3CQyxXGxH\
LMCy8uqK488o+9jrptQ+xFPHK7a9sRL1IXNaagCNN3ZxJsYapFj+JXbmaI5rtAdSf\
SvzPuBCh+ARHBmWuNo1UzVVdHXrl8ePL4cccqlazIJdC4QEjrF+Sn4IxBQzTZsL9y\
9TP5FsZYzHvDqbInkTNigBcE9cKOYNFCn4D/WM7F6TNuZO9EgtzepLWcjTymlHzK7\
aXq6Am6sfOrpIC49yXjj3ae6HRalVc/g==:
{"hello": "world"}
With the additional requirements that at least the method, path,
authority, and cache-control be signed, and that the signature
creation timestamp is recent enough at the time of verification, the
verification passes.
3.2.1. Enforcing Application Requirements
The verification requirements specified in this document are intended
as a baseline set of restrictions that are generally applicable to
all use cases. Applications using HTTP Message Signatures MAY impose
requirements above and beyond those specified by this document, as
appropriate for their use case.
Some non-normative examples of additional requirements an application
might define are:
* Requiring a specific set of header fields to be signed (e.g.,
Authorization, Digest).
* Enforcing a maximum signature age from the time of the created
time stamp.
* Rejection of signatures past the expiration time in the expires
time stamp. Note that the expiration time is a hint from the
signer and that a verifier can always reject a signature ahead of
its expiration time.
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* Prohibition of certain signature metadata parameters, such as
runtime algorithm signaling with the alg parameter when the
algorithm is determined from the key information.
* Ensuring successful dereferencing of the keyid parameter to valid
and appropriate key material.
* Prohibiting the use of certain algorithms, or mandating the use of
a specific algorithm.
* Requiring keys to be of a certain size (e.g., 2048 bits vs. 1024
bits).
* Enforcing uniqueness of a nonce value.
Application-specific requirements are expected and encouraged. When
an application defines additional requirements, it MUST enforce them
during the signature verification process, and signature verification
MUST fail if the signature does not conform to the application's
requirements.
Applications MUST enforce the requirements defined in this document.
Regardless of use case, applications MUST NOT accept signatures that
do not conform to these requirements.
3.3. Signature Algorithm Methods
HTTP Message signatures MAY use any cryptographic digital signature
or MAC method that is appropriate for the key material, environment,
and needs of the signer and verifier.
Each signature algorithm method takes as its input the signature base
defined in Section 2.3 as a byte array (M), the signing key material
(Ks), and outputs the signature output as a byte array (S):
HTTP_SIGN (M, Ks) -> S
Each verification algorithm method takes as its input the
recalculated signature base defined in Section 2.3 as a byte array
(M), the verification key material (Kv), and the presented signature
to be verified as a byte array (S) and outputs the verification
result (V) as a boolean:
HTTP_VERIFY (M, Kv, S) -> V
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This section contains several common algorithm methods. The method
to use can be communicated through the explicit algorithm signature
parameter alg defined in Section 2.2.1, by reference to the key
material, or through mutual agreement between the signer and
verifier.
3.3.1. RSASSA-PSS using SHA-512
To sign using this algorithm, the signer applies the RSASSA-PSS-SIGN
(K, M) function [RFC8017] with the signer's private signing key (K)
and the signature base (M) (Section 2.3). The mask generation
function is MGF1 as specified in [RFC8017] with a hash function of
SHA-512 [RFC6234]. The salt length (sLen) is 64 bytes. The hash
function (Hash) SHA-512 [RFC6234] is applied to the signature base to
create the digest content to which the digital signature is applied.
The resulting signed content byte array (S) is the HTTP message
signature output used in Section 3.1.
To verify using this algorithm, the verifier applies the RSASSA-PSS-
VERIFY ((n, e), M, S) function [RFC8017] using the public key portion
of the verification key material ((n, e)) and the signature base (M)
re-created as described in Section 3.2. The mask generation function
is MGF1 as specified in [RFC8017] with a hash function of SHA-512
[RFC6234]. The salt length (sLen) is 64 bytes. The hash function
(Hash) SHA-512 [RFC6234] is applied to the signature base to create
the digest content to which the verification function is applied.
The verifier extracts the HTTP message signature to be verified (S)
as described in Section 3.2. The results of the verification
function indicate if the signature presented is valid.
Note that the output of RSA PSS algorithms are non-deterministic, and
therefore it is not correct to re-calculate a new signature on the
signature base and compare the results to an existing signature.
Instead, the verification algorithm defined here needs to be used.
See Section 7.19.
Use of this algorithm can be indicated at runtime using the rsa-pss-
sha512 value for the alg signature parameter.
3.3.2. RSASSA-PKCS1-v1_5 using SHA-256
To sign using this algorithm, the signer applies the RSASSA-
PKCS1-V1_5-SIGN (K, M) function [RFC8017] with the signer's private
signing key (K) and the signature base (M) (Section 2.3). The hash
SHA-256 [RFC6234] is applied to the signature base to create the
digest content to which the digital signature is applied. The
resulting signed content byte array (S) is the HTTP message signature
output used in Section 3.1.
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To verify using this algorithm, the verifier applies the RSASSA-
PKCS1-V1_5-VERIFY ((n, e), M, S) function [RFC8017] using the public
key portion of the verification key material ((n, e)) and the
signature base (M) re-created as described in Section 3.2. The hash
function SHA-256 [RFC6234] is applied to the signature base to create
the digest content to which the verification function is applied.
The verifier extracts the HTTP message signature to be verified (S)
as described in Section 3.2. The results of the verification
function are compared to the http message signature to determine if
the signature presented is valid.
Use of this algorithm can be indicated at runtime using the rsa-
v1_5-sha256 value for the alg signature parameter.
3.3.3. HMAC using SHA-256
To sign and verify using this algorithm, the signer applies the HMAC
function [RFC2104] with the shared signing key (K) and the signature
base (text) (Section 2.3). The hash function SHA-256 [RFC6234] is
applied to the signature base to create the digest content to which
the HMAC is applied, giving the signature result.
For signing, the resulting value is the HTTP message signature output
used in Section 3.1.
For verification, the verifier extracts the HTTP message signature to
be verified (S) as described in Section 3.2. The output of the HMAC
function is compared to the value of the HTTP message signature, and
the results of the comparison determine the validity of the signature
presented.
Use of this algorithm can be indicated at runtime using the hmac-
sha256 value for the alg signature parameter.
3.3.4. ECDSA using curve P-256 DSS and SHA-256
To sign using this algorithm, the signer applies the ECDSA algorithm
[FIPS186-4] using curve P-256 with the signer's private signing key
and the signature base (Section 2.3). The hash SHA-256 [RFC6234] is
applied to the signature base to create the digest content to which
the digital signature is applied, (M). The signature algorithm
returns two integer values, r and s. These are both encoded in big-
endian unsigned integers, zero-padded to 32-octets each. These
encoded values are concatenated into a single 64-octet array
consisting of the encoded value of r followed by the encoded value of
s. The resulting concatenation of (r, s) is byte array of the HTTP
message signature output used in Section 3.1.
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To verify using this algorithm, the verifier applies the ECDSA
algorithm [FIPS186-4] using the public key portion of the
verification key material and the signature base re-created as
described in Section 3.2. The hash function SHA-256 [RFC6234] is
applied to the signature base to create the digest content to which
the signature verification function is applied, (M). The verifier
extracts the HTTP message signature to be verified (S) as described
in Section 3.2. This value is a 64-octet array consisting of the
encoded values of r and s concatenated in order. These are both
encoded in big-endian unsigned integers, zero-padded to 32-octets
each. The resulting signature value (r, s) is used as input to the
signature verification function. The results of the verification
function indicate if the signature presented is valid.
Note that the output of ECDSA algorithms are non-deterministic, and
therefore it is not correct to re-calculate a new signature on the
signature base and compare the results to an existing signature.
Instead, the verification algorithm defined here needs to be used.
See Section 7.19.
Use of this algorithm can be indicated at runtime using the ecdsa-
p256-sha256 value for the alg signature parameter.
3.3.5. EdDSA using curve edwards25519
To sign using this algorithm, the signer applies the Ed25519
algorithm Section 5.1.6 of [RFC8032] with the signer's private
signing key and the signature base (Section 2.3). The signature base
is taken as the input message (M) with no pre-hash function. The
signature is a 64-octet concatenation of R and S as specified in
Section 5.1.6 of [RFC8032], and this is taken as a byte array for the
HTTP message signature output used in Section 3.1.
To verify using this algorithm, the signer applies the Ed25519
algorithm Section 5.1.7 of [RFC8032] using the public key portion of
the verification key material (A) and the signature base re-created
as described in Section 3.2. The signature base is taken as the
input message (M) with no pre-hash function. The signature to be
verified is processed as the 64-octet concatenation of R and S as
specified in Section 5.1.7 of [RFC8032]. The results of the
verification function indicate if the signature presented is valid.
