HTTP                                                     A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                               J. Richer
Expires: 21 May 16 September 2021                           Bespoke Engineering
                                                               M. Sporny
                                                          Digital Bazaar
                                                        17 November 2020
                                                           15 March 2021

                         Signing HTTP Messages
                draft-ietf-httpbis-message-signatures-01
                draft-ietf-httpbis-message-signatures-02

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_

   This work was originally based

   Discussion of this draft takes place on draft-cavage-http-signatures-12,
   but has since diverged from it, to reflect discussion since adoption
   by the HTTP Working Group.  In particular, it addresses issues that
   have been identified, and adds features to support new use cases.  It working group
   mailing list (ietf-http-wg@w3.org), which is a work-in-progress 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 not yet suitable issues list for deployment. 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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 May 16 September 2021.

Copyright Notice

   Copyright (c) 2020 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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   3
     1.1.  Requirements Discussion . . . . . . . . . . . . . . . . .   5   4
     1.2.  HTTP Message Transformations  . . . . . . . . . . . . . .   5
     1.3.  Safe Transformations  . . . . . . . . . . . . . . . . . .   6   5
     1.4.  Conventions and Terminology . . . . . . . . . . . . . . .   6
     1.5.  Application of HTTP Message Signatures  . . . . . . . . .   7
   2.  Identifying and Canonicalizing Content  . . . . . . . . . . .   8
     2.1.  HTTP Header Fields Headers  . . . . . . . . . . . . . . . . . . . . . .   8
       2.1.1.  Canonicalized Structured HTTP Headers . . . . . . . .   9
       2.1.2.  Canonicalization Examples . . . . . . . . . . . . . .   9
     2.2.  Dictionary Structured Field Members . . . . . . . . . . .   9  10
       2.2.1.  Canonicalization Examples . . . . . . . . . . . . . .  10
     2.3.  List Prefixes . . . . . . . . . . . . . . . . . . . . . .  10  11
       2.3.1.  Canonicalization Examples . . . . . . . . . . . . . .  10
     2.4.  Signature Creation Time . . . . . . . . . . . . . . . . .  11
     2.5.  Signature Expiration Time
     2.4.  Specialty Content Fields  . . . . . . . . . . . . . . . .  11
     2.6.  12
       2.4.1.  Request Target Endpoint  . . . . . . . . . . . . . . . . . . .  12
       2.4.2.  Signature Parameters  . .  11
       2.6.1.  Canonicalization Examples . . . . . . . . . . . . . .  12  13
   3.  HTTP Message Signatures . . . . . . . . . . . . . . . . . . .  12  14
     3.1.  Signature Metadata  . . . . . . . . . . . . . . . . . . .  13  14
     3.2.  Creating a Signature  . . . . . . . . . . . . . . . . . .  13  16
       3.2.1.  Choose and Set Signature Metadata Properties  . . . .  14  16
       3.2.2.  Create the Signature Input  . . . . . . . . . . . . .  16  18
       3.2.3.  Sign the Signature Input  . . . . . . . . . . . . . .  17  19
     3.3.  Verifying a Signature . . . . . . . . . . . . . . . . . .  17  19
       3.3.1.  Enforcing Application Requirements  . . . . . . . . .  18  20

