HTTP                                                     A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                               J. Richer
Expires: 9 October 2021                              Bespoke Engineering
                                                               M. Sporny
                                                          Digital Bazaar
                                                            7 April 2021


                         Signing HTTP Messages
                draft-ietf-httpbis-message-signatures-03

Abstract

   This document describes a mechanism for creating, encoding, and
   verifying digital signatures or message authentication codes over
   content within 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.

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
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 9 October 2021.

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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   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Discussion . . . . . . . . . . . . . . . . .   4
     1.2.  HTTP Message Transformations  . . . . . . . . . . . . . .   5
     1.3.  Safe Transformations  . . . . . . . . . . . . . . . . . .   5
     1.4.  Conventions and Terminology . . . . . . . . . . . . . . .   6
     1.5.  Application of HTTP Message Signatures  . . . . . . . . .   7
   2.  HTTP Message Signature Covered Content  . . . . . . . . . . .   8
     2.1.  HTTP Headers  . . . . . . . . . . . . . . . . . . . . . .   9
       2.1.1.  Canonicalized Structured HTTP Headers . . . . . . . .   9
       2.1.2.  Canonicalization Examples . . . . . . . . . . . . . .   9
     2.2.  Dictionary Structured Field Members . . . . . . . . . . .  10
       2.2.1.  Canonicalization Examples . . . . . . . . . . . . . .  10
     2.3.  List Prefixes . . . . . . . . . . . . . . . . . . . . . .  11
       2.3.1.  Canonicalization Examples . . . . . . . . . . . . . .  11
     2.4.  Specialty Content Fields  . . . . . . . . . . . . . . . .  12
       2.4.1.  Request Target  . . . . . . . . . . . . . . . . . . .  12
       2.4.2.  Signature Parameters  . . . . . . . . . . . . . . . .  13
     2.5.  Creating the Signature Input String . . . . . . . . . . .  16
   3.  HTTP Message Signatures . . . . . . . . . . . . . . . . . . .  17
     3.1.  Creating a Signature  . . . . . . . . . . . . . . . . . .  18
     3.2.  Verifying a Signature . . . . . . . . . . . . . . . . . .  20
       3.2.1.  Enforcing Application Requirements  . . . . . . . . .  21
     3.3.  Signature Algorithm Methods . . . . . . . . . . . . . . .  22
       3.3.1.  RSASSA-PSS using SHA-512  . . . . . . . . . . . . . .  22
       3.3.2.  RSASSA-PKCS1-v1_5 using SHA-256 . . . . . . . . . . .  22



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       3.3.3.  HMAC using SHA-256  . . . . . . . . . . . . . . . . .  23
       3.3.4.  ECDSA using curve P-256 DSS and SHA-256 . . . . . . .  23
       3.3.5.  JSON Web Signature (JWS) algorithms . . . . . . . . .  24
   4.  Including a Message Signature in a Message  . . . . . . . . .  24
     4.1.  The 'Signature-Input' HTTP Header . . . . . . . . . . . .  24
     4.2.  The 'Signature' HTTP Header . . . . . . . . . . . . . . .  25
     4.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  25
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     5.1.  HTTP Signature Algorithms Registry  . . . . . . . . . . .  26
       5.1.1.  Registration Template . . . . . . . . . . . . . . . .  26
       5.1.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  27
     5.2.  HTTP Signature Metadata Parameters Registry . . . . . . .  28
       5.2.1.  Registration Template . . . . . . . . . . . . . . . .  28
       5.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  28
     5.3.  HTTP Signature Specialty Content Identifiers Registry . .  29
       5.3.1.  Registration Template . . . . . . . . . . . . . . . .  29
       5.3.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  29
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  30
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  31
   Appendix A.  Detecting HTTP Message Signatures  . . . . . . . . .  32
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  32
     B.1.  Example Keys  . . . . . . . . . . . . . . . . . . . . . .  32
       B.1.1.  Example Key RSA test  . . . . . . . . . . . . . . . .  32
     B.2.  Example keyid Values  . . . . . . . . . . . . . . . . . .  33
     B.3.  Test Cases  . . . . . . . . . . . . . . . . . . . . . . .  34
       B.3.1.  Signature Verification  . . . . . . . . . . . . . . .  34
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  35
   Document History  . . . . . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  38

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-



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   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 content within an HTTP message.  The mechanism
   allows applications to create digital signatures or message
   authentication codes (MACs) over only that content within the message
   that is 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 mechanism described in this document consists of three parts:

   *  A common nomenclature and canonicalization rule set for the
      different protocol elements and other content within HTTP
      messages.

