HTTP                                                     A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                               J. Richer
Expires: 14 February 2022                            Bespoke Engineering
                                                               M. Sporny
                                                          Digital Bazaar
                                                          13 August 2021


                        HTTP Message Signatures
                draft-ietf-httpbis-message-signatures-06

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.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/
   (https://lists.w3.org/Archives/Public/ietf-http-wg/).

   Working Group information can be found at https://httpwg.org/
   (https://httpwg.org/); source code and issues list for this draft can
   be found at https://github.com/httpwg/http-extensions/labels/
   signatures (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
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   This Internet-Draft will expire on 14 February 2022.

Copyright Notice

   Copyright (c) 2021 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/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Discussion . . . . . . . . . . . . . . . . .   5
     1.2.  HTTP Message Transformations  . . . . . . . . . . . . . .   5
     1.3.  Safe Transformations  . . . . . . . . . . . . . . . . . .   6
     1.4.  Conventions and Terminology . . . . . . . . . . . . . . .   7
     1.5.  Application of HTTP Message Signatures  . . . . . . . . .   9
   2.  HTTP Message Components . . . . . . . . . . . . . . . . . . .  10
     2.1.  HTTP Fields . . . . . . . . . . . . . . . . . . . . . . .  11
       2.1.1.  Canonicalized Structured HTTP Fields  . . . . . . . .  11
       2.1.2.  Canonicalization Examples . . . . . . . . . . . . . .  11
     2.2.  Dictionary Structured Field Members . . . . . . . . . . .  12
       2.2.1.  Canonicalization Examples . . . . . . . . . . . . . .  12
     2.3.  Specialty Components  . . . . . . . . . . . . . . . . . .  13
       2.3.1.  Signature Parameters  . . . . . . . . . . . . . . . .  14
       2.3.2.  Method  . . . . . . . . . . . . . . . . . . . . . . .  15
       2.3.3.  Target URI  . . . . . . . . . . . . . . . . . . . . .  16
       2.3.4.  Authority . . . . . . . . . . . . . . . . . . . . . .  16
       2.3.5.  Scheme  . . . . . . . . . . . . . . . . . . . . . . .  17
       2.3.6.  Request Target  . . . . . . . . . . . . . . . . . . .  17
       2.3.7.  Path  . . . . . . . . . . . . . . . . . . . . . . . .  19
       2.3.8.  Query . . . . . . . . . . . . . . . . . . . . . . . .  19
       2.3.9.  Query Parameters  . . . . . . . . . . . . . . . . . .  20
       2.3.10. Status Code . . . . . . . . . . . . . . . . . . . . .  21
       2.3.11. Request-Response Signature Binding  . . . . . . . . .  21
     2.4.  Creating the Signature Input String . . . . . . . . . . .  23



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   3.  HTTP Message Signatures . . . . . . . . . . . . . . . . . . .  25
     3.1.  Creating a Signature  . . . . . . . . . . . . . . . . . .  25
     3.2.  Verifying a Signature . . . . . . . . . . . . . . . . . .  27
       3.2.1.  Enforcing Application Requirements  . . . . . . . . .  29
     3.3.  Signature Algorithm Methods . . . . . . . . . . . . . . .  29
       3.3.1.  RSASSA-PSS using SHA-512  . . . . . . . . . . . . . .  30
       3.3.2.  RSASSA-PKCS1-v1_5 using SHA-256 . . . . . . . . . . .  31
       3.3.3.  HMAC using SHA-256  . . . . . . . . . . . . . . . . .  31
       3.3.4.  ECDSA using curve P-256 DSS and SHA-256 . . . . . . .  31
       3.3.5.  JSON Web Signature (JWS) algorithms . . . . . . . . .  32
   4.  Including a Message Signature in a Message  . . . . . . . . .  32
     4.1.  The 'Signature-Input' HTTP Field  . . . . . . . . . . . .  33
     4.2.  The 'Signature' HTTP Field  . . . . . . . . . . . . . . .  33
     4.3.  Multiple Signatures . . . . . . . . . . . . . . . . . . .  34
   5.  Requesting Signatures . . . . . . . . . . . . . . . . . . . .  36
     5.1.  The Accept-Signature Field  . . . . . . . . . . . . . . .  37
     5.2.  Processing an Accept-Signature  . . . . . . . . . . . . .  37
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
     6.1.  HTTP Signature Algorithms Registry  . . . . . . . . . . .  38
       6.1.1.  Registration Template . . . . . . . . . . . . . . . .  39
       6.1.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  39
     6.2.  HTTP Signature Metadata Parameters Registry . . . . . . .  41
       6.2.1.  Registration Template . . . . . . . . . . . . . . . .  41
       6.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  41
     6.3.  HTTP Signature Specialty Component Identifiers
           Registry  . . . . . . . . . . . . . . . . . . . . . . . .  41
       6.3.1.  Registration Template . . . . . . . . . . . . . . . .  42
       6.3.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  42
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  43
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  44
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  44
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  45
   Appendix A.  Detecting HTTP Message Signatures  . . . . . . . . .  46
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  46
     B.1.  Example Keys  . . . . . . . . . . . . . . . . . . . . . .  46
       B.1.1.  Example Key RSA test  . . . . . . . . . . . . . . . .  46
       B.1.2.  Example RSA PSS Key . . . . . . . . . . . . . . . . .  47
       B.1.3.  Example ECC P-256 Test Key  . . . . . . . . . . . . .  48
       B.1.4.  Example Shared Secret . . . . . . . . . . . . . . . .  49
     B.2.  Test Cases  . . . . . . . . . . . . . . . . . . . . . . .  49
       B.2.1.  Minimal Signature Using rsa-pss-sha512  . . . . . . .  50
       B.2.2.  Selective Covered Components using rsa-pss-sha512 . .  50
       B.2.3.  Full Coverage using rsa-pss-sha512  . . . . . . . . .  51
       B.2.4.  Signing a Response using ecdsa-p256-sha256  . . . . .  52
       B.2.5.  Signing a Request using hmac-sha256 . . . . . . . . .  53
     B.3.  TLS-Terminating Proxies . . . . . . . . . . . . . . . . .  53
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  55
   Document History  . . . . . . . . . . . . . . . . . . . . . . . .  56



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  59

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
   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.