   4.  Including a Message Signature in a Message  . . . . . . . . .  19  21
     4.1.  The 'Signature-Input' HTTP Header . . . . . . . . . . . .  19
       4.1.1.  Metadata Parameters . . . . . . . . . . . . . . . . .  19  21
     4.2.  The 'Signature' HTTP Header . . . . . . . . . . . . . . .  20  21
     4.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  20  22
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21  23
     5.1.  HTTP Signature Algorithms Registry  . . . . . . . . . . .  21  23
       5.1.1.  Registration Template . . . . . . . . . . . . . . . .  21  23
       5.1.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  22  24
     5.2.  HTTP Signature Metadata Parameters Registry . . . . . . .  24  25
       5.2.1.  Registration Template . . . . . . . . . . . . . . . .  24  25
       5.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  24
   6.  Security Considerations  25
     5.3.  HTTP Signature Specialty Content Identifiers Registry . .  26
       5.3.1.  Registration Template . . . . . . . . . . . . . . . .  26
       5.3.2.  Initial Contents  .  25
   7.  References . . . . . . . . . . . . . . . . .  26
   6.  Security Considerations . . . . . . . .  25
     7.1.  Normative References . . . . . . . . . . .  27
   7.  References  . . . . . . .  25
     7.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Examples .  27
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     7.2.  Informative References  . . .  27
     A.1.  Example Keys . . . . . . . . . . . . . . . . . . . . . .  27
       A.1.1.  Example Key RSA test  . . . . . . . . . . . . . . . .  27
     A.2.  Example keyId Values  . . . . . . . . . . . . . . . . . .  28
     A.3.  Test Cases  . . . . . . . . . . . . . . . . . . . . . . .  29
       A.3.1.  Signature Generation  . . . . . . .  28
   Appendix A.  Detecting HTTP Message Signatures  . . . . . . . . .  29
       A.3.2.  Signature Verification  . . . . . . . . . . . . . . .  32
   Appendix B.  Topics for Working Group Discussion  . . . . . . . .  34
     B.1.  Issues  . . . . . . .  Examples . . . . . . . . . . . . . . . . . .  34
       B.1.1.  Confusing guidance on algorithm and key
               identification . . . .  29
     B.1.  Example Keys  . . . . . . . . . . . . . . .  35
       B.1.2.  Lack of definition of keyId hurts interoperability .  35
       B.1.3.  Algorithm Registry duplicates work of JWA . . . . . .  35
       B.1.4.  Algorithm Registry should not be initialized with
               deprecated entries  29
       B.1.1.  Example Key RSA test  . . . . . . . . . . . . . . . .  29
     B.2.  Example keyid Values  .  36
       B.1.5.  No percent-encoding normalization of path/query . . .  36
       B.1.6.  Misleading name for headers parameter . . . . . . . .  36
       B.1.7.  Changes to whitespace in header field values break
               verification . . . . . .  30
     B.3.  Test Cases  . . . . . . . . . . . . . .  36
       B.1.8.  Multiple Set-Cookie headers are not well supported .  36
       B.1.9.  Covered Content list is not signed . . . . . . . .  31
       B.3.1.  Signature Generation  .  37
       B.1.10. Algorithm is not signed . . . . . . . . . . . . . . .  37
       B.1.11.  31
       B.3.2.  Signature Verification key identifier is not signed . . . . . .  37
       B.1.12. Max values, precision for Integer String and Decimal
               String not defined  . . . . . . . . . . . . . . .  34
   Acknowledgements  . .  37
       B.1.13. keyId parameter value could break list syntax . . . .  37
       B.1.14. Creation Time and Expiration Time do not allow for
               clock skew . . . . . . . . . . . . . . . . . .  36
   Document History  . . .  37
       B.1.15. Should require lowercased header field names as
               identifiers . . . . . . . . . . . . . . . . . . . . .  37
       B.1.16. Reconcile Date header and Creation Time . . .
   Authors' Addresses  . . . .  38
       B.1.17. Remove algorithm-specific rules for content
               identifiers . . . . . . . . . . . . . . . . . . . . .  38
       B.1.18. Add guidance for signing compressed headers . . . . .  38
       B.1.19. Transformations to Via header field value break
               verification  . . . . . . . . . . . . . . . . . . . .  38
       B.1.20. Case changes to case-insensitive header field values
               break verification  . . . . . . . . . . . . . . . . .  38
       B.1.21. Need more examples for Signature header . . . . . . .  38
       B.1.22. Expiration not needed . . . . . . . . . . . . . . . .  39

     B.2.  Features  . . . . . . . . . . . . . . . . . . . . . . . .  39
       B.2.1.  Define more content identifiers . . . . . . . . . . .  39
       B.2.2.  Multiple signature support  . . . . . . . . . . . . .  39
       B.2.3.  Support for incremental signing of header field value
               list items  . . . . . . . . . . . . . . . . . . . . .  40
       B.2.4.  Support expected authority changes  . . . . . . . . .  40
       B.2.5.  Support for signing specific cookies  . . . . . . . .  40
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  41
   Document History  . . . . . . . . . . . . . . . . . . . . . . . .  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  43

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 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 oringally 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.

   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.

   *  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"  39

1.  Introduction

   Message integrity and "Host" header field authenticity are important security properties
   that when
      applied together do not result in a change are critical to the message's
      effective request URI, as defined in Section 5.5 secure operation of [MESSAGING].

   Additionally, all changes to content not covered by many HTTP applications.
   Application developers typically rely on 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 transport layer to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and
   provide these properties, by operating their application over [TLS].
   However, TLS 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", guarantees these properties over a single TLS
   connection, 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 path between client and keyed MACs.  Similarly, the
   verb "sign" refers to application may be
   composed of multiple independent TLS connections (for example, if the generation of either
   application is hosted behind a digital signature TLS-terminating gateway or
   keyed MAC over if the
   client is behind a given input string.  The qualified term "digital
   signature" refers specifically 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 output binding of an asymmetric
   cryptographic signing operation.