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

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

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 signed content.  Since the raw
   bytes of the message cannot be relied upon as signed content, the
   signer and verifier must derive the signed content 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
   content is signed.




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   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).

   *  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 content
   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.





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   *  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 content 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 content not covered by the signature are
   considered safe.

1.4.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The terms "HTTP message", "HTTP request", "HTTP response", "absolute-
   form", "absolute-path", "effective request URI", "gateway", "header
   field", "intermediary", "request-target", "sender", and "recipient"
   are used as defined in [MESSAGING].

   The term "method" is to be interpreted as defined in Section 4 of
   [SEMANTICS].

   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:

   Signer:
      The entity that is generating or has generated an HTTP Message
      Signature.



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   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.

   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.  To improve readability, header fields may be split
   into multiple lines, using the "obs-fold" syntax.  This syntax is
   deprecated in [MESSAGING], and senders MUST NOT generate messages
   that include it.

   Additionally, some examples use '\' line wrapping for long values
   that contain no whitespace, as per [RFC8792].

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 content 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 2.4.2 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 content is appropriate for the key material.  For
      example, the process could use the "alg" parameter of the
      signature parameters Section 2.4.2 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.



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   *  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.

   The details of this kind of profiling are the purview of the
   application and outside the scope of this specification.

2.  HTTP Message Signature Covered Content

   In order to allow signers and verifiers to establish which content is
   covered by a signature, this document defines content identifiers for
   data items covered by an HTTP Message Signature as well as the means
   for combining these canonicalized values into a signature input
   string.

   Some content within HTTP messages can undergo transformations that
   change the bitwise value without altering meaning of the content (for
   example, the merging together of header fields with the same name).
   Message content 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 content
   identifier that transform the identifier's associated content into
   such a canonical form.

   Content identifiers are defined using production grammar defined by
   [RFC8941] section 4.  The content identifier is an "sf-string" value.
   The content identifier type MAY define parameters which are included
   using the "parameters" rule.

   content-identifier = sf-string parameters

   Note that this means the value of the 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 content identifier types, their
   parameters, their associated content, and their canonicalization
   rules.  The method for combining content identifiers into the
   signature input string is defined in Section 2.5.










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2.1.  HTTP Headers

   The content identifier for an HTTP header is the lowercased form of
   its header field name.  While HTTP header field names are case-
   insensitive, implementations MUST use lowercased field names (e.g.,
   "content-type", "date", "etag") when using them as content
   identifiers.

   Unless overridden by additional parameters and rules, the HTTP header
   field value MUST be canonicalized with the following steps:

   1.  Create an ordered list of the field values of each instance of
       the header 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 value.

2.1.1.  Canonicalized Structured HTTP Headers

   If value of the the HTTP header in question is a structured field
   [RFC8941], the content identifier MAY include the "sf" parameter.  If
   this parameter is included, the HTTP header value MUST be
   canonicalized using the rules specified in [RFC8941] section 4.  Note
   that this process will replace any optional whitespace with a single
   space.

   The resulting string is used as the field value input 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:

   HTTP/1.1 200 OK
   Server: 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




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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    |
        +---------------------+----------------------------------+
        | "server"            | www.example.com                  |
        +---------------------+----------------------------------+
        | "x-empty-header"    |                                  |
        +---------------------+----------------------------------+
        | "x-obs-fold-header" | Obsolete line folding.           |
        +---------------------+----------------------------------+
        | "x-ows-header"      | Leading and trailing whitespace. |
        +---------------------+----------------------------------+

             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 content identifier for
   the header.  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] on a Dictionary containing only that
   member.

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 assumed to be a Dictionary:

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

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






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              +======================+=====================+
              | Content Identifier   | Canonicalized 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.  List Prefixes

   A prefix of a List Structured Field consisting of the first N members
   in the field's value (where N is an integer greater than 0 and less
   than or equal to the number of members in the List) is identified by
   the parameter "prefix" with the value of N as an integer.

   A list prefix value is canonicalized by applying the serialization
   algorithm described in Section 4.1.1 of [RFC8941] on a List
   containing only the first N members as specified in the list prefix,
   in the order they appear in the original List.