Use of this algorithm can be indicated at runtime using the ed25519
value for the alg signature parameter.
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3.3.6. JSON Web Signature (JWS) algorithms
If the signing algorithm is a JOSE signing algorithm from the JSON
Web Signature and Encryption Algorithms Registry established by
[RFC7518], the JWS algorithm definition determines the signature and
hashing algorithms to apply for both signing and verification.
For both signing and verification, the HTTP messages signature base
(Section 2.3) is used as the entire "JWS Signing Input". The JOSE
Header defined in [RFC7517] is not used, and the signature base is
not first encoded in Base64 before applying the algorithm. The
output of the JWS signature is taken as a byte array prior to the
Base64url encoding used in JOSE.
The JWS algorithm MUST NOT be none and MUST NOT be any algorithm with
a JOSE Implementation Requirement of Prohibited.
JWA algorithm values from the JSON Web Signature and Encryption
Algorithms Registry are not included as signature parameters. In
fact, the explicit alg signature parameter is not used at all when
using JOSE signing algorithms, as the JWS algorithm can be signaled
using JSON Web Keys or other mechanisms common to JOSE
implementations.
4. Including a Message Signature in a Message
Message signatures can be included within an HTTP message via the
Signature-Input and Signature HTTP fields, both defined within this
specification. When attached to a message, an HTTP message signature
is identified by a label. This label MUST be unique within a given
HTTP message and MUST be used in both the Signature-Input and
Signature. The label is chosen by the signer, except where a
specific label is dictated by protocol negotiations.
An HTTP message signature MUST use both fields containing the same
labels: the Signature HTTP field contains the signature value, while
the Signature-Input HTTP field identifies the covered components and
parameters that describe how the signature was generated. Each field
contains labeled values and MAY contain multiple labeled values,
where the labels determine the correlation between the Signature and
Signature-Input fields.
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4.1. The 'Signature-Input' HTTP Field
The Signature-Input HTTP field is a Dictionary Structured Field
[RFC8941] containing the metadata for one or more message signatures
generated from components within the HTTP message. Each member
describes a single message signature. The member's name is an
identifier that uniquely identifies the message signature within the
context of the HTTP message. The member's value is the serialization
of the covered components including all signature metadata
parameters, using the serialization process defined in Section 2.2.1.
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig1=("@method" "@target-uri" "@authority" \
"content-digest" "cache-control");\
created=1618884475;keyid="test-key-rsa-pss"
To facilitate signature validation, the Signature-Input field value
MUST contain the same serialized value used in generating the
signature base's @signature-params value.
The signer MAY include the Signature-Input field as a trailer to
facilitate signing a message after its content has been processed by
the signer. However, since intermediaries are allowed to drop
trailers as per [SEMANTICS], it is RECOMMENDED that the Signature-
Input HTTP field be included only as a header to avoid signatures
being inadvertently stripped from a message.
Multiple Signature-Input fields MAY be included in a single HTTP
message. The signature labels MUST be unique across all field
values.
4.2. The 'Signature' HTTP Field
The Signature HTTP field is a Dictionary Structured field [RFC8941]
containing one or more message signatures generated from components
within the HTTP message. Each member's name is a signature
identifier that is present as a member name in the Signature-Input
Structured field within the HTTP message. Each member's value is a
Byte Sequence containing the signature value for the message
signature identified by the member name. Any member in the Signature
HTTP field that does not have a corresponding member in the HTTP
message's Signature-Input HTTP field MUST be ignored.
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NOTE: '\' line wrapping per RFC 8792
Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCiHz\
C87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW84jS8\
gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53r58Rmp\
Z+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCVRj05NrxA\
BNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:
The signer MAY include the Signature field as a trailer to facilitate
signing a message after its content has been processed by the signer.
However, since intermediaries are allowed to drop trailers as per
[SEMANTICS], it is RECOMMENDED that the Signature-Input HTTP field be
included only as a header to avoid signatures being inadvertently
stripped from a message.
Multiple Signature fields MAY be included in a single HTTP message.
The signature labels MUST be unique across all field values.
4.3. Multiple Signatures
Multiple distinct signatures MAY be included in a single message.
Each distinct signature MUST have a unique label. Since Signature-
Input and Signature are both defined as Dictionary Structured fields,
they can be used to include multiple signatures within the same HTTP
message by using distinct signature labels. These multiple
signatures could be added all by the same signer or could come from
several different signers. For example, a signer may include
multiple signatures signing the same message components with
different keys or algorithms to support verifiers with different
capabilities, or a reverse proxy may include information about the
client in fields when forwarding the request to a service host,
including a signature over the client's original signature values.
The following is a non-normative example starts with a signed request
from the client. The proxy takes this request validates the client's
signature.
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NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
Signature-Input: sig1=("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
{"hello": "world"}
The proxy then alters the message before forwarding it on to the
origin server, changing the target host and adding the Forwarded
header defined in [RFC7239].
NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: origin.host.internal.example
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
Forwarded: for=192.0.2.123
Signature-Input: sig1=("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
{"hello": "world"}
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The proxy includes the client's signature value under the label sig1,
which the proxy signs in addition to the Forwarded header. Note that
since the client's signature already covers the client's Signature-
Input value for sig1, this value is transitively covered by the
proxy's signature and need not be added explicitly. The proxy
identifies its own key and algorithm and, in this example, includes
an expiration for the signature to indicate to downstream systems
that the proxy will not vouch for this signed message past this short
time window. This results in a signature base of:
NOTE: '\' line wrapping per RFC 8792
"signature";key="sig1": :LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8\
r5MW9S0RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkB\
IS1M8Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpW\
INTEzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2T\
r65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZEl\
YyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
"forwarded": for=192.0.2.123
"@signature-params": ("signature";key="sig1" "forwarded")\
;created=1618884480;expires=1618884540;keyid="test-key-rsa"\
;alg="rsa-v1_5-sha256"
And a signature output value of:
NOTE: '\' line wrapping per RFC 8792
G1WLTL4/9PGSKEQbSAMypZNk+I2dpLJ6qvl2JISahlP31OO/QEUd8/HdO2O7vYLi5k3\
JIiAK3UPK4U+kvJZyIUidsiXlzRI+Y2se3SGo0D8dLfhG95bKr6ukYXl60QHpsGRTfS\
iwdtvYKXGpKNrMlISJYd+oGrGRyI9gbCy0aFhc6I/okIMLeK4g9PgzpC3YTwhUQ98KI\
BNLWHgREfBgJxjPbxFlsgJ9ykPviLj8GKJ81HwsK3XM9P7WaS7fMGOt8h1kSqgkZQB9\
YqiIo+WhHvJa7iPy8QrYFKzx9BBEY6AwfStZAsXXz3LobZseyxsYcLJLs8rY0wVA9NP\
sxKrHGA==
These values are added to the HTTP request message by the proxy. The
original signature is included under the identifier sig1, and the
reverse proxy's signature is included under the label proxy_sig. The
proxy uses the key test-key-rsa to create its signature using the
rsa-v1_5-sha256 signature algorithm, while the client's original
signature was made using the key id of test-key-rsa-pss and an RSA
PSS signature algorithm.
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NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: origin.host.internal.example
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
Forwarded: for=192.0.2.123
Signature-Input: sig1=("@method" "@authority" "@path" \
"content-digest" "content-length" "content-type")\
;created=1618884475;keyid="test-key-rsa-pss", \
proxy_sig=("signature";key="sig1" "forwarded")\
;created=1618884480;expires=1618884540;keyid="test-key-rsa"\
;alg="rsa-v1_5-sha256"
Signature: sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8\
Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINT\
EzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr\
65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZE\
lYyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:, \
proxy_sig=:G1WLTL4/9PGSKEQbSAMypZNk+I2dpLJ6qvl2JISahlP31OO/QEUd8/\
HdO2O7vYLi5k3JIiAK3UPK4U+kvJZyIUidsiXlzRI+Y2se3SGo0D8dLfhG95bKr\
6ukYXl60QHpsGRTfSiwdtvYKXGpKNrMlISJYd+oGrGRyI9gbCy0aFhc6I/okIML\
eK4g9PgzpC3YTwhUQ98KIBNLWHgREfBgJxjPbxFlsgJ9ykPviLj8GKJ81HwsK3X\
M9P7WaS7fMGOt8h1kSqgkZQB9YqiIo+WhHvJa7iPy8QrYFKzx9BBEY6AwfStZAs\
XXz3LobZseyxsYcLJLs8rY0wVA9NPsxKrHGA==:
{"hello": "world"}
The proxy's signature and the client's original signature can be
verified independently for the same message, based on the needs of
the application. Since the proxy's signature covers the client
signature, the backend service fronted by the proxy can trust that
the proxy has validated the incoming signature.