   In addition application-
   level key to those listed above, this document uses the following
   terms:

   Decimal String

      An Integer String optionally concatenated with a period "."
      followed by a second Integer String, representing a positive real
      number expressed HTTP message, separate from any TLS certificates in base 10.  The first Integer String represents
      the integral portion of the number,
   use.  Consequently, while the optional second
      Integer String represents the fractional portion of the number.
      (( Editor's note: There's got to be a definition for this that we TLS can reference. ))

   Integer String

      A US-ASCII string of one or more digits "0-9", representing meet message integrity and
   authenticity needs for many HTTP-based applications, it is not a
      positive integer in base 10. (( Editor's note: There's got to be
   universal solution.

   This document defines a
      definition mechanism for this that we can reference. ))

   Signer

      The entity that is generating or has generated providing end-to-end integrity
   and authenticity for content within an HTTP Message
      Signature.

   Verifier
      An entity message.  The mechanism
   allows applications to create digital signatures or message
   authentication codes (MACs) over only that content within the message
   that is verifying or has verified an HTTP Message
      Signature against an HTTP Message.  Note meaningful and appropriate for the application.  Strict
   canonicalization rules ensure that an HTTP Message
      Signature may be verified multiple times, potentially the verifier can verify the
   signature even if the message has been transformed in any of the many
   ways permitted by different
      entities.

   This HTTP.

   The mechanism described in this document contains non-normative examples consists of partial three parts:

   *  A common nomenclature and complete canonicalization rule set for the
      different protocol elements and other content within HTTP
      messages.  To improve readability, header fields may be split
   into multiple lines,

   *  Algorithms for generating and verifying signatures over HTTP
      message content using the "obs-fold" syntax.  This syntax is
   deprecated in [MESSAGING], this nomenclature and senders MUST NOT generate messages
   that include it.

2.  Identifying rule set.

   *  A mechanism for attaching a signature and Canonicalizing Content

   In order related metadata to allow signers an
      HTTP message.

1.1.  Requirements Discussion

   HTTP permits and verifiers sometimes requires intermediaries to establish which content transform
   messages in a variety of ways.  This may result in a recipient
   receiving a message that is
   covered by not bitwise equivalent to the message
   that was oringally sent.  In such a case, the recipient will be
   unable to verify a signature, this document defines content identifiers for signature metadata over the raw bytes of the sender's HTTP
   message, as verifying digital signatures or MACs requires both signer
   and discrete pieces verifier to have the exact same signed content.  Since the raw
   bytes of the message content that may cannot be
   covered by an HTTP Message Signature.

   Some relied upon as signed content, the
   signer and verifier must derive the signed content within HTTP messages may undergo transformations that
   change from their
   respective versions of the message, via a mechanism that is resilient
   to safe changes that do not alter the bitwise value without altering meaning of the content (for
   example, the merging together message.

   For a variety of header fields with the same name).
   Message content must therefore be canonicalized before reasons, it is signed, impractical to ensure that strictly define what
   constitutes a signature can be verified despite such innocuous
   transformations.  This document defines rules for each content
   identifier that transform the identifier's associated content into
   such safe change versus an unsafe one.  Applications use
   HTTP in a canonical form.

   The following sections define content identifiers, their associated
   content, wide variety of ways, and their canonicalization rules.

2.1.  HTTP Header Fields

   An HTTP may disagree on whether a
   particular piece of information in a message (e.g., the body, or the
   "Date" header field field) is identified by 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 relevant.  Thus a general purpose solution
   must provide signers with some degree of control over which message
   content identifiers.

   An HTTP header field value is canonicalized signed.

   HTTP applications may be running in environments that do not provide
   complete access to or control over HTTP messages (such as follows:

   1.  Create an ordered list of a web
   browser's JavaScript environment), or may be using libraries that
   abstract away the field values of each instance details of the header field in the message, in protocol (such as the order that they occur (or
       will occur) in 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.

   2.  Strip leading

1.2.  HTTP Message Transformations

   As mentioned earlier, HTTP explicitly permits and trailing whitespace from each item in the list.

   3.  Concatenate the list items together, with some cases
   requires implementations to transform messages in a comma "," and space "
       " between each item.  The resulting string variety of ways.
   Implementations are required to tolerate many of these
   transformations.  What follows is the canonicalized
       value.