2.3.1.  Canonicalization Examples

   This section contains non-normative examples of canonicalized values
   for list prefixes given the following example header fields, whose
   values are assumed to be Dictionaries:

   X-List-A: (a b c d e f)
   X-List-B: ()

   The following table shows example canonicalized values for different
   content identifiers, given those fields:















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               +=====================+=====================+
               | Content Identifier  | Canonicalized Value |
               +=====================+=====================+
               | "x-list-a";prefix=0 | ()                  |
               +---------------------+---------------------+
               | "x-list-a";prefix=1 | (a)                 |
               +---------------------+---------------------+
               | "x-list-a";prefix=3 | (a, b, c)           |
               +---------------------+---------------------+
               | "x-list-a";prefix=6 | (a, b, c, d, e, f)  |
               +---------------------+---------------------+
               | "x-list-b";prefix=0 | ()                  |
               +---------------------+---------------------+

                  Table 3: Non-normative examples of list
                          prefix canonicalization.

2.4.  Specialty Content Fields

   Content not found in an HTTP header can be included in the signature
   base string by defining a content identifier and the canonicalization
   method for its content.

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

   @request-target  The target request endpoint.  Section 2.4.1

   @signature-params  The signature metadata parameters for this
      signature.  Section 2.4.2

   Additional specialty content identifiers MAY be defined and
   registered in the HTTP Signatures Specialty Content Identifier
   Registry.  Section 5.3

2.4.1.  Request Target

   The request target endpoint, consisting of the request method and the
   path and query of the effective request URI, is identified by the
   "@request-target" identifier.

   Its value is canonicalized as follows:

   1.  Take the lowercased HTTP method of the message.

   2.  Append a space " ".



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   3.  Append the path and query of the request target of the message,
       formatted according to the rules defined for the :path pseudo-
       header in [HTTP2], Section 8.1.2.3.  The resulting string is the
       canonicalized value.

2.4.1.1.  Canonicalization Examples

   The following table contains non-normative example HTTP messages and
   their canonicalized "@request-target" values.

       +=========================+=================+
       |HTTP Message             | @request-target |
       +=========================+=================+
       |   POST /?param=value HTTP/1.1| post            |
       |   Host: www.example.com | /?param=value   |
       +-------------------------+-----------------+
       |   POST /a/b HTTP/1.1    | post /a/b       |
       |   Host: www.example.com |                 |
       +-------------------------+-----------------+
       |   GET http://www.example.com/a/ HTTP/1.1| get /a/         |
       +-------------------------+-----------------+
       |   GET http://www.example.com HTTP/1.1| get /           |
       +-------------------------+-----------------+
       |   CONNECT server.example.com:80 HTTP/1.1| connect /       |
       |   Host: server.example.com|                 |
       +-------------------------+-----------------+
       |   OPTIONS * HTTP/1.1    | options *       |
       |   Host: server.example.com|                 |
       +-------------------------+-----------------+

            Table 4: Non-normative examples of "@request-target"
                             canonicalization.

2.4.2.  Signature Parameters

   HTTP Message Signatures have metadata properties that provide
   information regarding the signature's generation and/or verification.

   The signature parameters special content is identified by the
   "@signature-params" identifier.

   Its canonicalized value is the serialization of the signature
   parameters for this signature, including the covered content list
   with all associated parameters.  The following metadata properties
   are defined:

   Covered Content:




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      An ordered list of content identifiers for headers Section 2.1 and
      specialty content Section 2.4 that indicates the metadata and
      message content that is covered by the signature.  This list MUST
      NOT include the "@signature-params" specialty content identifier
      itself.

   Algorithm:
      An HTTP Signature Algorithm defined in the HTTP Signature
      Algorithms Registry defined in this document, represented as a
      string.  It describes the signing and verification algorithms for
      the signature.

   Key Material:
      The key material required to create or verify the signature.

   Creation Time:
      A timestamp representing the point in time that the signature was
      generated, represented as an integer.  Sub-second precision is not
      supported.  A signature's Creation Time MAY be undefined,
      indicating that it is unknown.

   Expiration Time:
      A timestamp representing the point in time at which the signature
      expires, represented as an integer.  An expired signature always
      fails verification.  A signature's Expiration Time MAY be
      undefined, indicating that the signature does not expire.

   The signature parameters are serialized using the rules in [RFC8941]
   section 4 as follows:

   1.  Let the output be an empty string.

   2.  Serialize the content identifiers of the covered content as an
       ordered "inner-list" according to [RFC8941] section 4.1.1.1 and
       append this to the output.

   3.  Append the signature metadata as parameters according to
       [RFC8941] section 4.1.1.2 in the any order, skipping fields that
       are not available:

       *  "alg": Algorithm as an "sf-string" value.