5. Requesting Signatures
While a signer is free to attach a signature to a request or response
without prompting, it is often desirable for a potential verifier to
signal that it expects a signature from a potential signer using the
Accept-Signature field.
The message to which the requested signature is applied is known as
the "target message". When the Accept-Signature field is sent in an
HTTP Request message, the field indicates that the client desires the
server to sign the response using the identified parameters and the
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target message is the response to this request. All responses from
resources that support such signature negotiation SHOULD either be
uncacheable or contain a Vary header field that lists Accept-
Signature, in order to prevent a cache from returning a response with
a signature intended for a different request.
When the Accept-Signature field is used in an HTTP Response message,
the field indicates that the server desires the client to sign its
next request to the server with the identified parameters, and the
target message is the client's next request. The client can choose
to also continue signing future requests to the same server in the
same way.
The target message of an Accept-Signature field MUST include all
labeled signatures indicated in the Accept-Header signature, each
covering the same identified components of the Accept-Signature
field.
The sender of an Accept-Signature field MUST include identifiers that
are appropriate for the type of the target message. For example, if
the target message is a response, the identifiers can not include the
@status identifier.
5.1. The Accept-Signature Field
The Accept-Signature HTTP header field is a Dictionary Structured
field [RFC8941] containing the metadata for one or more requested
message signatures to be generated from message components of the
target HTTP message. Each member describes a single message
signature. The member's name is an identifier that uniquely
identifies the requested message signature within the context of the
target HTTP message. The member's value is the serialization of the
desired covered components of the target message, including any
allowed signature metadata parameters, using the serialization
process defined in Section 2.2.1.
NOTE: '\' line wrapping per RFC 8792
Accept-Signature: sig1=("@method" "@target-uri" "@authority" \
"content-digest" "cache-control");\
created=1618884475;keyid="test-key-rsa-pss"
The requested signature MAY include parameters, such as a desired
algorithm or key identifier. These parameters MUST NOT include
parameters that the signer is expected to generate, including the
created and nonce parameters.
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5.2. Processing an Accept-Signature
The receiver of an Accept-Signature field fulfills that header as
follows:
1. Parse the field value as a Dictionary
2. For each member of the dictionary:
1. The name of the member is the label of the output signature
as specified in Section 4.1
2. Parse the value of the member to obtain the set of covered
component identifiers
3. Process the requested parameters, such as the signing
algorithm and key material. If any requested parameters
cannot be fulfilled, or if the requested parameters conflict
with those deemed appropriate to the target message, the
process fails and returns an error.
4. Select any additional parameters necessary for completing the
signature
5. Create the Signature-Input and Signature header values and
associate them with the label
3. Optionally create any additional Signature-Input and Signature
values, with unique labels not found in the Accept-Signature
field
4. Combine all labeled Signature-Input and Signature values and
attach both headers to the target message
Note that by this process, a signature applied to a target message
MUST have the same label, MUST have the same set of covered
component, and MAY have additional parameters. Also note that the
target message MAY include additional signatures not specified by the
Accept-Signature field.
6. IANA Considerations
IANA is requested to create three registries and to populate those
registries with initial values as described in this section.
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6.1. HTTP Signature Algorithms Registry
This document defines HTTP Signature Algorithms, for which IANA is
asked to create and maintain a new registry titled "HTTP Signature
Algorithms". Initial values for this registry are given in
Section 6.1.2. Future assignments and modifications to existing
assignment are to be made through the Expert Review registration
policy [RFC8126] and shall follow the template presented in
Section 6.1.1.
Algorithms referenced by algorithm identifiers have to be fully
defined with all parameters fixed. Algorithm identifiers in this
registry are to be interpreted as whole string values and not as a
combination of parts. That is to say, it is expected that
implementors understand rsa-pss-sha512 as referring to one specific
algorithm with its hash, mask, and salt values set as defined here.
Implementors do not parse out the rsa, pss, and sha512 portions of
the identifier to determine parameters of the signing algorithm from
the string.
Algorithms added to this registry MUST NOT be aliases for other
entries in the registry.
6.1.1. Registration Template
Algorithm Name:
An identifier for the HTTP Signature Algorithm. The name MUST be
an ASCII string consisting only of lower-case characters ("a" -
"z"), digits ("0" - "9"), and hyphens ("-"), and SHOULD NOT exceed
20 characters in length. The identifier MUST be unique within the
context of the registry.
Status:
A brief text description of the status of the algorithm. The
description MUST begin with one of "Active" or "Deprecated", and
MAY provide further context or explanation as to the reason for
the status.
Description:
A brief description of the algorithm used to sign the signature
base.
Specification document(s):
Reference to the document(s) that specify the token endpoint
authorization method, preferably including a URI that can be used
to retrieve a copy of the document(s). An indication of the
relevant sections may also be included but is not required.
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6.1.2. Initial Contents
+===================+========+===================+===============+
| Algorithm Name | Status | Description | Specification |
| | | | document(s) |
+===================+========+===================+===============+
| rsa-pss-sha512 | Active | RSASSA-PSS using | [[This |
| | | SHA-512 | document]], |
| | | | Section 3.3.1 |
+-------------------+--------+-------------------+---------------+
| rsa-v1_5-sha256 | Active | RSASSA-PKCS1-v1_5 | [[This |
| | | using SHA-256 | document]], |
| | | | Section 3.3.2 |
+-------------------+--------+-------------------+---------------+
| hmac-sha256 | Active | HMAC using | [[This |
| | | SHA-256 | document]], |
| | | | Section 3.3.3 |
+-------------------+--------+-------------------+---------------+
| ecdsa-p256-sha256 | Active | ECDSA using curve | [[This |
| | | P-256 DSS and | document]], |
| | | SHA-256 | Section 3.3.4 |
+-------------------+--------+-------------------+---------------+
| ed25519 | Active | Edwards Curve DSA | [[This |
| | | using curve | document]], |
| | | edwards25519 | Section 3.3.5 |
+-------------------+--------+-------------------+---------------+
Table 1
6.2. HTTP Signature Metadata Parameters Registry
This document defines the signature parameters structure, the values
of which may have parameters containing metadata about a message
signature. IANA is asked to create and maintain a new registry
titled "HTTP Signature Metadata Parameters" to record and maintain
the set of parameters defined for use with member values in the
signature parameters structure. Initial values for this registry are
given in Section 6.2.2. Future assignments and modifications to
existing assignments are to be made through the Expert Review
registration policy [RFC8126] and shall follow the template presented
in Section 6.2.1.
6.2.1. Registration Template
Name:
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An identifier for the HTTP signature metadata parameter. The name
MUST be an ASCII string consisting only of lower-case characters
("a" - "z"), digits ("0" - "9"), and hyphens ("-"), and SHOULD NOT
exceed 20 characters in length. The identifier MUST be unique
within the context of the registry.
Description:
A brief description of the metadata parameter and what it
represents.
Specification document(s):
Reference to the document(s) that specify the token endpoint
authorization method, preferably including a URI that can be used
to retrieve a copy of the document(s). An indication of the
relevant sections may also be included but is not required.
6.2.2. Initial Contents
The table below contains the initial contents of the HTTP Signature
Metadata Parameters Registry. Each row in the table represents a
distinct entry in the registry.
+=========+===============================+==================+
| Name | Description | Specification |
| | | document(s) |
+=========+===============================+==================+
| alg | Explicitly declared signature | Section 2.2.1 of |
| | algorithm | this document |
+---------+-------------------------------+------------------+
| created | Timestamp of signature | Section 2.2.1 of |
| | creation | this document |
+---------+-------------------------------+------------------+
| expires | Timestamp of proposed | Section 2.2.1 of |
| | signature expiration | this document |
+---------+-------------------------------+------------------+
| keyid | Key identifier for the | Section 2.2.1 of |
| | signing and verification keys | this document |
| | used to create this signature | |
+---------+-------------------------------+------------------+
| nonce | A single-use nonce value | Section 2.2.1 of |
| | | this document |
+---------+-------------------------------+------------------+
Table 2: Initial contents of the HTTP Signature Metadata
Parameters Registry.
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6.3. HTTP Signature Derived Component Identifiers Registry
This document defines a method for canonicalizing HTTP message
components, including components that can be derived from the context
of the HTTP message outside of the HTTP fields. These components are
identified by a unique string, known as the component identifier.
Component identifiers for derived components always start with the
"@" (at) symbol to distinguish them from HTTP header fields. IANA is
asked to create and maintain a new registry typed "HTTP Signature
Derived Component Identifiers" to record and maintain the set of non-
field component identifiers and the methods to produce their
associated component values. Initial values for this registry are
given in Section 6.3.2. Future assignments and modifications to
existing assignments are to be made through the Expert Review
registration policy [RFC8126] and shall follow the template presented
in Section 6.3.1.