2.1.1.  Canonicalization Examples

   This section contains a 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

   The following table shows example canonicalized values for header
   fields, given non-exhaustive
   list of transformations 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 may occur under HTTP, provided as
   context:

   *  Re-ordering of header fields with different header field
                            canonicalization.

2.2.  Dictionary Structured Field Members

   An individual member in names
      ([MESSAGING], Section 3.2.2).

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

   *  Removal of a Dictionary Structured Field is
   identified by header fields listed in the lowercased "Connection" header field name, followed by
      ([MESSAGING], Section 6.1).

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

   *  Addition or removal of a semicolon
   "":"", followed by the member name.  An individual member in 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
   value definition of a Dictionary Structured Field is canonicalized by applying HTTP and the serialization algorithm requirements described in Section 4.1.2 above,
   we can identify certain types of
   [StructuredFields] on a Dictionary containing only transformations that member.

2.2.1.  Canonicalization Examples

   This section contains non-normative examples of canonicalized values
   for Dictionary Structured Field Members given should not
   prevent signature verification, even when performed on content
   covered by 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) signature.  The following table shows example canonicalized values for different
   content identifiers, given that field:

               +====================+=====================+
               | Content Identifier | Canonicalized Value |
               +====================+=====================+
               | x-dictionary:a     | 1                   |
               +--------------------+---------------------+
               | x-dictionary:b     | 2;x=1;y=2           |
               +--------------------+---------------------+
               | x-dictionary:c     | (a, b, c)           |
               +--------------------+---------------------+

                    Table 2: Non-normative examples list describes those
   transformations:

   *  Combination of
                   Dictionary member canonicalization.

2.3.  List Prefixes

   A prefix header fields with the same field name.

   *  Reordering of a List Structured Field consisting header fields with different names.

   *  Conversion between different versions of the first N members HTTP protocol (e.g.,
      HTTP/1.x to HTTP/2, or vice-versa).

   *  Changes in the field's value (where N is an integer greater than 0 and less
   than casing (e.g., "Origin" to "origin") of any case-
      insensitive content such as header field names, request URI
      scheme, or equal host.

   *  Addition or removal of leading or trailing whitespace to the number a header
      field value.

   *  Addition or removal of members in the List) is identified by "obs-folds".

   *  Changes to the lowercased "request-target" and "Host" header field name, followed by that when
      applied together do not result in a semicolon "":"", followed by
   N expressed as an Integer String.  A list prefix is canonicalized by
   applying change to the serialization algorithm described message's
      effective request URI, as defined in Section 4.1.1 5.5 of
   [StructuredFields] on a List containing only [MESSAGING].

   Additionally, all changes to content not covered by the first N members as
   specified 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 the list prefix, this document are to be interpreted as described in the order
   BCP 14 [RFC2119] [RFC8174] when, and only when, 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:

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

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

2.4.  Signature Creation Time

   The signature's Creation Time (Section 3.1) is identified by the
   "*created" identifier.

   Its canonicalized value is an Integer String containing the
   signature's Creation Time expressed all
   capitals, as the number of seconds since
   the Epoch, 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 Section 4.16
   (https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
   V1_chap04.html#tag_04_16) of [POSIX.1].

      The use of seconds since the Epoch to canonicalize a timestamp
      simplifies processing and avoids timezone management required by
      specifications such as [RFC3339].

2.5.  Signature Expiration Time [MESSAGING].

   The signature's Expiration Time (Section 3.1) is identified by the
   "*expires" identifier.

   Its canonicalized value term "method" is a Decimal String containing the
   signature's Expiration Time expressed as the number of seconds since
   the Epoch, to be interpreted as defined in Section 4.16
   (https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
   V1_chap04.html#tag_04_16) of [POSIX.1].

2.6.  Target Endpoint

   The request target endpoint, consisting of the request method and the
   path and query 4 of
   [SEMANTICS].

   For brevity, the effective request URI, is identified by the
   "*request-target" identifier.

   Its value term "signature" on its own is canonicalized as follows:

   1.  Take the lowercased HTTP method of the message.

   2.  Append a space " ".

   3.  Append the path used in this document
   to refer to both digital signatures and query of the request target of keyed MACs.  Similarly, the message,
       formatted according
   verb "sign" refers to the rules defined for the :path pseudo-
       header in [HTTP2], Section 8.1.2.3.  The resulting string is the
       canonicalized value.

2.6.1.  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 generation of "*request-target"
                             canonicalization.

3.  HTTP Message Signatures

   An HTTP Message Signature is either a digital signature or
   keyed MAC over a string generated from
   a subset of the content in an HTTP message and metadata about given input string.  The qualified term "digital
   signature" refers specifically to the
   signature itself.  When successfully verified against output of an HTTP
   message, it provides asymmetric
   cryptographic proof that with respect signing operation.