       *  "keyid": Identifier for the key material as an "sf-string"
          value.

       *  "created": Creation time as an "sf-integer" timestamp value.

       *  "expires": Expiration time as an "sf-integer" timestamp value.



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   Note that the "inner-list" serialization is used for the covered
   content instead of the "sf-list" serialization in order to facilitate
   this value's additional inclusion in the "Signature-Input" header'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
   ("@request-target" "host" "date" "cache-control" "x-empty-header"
     "x-example"); keyid="test-key-a"; alg="rsa-pss-sha512"; \
     created=1402170695; expires=1402170995

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

2.4.2.1.  Canonicalization Examples

   Given the following signature parameters:

        +==============+=========================================+
        | Property     | Value                                   |
        +==============+=========================================+
        | Algorithm    | rsa-pss-sha512                          |
        +--------------+-----------------------------------------+
        | Covered      | "@request-target", "host", "date",      |
        | Content      | "cache-control", "x-emptyheader",       |
        |              | "x-example", "x-dictionary;key=b",      |
        |              | "x-dictionary;key=a", "x-list;prefix=3" |
        +--------------+-----------------------------------------+
        | Creation     | 1402174295                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Expiration   | 1402174595                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Verification | The public key provided in              |
        | Key Material | Appendix B.1.1 and identified by the    |
        |              | "keyid" value "test-key-a".             |
        +--------------+-----------------------------------------+

                                 Table 5

   The signature parameter value is defined as:







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 # NOTE: '\' line wrapping per RFC 8792
 "@signature-params": ("@request-target" "host" "date" "cache-control" \
   "x-empty-header" "x-example" "x-dictionary";key=b \
   "x-dictionary";key=a "x-list";prefix=3); keyid="test-key-a"; \
   alg="rsa-pss-sha512"; created=1402170695; expires=1402170995

2.5.  Creating the Signature Input String

   The signature input is a US-ASCII string containing the content that
   is 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 content and parameters using
   the following algorithm:

   1.  Let the output be an empty string.

   2.  For each covered content item in the covered content list (in
       order):

       1.  Append the identifier for the covered content serialized
           according to the "content-identifier" rule.

       2.  Append a single colon "":""

       3.  Append a single space "" ""

       4.  Append the covered content's canonicalized value, as defined
           by the covered content type.  Section 2.1 and Section 2.4

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

   3.  Append the signature parameters Section 2.4.2 as follows:

       1.  Append the identifier for the signature parameters serialized
           according to the "content-identifier" rule, ""@signature-
           params""

       2.  Append a single colon "":""

       3.  Append a single space "" ""

       4.  Append the signature parameters' canonicalized value as
           defined in Section 2.4.2

   4.  Return the output string.






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   If covered content references an identifier that cannot be resolved
   to a 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 content identifier. * The identifier
   identifies a header field that is not present in the message or whose
   value is malformed. * The identifier is a Dictionary member
   identifier that references a header field that is not present in the
   message, is not a Dictionary Structured Field, or whose value is
   malformed. * The identifier is a List Prefix member identifier that
   references a header field that is not present in the message, is not
   a List Structured Field, or whose value is malformed. * The
   identifier is a Dictionary member identifier that references a member
   that is not present in the header 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" * The
   identifier is a List Prefix member identifier that specifies more
   List members than are present the header field.  E.g., the identifier
   is ""x-list";prefix=3" and the value of the "x-list" header field is
   "(1, 2)".

   For the non-normative example Signature metadata in Table 6, the
   corresponding Signature Input is:

 # NOTE: '\' line wrapping per RFC 8792
 "@request-target": get /foo
 "host": example.org
 "date": Tue, 07 Jun 2014 20:51:35 GMT
 "cache-control": max-age=60, must-revalidate
 "x-emptyheader":
 "x-example": Example header with some whitespace.
 "x-dictionary";key=b: 2
 "x-dictionary";key=a: 1
 "x-list";prefix=3: (a, b, c)
 "@signature-params": ("@request-target" "host" "date" "cache-control" \
   "x-empty-header" "x-example" "x-dictionary";key=b \
   "x-dictionary";key=a "x-list";prefix=3); keyid="test-key-a"; \
   created=1402170695; expires=1402170995

            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 content in an HTTP message and metadata about the
   signature itself.  When successfully verified against an HTTP
   message, it provides cryptographic proof that with respect to the
   subset of content that was signed, the message is semantically
   equivalent to the message for which the signature was generated.