6.3.1. Registration Template
Identifier:
An identifier for the HTTP derived component identifier. The name
MUST begin with the "@" character followed by an ASCII string
consisting only of lower-case characters ("a" - "z"), digits ("0"
- "9"), and hyphens ("-"), and SHOULD NOT exceed 20 characters in
length. The identifier MUST be unique within the context of the
registry.
Status:
A brief text description of the status of the algorithm. The
description MUST begin with one of "Active" or "Deprecated", and
MAY provide further context or explanation as to the reason for
the status.
Target:
The valid message targets for the derived parameter. MUST be one
of the values "Request", "Request, Response", "Request, Related-
Response", or "Related-Response". The semantics of these are
defined in Section 2.2.
Specification document(s):
Reference to the document(s) that specify the token endpoint
authorization method, preferably including a URI that can be used
to retrieve a copy of the document(s). An indication of the
relevant sections may also be included but is not required.
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6.3.2. Initial Contents
The table below contains the initial contents of the HTTP Signature
Derived Component Identifiers Registry.
+===================+========+==================+==================+
| Identifier | Status | Target | Specification |
| | | | document(s) |
+===================+========+==================+==================+
| @signature-params | Active | Request, | Section 2.2.1 of |
| | | Response | this document |
+-------------------+--------+------------------+------------------+
| @method | Active | Request, | Section 2.2.2 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @authority | Active | Request, | Section 2.2.4 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @scheme | Active | Request, | Section 2.2.5 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @target-uri | Active | Request, | Section 2.2.3 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @request-target | Active | Request, | Section 2.2.6 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @path | Active | Request, | Section 2.2.7 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @query | Active | Request, | Section 2.2.8 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @query-params | Active | Request, | Section 2.2.9 of |
| | | Related-Response | this document |
+-------------------+--------+------------------+------------------+
| @status | Active | Response | Section 2.2.10 |
| | | | of this document |
+-------------------+--------+------------------+------------------+
| @request-response | Active | Related-Response | Section 2.2.11 |
| | | | of this document |
+-------------------+--------+------------------+------------------+
Table 3: Initial contents of the HTTP Signature Derived
Component Identifiers Registry.
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7. Security Considerations
In order for an HTTP message to be considered covered by a signature,
all of the following conditions have to be true:
* a signature is expected or allowed on the message by the verifier
* the signature exists on the message
* the signature is verified against the identified key material and
algorithm
* the key material and algorithm are appropriate for the context of
the message
* the signature is within expected time boundaries
* the signature covers the expected content, including any critical
components
7.1. Signature Verification Skipping
HTTP Message Signatures only provide security if the signature is
verified by the verifier. Since the message to which the signature
is attached remains a valid HTTP message without the signature
fields, it is possible for a verifier to ignore the output of the
verification function and still process the message. Common reasons
for this could be relaxed requirements in a development environment
or a temporary suspension of enforcing verification during debugging
an overall system. Such temporary suspensions are difficult to
detect under positive-example testing since a good signature will
always trigger a valid response whether or not it has been checked.
To detect this, verifiers should be tested using both valid and
invalid signatures, ensuring that the invalid signature fails as
expected.
7.2. Use of TLS
The use of HTTP Message Signatures does not negate the need for TLS
or its equivalent to protect information in transit. Message
signatures provide message integrity over the covered message
components but do not provide any confidentiality for the
communication between parties.
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TLS provides such confidentiality between the TLS endpoints. As part
of this, TLS also protects the signature data itself from being
captured by an attacker, which is an important step in preventing
signature replay (Section 7.3).
When TLS is used, it needs to be deployed according to the
recommendations in [BCP195].
7.3. Signature Replay
Since HTTP Message Signatures allows sub-portions of the HTTP message
to be signed, it is possible for two different HTTP messages to
validate against the same signature. The most extreme form of this
would be a signature over no message components. If such a signature
were intercepted, it could be replayed at will by an attacker,
attached to any HTTP message. Even with sufficient component
coverage, a given signature could be applied to two similar HTTP
messages, allowing a message to be replayed by an attacker with the
signature intact.
To counteract these kinds of attacks, it's first important for the
signer to cover sufficient portions of the message to differentiate
it from other messages. In addition, the signature can use the nonce
signature parameter to provide a per-message unique value to allow
the verifier to detect replay of the signature itself if a nonce
value is repeated. Furthermore, the signer can provide a timestamp
for when the signature was created and a time at which the signer
considers the signature to be invalid, limiting the utility of a
captured signature value.
If a verifier wants to trigger a new signature from a signer, it can
send the Accept-Signature header field with a new nonce parameter.
An attacker that is simply replaying a signature would not be able to
generate a new signature with the chosen nonce value.
7.4. Insufficient Coverage
Any portions of the message not covered by the signature are
susceptible to modification by an attacker without affecting the
signature. An attacker can take advantage of this by introducing a
header field or other message component that will change the
processing of the message but will not be covered by the signature.
Such an altered message would still pass signature verification, but
when the verifier processes the message as a whole, the unsigned
content injected by the attacker would subvert the trust conveyed by
the valid signature and change the outcome of processing the message.
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To combat this, an application of this specification should require
as much of the message as possible to be signed, within the limits of
the application and deployment. The verifier should only trust
message components that have been signed. Verifiers could also strip
out any sensitive unsigned portions of the message before processing
of the message continues.
7.5. Cryptography and Signature Collision
The HTTP Message Signatures specification does not define any of its
own cryptographic primitives, and instead relies on other
specifications to define such elements. If the signature algorithm
or key used to process the signature base is vulnerable to any
attacks, the resulting signature will also be susceptible to these
same attacks.
A common attack against signature systems is to force a signature
collision, where the same signature value successfully verifies
against multiple different inputs. Since this specification relies
on reconstruction of the input string based on an HTTP message, and
the list of components signed is fixed in the signature, it is
difficult but not impossible for an attacker to effect such a
collision. An attacker would need to manipulate the HTTP message and
its covered message components in order to make the collision
effective.
To counter this, only vetted keys and signature algorithms should be
used to sign HTTP messages. The HTTP Message Signatures Algorithm
Registry is one source of potential trusted algorithms.
While it is possible for an attacker to substitute the signature
parameters value or the signature value separately, the signature
base generation algorithm (Section 2.3) always covers the signature
parameters as the final value in the input string using a
deterministic serialization method. This step strongly binds the
signature base with the signature value in a way that makes it much
more difficult for an attacker to perform a partial substitution on
the signature bases.
7.6. Key Theft
A foundational assumption of signature-based cryptographic systems is
that the signing key is not compromised by an attacker. If the keys
used to sign the message are exfiltrated or stolen, the attacker will
be able to generate their own signatures using those keys. As a
consequence, signers have to protect any signing key material from
exfiltration, capture, and use by an attacker.
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To combat this, signers can rotate keys over time to limit the amount
of time stolen keys are useful. Signers can also use key escrow and
storage systems to limit the attack surface against keys.
Furthermore, the use of asymmetric signing algorithms exposes key
material less than the use of symmetric signing algorithms
(Section 7.11).
7.7. Modification of Required Message Parameters
An attacker could effectively deny a service by modifying an
otherwise benign signature parameter or signed message component.
While rejecting a modified message is the desired behavior,
consistently failing signatures could lead to the verifier turning
off signature checking in order to make systems work again (see
Section 7.1).
If such failures are common within an application, the signer and
verifier should compare their generated signature bases with each
other to determine which part of the message is being modified.
However, the signer and verifier should not remove the requirement to
sign the modified component when it is suspected an attacker is
modifying the component.
7.8. Mismatch of Signature Parameters from Message
The verifier needs to make sure that the signed message components
match those in the message itself. This specification encourages
this by requiring the verifier to derive these values from the
message, but lazy cacheing or conveyance of the signature base to a
processing system could lead to downstream verifiers accepting a
message that does not match the presented signature.
7.9. Multiple Signature Confusion
Since multiple signatures can be applied to one message
(Section 4.3), it is possible for an attacker to attach their own
signature to a captured message without modifying existing
signatures. This new signature could be completely valid based on
the attacker's key, or it could be an invalid signature for any
number of reasons. Each of these situations need to be accounted
for.
A verifier processing a set of valid signatures needs to account for
all of the signers, identified by the signing keys. Only signatures
from expected signers should be accepted, regardless of the
cryptographic validity of the signature itself.
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A verifier processing a set of signatures on a message also needs to
determine what to do when one or more of the signatures are not
valid. If a message is accepted when at least one signature is
valid, then a verifier could drop all invalid signatures from the
request before processing the message further. Alternatively, if the
verifier rejects a message for a single invalid signature, an
attacker could use this to deny service to otherwise valid messages
by injecting invalid signatures alongside the valid ones.
7.10. Signature Labels
HTTP Message Signature values are identified in the Signature and
Signature-Input field values by unique labels. These labels are
chosen only when attaching the signature values to the message and
are not accounted for in the signing process. An intermediary adding
its own signature is allowed to re-label an existing signature when
processing the message.