   *  Algorithms for generating and verifying signatures over HTTP
      message components using this nomenclature and rule set.

   *  A mechanism for attaching a signature and related metadata to an
      HTTP message.








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   This document also provides a mechanism for one party to signal to
   another party 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 input.  Since the exact
   raw bytes of the message cannot be relied upon as a reliable source
   of signature input, the signer and verifier must derive the signature
   input 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.

   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
      ([MESSAGING], Section 3.2.2).



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   *  Combination of header fields with the same field name
      ([MESSAGING], Section 3.2.2).

   *  Removal of header fields listed in the "Connection" header field
      ([MESSAGING], Section 6.1).

   *  Addition of header fields that indicate control options
      ([MESSAGING], Section 6.1).

   *  Addition or removal of a transfer coding ([MESSAGING],
      Section 5.7.2).

   *  Addition of header fields such as "Via" ([MESSAGING],
      Section 5.7.1) and "Forwarded" ([RFC7239], Section 4).

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.






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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].

   For brevity, the term "signature" on its own is used in this document
   to refer to both digital signatures and keyed MACs.  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:




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      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:
      An ordered set of HTTP message component identifiers for fields
      (Section 2.1) and specialty components (Section 2.3) that
      indicates the set of message components covered by the signature,
      not including the "@signature-params" specialty identifier itself.
      The order of this set is preserved and communicated between the
      signer and verifier to facilitate reconstruction of the signature
      input.

   Signature Input:
      The sequence of bytes processed by the HTTP Message Signature
      algorithm to produce the HTTP Message Signature.  The signature
      input 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.  When expressed
      explicitly, the value maps to a string defined in the HTTP
      Signature Algorithms Registry defined in this document.

   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 at which the signature
      expires, as asserted by the signer.  A signature's expiration time
      could be undefined, indicating that the signature does not expire
      from the perspective of the signer.





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   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.

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 2.3.1) 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 2.3.1) 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 input string.  For example, a server behind a reverse proxy



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   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.

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 input
   string.  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 [RFC8941].  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 value 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"".

   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 input is defined in Section 2.4.





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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 with the following steps:

   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.

   3.  Concatenate the list items together, with a comma "," and space "
       " between each item.

   The resulting string is the canonicalized component value.

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.
   If this parameter is included, the HTTP field value MUST be
   canonicalized using the rules specified in Section 4 of RFC8941
   [RFC8941].  For example, this process will replace any optional
   internal whitespace with a single space character.

   The resulting string is used as the component value in Section 2.1.

2.1.2.  Canonicalization Examples

   This section contains non-normative examples of canonicalized values
   for header fields, given the following example HTTP message:

   Host: www.example.com
   Date: Tue, 07 Jun 2014 20:51:35 GMT
   X-OWS-Header:   Leading and trailing whitespace.
   X-Obs-Fold-Header: Obsolete
       line folding.
   X-Empty-Header:
   Cache-Control: max-age=60
   Cache-Control:    must-revalidate
   X-Dictionary:  a=1,    b=2;x=1;y=2,   c=(a   b   c)





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   The following table shows example canonicalized values for header
   fields, given that message:

        +=====================+==================================+
        | Header Field        | Canonicalized Value              |
        +=====================+==================================+
        | "cache-control"     | max-age=60, must-revalidate      |
        +---------------------+----------------------------------+
        | "date"              | Tue, 07 Jun 2014 20:51:35 GMT    |
        +---------------------+----------------------------------+
        | "host"              | www.example.com                  |
        +---------------------+----------------------------------+
        | "x-empty-header"    |                                  |
        +---------------------+----------------------------------+
        | "x-obs-fold-header" | Obsolete line folding.           |
        +---------------------+----------------------------------+
        | "x-ows-header"      | Leading and trailing whitespace. |
        +---------------------+----------------------------------+
        | "x-dictionary"      | a=1, b=2;x=1;y=2, c=(a b c)      |
        +---------------------+----------------------------------+
        | "x-dictionary";sf   | a=1, b=2;x=1;y=2, c=(a b c)      |
        +---------------------+----------------------------------+

             Table 1: Non-normative examples of header field
                            canonicalization.

2.2.  Dictionary Structured Field Members

   An individual member in the value of a Dictionary Structured Field is
   identified by using the parameter "key" on the component identifier
   for the field.  The value of this parameter is a the key being
   identified, without any parameters present on that key in the
   original dictionary.

   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 [RFC8941] on a Dictionary containing only
   that item.

2.2.1.  Canonicalization Examples

   This section contains 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:

   X-Dictionary:  a=1, b=2;x=1;y=2, c=(a b c)





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   The following table shows example canonicalized values for different
   component identifiers, given that field:

                +======================+=================+
                | Component Identifier | Component Value |
                +======================+=================+
                | "x-dictionary";key=a | 1               |
                +----------------------+-----------------+
                | "x-dictionary";key=b | 2;x=1;y=2       |
                +----------------------+-----------------+
                | "x-dictionary";key=c | (a, b, c)       |
                +----------------------+-----------------+

                    Table 2: Non-normative examples of
                   Dictionary member canonicalization.

2.3.  Specialty Components

   Message components not found in an HTTP field can be included in the
   signature input by defining a component identifier and the
   canonicalization method for its component value.

   To differentiate specialty component identifiers from HTTP fields,
   specialty component identifiers MUST start with the "at" "@"
   character.  This specification defines the following specialty
   component identifiers:

   @signature-params  The signature metadata parameters for this
      signature.  (Section 2.3.1)

   @method  The method used for a request.  (Section 2.3.2)

   @target-uri  The full target URI for a request.  (Section 2.3.3)

   @authority  The authority of the target URI for a request.
      (Section 2.3.4)

   @scheme  The scheme of the target URI for a request.  (Section 2.3.5)

   @request-target  The request target.  (Section 2.3.6)

   @path  The absolute path portion of the target URI for a request.
      (Section 2.3.7)

   @query  The query portion of the target URI for a request.
      (Section 2.3.8)

   @query-params  The parsed query parameters of the target URI for a



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      request.  (Section 2.3.9)

   @status  The status code for a response.  (Section 2.3.10).