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3.1.  Creating a Signature

   In order to create a signature, a signer completes the following
   process:

   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.

   4.  The signer creates an ordered list of content identifiers
       representing the message content and signature metadata to be
       covered by the signature, and assigns this list as the
       signature's Covered Content.

       *  Each covered content identifier MUST reference either an HTTP
          header or a specialty content field listed in Section 2.4 or
          its associated registry.

       *  Signers SHOULD include "@request-target" in the covered
          content list list.

       *  Signers SHOULD include a date stamp in some form, such as
          using the "date" header.  Alternatively, the "created"
          signature metadata parameter can fulfil this role.

       *  Further guidance on what to include in this list and in what
          order is out of scope for this document.  However, note that
          the list order is significant and once established for a given
          signature it MUST be preserved for that signature.

       *  Note that the "@signature-params" specialty identifier is not
          explicitly listed in the list of covered content 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.

   5.  The signer creates the signature input string.  Section 2.5





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   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 signer then encodes the result of that operation as a
       Base64-encoded string [RFC4648].  This string is the signature
       output value.

   For example, given the following HTTP message:

   GET /foo HTTP/1.1
   Host: example.org
   Date: Sat, 07 Jun 2014 20:51:35 GMT
   X-Example: Example header
           with some whitespace.
   X-EmptyHeader:
   X-Dictionary: a=1, b=2
   X-List: (a b c d)
   Cache-Control: max-age=60
   Cache-Control: must-revalidate

   The following table presents a non-normative example of metadata
   values that a signer may choose:

        +==============+=========================================+
        | Property     | Value                                   |
        +==============+=========================================+
        | Covered      | "@request-target", "host", "date",      |
        | Content      | "cache-control", "x-emptyheader",       |
        |              | "x-example", "x-dictionary;key=b",      |
        |              | "x-dictionary;key=a", "x-list;prefix=3" |
        +--------------+-----------------------------------------+
        | Creation     | 1402174295                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Expiration   | 1402174595                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Verification | The public key provided in              |
        | Key Material | Appendix B.1.1 and identified by the    |
        |              | "keyid" value "test-key-a".             |
        +--------------+-----------------------------------------+

              Table 6: Non-normative example metadata values

   For the non-normative example signature metadata and signature input
   in Figure 1, the corresponding signature value is:




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  # NOTE: '\' line wrapping per RFC 8792
  K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUeZx/Kdrq32DrfakQ6b\
  PsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibeoHyqU/yCjphSmEdd7WD+z\
  rchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4CaB8X/I5/+HLZLGvDiezqi6/7\
  p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg1Q7MpWYZs0soHjttq0uLIA3DIbQfL\
  iIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZgFquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==

             Figure 2: Non-normative example signature value

3.2.  Verifying a Signature

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

   1.  Examine the signature's 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
       contents are required to be covered by the signature.
       Section 3.2.1

   2.  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
       signature is presented.

   3.  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.









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   4.  Use the received HTTP message and the signature's metadata to
       recreate the signature input, using the process described in
       Section 2.5.  The value of the "@signature-params" input is the
       value of the SignatureInput header field for this signature
       serialized according to the rules described in Section 2.4.2, not
       including the signature's label from the SignatureInput header.

   5.  If the key material is appropriate for the algorithm, apply the
       verification algorithm to the signature, signature input,
       signature parameters, key material, and algorithm.  The results
       of the verification algorithm function are the final results of
       the signature verification.  Several algorithms are defined in
       Section 3.3.

   If any of the above steps fail, the signature validation fails.

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.

   *  Prohibiting the use of certain algorithms, or mandating the use of
      an algorithm.

   *  Requiring keys to be of a certain size (e.g., 2048 bits vs. 1024
      bits).

   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.




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3.3.  Signature Algorithm Methods

   HTTP Message signatures MAY use any cryptographic digital signature
   or MAC method that allows for the signing of the signature input
   string.  This section contains several common algorithm parameters
   that can be communicated through the algorithm signature parameter
   defined in Section 2.4.2, by reference to the key material, or
   through agreement between the signer and verifier.

   Signatures are generated from and verified against the byte values of
   the signature input string defined in Section 2.5.

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 2.5.  The 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 ("S") is Base64-encoded as described in
   Section 3.1.  The resulting encoded value is the HTTP message
   signature output.