Therefore, applications should not rely on specific labels being
present, and applications should not put semantic meaning on the
labels themselves. Instead, additional signature parmeters can be
used to convey whatever additional meaning is required to be attached
to and covered by the signature.
7.11. Symmetric Cryptography
The HTTP Message Signatures specification allows for both asymmetric
and symmetric cryptography to be applied to HTTP messages. By its
nature, symmetric cryptographic methods require the same key material
to be known by both the signer and verifier. This effectively means
that a verifier is capable of generating a valid signature, since
they have access to the same key material. An attacker that is able
to compromise a verifier would be able to then impersonate a signer.
Where possible, asymmetric methods or secure key agreement mechanisms
should be used in order to avoid this type of attack. When symmetric
methods are used, distribution of the key material needs to be
protected by the overall system. One technique for this is the use
of separate cryptographic modules that separate the verification
process (and therefore the key material) from other code, minimizing
the vulnerable attack surface. Another technique is the use of key
derivation functions that allow the signer and verifier to agree on
unique keys for each message without having to share the key values
directly.
Additionally, if symmetric algorithms are allowed within a system,
special care must be taken to avoid key downgrade attacks
(Section 7.15).
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7.12. Canonicalization Attacks
Any ambiguity in the generation of the signature base could provide
an attacker with leverage to substitute or break a signature on a
message. Some message component values, particularly HTTP field
values, are potentially susceptible to broken implementations that
could lead to unexpected and insecure behavior. Naive
implementations of this specification might implement HTTP field
processing by taking the single value of a field and using it as the
direct component value without processing it appropriately.
For example, if the handling of obs-fold field values does not remove
the internal line folding and whitespace, additional newlines could
be introduced into the signature base by the signer, providing a
potential place for an attacker to mount a signature collision
(Section 7.5) attack. Alternatively, if header fields that appear
multiple times are not joined into a single string value, as is
required by this specification, similar attacks can be mounted as a
signed component value would show up in the input string more than
once and could be substituted or otherwise attacked in this way.
To counter this, the entire field processing algorithm needs to be
implemented by all implementations of signers and verifiers.
7.13. Key Specification Mix-Up
The existence of a valid signature on an HTTP message is not
sufficient to prove that the message has been signed by the
appropriate party. It is up to the verifier to ensure that a given
key and algorithm are appropriate for the message in question. If
the verifier does not perform such a step, an attacker could
substitute their own signature using their own key on a message and
force a verifier to accept and process it. To combat this, the
verifier needs to ensure that not only does the signature validate
for a message, but that the key and algorithm used are appropriate.
7.14. HTTP Versions and Component Ambiguity
Some message components are expressed in different ways across HTTP
versions. For example, the authority of the request target is sent
using the Host header field in HTTP 1.1 but with the :authority
pseudo-header in HTTP 2. If a signer sends an HTTP 1.1 message and
signs the Host field, but the message is translated to HTTP 2 before
it reaches the verifier, the signature will not validate as the Host
header field could be dropped.
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It is for this reason that HTTP Message Signatures defines a set of
derived components that define a single way to get value in question,
such as the @authority derived component identifier (Section 2.2.4)
in lieu of the Host header field. Applications should therefore
prefer derived component identifiers for such options where possible.
7.15. Key and Algorithm Specification Downgrades
Applications of this specification need to protect against key
specification downgrade attacks. For example, the same RSA key can
be used for both RSA-PSS and RSA v1.5 signatures. If an application
expects a key to only be used with RSA-PSS, it needs to reject
signatures for that key using the weaker RSA 1.5 specification.
Another example of a downgrade attack occurs when an asymmetric
algorithm is expected, such as RSA-PSS, but an attacker substitutes a
signature using symmetric algorithm, such as HMAC. A naive verifier
implementation could use the value of the public RSA key as the input
to the HMAC verification function. Since the public key is known to
the attacker, this would allow the attacker to create a valid HMAC
signature against this known key. To prevent this, the verifier
needs to ensure that both the key material and the algorithm are
appropriate for the usage in question. Additionally, while this
specification does allow runtime specification of the algorithm using
the alg signature parameter, applications are encouraged to use other
mechanisms such as static configuration or higher protocol-level
algorithm specification instead.
7.16. Parsing Structured Field Values
Several parts of this specification rely on the parsing of structured
field values [RFC8941]. In particular, normalization of HTTP
structured field values (Section 2.1.1), referencing members of a
dictionary structured field (Section 2.1.2), and processing the
@signature-input value when verifying a signature (Section 3.2).
While structured field values are designed to be relatively simple to
parse, a naive or broken implementation of such a parser could lead
to subtle attack surfaces being exposed in the implementation.
For example, if a buggy parser of the @signature-input value does not
enforce proper closing of quotes around string values within the list
of component identifiers, an attacker could take advantage of this
and inject additional content into the signature base through
manipulating the Signature-Input field value on a message.
To counteract this, implementations should use fully compliant and
trusted parsers for all structured field processing, both on the
signer and verifier side.
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7.17. Choosing Message Components
Applications of HTTP Message Signatures need to decide which message
components will be covered by the signature. Depending on the
application, some components could be expected to be changed by
intermediaries prior to the signature's verification. If these
components are covered, such changes would, by design, break the
signature.
However, the HTTP Message Signature standard allows for flexibility
in determining which components are signed precisely so that a given
application can choose the appropriate portions of the message that
need to be signed, avoiding problematic components. For example, a
web application framework that relies on rewriting query parameters
might avoid use of the @query content identifier in favor of sub-
indexing the query value using @query-params content identifier
instead.
Some components are expected to be changed by intermediaries and
ought not to be signed under most circumstance. The Via and
Forwarded header fields, for example, are expected to be manipulated
by proxies and other middle-boxes, including replacing or entirely
dropping existing values. These fields should not be covered by the
signature except in very limited and tightly-coupled scenarios.
Additional considerations for choosing signature aspects are
discussed in Section 1.5.
7.18. Confusing HTTP Field Names for Derived Component Identifiers
The definition of HTTP field names does not allow for the use of the
@ character anywhere in the name. As such, since all derived
component identifiers start with the @ character, these namespaces
should be completely separate. However, some HTTP implementations
are not sufficiently strict about the characters accepted in HTTP
headers. In such implementations, a sender (or attacker) could
inject a header field starting with an @ character and have it passed
through to the application code. These invalid header fields could
be used to override a portion of the derived message content and
substitute an arbitrary value, providing a potential place for an
attacker to mount a signature collision (Section 7.5) attack.
To combat this, when selecting values for a message component, if the
component identifier starts with the @ character, it needs to be
processed as a derived component and never taken as a fields. Only
if the component identifier does not start with the @ character can
it be taken from the fields of the message. The algorithm discussed
in Section 2.3 provides a safe order of operations.
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7.19. Non-deterministic Signature Primitives
Some cryptographic primitives such as RSA PSS and ECDSA have non-
deterministic outputs, which include some amount of entropy within
the algorithm. For such algorithms, multiple signatures generated in
succession will not match. A lazy implementation of a verifier could
ignore this distinction and simply check for the same value being
created by re-signing the signature base. Such an implementation
would work for deterministic algorithms such as HMAC and EdDSA but
fail to verify valid signatures made using non-deterministic
algorithms. It is therefore important that a verifier always use the
correctly-defined verification function for the algorithm in question
and not do a simple comparison.
7.20. Choosing Signature Parameters and Derived Components over HTTP
Fields
Some HTTP fields have values and interpretations that are similar to
HTTP signature parameters or derived components. In most cases, it
is more desirable to sign the non-field alternative. In particular,
the following fields should usually not be included in the signature
unless the application specifically requires it:
"date" The "date" field value represents the timestamp of the HTTP
message. However, the creation time of the signature itself is
encoded in the created signature parameter. These two values can
be different, depending on how the signature and the HTTP message
are created and serialized. Applications processing signatures
for valid time windows should use the created signature parameter
for such calculations. An application could also put limits on
how much skew there is between the "date" field and the created
signature parameter, in order to limit the application of a
generated signature to different HTTP messages. See also
Section 7.3 and Section 7.4.
"host" The "host" header field is specific to HTTP 1.1, and its
functionality is subsumed by the "@authority" derived component,
defined in Section 2.2.4. In order to preserve the value across
different HTTP versions, applications should always use the
"@authority" derived component.
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7.21. Semantically Equivalent Field Values
The signature base generation algorithm (Section 2.3) uses the value
of an HTTP field as its component value. In the common case, this
amounts to taking the actual bytes of the field value as the
component value for both the signer and verifier. However, some
field values allow for transformation of the values in semantically
equivalent ways that alter the bytes used in the value itself. For
example, a field definition can declare some or all of its value to
be case-insensitive, or to have special handling of internal
whitespace characters. Other fields have expected transformations
from intermediaries, such as the removal of comments in the Via
header field. In such cases, a verifier could be tripped up by using
the equivalent transformed field value, which would differ from the
byte value used by the signer. The verifier would have have a
difficult time finding this class of errors since the value of the
field is still acceptable for the application, but the actual bytes
required by the signature base would not match.