   In addition to those listed above, this document uses the
   subset of content following
   terms:

   Signer:
      The entity that was signed, the message is semantically
   equivalent to the message for which the signature was generated.

3.1.  Signature Metadata generating or has generated an HTTP Message Signatures have metadata properties that provide
   information regarding the signature's generation and/or verification.
   The following metadata properties are defined:

   Algorithm
      Signature.

   Verifier:
      An entity that is verifying or has verified an HTTP Message
      Signature Algorithm defined in the against an HTTP Message.  Note that an HTTP Message
      Signature
      Algorithms Registry may be verified multiple times, potentially by different
      entities.

   The term "Unix time" is defined in this document.  It describes the
      signing 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 verification algorithms for the signature.

   Creation Time

      A timestamp representing complete
   HTTP messages.  To improve readability, header fields may be split
   into multiple lines, using the point "obs-fold" syntax.  This syntax is
   deprecated in time [MESSAGING], and senders MUST NOT generate messages
   that the signature was
      generated.  Sub-second precision is not supported.  A signature's
      Creation Time MAY be undefined, indicating include it.

   Additionally, some examples use '\' line wrapping for long values
   that it is unknown.

   Covered Content

      An ordered list 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 indicates
      the metadata are expected and message content
      required.  For example, an authorization protocol would mandate
      that is the "Authorization" header be covered by to protect the
      authorization credentials, as well as a "*created" field to allow
      replay detection.

   *  A means of retrieving the key material used to verify the
      signature.
      The order  An application will usually use the "keyid" field of identifiers in this list affects signature generation
      and verification,
      the "Signature-Input" header value and therefore MUST be preserved.

   Expiration Time define rules for resolving
      a key from there.

   *  A timestamp representing the point in time at which means of determining the signature
      expires.  An expired algorithm used to verify the
      signature always fails verification. content is appropriate for the key material.

   *  A
      signature's Expiration Time MAY be undefined, indicating means of determining that the
      signature does not expire.

   Verification Key Material

      The a given key material required to verify and algorithm presented in
      the signature.

3.2.  Creating request are appropriate for the request being made.  For
      example, a Signature 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.  Identifying and Canonicalizing Content

   In order to create 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.

   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, 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 signer completes 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 following
   process:

   1.  Choose key material and algorithm, and set metadata properties
       Section 3.2.1

   2.  Create "parameters" rule.

   content-identifier = sf-string parameters

   Note that this means the Signature Input Section 3.2.2

   3.  Sign value of the Signature Input Section 3.2.3 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 describe each of these steps in detail.

3.2.1.  Choose define content identifier types, their
   parameters, their associated content, and Set Signature Metadata Properties

   1. their canonicalization
   rules.

2.1.  HTTP Headers

   The signer chooses content identifier for an HTTP Signature Algorithm from those
       registered in header is the lowercased form of
   its header field name.  While HTTP Signature Algorithms Registry defined 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
       this document, additional parameters and sets rules, the signature's Algorithm property to
       that value.  The signer HTTP header
   field value MUST NOT choose an algorithm marked
       "Deprecated".  The mechanism by which be canonicalized with the signer chooses following steps:

   1.  Create an
       algorithm is out ordered list of scope for this document. 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.  The signer chooses key material to use for signing and
       verification,  Strip leading and sets trailing whitespace from each item in the signature's Verification Key Material
       property to list.

   3.  Concatenate the key material required for verification. list items together, with a comma "," and space "
       " between each item.

   The
       signer MUST choose key material that resulting string is appropriate for the
       signature's Algorithm, and that conforms to any requirements
       defined by canonicalized value.

2.1.1.  Canonicalized Structured HTTP Headers

   If value of the Algorithm, such as key size or format.  The
       mechanism by which the signer chooses key material HTTP header in question is out of
       scope for a structured field
   [RFC8941], the content identifier MAY include the "sf" parameter.  If
   this document.

   3.  The signer sets parameter is included, the signature's Creation Time property to HTTP header value MUST be
   canonicalized using the
       current time. rules specified in [RFC8941] section 4.  Note
   that this process will replace any optional whitespace with a single
   space.

   The signer sets the signature's Expiration Time property to the
       time at which the signature resulting string is to expire, or to undefined if used as the
       signature will not expire.

   5. 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

   The signer creates an ordered list 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 content identifiers
       representing header field
                            canonicalization.