   @request-response  A signature from a request message that resulted
      in this response message.  (Section 2.3.11)

   Additional specialty component identifiers MAY be defined and
   registered in the HTTP Signatures Specialty Component Identifier
   Registry.  (Section 6.3)

2.3.1.  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.

   The signature parameters component identifier is "@signature-params".

   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.

   *  "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
   [RFC8941] as follows:

   1.  Let the output be an empty string.



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   2.  Determine an order for the component identifiers of the covered
       components.  Once this order is chosen, it cannot be changed.
       This order MUST be the same order as used in creating the
       signature input (Section 2.4).

   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 [RFC8941] and append this to the
       output.

   4.  Determine an order for any signature parameters.  Once this order
       is chosen, it cannot be changed.

   5.  Append the parameters to the "inner-list" in the chosen order
       according to Section 4.1.1.2 of RFC8941 [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" "x-empty-header" \
     "x-example");keyid="test-key-rsa-pss";alg="rsa-pss-sha512";\
     created=1618884475;expires=1618884775

   Note that an HTTP message could contain multiple signatures, but only
   the signature parameters used for the current signature are included
   in the entry.

2.3.2.  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.




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   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 response message, the "@method" component identifier
   refers to the associated component value of the request that
   triggered the response message being signed.

2.3.3.  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 response message, the "@target-uri" component identifier
   refers to the associated component value of the request that
   triggered the response message being signed.

2.3.4.  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.



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   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 response message, the "@authority" component identifier
   refers to the associated component value of the request that
   triggered the response message being signed.

2.3.5.  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 input string.  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 response message, the "@scheme" component identifier
   refers to the associated component value of the request that
   triggered the response message being signed.

2.3.6.  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.








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   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:

   "@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": *






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   If used in a response message, the "@request-target" component
   identifier refers to the associated component value of the request
   that triggered the response message being signed.

2.3.7.  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:

   POST /path?param=value HTTP/1.1
   Host: www.example.com

   Would result in the following "@path" value:

   "@path": /path

   If used in a response message, the "@path" identifier refers to the
   associated component value of the request that triggered the response
   message being signed.

2.3.8.  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




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   The following request message:

   POST /path?queryString HTTP/1.1
   Host: www.example.com

   Would result in the following "@query" value:

   "@query": ?queryString

   If used in a response message, the "@query" component identifier
   refers to the associated component value of the request that
   triggered the response message being signed.

2.3.9.  Query Parameters

   If a request target URI uses HTML form parameters in the query string
   as defined in [HTMLURL] Section 5, the "@query-params" component
   identifier allows addressing of individual query parameters.  The
   query parameters MUST be parsed according to [HTMLURL] Section 5.1,
   resulting in a list of ("nameString", "valueString") tuples.  The
   REQUIRED "name" parameter of each input identifier contains the
   "nameString" of a single query parameter.  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, 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 parameter name occurs multiple times in a request, all parameter
   values of that name MUST be included in separate signature input
   lines in the order in which the parameters occur in the target URI.

   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



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   If used in a response message, the "@query-params" component
   identifier refers to the associated component value of the request
   that triggered the response message being signed.

2.3.10.  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.

2.3.11.  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 input 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-Length: 18
   Signature-Input: sig1=("@authority" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature: sig1=:KuhJjsOKCiISnKHh2rln5ZNIrkRvue0DSu5rif3g7ckTbbX7C4\
     Jp3bcGmi8zZsFRURSQTcjbHdJtN8ZXlRptLOPGHkUa/3Qov79gBeqvHNUO4bhI27p\
     4WzD1bJDG9+6ml3gkrs7rOvMtROObPuc78A95fa4+skS/t2T7OjkfsHAm/enxf1fA\
     wkk15xj0n6kmriwZfgUlOqyff0XLwuH4XFvZ+ZTyxYNoo2+EfFg4NVfqtSJch2WDY\
     7n/qmhZOzMfyHlggWYFnDpyP27VrzQCQg8rM1Crp6MrwGLa94v6qP8pq0sQVq2DLt\
     4NJSoRRqXTvqlWIRnexmcKXjQFVz6YSA==:

   {"hello": "world"}

   This would result in the following unsigned response message:

   HTTP/1.1 200 OK
   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"}

   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 input string for this example is:

   NOTE: '\' line wrapping per RFC 8792

   "content-type": application/json
   "content-length": 62
   "@status": 200
   "@request-response";key="sig1": :KuhJjsOKCiISnKHh2rln5ZNIrkRvue0DSu\
     5rif3g7ckTbbX7C4Jp3bcGmi8zZsFRURSQTcjbHdJtN8ZXlRptLOPGHkUa/3Qov79\
     gBeqvHNUO4bhI27p4WzD1bJDG9+6ml3gkrs7rOvMtROObPuc78A95fa4+skS/t2T7\
     OjkfsHAm/enxf1fAwkk15xj0n6kmriwZfgUlOqyff0XLwuH4XFvZ+ZTyxYNoo2+Ef\
     Fg4NVfqtSJch2WDY7n/qmhZOzMfyHlggWYFnDpyP27VrzQCQg8rM1Crp6MrwGLa94\
     v6qP8pq0sQVq2DLt4NJSoRRqXTvqlWIRnexmcKXjQFVz6YSA==:
   "@signature-params": ("content-type" "content-length" "@status" \
     "@request-response";key="sig1");created=1618884475\
     ;keyid="test-key-ecc-p256"

   The signed response message is:




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   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 200 OK
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Length: 62
   Signature-Input: sig1=("content-type" "content-length" "@status" \
     "@request-response";key="sig1");created=1618884475\
     ;keyid="test-key-ecc-p256"
   Signature: sig1=:crVqK54rxvdx0j7qnt2RL1oQSf+o21S/6Uk2hyFpoIfOT0q+Hv\
     msYAXUXzo0Wn8NFWh/OjWQOXHAQdVnTk87Pw==:

   {"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.