When processing such fields, the signer and verifier have to agree
how to handle such transformations, if at all. One option is to not
sign problematic fields, but care must be taken to ensure that there
is still sufficient signature coverage (Section 7.4) for the
application. Another option is to define an application-specific
canonicalization value for the field before it is added to the HTTP
message, such as to always remove internal comments before signing,
or to always transform values to lowercase. Since these
transformations are applied prior to the field being used as input to
the signature base generation algorithm, the signature base will
still simply contain the byte value of the field as it appears within
the message. If the transformations were to be applied after the
value is extracted from the message but before it is added to the
signature base, different attack surfaces such as value substitution
attacks could be launched against the application. All application-
specific additional rules are outside the scope of this
specification, and by their very nature these transformations would
harm interoperability of the implementation outside of this specific
application. It is recommended that applications avoid the use of
such additional rules wherever possible.
8. Privacy Considerations
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8.1. Identification through Keys
If a signer uses the same key with multiple verifiers, or uses the
same key over time with a single verifier, the ongoing use of that
key can be used to track the signer throughout the set of verifiers
that messages are sent to. Since cryptographic keys are meant to be
functionally unique, the use of the same key over time is a strong
indicator that it is the same party signing multiple messages.
In many applications, this is a desirable trait, and it allows HTTP
Message Signatures to be used as part of authenticating the signer to
the verifier. However, unintentional tracking that a signer might
not be aware of. To counter this kind of tracking, a signer can use
a different key for each verifier that it is in communication with.
Sometimes, a signer could also rotate their key when sending messages
to a given verifier. These approaches do not negate the need for
other anti-tracking techniques to be applied as necessary.
8.2. Signatures do not provide confidentiality
HTTP Message Signatures do not provide confidentiality of any of the
information protected by the signature. The content of the HTTP
message, including the value of all fields and the value of the
signature itself, is presented in plaintext to any party with access
to the message.
To provide confidentiality at the transport level, TLS or its
equivalent can be used as discussed in Section 7.2.
8.3. Oracles
It is important to balance the need for providing useful feedback to
developers on error conditions without providing additional
information to an attacker. For example, a naive but helpful server
implementation might try to indicate the required key identifier
needed for requesting a resource. If someone knows who controls that
key, a correlation can be made between the resource's existence and
the party identified by the key. Access to such information could be
used by an attacker as a means to target the legitimate owner of the
resource for further attacks.
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8.4. Required Content
A core design tenet of this specification is that all message
components covered by the signature need to be available to the
verifier in order to recreate the signature base and verify the
signature. As a consequence, if an application of this specification
requires that a particular field be signed, the verifier will need
access to the value of that field.
For example, in some complex systems with intermediary processors
this could cause the surprising behavior of an intermediary not being
able to remove privacy-sensitive information from a message before
forwarding it on for processing, for fear of breaking the signature.
A possible mitigation for this specific situation would be for the
intermediary to verify the signature itself, then modifying the
message to remove the privacy-sensitive information. The
intermediary can add its own signature at this point to signal to the
next destination that the incoming signature was validated, as is
shown in the example in Section 4.3.
9. References
9.1. Normative References
[FIPS186-4]
"Digital Signature Standard (DSS)", 2013,
<https://csrc.nist.gov/publications/detail/fips/186/4/
final>.
[HTMLURL] "URL (Living Standard)", 2021,
<https://url.spec.whatwg.org/>.
[MESSAGING]
Fielding, R. T., Nottingham, M., and J. Reschke,
"HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf-
httpbis-messaging-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
messaging-19>.
[POSIX.1] "The Open Group Base Specifications Issue 7, 2018
edition", 2018,
<https://pubs.opengroup.org/onlinepubs/9699919799/>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/rfc/rfc2104>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/rfc/rfc6234>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/rfc/rfc7517>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/rfc/rfc7518>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/rfc/rfc8017>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/rfc/rfc8032>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/rfc/rfc8792>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
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[SEMANTICS]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
9.2. Informative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, May 2015.
Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
1.1", BCP 195, RFC 8996, March 2021.
<https://www.rfc-editor.org/info/bcp195>
[I-D.ietf-httpbis-client-cert-field]
Campbell, B. and M. Bishop, "Client-Cert HTTP Header
Field", Work in Progress, Internet-Draft, draft-ietf-
httpbis-client-cert-field-01, 25 January 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
client-cert-field-01>.
[RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
RFC 7239, DOI 10.17487/RFC7239, June 2014,
<https://www.rfc-editor.org/rfc/rfc7239>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
Appendix A. Detecting HTTP Message Signatures
There have been many attempts to create signed HTTP messages in the
past, including other non-standardized definitions of the Signature
field, which is used within this specification. It is recommended
that developers wishing to support both this specification and other
historical drafts do so carefully and deliberately, as
incompatibilities between this specification and various versions of
other drafts could lead to unexpected problems.
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It is recommended that implementers first detect and validate the
Signature-Input field defined in this specification to detect that
this standard is in use and not an alternative. If the Signature-
Input field is present, all Signature fields can be parsed and
interpreted in the context of this draft.
Appendix B. Examples
The following non-normative examples are provided as a means of
testing implementations of HTTP Message Signatures. The signed
messages given can be used to create the signature base with the
stated parameters, creating signatures using the stated algorithms
and keys.
The private keys given can be used to generate signatures, though
since several of the demonstrated algorithms are nondeterministic,
the results of a signature are expected to be different from the
exact bytes of the examples. The public keys given can be used to
validate all signed examples.
B.1. Example Keys
This section provides cryptographic keys that are referenced in
example signatures throughout this document. These keys MUST NOT be
used for any purpose other than testing.
The key identifiers for each key are used throughout the examples in
this specification. It is assumed for these examples that the signer
and verifier can unambiguously dereference all key identifiers used
here, and that the keys and algorithms used are appropriate for the
context in which the signature is presented.
The components for each private key in PEM format can be displayed by
executing the following OpenSSL command:
openssl pkey -text
This command was tested with all the example keys on OpenSSL version
1.1.1m. Note that some systems cannot produce or use these keys
directly, and may require additional processing.
B.1.1. Example Key RSA test
The following key is a 2048-bit RSA public and private key pair,
referred to in this document as test-key-rsa. This key is encoded in
PEM Format, with no encryption.
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-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsPBRrw
WEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsdJKFq
MGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75jfZg
kne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKIlE0P
uKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZSFlQ
PSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQAB
-----END RSA PUBLIC KEY-----
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
B.1.2. Example RSA PSS Key
The following key is a 2048-bit RSA public and private key pair,
referred to in this document as test-key-rsa-pss. This key is PCKS#8
encoded in PEM format, with no encryption.
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-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAr4tmm3r20Wd/PbqvP1s2
+QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvMs8ct+Lh1GH45x28Rw3Ry53mm+
oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95AndTrifbIFPNU8PPMO7OyrFAHq
gDsznjPFmTOtCEcN2Z1FpWgchwuYLPL+Wokqltd11nqqzi+bJ9cvSKADYdUAAN5W
Utzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSyZYoA485mqcO0GVAdVw9lq4
aOT9v6d+nb4bnNkQVklLQ3fVAvJm+xdDOp9LCNCN48V2pnDOkFV6+U9nV5oyc6XI
2wIDAQAB
-----END PUBLIC KEY-----
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
B.1.3. Example ECC P-256 Test Key
The following key is a public and private elliptical curve key pair
over the curve P-256, referred to in this document as `test-key-ecc-
p256. This key is encoded in PEM format, with no encryption.
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-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lf
w0EkjqF7xB4FivAxzic30tMM4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
-----END PUBLIC KEY-----
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIFKbhfNZfpDsW43+0+JjUr9K+bTeuxopu653+hBaXGA7oAoGCCqGSM49
AwEHoUQDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lfw0EkjqF7xB4FivAxzic30tMM
4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
-----END EC PRIVATE KEY-----
B.1.4. Example Ed25519 Test Key
The following key is an elliptical curve key over the Edwards curve
ed25519, referred to in this document as test-key-ed25519. This key
is PCKS#8 encoded in PEM format, with no encryption.
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAJrQLj5P/89iXES9+vFgrIy29clF9CC/oPPsw3c5D0bs=
-----END PUBLIC KEY-----
-----BEGIN PRIVATE KEY-----
MC4CAQAwBQYDK2VwBCIEIJ+DYvh6SEqVTm50DFtMDoQikTmiCqirVv9mWG9qfSnF
-----END PRIVATE KEY-----
B.1.5. Example Shared Secret
The following shared secret is 64 randomly-generated bytes encoded in
Base64, referred to in this document as test-shared-secret.