2.2.  Dictionary Structured Field Members

   An individual member in the message content and signature metadata to be
       covered value of a Dictionary Structured Field is
   identified by using the signature, and assigns this list as parameter "key" on the
       signature's Covered Content.

       *  Each content identifier MUST be one for
   the header.  The value of those defined in Section 2.

       *  This list MUST NOT be empty, as this would result in creating parameter is a signature over the empty string.

       *  If the signature's Algorithm name does not start with rsa,
          hmac, or ecdsa, signers SHOULD include "*created" and
          "*request-target" key being
   identified, without any parameters present on that key in the list.

       *  If the signature's Algorithm starts with rsa, hmac, or ecdsa,
          signers SHOULD include "date" and "*request-target"
   original dictionary.

   An individual member in the
          list.

       *  Further guidance on what to include in this list and in what
          order is out value of scope for this document.  However, the list
          order a Dictionary Structured Field is significant and once established for
   canonicalized by applying the serialization algorithm described in
   Section 4.1.2 of [RFC8941] on a given
          signature it MUST be preserved for Dictionary containing only that signature.

   For example,
   member.

2.2.1.  Canonicalization Examples

   This section contains non-normative examples of canonicalized values
   for Dictionary Structured Field Members 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: example
   header field, whose value is assumed to be a Dictionary:

   X-Dictionary:  a=1, b=2
   X-List: (a, b, c, d)
   Cache-Control: max-age=60
   Cache-Control: must-revalidate b=2;x=1;y=2, c=(a b c)

   The following table presents a non-normative shows example of metadata canonicalized values for different
   content identifiers, given that a signer may choose:

     +==============+================================================+
     | Property     | Value                                          |
     +==============+================================================+
     | Algorithm    | hs2019                                         |
     +--------------+------------------------------------------------+
     | Covered      | "*request-target", "*created", "host", "date", | field:

              +======================+=====================+
              | Content Identifier   | "cache-contol", "x-emptyheader", "x-example",  |
     |              | "x-dictionary:b", "x-dictionary:a", "x-list:3" |
     +--------------+------------------------------------------------+
     | Creation     | 1402174295                                     |
     | Time         |                                                |
     +--------------+------------------------------------------------+
     | Expiration   | 1402174595 Canonicalized Value |
              +======================+=====================+
              | Time "x-dictionary";key=a | 1                   |
     +--------------+------------------------------------------------+
              +----------------------+---------------------+
              | Verification "x-dictionary";key=b | The public key provided in Appendix A.1.1 and 2;x=1;y=2           |
              +----------------------+---------------------+
              | Key Material "x-dictionary";key=c | identified by the "keyId" value "test-key-a". (a, b, c)           |
     +--------------+------------------------------------------------+
              +----------------------+---------------------+

                    Table 5: 2: Non-normative example metadata values

3.2.2.  Create the Signature Input

   The Signature Input is a US-ASCII string containing the content that
   will be signed.  To create it, the signer concatenates together
   entries for each identifier in the signature's Covered Content in the
   order it occurs in the list, with each entry separated by a newline
   ""\n"".  An identifier's entry is examples of
                   Dictionary member canonicalization.

2.3.  List Prefixes

   A prefix of a US-ASCII string List Structured Field consisting of the
   lowercased identifier followed with a colon "":"", a space "" "", and first N members
   in the identifier's canonicalized field's value (described below).

   If Covered Content contains "*created" and the signature's Creation
   Time is undefined or the signature's Algorithm name starts with
   "rsa", "hmac", or "ecdsa" an implementation MUST produce an error.

   If Covered Content contains "*expires" and the signature does not
   have an Expiration Time or the signature's Algorithm name starts with
   "rsa", "hmac", or "ecdsa" an implementation MUST produce an error.

   If Covered Content contains an identifier for a header field that (where N is
   not present an integer greater than 0 and less
   than or malformed in the message, equal to the implementation MUST
   produce an error.

   If Covered Content contains an identifier for a Dictionary member
   that references a header field that is not present, is malformed number of members in the message, or List) is not a Dictionary Structured Field, identified by
   the
   implementation MUST produce an error.  If parameter "prefix" with the header field value does
   not contain the specified member, the implementation MUST produce an
   error.

   If Covered Content contains of N as an identifier for a List Prefix that
   references a header field that is not present, integer.

   A list prefix value is malformed in canonicalized by applying the
   message, or is not serialization
   algorithm described in Section 4.1.1 of [RFC8941] on a List Structured Field, the implementation MUST
   produce an error.  If the header field value contains fewer than
   containing only the first N members as specified number of members, in the implementation MUST produce an
   error.