   The "@request-response" component identifier MUST NOT be used in a
   request message.

2.4.  Creating the Signature Input String

   The signature input is a US-ASCII string containing the canonicalized
   HTTP message components covered by the signature.  To create the
   signature input string, 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.

       2.  Append a single colon "":""

       3.  Append a single space "" ""

       4.  Append the covered component's canonicalized component value,
           as defined by the HTTP message component type.  (Section 2.1
           and Section 2.3)

       5.  Append a single newline ""\\n""





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   3.  Append the signature parameters component (Section 2.3.1) 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 2.3.1

   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.  Such situations are included but not limited to:

   *  The signer or verifier does not understand the component
      identifier.

   *  The component identifier identifies a field that is not present in
      the message or whose value is malformed.

   *  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 that
      references a member that is not present in the field value, or
      whose value is malformed.  E.g., the identifier is
      ""x-dictionary";key="c"" and the value of the "x-dictionary"
      header field is "a=1, b=2"

   In the following non-normative example, the HTTP message being signed
   is the following request:

   GET /foo HTTP/1.1
   Host: example.org
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   X-Example: Example header
           with some whitespace.
   X-Empty-Header:
   Cache-Control: max-age=60
   Cache-Control: must-revalidate




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   The covered components consist of the "@method", "@path", and
   "@authority" specialty component identifiers followed by the "Cache-
   Control", "X-Empty-Header", "X-Example" HTTP headers, in order.  The
   signature parameters consist of a creation timestamp is "1618884475"
   and the key identifier is "test-key-rsa-pss".  The signature input
   string for this message with these parameters is:

   NOTE: '\' line wrapping per RFC 8792

   "@method": GET
   "@path": /foo
   "@authority": example.org
   "cache-control": max-age=60, must-revalidate
   "x-empty-header":
   "x-example": Example header with some whitespace.
   "@signature-params": ("@method" "@path" "@authority" \
     "cache-control" "x-empty-header" "x-example");created=1618884475\
     ;keyid="test-key-rsa-pss"

              Figure 1: Non-normative example Signature Input

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

   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.



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   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 specialty component identifier
          listed in Section 2.3 or its associated registry.

       *  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" specialty 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 input.  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 input string based on these
       signature parameters.  (Section 2.4)

   6.  The signer signs the signature input with the chosen signing
       algorithm using the key material chosen by the signer.  Several
       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 2.4, the example signature input string when
   signed with the "test-key-rsa-pss" key in Appendix B.1.2 gives the
   following message signature output value, encoded in Base64:







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   NOTE: '\' line wrapping per RFC 8792

   P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo1RSHi+oEF1FuX6O29\
   d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCiHzC87qmSQjvu1CFyFuWSj\
   dGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW84jS8gyarxAiWI97mPXU+OVM64\
   +HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53r58RmpZ+J9eKR2CD6IJQvacn5A4Ix\
   5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCVRj05NrxABNFv3r5S9IXf2fYJK+eyW4AiG\
   VMvMcOg==

              Figure 2: Non-normative example signature value

3.2.  Verifying a Signature

   A verifier processes a signature and its associated signature input
   parameters in concert with each other.

   In order to verify a signature, a verifier MUST follow the following
   algorithm:

   1.  Parse the "Signature" and "Signature-Input" fields 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.  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 to get the
       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 input, using the process described in
       Section 2.4.  The value of the "@signature-params" input is the
       value of the "SignatureInput" field for this signature serialized
       according to the rules described in Section 2.3.1, not including
       the signature's label from the "Signature-Input" field.

   8.  If the key material is appropriate for the algorithm, apply the
       verification algorithm to the signature, recalculated signature
       input, signature parameters, key material, and algorithm.
       Several algorithms are defined in Section 3.3.

   9.  The results of the verification algorithm function are the final
       results of the signature verification.

   If any of the above steps fail or produce an error, the signature
   validation fails.









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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.

   *  Prohibition of signature metadata parameters, such as runtime
      algorithm signaling with the "alg" parameter.

   *  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.  All signatures are generated
   from and verified against the byte values of the signature input
   string defined in Section 2.4.







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   Each signature algorithm method takes as its input the signature
   input string as a set of byte values ("I"), the signing key material
   ("Ks"), and outputs the signature output as a set of byte values
   ("S"):

   HTTP_SIGN (I, Ks)  ->  S

   Each verification algorithm method takes as its input the
   recalculated signature input string as a set of byte values ("I"),
   the verification key material ("Kv"), and the presented signature to
   be verified as a set of byte values ("S") and outputs the
   verification result ("V") as a boolean:

   HTTP_VERIFY (I, Kv, S) -> V

   This section contains several common algorithm methods.  The method
   to use can be communicated through the algorithm signature parameter
   defined in Section 2.3.1, 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 input string ("M") (Section 2.4).  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 input string 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
   input string ("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 input string 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.







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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 input string ("M") (Section 2.4).
   The hash SHA-256 [RFC6234] is applied to the signature input string
   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-
   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 input string ("M") re-created as described in Section 3.2.
   The hash function SHA-256 [RFC6234] is applied to the signature input
   string 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.

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 input string ("text") (Section 2.4).  The hash function
   SHA-256 [RFC6234] is applied to the signature input string 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.

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 input string (Section 2.4).  The hash
   SHA-256 [RFC6234] is applied to the signature input string to create
   the digest content to which the digital signature is applied.  The
   resulting signed content byte array is 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 input string re-created
   as described in Section 3.2.  The hash function SHA-256 [RFC6234] is
   applied to the signature input string 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.

3.3.5.  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.  There
   is no use of the explicit "alg" signature parameter when using JOSE
   signing algorithms.

   For both signing and verification, the HTTP messages signature input
   string (Section 2.4) is used as the entire "JWS Signing Input".  The
   JOSE Header defined in [RFC7517] is not used, and the signature input
   string 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".