NOTE: '\' line wrapping per RFC 8792
uzvJfB4u3N0Jy4T7NZ75MDVcr8zSTInedJtkgcu46YW4XByzNJjxBdtjUkdJPBt\
bmHhIDi6pcl8jsasjlTMtDQ==
B.2. Test Cases
This section provides non-normative examples that may be used as test
cases to validate implementation correctness. These examples are
based on the following HTTP messages:
For requests, this test-request message is used:
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POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
Content-Length: 18
{"hello": "world"}
For responses, this test-response message is used:
HTTP/1.1 200 OK
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Digest: sha-512=:JlEy2bfUz7WrWIjc1qV6KVLpdr/7L5/L4h7Sxvh6sN\
HpDQWDCL+GauFQWcZBvVDhiyOnAQsxzZFYwi0wDH+1pw==:
Content-Length: 23
{"message": "good dog"}
B.2.1. Minimal Signature Using rsa-pss-sha512
This example presents a minimal signature using the rsa-pss-sha512
algorithm over test-request, covering none of the components of the
HTTP message, but providing a timestamped signature proof of
possession of the key with a signer-provided nonce.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"@signature-params": ();created=1618884473;keyid="test-key-rsa-pss"\
;nonce="b3k2pp5k7z-50gnwp.yemd"
This results in the following Signature-Input and Signature headers
being added to the message under the signature label sig-b21:
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b21=();created=1618884473\
;keyid="test-key-rsa-pss";nonce="b3k2pp5k7z-50gnwp.yemd"
Signature: sig-b21=:d2pmTvmbncD3xQm8E9ZV2828BjQWGgiwAaw5bAkgibUopem\
LJcWDy/lkbbHAve4cRAtx31Iq786U7it++wgGxbtRxf8Udx7zFZsckzXaJMkA7ChG\
52eSkFxykJeNqsrWH5S+oxNFlD4dzVuwe8DhTSja8xxbR/Z2cOGdCbzR72rgFWhzx\
2VjBqJzsPLMIQKhO4DGezXehhWwE56YCE+O6c0mKZsfxVrogUvA4HELjVKWmAvtl6\
UnCh8jYzuVG5WSb/QEVPnP5TmcAnLH1g+s++v6d4s8m0gCw1fV5/SITLq9mhho8K3\
+7EPYTU8IU1bLhdxO5Nyt8C8ssinQ98Xw9Q==:
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Note that since the covered components list is empty, this signature
could be applied by an attacker to an unrelated HTTP message. In
this example, the nonce parameter is included to prevent the same
signature from being replayed more than once, but if an attacker
intercepts the signature and prevents its delivery to the verifier,
the attacker could apply this signature to another message.
Therefore, use of an empty covered components set is discouraged.
See Section 7.4 for more discussion.
Note that the RSA PSS algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
B.2.2. Selective Covered Components using rsa-pss-sha512
This example covers additional components in test-request using the
rsa-pss-sha512 algorithm.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"@authority": example.com
"content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
"@signature-params": ("@authority" "content-digest")\
;created=1618884473;keyid="test-key-rsa-pss"
This results in the following Signature-Input and Signature headers
being added to the message under the label sig-b22:
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b22=("@authority" "content-digest")\
;created=1618884473;keyid="test-key-rsa-pss"
Signature: sig-b22=:Fee1uy9YGZq5UUwwYU6vz4dZNvfw3GYrFl1L6YlVIyUMuWs\
wWDNSvql4dVtSeidYjYZUm7SBCENIb5KYy2ByoC3bI+7gydd2i4OAT5lyDtmeapnA\
a8uP/b9xUpg+VSPElbBs6JWBIQsd+nMdHDe+ls/IwVMwXktC37SqsnbNyhNp6kcvc\
WpevjzFcD2VqdZleUz4jN7P+W5A3wHiMGfIjIWn36KXNB+RKyrlGnIS8yaBBrom5r\
cZWLrLbtg6VlrH1+/07RV+kgTh/l10h8qgpl9zQHu7mWbDKTq0tJ8K4ywcPoC4s2I\
4rU88jzDKDGdTTQFZoTVZxZmuTM1FvHfzIw==:
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Note that the RSA PSS algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
B.2.3. Full Coverage using rsa-pss-sha512
This example covers all applicable in test-request (including the
content type and length) plus many derived components, again using
the rsa-pss-sha512 algorithm. Note that the Host header field is not
covered because the @authority derived component is included instead.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"date": Tue, 20 Apr 2021 02:07:55 GMT
"@method": POST
"@path": /foo
"@query": ?param=Value&Pet=dog
"@authority": example.com
"content-type": application/json
"content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
"content-length": 18
"@signature-params": ("date" "@method" "@path" "@query" \
"@authority" "content-type" "content-digest" "content-length")\
;created=1618884473;keyid="test-key-rsa-pss"
This results in the following Signature-Input and Signature headers
being added to the message under the label sig-b23:
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b23=("date" "@method" "@path" "@query" \
"@authority" "content-type" "content-digest" "content-length")\
;created=1618884473;keyid="test-key-rsa-pss"
Signature: sig-b23=:bbN8oArOxYoyylQQUU6QYwrTuaxLwjAC9fbY2F6SVWvh0yB\
iMIRGOnMYwZ/5MR6fb0Kh1rIRASVxFkeGt683+qRpRRU5p2voTp768ZrCUb38K0fU\
xN0O0iC59DzYx8DFll5GmydPxSmme9v6ULbMFkl+V5B1TP/yPViV7KsLNmvKiLJH1\
pFkh/aYA2HXXZzNBXmIkoQoLd7YfW91kE9o/CCoC1xMy7JA1ipwvKvfrs65ldmlu9\
bpG6A9BmzhuzF8Eim5f8ui9eH8LZH896+QIF61ka39VBrohr9iyMUJpvRX2Zbhl5Z\
JzSRxpJyoEZAFL2FUo5fTIztsDZKEgM4cUA==:
Note in this example that the value of the Date header and the value
of the created signature parameter need not be the same. This is due
to the fact that the Date header is added when creating the HTTP
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Message and the created parameter is populated when creating the
signature over that message, and these two times could vary. If the
Date header is covered by the signature, it is up to the verifier to
determine whether its value has to match that of the created
parameter or not. See Section 7.20 for more discussion.
Note that the RSA PSS algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
B.2.4. Signing a Response using ecdsa-p256-sha256
This example covers portions of the test-response response message
using the ecdsa-p256-sha256 algorithm and the key test-key-ecc-p256.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"@status": 200
"content-type": application/json
"content-digest": sha-512=:JlEy2bfUz7WrWIjc1qV6KVLpdr/7L5/L4h7Sxvh6\
sNHpDQWDCL+GauFQWcZBvVDhiyOnAQsxzZFYwi0wDH+1pw==:
"content-length": 23
"@signature-params": ("@status" "content-type" "content-digest" \
"content-length");created=1618884473;keyid="test-key-ecc-p256"
This results in the following Signature-Input and Signature headers
being added to the message under the label sig-b24:
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b24=("@status" "content-type" \
"content-digest" "content-length");created=1618884473\
;keyid="test-key-ecc-p256"
Signature: sig-b24=:0Ry6HsvzS5VmA6HlfBYS/fYYeNs7fYuA7s0tAdxfUlPGv0C\
SVuwrrzBOjcCFHTxVRJ01wjvSzM2BetJauj8dsw==:
Note that the ECDSA algorithm in use here is non-deterministic,
meaning a different signature value will be created every time the
algorithm is run. The signature value provided here can be validated
against the given keys, but newly-generated signature values are not
expected to match the example. See Section 7.19.
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B.2.5. Signing a Request using hmac-sha256
This example covers portions of the test-request using the hmac-
sha256 algorithm and the secret test-shared-secret.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"date": Tue, 20 Apr 2021 02:07:55 GMT
"@authority": example.com
"content-type": application/json
"@signature-params": ("date" "@authority" "content-type")\
;created=1618884473;keyid="test-shared-secret"
This results in the following Signature-Input and Signature headers
being added to the message under the label sig-b25:
NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b25=("date" "@authority" "content-type")\
;created=1618884473;keyid="test-shared-secret"
Signature: sig-b25=:pxcQw6G3AjtMBQjwo8XzkZf/bws5LelbaMk5rGIGtE8=:
Before using symmetric signatures in practice, see the discussion of
the security tradeoffs in Section 7.11.
B.2.6. Signing a Request using ed25519
This example covers portions of the test-request using the ed25519
algorithm and the key test-key-ed25519.