   For list prefix,
   in the non-normative example Signature metadata order they appear in Table 5, the
   corresponding Signature Input is:

   *request-target: get /foo
   *created: 1402170695
   host: example.org
   date: Tue, 07 Jun 2014 20:51:35 GMT
   cache-control: max-age=60, must-revalidate
   x-emptyheader:
   x-example: Example original List.

2.3.1.  Canonicalization Examples

   This section contains non-normative examples of canonicalized values
   for list prefixes given the following example header with some whitespace.
   x-dictionary: b=2
   x-dictionary: a=1
   x-list: 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:

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

              Figure 1:           |
               +---------------------+---------------------+
               | "x-list-a";prefix=6 | (a, b, c, d, e, f)  |
               +---------------------+---------------------+
               | "x-list-b";prefix=0 | ()                  |
               +---------------------+---------------------+

                  Table 3: Non-normative example Signature Input

3.2.3.  Sign the Signature Input

   The signer signs the Signature Input using examples of list
                          prefix canonicalization.

2.4.  Specialty Content Fields

   Content not found in an HTTP header can be included in the signing algorithm
   described signature
   base string by the signature's Algorithm property, defining a content identifier and the key material
   chosen by the signer.  The signer then encodes canonicalization
   method for its content.

   To differentiate speciality content identifiers from HTTP headers,
   specialty content identifiers MUST start with the result of that
   operation as a base 64-encoded string [RFC4648]. "at" "@" character.
   This string is the
   signature value.

   For specification defines the non-normative example Signature metadata in following specialty content
   identifiers:

   @request-target  The target request endpoint.  Section 3.2.1 and
   Signature Input in Figure 1, the corresponding signature value is:

   K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUeZx/Kdrq32DrfakQ6b
   PsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibeoHyqU/yCjphSmEdd7WD+z
   rchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4CaB8X/I5/+HLZLGvDiezqi6/7
   p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg1Q7MpWYZs0soHjttq0uLIA3DIbQfL
   iIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZgFquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==

              Figure 2: Non-normative example 2.4.1

   @signature-params  The signature value

3.3.  Verifying a Signature

   In order to verify a signature, a verifier MUST:

   1.  Examine the signature's metadata to confirm that the signature
       meets the requirements described in parameters for this document, as well as any
       additional requirements defined by the application such as which
       header fields or other
      signature.  Section 2.4.2

   Additional specialty content are required to identifiers MAY be covered by the
       signature.

   2.  Use the received HTTP message defined and the signature's metadata to
       recreate the Signature Input, using the process described
   registered in the HTTP Signatures Specialty Content Identifier
   Registry.  Section 3.2.2.

   3.  Use 5.3

2.4.1.  Request Target

   The request target endpoint, consisting of the signature's Algorithm request method and Verification Key Material with the recreated Signing Input to verify
   path and query of the signature value.

   A signature with a Creation Time that effective request URI, is in identified by the future or an
   Expiration Time that
   "@request-target" identifier.

   Its value is in canonicalized as follows:

   1.  Take the past MUST NOT be processed.

   The verifier MUST ensure that lowercased HTTP method of the message.

   2.  Append a signature's Algorithm is appropriate
   for space " ".

   3.  Append the key material path and query of the verifier will use to verify request target of the signature.
   If message,
       formatted according to the Algorithm is not appropriate rules defined for the key material (for
   example, if it is the wrong size, or :path pseudo-
       header in [HTTP2], Section 8.1.2.3.  The resulting string is the wrong format), the
   signature MUST NOT be processed.

3.3.1.  Enforcing Application Requirements
       canonicalized value.

2.4.1.1.  Canonicalization Examples

   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 following table contains non-normative example HTTP Message Signatures MAY impose
   requirements above messages 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. 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 *  Requiring keys to be HTTP/1.1    | options *       |
       |   Host: server.example.com|                 |
       +-------------------------+-----------------+

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

2.4.2.  Signature Parameters

   The signature verification
   MUST fail if parameters special content is identified by the signature does not conform to
   "@signature-params" identifier.

   Its canonicalized value is the application's
   requirements.

   Applications MUST enforce serialization of the requirements defined in signature
   parameters for this document.
   Regardless of use case, applications MUST NOT accept signatures signature, including the covered content list
   with all associated parameters.  Section 3.1

   Note that
   do not conform to these requirements.