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 2.3.1.

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@method" "@target-uri" "host" "date" \
     "cache-control" "x-empty-header" "x-example");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 input string'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.
   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.  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 of header fields a reverse
   proxy sets in addition to the examples in the previous sections.

   NOTE: '\' line wrapping per RFC 8792

   Forwarded: for=192.0.2.123
   Signature-Input: sig1=("@method" "@path" "@authority" \
       "cache-control" "x-empty-header" "x-example")\
       ;created=1618884475;keyid="test-key-rsa-pss"
   Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
       1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCi\
       HzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW8\
       4jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53\
       r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
       Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:




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   The client's request includes a signature value under the label
   "sig1", which the proxy signs in addition to the "Forwarded" header
   defined in [RFC7239].  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.  This results in a signature input string of:

   NOTE: '\' line wrapping per RFC 8792

   "signature";key="sig1": :P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP\
     4uKwxyJo1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9Gl\
     yntiCiHzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyo\
     yZW84jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg\
     53r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
     Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:
   "forwarded": for=192.0.2.123
   "@signature-params": ("signature";key="sig1" "forwarded")\
     ;created=1618884480;keyid="test-key-rsa";alg="rsa-v1_5-sha256"

   And a signature output value of:

   NOTE: '\' line wrapping per RFC 8792

   cjGvZwbsq9JwexP9TIvdLiivxqLINwp/ybAc19KOSQuLvtmMt3EnZxNiE+797dXK2cj\
   PPUFqoZxO8WWx1SnKhAU9SiXBr99NTXRmA1qGBjqus/1Yxwr8keB8xzFt4inv3J3zP0\
   k6TlLkRJstkVnNjuhRIUA/ZQCo8jDYAl4zWJJjppy6Gd1XSg03iUa0sju1yj6rcKbMA\
   BBuzhUz4G0u1hZkIGbQprCnk/FOsqZHpwaWvY8P3hmcDHkNaavcokmq+3EBDCQTzgwL\
   qfDmV0vLCXtDda6CNO2Zyum/pMGboCnQn/VkQ+j8kSydKoFg6EbVuGbrQijth6I0dDX\
   2/HYcJg==

   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

   Forwarded: for=192.0.2.123
   Signature-Input: sig1=("@method" "@path" "@authority" \
       "cache-control" "x-empty-header" "x-example")\
       ;created=1618884475;keyid="test-key-rsa-pss", \
     proxy_sig=("signature";key="sig1" "forwarded")\
       ;created=1618884480;keyid="test-key-rsa";alg="rsa-v1_5-sha256"
   Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
       1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCi\
       HzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW8\
       4jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53\
       r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
       Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:, \
     proxy_sig=:cjGvZwbsq9JwexP9TIvdLiivxqLINwp/ybAc19KOSQuLvtmMt3EnZx\
       NiE+797dXK2cjPPUFqoZxO8WWx1SnKhAU9SiXBr99NTXRmA1qGBjqus/1Yxwr8k\
       eB8xzFt4inv3J3zP0k6TlLkRJstkVnNjuhRIUA/ZQCo8jDYAl4zWJJjppy6Gd1X\
       Sg03iUa0sju1yj6rcKbMABBuzhUz4G0u1hZkIGbQprCnk/FOsqZHpwaWvY8P3hm\
       cDHkNaavcokmq+3EBDCQTzgwLqfDmV0vLCXtDda6CNO2Zyum/pMGboCnQn/VkQ+\
       j8kSydKoFg6EbVuGbrQijth6I0dDX2/HYcJg==:

   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 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.








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   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 2.3.1.

   NOTE: '\' line wrapping per RFC 8792

   Accept-Signature: sig1=("@method" "@target-uri" "host" "date" \
     "cache-control" "x-empty-header" "x-example")\
     ;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.

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




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   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

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



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   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.

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
      input string.

   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.

6.1.2.  Initial Contents

6.1.2.1.  rsa-pss-sha512

   Algorithm Name:
      "rsa-pss-sha512"

   Status:
      Active

   Definition:
      RSASSA-PSS using SHA-256

   Specification document(s):
      [[This document]], Section 3.3.1




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6.1.2.2.  rsa-v1_5-sha256

   Algorithm Name:
      "rsa-v1_5-sha256"

   Status:
      Active

   Description:
      RSASSA-PKCS1-v1_5 using SHA-256

   Specification document(s):
      [[This document]], Section 3.3.2

6.1.2.3.  hmac-sha256

   Algorithm Name:
      "hmac-sha256"

   Status:
      Active

   Description:
      HMAC using SHA-256

   Specification document(s):
      [[This document]], Section 3.3.3

6.1.2.4.  ecdsa-p256-sha256

   Algorithm Name:
      "ecdsa-p256-sha256"

   Status:
      Active

   Description:
      ECDSA using curve P-256 DSS and SHA-256

   Specification document(s):
      [[This document]], Section 3.3.4










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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

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    | Status | Reference(s)                   |
           +=========+========+================================+
           | alg     | Active | Section 2.3.1 of this document |
           +---------+--------+--------------------------------+
           | created | Active | Section 2.3.1 of this document |
           +---------+--------+--------------------------------+
           | expires | Active | Section 2.3.1 of this document |
           +---------+--------+--------------------------------+
           | keyid   | Active | Section 2.3.1 of this document |
           +---------+--------+--------------------------------+
           | nonce   | Active | Section 2.3.1 of this document |
           +---------+--------+--------------------------------+

              Table 3: Initial contents of the HTTP Signature
                       Metadata Parameters Registry.