The corresponding signature base is:
NOTE: '\' line wrapping per RFC 8792
"date": Tue, 20 Apr 2021 02:07:55 GMT
"@method": POST
"@path": /foo
"@authority": example.com
"content-type": application/json
"content-length": 18
"@signature-params": ("date" "@method" "@path" "@authority" \
"content-type" "content-length");created=1618884473\
;keyid="test-key-ed25519"
This results in the following Signature-Input and Signature headers
being added to the message under the label sig-b26:
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NOTE: '\' line wrapping per RFC 8792
Signature-Input: sig-b26=("date" "@method" "@path" "@authority" \
"content-type" "content-length");created=1618884473\
;keyid="test-key-ed25519"
Signature: sig-b26=:wqcAqbmYJ2ji2glfAMaRy4gruYYnx2nEFN2HN6jrnDnQCK1\
u02Gb04v9EDgwUPiu4A0w6vuQv5lIp5WPpBKRCw==:
B.3. TLS-Terminating Proxies
In this example, there is a TLS-terminating reverse proxy sitting in
front of the resource. The client does not sign the request but
instead uses mutual TLS to make its call. The terminating proxy
validates the TLS stream and injects a Client-Cert header according
to [I-D.ietf-httpbis-client-cert-field], and then applies a signature
to this field. By signing this header field, a reverse proxy can not
only attest to its own validation of the initial request's TLS
parameters but also authenticate itself to the backend system
independently of the client's actions.
The client makes the following request to the TLS terminating proxy
using mutual TLS:
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
{"hello": "world"}
The proxy processes the TLS connection and extracts the client's TLS
certificate to a Client-Cert header field and passes it along to the
internal service hosted at service.internal.example. This results in
the following unsigned request:
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NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: service.internal.example
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
{"hello": "world"}
Without a signature, the internal service would need to trust that
the incoming connection has the right information. By signing the
Client-Cert header and other portions of the internal request, the
internal service can be assured that the correct party, the trusted
proxy, has processed the request and presented it to the correct
service. The proxy's signature base consists of the following:
NOTE: '\' line wrapping per RFC 8792
"@path": /foo
"@query": ?param=Value&Pet=dog
"@method": POST
"@authority": service.internal.example
"client-cert": :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQ\
KDBJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBD\
QTAeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDM\
FkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXm\
ckC8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQY\
DVR0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8B\
Af8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQ\
GV4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0\
Q6bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
"@signature-params": ("@path" "@query" "@method" "@authority" \
"client-cert");created=1618884473;keyid="test-key-ecc-p256"
This results in the following signature:
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Internet-Draft HTTP Message Signatures March 2022
NOTE: '\' line wrapping per RFC 8792
xVMHVpawaAC/0SbHrKRs9i8I3eOs5RtTMGCWXm/9nvZzoHsIg6Mce9315T6xoklyy0y\
zhD9ah4JHRwMLOgmizw==
Which results in the following signed request sent from the proxy to
the internal service with the proxy's signature under the label ttrp:
NOTE: '\' line wrapping per RFC 8792
POST /foo?param=Value&Pet=dog HTTP/1.1
Host: service.internal.example
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
Signature-Input: ttrp=("@path" "@query" "@method" "@authority" \
"client-cert");created=1618884473;keyid="test-key-ecc-p256"
Signature: ttrp=:xVMHVpawaAC/0SbHrKRs9i8I3eOs5RtTMGCWXm/9nvZzoHsIg6\
Mce9315T6xoklyy0yzhD9ah4JHRwMLOgmizw==:
{"hello": "world"}
The internal service can validate the proxy's signature and therefore
be able to trust that the client's certificate has been appropriately
processed.
Acknowledgements
This specification was initially based on the draft-cavage-http-
signatures internet draft. The editors would like to thank the
authors of that draft, Mark Cavage and Manu Sporny, for their work on
that draft and their continuing contributions. The specification
also includes contributions from the draft-oauth-signed-http-request
internet draft and other similar efforts.
The editors would also like to thank the following individuals for
feedback, insight, and implementation of this draft and its
predecessors (in alphabetical order): Mark Adamcin, Mark Allen, Paul
Annesley, Karl Böhlmark, Stéphane Bortzmeyer, Sarven Capadisli, Liam
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Internet-Draft HTTP Message Signatures March 2022
Dennehy, Stephen Farrell, Phillip Hallam-Baker, Eric Holmes, Andrey
Kislyuk, Adam Knight, Dave Lehn, Dave Longley, Ilari Liusvaara, James
H. Manger, Kathleen Moriarty, Mark Nottingham, Yoav Nir, Adrian
Palmer, Lucas Pardue, Roberto Polli, Julian Reschke, Michael
Richardson, Wojciech Rygielski, Rich Salz, Adam Scarr, Cory J. Slep,
Dirk Stein, Henry Story, Lukasz Szewc, Chris Webber, and Jeffrey
Yasskin.
Document History
_RFC EDITOR: please remove this section before publication_
* draft-ietf-httpbis-message-signatures
- -09
o Explained key formats better.
o Removed "host" and "date" from most examples.
o Fixed query component generation.
o Renamed "signature input" and "signature input string" to
"signature base".
o Added consideration for semantically equivalent field
values.
- -08
o Editorial fixes.
o Changed "specialty component" to "derived component".
o Expanded signature input generation and ABNF rules.
o Added Ed25519 algorithm.
o Clarified encoding of ECDSA signature.
o Clarified use of non-deterministic algorithms.
- -07
o Added security and privacy considerations.
o Added pointers to algorithm values from definition sections.
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o Expanded IANA registry sections.
o Clarified that the signing and verification algorithms take
application requirements as inputs.
o Defined "signature targets" of request, response, and
related-response for specialty components.
- -06
o Updated language for message components, including
identifiers and values.
o Clarified that Signature-Input and Signature are fields
which can be used as headers or trailers.
o Add "Accept-Signature" field and semantics for signature
negotiation.
o Define new specialty content identifiers, re-defined
request-target identifier.
o Added request-response binding.
- -05
o Remove list prefixes.
o Clarify signature algorithm parameters.
o Update and fix examples.
o Add examples for ECC and HMAC.
- -04
o Moved signature component definitions up to intro.
o Created formal function definitions for algorithms to
fulfill.
o Updated all examples.
o Added nonce parameter field.
- -03
o Clarified signing and verification processes.
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Internet-Draft HTTP Message Signatures March 2022
o Updated algorithm and key selection method.
o Clearly defined core algorithm set.
o Defined JOSE signature mapping process.
o Removed legacy signature methods.
o Define signature parameters separately from "signature"
object model.
o Define serialization values for signature-input header based
on signature input.
- -02
o Removed editorial comments on document sources.
o Removed in-document issues list in favor of tracked issues.
o Replaced unstructured Signature header with Signature-Input
and Signature Dictionary Structured Header Fields.
o Defined content identifiers for individual Dictionary
members, e.g., "x-dictionary-field";key=member-name.
o Defined content identifiers for first N members of a List,
e.g., "x-list-field":prefix=4.
o Fixed up examples.
o Updated introduction now that it's adopted.
o Defined specialty content identifiers and a means to extend
them.
o Required signature parameters to be included in signature.
o Added guidance on backwards compatibility, detection, and
use of signature methods.
- -01
o Strengthened requirement for content identifiers for header
fields to be lower-case (changed from SHOULD to MUST).
o Added real example values for Creation Time and Expiration
Time.
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Internet-Draft HTTP Message Signatures March 2022
o Minor editorial corrections and readability improvements.
- -00
o Initialized from draft-richanna-http-message-signatures-00,
following adoption by the working group.
* draft-richanna-http-message-signatures
- -00
o Converted to xml2rfc v3 and reformatted to comply with RFC
style guides.
o Removed Signature auth-scheme definition and related
content.
o Removed conflicting normative requirements for use of
algorithm parameter. Now MUST NOT be relied upon.
o Removed Extensions appendix.
o Rewrote abstract and introduction to explain context and
need, and challenges inherent in signing HTTP messages.
o Rewrote and heavily expanded algorithm definition, retaining
normative requirements.
o Added definitions for key terms, referenced RFC 7230 for
HTTP terms.
o Added examples for canonicalization and signature generation
steps.
o Rewrote Signature header definition, retaining normative
requirements.
o Added default values for algorithm and expires parameters.
o Rewrote HTTP Signature Algorithms registry definition.
Added change control policy and registry template. Removed
suggested URI.
o Added IANA HTTP Signature Parameter registry.
o Added additional normative and informative references.
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o Added Topics for Working Group Discussion section, to be
removed prior to publication as an RFC.
Authors' Addresses
Annabelle Backman (editor)
Amazon
P.O. Box 81226
Seattle, WA 98108-1226
United States of America
Email: richanna@amazon.com
URI: https://www.amazon.com/
Justin Richer
Bespoke Engineering
Email: ietf@justin.richer.org
URI: https://bspk.io/
Manu Sporny
Digital Bazaar
203 Roanoke Street W.
Blacksburg, VA 24060
United States of America
Email: msporny@digitalbazaar.com
URI: https://manu.sporny.org/
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