   To verify using this algorithm, the verifier applies the "RSASSA-PSS-
   VERIFY ((n, e), M, S)" function [RFC8017] using the public key
   material ("(n, e)").  The verifier re-creates the signature input
   string ("M") from the received message, as defined in Section 2.5.
   The hash function SHA-512 [RFC6234] is applied to the signature input
   string to create the digest content to which the verification
   function is applied.  The verifier decodes the HTTP message signature
   from Base64 as described in Section 3.2 to give the http message
   signature to be verified ("S").  The results of the verification
   function are compared to the http message signature to determine if
   the signature presented is valid.

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] to signer's private
   signing key ("K") and the signature input string ("M") Section 2.5.
   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 ("S") is Base64-encoded as
   described in Section 3.1.  The resulting encoded value is the HTTP
   message signature output.






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   To verify using this algorithm, the verifier applies the "RSASSA-
   PKCS1-V1_5-VERIFY ((n, e), M, S)" function [RFC8017] using the public
   key material ("(n, e)").  The verifier re-creates the signature input
   string ("M") from the received message, as defined in Section 2.5.
   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 decodes the HTTP message signature
   from Base64 as described in Section 3.2 to give the http message
   signature to be verified ("S").  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 2.5.  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 signed content is Base64-encoded as
   described in Section 3.1.  The resulting encoded value is the HTTP
   message signature output.

   For verification, the verifier decodes the HTTP message signature
   from Base64 as described in Section 3.2 to give the signature to be
   compared to the output of the HMAC function.  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 signer's private signing
   key and the signature input string Section 2.5.  The hash function
   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 is Base64-encoded as described in
   Section 3.1.  The resulting encoded value is the HTTP message
   signature output.

   To verify using this algorithm, the verifier applies the "ECDSA"
   algorithm [FIPS186-4] using the public key material.  The verifier
   re-creates the signature input string defined in Section 2.5.  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 decodes the HTTP message signature
   from Base64 as described in Section 3.2 to give the signature to be



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   verified.  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.

   For both signing and verification, the HTTP messages signature input
   string Section 2.5 is used as the entire "JWS Signing Input".  The
   JWS Header defined in [RFC7517] is not used, nor is the input string
   first encoded in Base64 before applying the algorithm.

   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 header fields, both defined
   within this specification.  The "Signature" HTTP header field
   contains signature values, while the "Signature-Input" HTTP header
   field identifies the Covered Content and metadata that describe how
   each signature was generated.

4.1.  The 'Signature-Input' HTTP Header

   The "Signature-Input" HTTP header field is a Dictionary Structured
   Header [RFC8941] containing the metadata for zero or more message
   signatures generated from content 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 content including all signature metadata parameters,
   using the serialization process defined in Section 2.4.2.

  # NOTE: '\' line wrapping per RFC 8792
  Signature-Input: sig1=("@request-target" "host" "date"
      "cache-control" "x-empty-header" "x-example"); keyid="test-key-a";
      alg="rsa-pss-sha512"; created=1402170695; expires=1402170995

   To facilitate signature validation, the "Signature-Input" header MUST
   contain the same serialization value used in generating the signature
   input.




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4.2.  The 'Signature' HTTP Header

   The "Signature" HTTP header field is a Dictionary Structured Header
   [RFC8941] containing zero or more message signatures generated from
   content within the HTTP message.  Each member's name is a signature
   identifier that is present as a member name in the "Signature-Input"
   Structured Header 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 header field that does not have a corresponding
   member in the HTTP message's "Signature-Input" HTTP header field MUST
   be ignored.

  # NOTE: '\' line wrapping per RFC 8792
  Signature: sig1=:K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUe\
      Zx/Kdrq32DrfakQ6bPsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibe\
      oHyqU/yCjphSmEdd7WD+zrchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4\
      CaB8X/I5/+HLZLGvDiezqi6/7p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg\
      1Q7MpWYZs0soHjttq0uLIA3DIbQfLiIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZg\
      FquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==:

4.3.  Examples

   The following is a non-normative example of "Signature-Input" and
   "Signature" HTTP header fields representing the signature in
   Figure 2:

   # NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@request-target" "host" "date"
       "cache-control" "x-empty-header" "x-example"); keyid="test-key-a";
       alg="rsa-pss-sha512"; created=1402170695; expires=1402170995
   Signature: sig1=:K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUe\
       Zx/Kdrq32DrfakQ6bPsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibe\
       oHyqU/yCjphSmEdd7WD+zrchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4\
       CaB8X/I5/+HLZLGvDiezqi6/7p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg\
       1Q7MpWYZs0soHjttq0uLIA3DIbQfLiIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZg\
       FquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==:













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   Since "Signature-Input" and "Signature" are both defined as
   Dictionary Structured Headers, they can be used to easily include
   multiple signatures within the same HTTP message.  For example, a
   signer may include multiple signatures signing the same content with
   different keys and/or algorithms to support verifiers with different
   capabilities, or a reverse proxy may include information about the
   client in header fields when forwarding the request to a service
   host, and may also include a signature over those fields and the
   client's signature.  The following is a non-normative example of
   header fields a reverse proxy might add to a forwarded request that
   contains the signature in the above example:

   # NOTE: '\' line wrapping per RFC 8792

   X-Forwarded-For: 192.0.2.123
   Signature-Input: reverse_proxy_sig=("host" "date"
       "signature";key=sig1 "x-forwarded-for"); keyid="test-key-a";
       alg="rsa-pss-sha512"; created=1402170695; expires=1402170695
   Signature: reverse_proxy_sig=:ON3HsnvuoTlX41xfcGWaOEVo1M3bJDRBOp0Pc/O\
       jAOWKQn0VMY0SvMMWXS7xG+xYVa152rRVAo6nMV7FS3rv0rR5MzXL8FCQ2A35DCEN\
       LOhEgj/S1IstEAEFsKmE9Bs7McBsCtJwQ3hMqdtFenkDffSoHOZOInkTYGafkoy78\
       l1VZvmb3Y4yf7McJwAvk2R3gwKRWiiRCw448Nt7JTWzhvEwbh7bN2swc/v3NJbg/w\
       JYyYVbelZx4IywuZnYFxgPl/qvqbAjeEVvaLKLgSMr11y+uzxCHoMnDUnTYhMrmOT\
       4O8lBLfRFOcoJPKBdoKg9U0a96U2mUug1bFOozEVYFg==:

5.  IANA Considerations

5.1.  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 5.1.2.  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 5.1.1.

5.1.1.  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:




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      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.

5.1.2.  Initial Contents

5.1.2.1.  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

5.1.2.2.  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

5.1.2.3.  hmac-sha256

   Algorithm Name:



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      "hmac-sha256"

   Status:
      Active

   Description:
      HMAC using SHA-256

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

5.1.2.4.  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

5.2.  HTTP Signature Metadata Parameters Registry

   This document defines the "Signature-Input" Structured Header, whose
   member values 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-Input" Structured Header.  Initial values for this
   registry are given in Section 5.2.2.  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 5.2.1.

5.2.1.  Registration Template

5.2.2.  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.






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           +=========+========+================================+
           | Name    | Status | Reference(s)                   |
           +=========+========+================================+
           | alg     | Active | Section 2.4.2 of this document |
           +---------+--------+--------------------------------+
           | created | Active | Section 2.4.2 of this document |
           +---------+--------+--------------------------------+
           | expires | Active | Section 2.4.2 of this document |
           +---------+--------+--------------------------------+
           | keyid   | Active | Section 2.4.2 of this document |
           +---------+--------+--------------------------------+

              Table 7: Initial contents of the HTTP Signature
                       Metadata Parameters Registry.

5.3.  HTTP Signature Specialty Content Identifiers Registry

   This document defines a method for canonicalizing HTTP message
   content, including content that can be generated from the context of
   the HTTP message outside of the HTTP headers.  This content is
   identified by a unique key.  IANA is asked to create and maintain a
   new registry typed "HTTP Signature Specialty Content Identifiers" to
   record and maintain the set of non-header content identifiers and
   their canonicalization method.  Initial values for this registry are
   given in Section 5.3.2.  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 5.3.1.

5.3.1.  Registration Template

5.3.2.  Initial Contents

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

      +===================+========+================================+
      | Name              | Status | Reference(s)                   |
      +===================+========+================================+
      | @request-target   | Active | Section 2.4.1 of this document |
      +-------------------+--------+--------------------------------+
      | @signature-params | Active | Section 2.4.2 of this document |
      +-------------------+--------+--------------------------------+

         Table 8: Initial contents of the HTTP Signature Specialty
                       Content Identifiers Registry.





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6.  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
   content needs to be signed for a given use case. ))

   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].

7.  References

7.1.  Normative References

   [FIPS186-4]
              "Digital Signature Standard (DSS)", 2013,
              <https://csrc.nist.gov/publications/detail/fips/186/4/
              final>.