6.3.  HTTP Signature Specialty Component Identifiers Registry

   This document defines a method for canonicalizing HTTP message
   components, including components that can be generated 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.  IANA is asked to create and maintain a new registry
   typed "HTTP Signature Specialty 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



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   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

6.3.2.  Initial Contents

   The table below contains the initial contents of the HTTP Signature
   Specialty Component Identifiers Registry.








































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   +===================+========+===================+==================+
   | Name              | Status | Target            | Reference        |
   +===================+========+===================+==================+
   | @signature-params | Active | Request,          | Section 2.3.1 of |
   |                   |        | Response          | this document    |
   +-------------------+--------+-------------------+------------------+
   | @method           | Active | Request,          | Section 2.3.2 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @authority        | Active | Request,          | Section 2.3.4 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @scheme           | Active | Request,          | Section 2.3.5 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @target-uri       | Active | Request,          | Section 2.3.3 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @request-target   | Active | Request,          | Section 2.3.6 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @path             | Active | Request,          | Section 2.3.7 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @query            | Active | Request,          | Section 2.3.8 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @query-params     | Active | Request,          | Section 2.3.9 of |
   |                   |        | Related-Response  | this document    |
   +-------------------+--------+-------------------+------------------+
   | @status           | Active | Response          | Section 2.3.10   |
   |                   |        |                   | of this document |
   +-------------------+--------+-------------------+------------------+
   | @request-response | Active | Section 2.3.11    |                  |
   |                   |        | of this document  |                  |
   +-------------------+--------+-------------------+------------------+

    Table 4: Initial contents of the HTTP Signature Specialty Component
                           Identifiers Registry.

7.  Security Considerations

   (( TODO: need to dive deeper on this section; not sure how much of
   what's referenced below is actually applicable, or if it covers
   everything we need to worry about. ))

   (( TODO: Should provide some recommendations on how to determine what
   components need to be signed for a given use case. ))



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   There are a number of security considerations to take into account
   when implementing or utilizing this specification.  A thorough
   security analysis of this protocol, including its strengths and
   weaknesses, can be found in [WP-HTTP-Sig-Audit].

8.  References

8.1.  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-17, 25 July 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              messaging-17>.

   [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>.

   [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>.

   [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>.





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   [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>.

   [SEMANTICS]
              Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
              Semantics", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-semantics-17, 25 July 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              semantics-17>.

8.2.  Informative References

   [I-D.ietf-httpbis-client-cert-field]
              Campbell, B. and M. Bishop, "Client-Cert HTTP Header
              Field: Conveying Client Certificate Information from TLS
              Terminating Reverse Proxies to Origin Server
              Applications", Work in Progress, Internet-Draft, draft-
              ietf-httpbis-client-cert-field-00, 8 June 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              client-cert-field-00>.

   [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>.

   [RFC7239]  Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
              RFC 7239, DOI 10.17487/RFC7239, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7239>.

   [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>.



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   [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>.

   [WP-HTTP-Sig-Audit]
              "Security Considerations for HTTP Signatures", 2013,
              <https://web-payments.org/specs/source/http-signatures-
              audit/>.

Appendix A.  Detecting HTTP Message Signatures

   There have been many attempts to create signed HTTP messages in the
   past, including other non-standard definitions of the "Signature"
   field 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.

   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

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.

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":



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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-----
   MIIEqAIBAAKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsP
   BRrwWEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsd
   JKFqMGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75
   jfZgkne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKI
   lE0PuKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZ
   SFlQPSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQABAoIBAG/JZuSWdoVHbi56
   vjgCgkjg3lkO1KrO3nrdm6nrgA9P9qaPjxuKoWaKO1cBQlE1pSWp/cKncYgD5WxE
   CpAnRUXG2pG4zdkzCYzAh1i+c34L6oZoHsirK6oNcEnHveydfzJL5934egm6p8DW
   +m1RQ70yUt4uRc0YSor+q1LGJvGQHReF0WmJBZHrhz5e63Pq7lE0gIwuBqL8SMaA
   yRXtK+JGxZpImTq+NHvEWWCu09SCq0r838ceQI55SvzmTkwqtC+8AT2zFviMZkKR
   Qo6SPsrqItxZWRty2izawTF0Bf5S2VAx7O+6t3wBsQ1sLptoSgX3QblELY5asI0J
   YFz7LJECgYkAsqeUJmqXE3LP8tYoIjMIAKiTm9o6psPlc8CrLI9CH0UbuaA2JCOM
   cCNq8SyYbTqgnWlB9ZfcAm/cFpA8tYci9m5vYK8HNxQr+8FS3Qo8N9RJ8d0U5Csw
   DzMYfRghAfUGwmlWj5hp1pQzAuhwbOXFtxKHVsMPhz1IBtF9Y8jvgqgYHLbmyiu1
   mwJ5AL0pYF0G7x81prlARURwHo0Yf52kEw1dxpx+JXER7hQRWQki5/NsUEtv+8RT
   qn2m6qte5DXLyn83b1qRscSdnCCwKtKWUug5q2ZbwVOCJCtmRwmnP131lWRYfj67
   B/xJ1ZA6X3GEf4sNReNAtaucPEelgR2nsN0gKQKBiGoqHWbK1qYvBxX2X3kbPDkv
   9C+celgZd2PW7aGYLCHq7nPbmfDV0yHcWjOhXZ8jRMjmANVR/eLQ2EfsRLdW69bn
   f3ZD7JS1fwGnO3exGmHO3HZG+6AvberKYVYNHahNFEw5TsAcQWDLRpkGybBcxqZo
   81YCqlqidwfeO5YtlO7etx1xLyqa2NsCeG9A86UjG+aeNnXEIDk1PDK+EuiThIUa
   /2IxKzJKWl1BKr2d4xAfR0ZnEYuRrbeDQYgTImOlfW6/GuYIxKYgEKCFHFqJATAG
   IxHrq1PDOiSwXd2GmVVYyEmhZnbcp8CxaEMQoevxAta0ssMK3w6UsDtvUvYvF22m
   qQKBiD5GwESzsFPy3Ga0MvZpn3D6EJQLgsnrtUPZx+z2Ep2x0xc5orneB5fGyF1P
   WtP+fG5Q6Dpdz3LRfm+KwBCWFKQjg7uTxcjerhBWEYPmEMKYwTJF5PBG9/ddvHLQ
   EQeNC8fHGg4UXU8mhHnSBt3EA10qQJfRDs15M38eG2cYwB1PZpDHScDnDA0=
   -----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":










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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-----
   MIIEvgIBADALBgkqhkiG9w0BAQoEggSqMIIEpgIBAAKCAQEAr4tmm3r20Wd/Pbqv
   P1s2+QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvMs8ct+Lh1GH45x28Rw3Ry5
   3mm+oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95AndTrifbIFPNU8PPMO7Oyr
   FAHqgDsznjPFmTOtCEcN2Z1FpWgchwuYLPL+Wokqltd11nqqzi+bJ9cvSKADYdUA
   AN5WUtzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSyZYoA485mqcO0GVAdVw
   9lq4aOT9v6d+nb4bnNkQVklLQ3fVAvJm+xdDOp9LCNCN48V2pnDOkFV6+U9nV5oy
   c6XI2wIDAQABAoIBAQCUB8ip+kJiiZVKF8AqfB/aUP0jTAqOQewK1kKJ/iQCXBCq
   pbo360gvdt05H5VZ/RDVkEgO2k73VSsbulqezKs8RFs2tEmU+JgTI9MeQJPWcP6X
   aKy6LIYs0E2cWgp8GADgoBs8llBq0UhX0KffglIeek3n7Z6Gt4YFge2TAcW2WbN4
   XfK7lupFyo6HHyWRiYHMMARQXLJeOSdTn5aMBP0PO4bQyk5ORxTUSeOciPJUFktQ
   HkvGbym7KryEfwH8Tks0L7WhzyP60PL3xS9FNOJi9m+zztwYIXGDQuKM2GDsITeD
   2mI2oHoPMyAD0wdI7BwSVW18p1h+jgfc4dlexKYRAoGBAOVfuiEiOchGghV5vn5N
   RDNscAFnpHj1QgMr6/UG05RTgmcLfVsI1I4bSkbrIuVKviGGf7atlkROALOG/xRx
   DLadgBEeNyHL5lz6ihQaFJLVQ0u3U4SB67J0YtVO3R6lXcIjBDHuY8SjYJ7Ci6Z6
   vuDcoaEujnlrtUhaMxvSfcUJAoGBAMPsCHXte1uWNAqYad2WdLjPDlKtQJK1diCm
   rqmB2g8QE99hDOHItjDBEdpyFBKOIP+NpVtM2KLhRajjcL9Ph8jrID6XUqikQuVi
   4J9FV2m42jXMuioTT13idAILanYg8D3idvy/3isDVkON0X3UAVKrgMEne0hJpkPL
   FYqgetvDAoGBAKLQ6JZMbSe0pPIJkSamQhsehgL5Rs51iX4m1z7+sYFAJfhvN3Q/
   OGIHDRp6HjMUcxHpHw7U+S1TETxePwKLnLKj6hw8jnX2/nZRgWHzgVcY+sPsReRx
   NJVf+Cfh6yOtznfX00p+JWOXdSY8glSSHJwRAMog+hFGW1AYdt7w80XBAoGBAImR
   NUugqapgaEA8TrFxkJmngXYaAqpA0iYRA7kv3S4QavPBUGtFJHBNULzitydkNtVZ
   3w6hgce0h9YThTo/nKc+OZDZbgfN9s7cQ75x0PQCAO4fx2P91Q+mDzDUVTeG30mE
   t2m3S0dGe47JiJxifV9P3wNBNrZGSIF3mrORBVNDAoGBAI0QKn2Iv7Sgo4T/XjND
   dl2kZTXqGAk8dOhpUiw/HdM3OGWbhHj2NdCzBliOmPyQtAr770GITWvbAI+IRYyF
   S7Fnk6ZVVVHsxjtaHy1uJGFlaZzKR4AGNaUTOJMs6NadzCmGPAxNQQOCqoUjn4XR
   rOjr9w349JooGXhOxbu8nOxX
   -----END PRIVATE KEY-----

B.1.3.  Example ECC P-256 Test Key

   The following key is an elliptical curve key over the curve P-256,
   referred to in this document as "test-key-ecc-p256".








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   -----BEGIN EC PRIVATE KEY-----
   MHcCAQEEIFKbhfNZfpDsW43+0+JjUr9K+bTeuxopu653+hBaXGA7oAoGCCqGSM49
   AwEHoUQDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lfw0EkjqF7xB4FivAxzic30tMM
   4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
   -----END EC PRIVATE KEY-----

   -----BEGIN PUBLIC KEY-----
   MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lf
   w0EkjqF7xB4FivAxzic30tMM4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
   -----END PUBLIC KEY-----

B.1.4.  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:

   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
   Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   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
   Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   Content-Length: 18

   {"hello": "world"}




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B.2.1.  Minimal Signature Using rsa-pss-sha512

   This example presents a minimal "Signature-Input" and "Signature"
   header for a signature using the "rsa-pss-sha512" algorithm over
   "test-request", covering none of the components of the HTTP message
   request but providing a timestamped signature proof of possession of
   the key.

   The corresponding signature input is:

   NOTE: '\' line wrapping per RFC 8792

   "@signature-params": ();created=1618884475\
     ;keyid="test-key-rsa-pss";alg="rsa-pss-sha512"

   This results in the following "Signature-Input" and "Signature"
   headers being added to the message:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=();created=1618884475\
     ;keyid="test-key-rsa-pss";alg="rsa-pss-sha512"
   Signature: sig1=:HWP69ZNiom9Obu1KIdqPPcu/C1a5ZUMBbqS/xwJECV8bhIQVmE\
     AAAzz8LQPvtP1iFSxxluDO1KE9b8L+O64LEOvhwYdDctV5+E39Jy1eJiD7nYREBgx\
     TpdUfzTO+Trath0vZdTylFlxK4H3l3s/cuFhnOCxmFYgEa+cw+StBRgY1JtafSFwN\
     cZgLxVwialuH5VnqJS4JN8PHD91XLfkjMscTo4jmVMpFd3iLVe0hqVFl7MDt6TMkw\
     IyVFnEZ7B/VIQofdShO+C/7MuupCSLVjQz5xA+Zs6Hw+W9ESD/6BuGs6LF1TcKLxW\
     +5K+2zvDY/Cia34HNpRW5io7Iv9/b7iQ==:

   Note that since the covered components list is empty, this signature
   could be applied by an attacker to an unrelated HTTP message.
   Therefore, use of an empty covered components set is discouraged.