   [HTTP2]    Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7540>.

   [MESSAGING]
              Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7230>.

   [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>.




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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/rfc/rfc8792>.

   [RFC8941]  Nottingham, M. and P-H. Kamp, "Structured Field Values for
              HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
              <https://www.rfc-editor.org/rfc/rfc8941>.

   [SEMANTICS]
              Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7231>.

7.2.  Informative References

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

   [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"
   header used within this specification.  It is recommended that
   developers wishing to support both this specification and other
   historial drafts do so carefully and deliberately, as
   incompatibilities between this specification and various versions of
   other drafts could lead to problems.

   It is recommended that implementers first detect and validate the
   "Signature-Input" header defined in this specification to detect that
   this standard is in use and not an alternative.  If the "Signature-
   Input" header is present, all "Signature" headers 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.

B.1.1.  Example Key RSA test

   The following key is a 2048-bit RSA public and private key pair:










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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.2.  Example keyid Values

   The table below maps example "keyid" values to associated algorithms
   and/or keys.  These are example mappings that are valid only within
   the context of examples in examples within this and future documents
   that reference this section.  Unless otherwise specified, within the
   context of examples it should be assumed that the signer and verifier
   understand these "keyid" mappings.  These "keyid" values are not
   reserved, and deployments are free to use them, with these
   associations or others.




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        +============+=================+==========================+
        | keyid      | Algorithm       | Verification Key         |
        +============+=================+==========================+
        | test-key-a | rsa-pss-sha512  | The public key specified |
        |            |                 | in Appendix B.1.1        |
        +------------+-----------------+--------------------------+
        | test-key-b | rsa-v1_5-sha256 | The public key specified |
        |            |                 | in Appendix B.1.1        |
        +------------+-----------------+--------------------------+

                                  Table 9

B.3.  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 message:

   POST /foo?param=value&pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 07 Jun 2014 20:51:35 GMT
   Content-Type: application/json
   Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   Content-Length: 18

   {"hello": "world"}

B.3.1.  Signature Verification

B.3.1.1.  Minimal Signature Header using rsa-pss-sha512

   This presents a minimal "Signature-Input" and "Signature" header for
   a signature using the "rsa-pss-sha512" algorithm:

   # NOTE: '\' line wrapping per RFC 8792

   Signature: sig1=("date"); alg="rsa-pss-sha512"; keyid="test-key-b"
   Signature: sig1=:HtXycCl97RBVkZi66ADKnC9c5eSSlb57GnQ4KFqNZplOpNfxqk62\
       JzZ484jXgLvoOTRaKfR4hwyxlcyb+BWkVasApQovBSdit9Ml/YmN2IvJDPncrlhPD\
       VDv36Z9/DiSO+RNHD7iLXugdXo1+MGRimW1RmYdenl/ITeb7rjfLZ4b9VNnLFtVWw\
       rjhAiwIqeLjodVImzVc5srrk19HMZNuUejK6I3/MyN3+3U8tIRW4LWzx6ZgGZUaEE\
       P0aBlBkt7Fj0Tt5/P5HNW/Sa/m8smxbOHnwzAJDa10PyjzdIbywlnWIIWtZKPPsoV\
       oKVopUWEU3TNhpWmaVhFrUL/O6SN3w==:

   The corresponding signature metadata derived from this header field
   is:





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         +===========================+==========================+
         | Property                  | Value                    |
         +===========================+==========================+
         | Algorithm                 | rsa-pss-sha512           |
         +---------------------------+--------------------------+
         | Covered Content           | date                     |
         +---------------------------+--------------------------+
         | Creation Time             | Undefined                |
         +---------------------------+--------------------------+
         | Expiration Time           | Undefined                |
         +---------------------------+--------------------------+
         | Verification Key Material | The public key specified |
         |                           | in Appendix B.1.1.       |
         +---------------------------+--------------------------+

                                 Table 10

   The corresponding Signature Input is:

 "date": Tue, 07 Jun 2014 20:51:35 GMT
 "@signature-params": ("date"); alg="rsa-pss-sha512"; keyid="test-key-b"

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 editor would also like to thank the following individuals for
   feedback on and implementations of the draft-cavage-http-signatures
   draft (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, James H.
   Manger, Ilari Liusvaara, 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

      -  -03




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         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

         o  Strengthened requirement for content identifiers for header
            fields to be lower-case (changed from SHOULD to MUST).




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         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.

         o  Added IANA HTTP Signature Parameter registry.




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         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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