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 input is:

   NOTE: '\' line wrapping per RFC 8792

   "@authority": example.com
   "content-type": application/json
   "@signature-params": ("@authority" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"





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   This results in the following "Signature-Input" and "Signature"
   headers being added to the message:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@authority" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature: sig1=:ik+OtGmM/kFqENDf9Plm8AmPtqtC7C9a+zYSaxr58b/E6h81gh\
     JS3PcH+m1asiMp8yvccnO/RfaexnqanVB3C72WRNZN7skPTJmUVmoIeqZncdP2mlf\
     xlLP6UbkrgYsk91NS6nwkKC6RRgLhBFqzP42oq8D2336OiQPDAo/04SxZt4Wx9nDG\
     uy2SfZJUhsJqZyEWRk4204x7YEB3VxDAAlVgGt8ewilWbIKKTOKp3ymUeQIwptqYw\
     v0l8mN404PPzRBTpB7+HpClyK4CNp+SVv46+6sHMfJU4taz10s/NoYRmYCGXyadzY\
     YDj0BYnFdERB6NblI/AOWFGl5Axhhmjg==:

B.2.3.  Full Coverage using rsa-pss-sha512

   This example covers all headers in "test-request" (including the
   message body "Digest") plus various elements of the control data,
   using the "rsa-pss-sha512" algorithm.

   The corresponding signature input is:

   NOTE: '\' line wrapping per RFC 8792

   "date": Tue, 20 Apr 2021 02:07:56 GMT
   "@method": POST
   "@path": /foo
   "@query": ?param=value&pet=dog
   "@authority": example.com
   "content-type": application/json
   "digest": SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   "content-length": 18
   "@signature-params": ("date" "@method" "@path" "@query" \
     "@authority" "content-type" "digest" "content-length")\
     ;created=1618884475;keyid="test-key-rsa-pss"

   This results in the following "Signature-Input" and "Signature"
   headers being added to the message:













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   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("date" "@method" "@path" "@query" \
     "@authority" "content-type" "digest" "content-length")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature: sig1=:JuJnJMFGD4HMysAGsfOY6N5ZTZUknsQUdClNG51VezDgPUOW03\
     QMe74vbIdndKwW1BBrHOHR3NzKGYZJ7X3ur23FMCdANe4VmKb3Rc1Q/5YxOO8p7Ko\
     yfVa4uUcMk5jB9KAn1M1MbgBnqwZkRWsbv8ocCqrnD85Kavr73lx51k1/gU8w673W\
     T/oBtxPtAn1eFjUyIKyA+XD7kYph82I+ahvm0pSgDPagu917SlqUjeaQaNnlZzO03\
     Iy1RZ5XpgbNeDLCqSLuZFVID80EohC2CQ1cL5svjslrlCNstd2JCLmhjL7xV3NYXe\
     rLim4bqUQGRgDwNJRnqobpS6C1NBns/Q==:

   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 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.

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 input is:

   NOTE: '\' line wrapping per RFC 8792

   "content-type": application/json
   "digest": SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   "content-length": 18
   "@signature-params": ("content-type" "digest" "content-length")\
     ;created=1618884475;keyid="test-key-ecc-p256"

   This results in the following "Signature-Input" and "Signature"
   headers being added to the message:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("content-type" "digest" "content-length")\
     ;created=1618884475;keyid="test-key-ecc-p256"
   Signature: sig1=:n8RKXkj0iseWDmC6PNSQ1GX2R9650v+lhbb6rTGoSrSSx18zmn\
     6fPOtBx48/WffYLO0n1RHHf9scvNGAgGq52Q==:





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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 input is:

   NOTE: '\' line wrapping per RFC 8792

   "@authority": example.com
   "date": Tue, 20 Apr 2021 02:07:55 GMT
   "content-type": application/json
   "@signature-params": ("@authority" "date" "content-type")\
     ;created=1618884475;keyid="test-shared-secret"

   This results in the following "Signature-Input" and "Signature"
   headers being added to the message:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@authority" "date" "content-type")\
     ;created=1618884475;keyid="test-shared-secret"
   Signature: sig1=:fN3AMNGbx0V/cIEKkZOvLOoC3InI+lM2+gTv22x3ia8=:

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].  By signing this header
   field, a reverse proxy can not only attest to its own validation of
   the initial request 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 input 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=1618884475;keyid="test-key-ecc-p256"

   This results in the following signature:






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   NOTE: '\' line wrapping per RFC 8792

   5gudRjXaHrAYbEaQUOoY9TuvqWOdPcspkp7YyKCB0XhyAG9cB715hucPPanEK0OVyiN\
   LJqcoq2Yn1DPWQcnbog==

   Which results in the following signed request sent from the proxy to
   the internal service:

   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=1618884475;keyid="test-key-ecc-p256"
   Signature: ttrp=:5gudRjXaHrAYbEaQUOoY9TuvqWOdPcspkp7YyKCB0XhyAG9cB7\
     15hucPPanEK0OVyiNLJqcoq2Yn1DPWQcnbog==:

   {"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 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 Boehlmark, Stephane Bortzmeyer, Sarven Capadisli, Liam
   Dennehy, ductm54, Stephen Farrell, Phillip Hallam-Baker, Eric Holmes,
   Andrey Kislyuk, Adam Knight, Dave Lehn, Dave Longley, Ilari



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   Liusvaara, James H.  Manger, Kathleen Moriarty, Mark Nottingham, Yoav
   Nir, Adrian Palmer, Lucas Pardue, Roberto Polli, Julian Reschke,
   Michael Richardson, Wojciech Rygielski, 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

      -  -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.



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      -  -03

         o  Clarified signing and verification processes.

         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





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         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.

         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.



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         o  Added IANA HTTP Signature Parameter registry.

         o  Added additional normative and informative references.

         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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