4.  Including a Message Signature in a Message

   Message signatures can be included within an HTTP message via could contain multiple signatures, but only
   the
   "Signature-Input" and "Signature" HTTP header fields, both defined
   within this specification.  The "Signature" HTTP header field
   contains signature values, while parameters used for the "Signature-Input" HTTP header
   field identifies current signature are included.

2.4.2.1.  Canonicalization Examples

   Given the following signature parameters:

        +==============+=========================================+
        | Property     | Value                                   |
        +==============+=========================================+
        | Algorithm    | hs2019                                  |
        +--------------+-----------------------------------------+
        | 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 metadata that describe how
   each signature was generated.

4.1. identified by the    |
        |              | "keyid" value "test-key-a".             |
        +--------------+-----------------------------------------+

                                 Table 5

   The 'Signature-Input' signature parameter value is defined as:

"@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="hs2019"; created=1402170695; expires=1402170995

3.  HTTP Header

   The "Signature-Input" Message Signatures

   An HTTP header field Message Signature is a Dictionary Structured
   Header [StructuredFields] containing the metadata for zero or more
   message signatures signature over a string generated from content within
   a subset of the content in an HTTP message.
   Each member describes a single message signature.  The member's name
   is an identifier that uniquely identifies and metadata about the message
   signature
   within itself.  When successfully verified against an HTTP
   message, it provides cryptographic proof that with respect to the context
   subset of content that was signed, the HTTP message.  The member's value message is semantically
   equivalent to the message signature's Covered Content, expressed as a List of Tokens.
   Further for which the signature was generated.

3.1.  Signature Metadata

   HTTP Message Signatures have metadata is expressed in parameters on properties that provide
   information regarding the member
   value, as described below.

4.1.1.  Metadata Parameters signature's generation and/or verification.
   The parameters on each "Signature-Input" member value contain following metadata about the signature.  Each parameter name MUST be a
   parameter name registered in the IANA properties are defined:

   Algorithm:

      An HTTP Signatures Metadata
   Parameters Registry Signature Algorithm defined in Section 5.2 of this document.  This
   document defines the following parameters, and registers them as the
   initial contents of the registry:

   alg

      RECOMMENDED.  The "alg" parameter is a Token containing the name
      of the signature's Algorithm, as registered in the HTTP Signature
      Algorithms Registry defined by in this document.  Verifiers MUST
      determine the signature's Algorithm from document, represented as a
      string.  It describes the "keyId" parameter
      rather than from "alg".  If "alg" is provided signing and differs from or
      is incompatible with the algorithm or key material identified by
      "keyId" (for example, "alg" has a value of "rsa-sha256" but
      "keyId" identifies an EdDSA key), then implementations MUST
      produce an error.

   created

      RECOMMENDED.  The "created" parameter is a Decimal containing verification algorithms for
      the
      signature's signature.

   Creation Time, expressed as Time:
      A timestamp representing the canonicalized value of point in time that the "*created" content identifier, signature was
      generated, represented as defined in Section 2.  If an integer.  Sub-second precision is not specified, the
      supported.  A signature's Creation Time MAY be undefined,
      indicating that it is undefined.  This
      parameter is useful when signers are not capable of controlling
      the Date HTTP Header such as when operating in certain web browser
      environments.

   expires

      OPTIONAL.  The "expires" parameter is a Decimal containing the
      signature's unknown.

   Expiration Time, expressed as the canonicalized value
      of Time:
      A timestamp representing the "*expires" content identifier, as defined point in Section 2.  If time at which the signature does not have
      expires, represented as an Expiration Time, this parameter
      MUST be omitted.  If not specified, the integer.  An expired signature always
      fails verification.  A signature's Expiration Time is undefined.

   keyId

      REQUIRED.  The "keyId" parameter is a String whose value can MAY be
      used by a verifier to identify and/or obtain
      undefined, indicating that the signature's signature does not expire.

   Verification Key Material.  Further format and semantics of this
      value are out of scope for this document.

4.2.  The 'Signature' HTTP Header Material:
      The "Signature" HTTP header field is a Dictionary Structured Header
   [StructuredFields] containing zero or more message signatures
   generated from key material required to verify the signature.

   Covered Content:
      An ordered list of content within identifiers (Section 2) that indicates
      the HTTP message.  Each member's name
   is a signature identifier metadata and message content that is present as a member name in covered by the
   "Signature-Input" Structured Header within signature.
      This list MUST NOT include the HTTP message.  Each
   member's value "@signature-params" content
      identifier.

   The signature metadata is a Byte Sequence containing serialized using the signature value for rules in [RFC8941]
   section 4 as follows:

   1.  Let the output be an empty string.

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

   3.  Append the member name.  Any member signature metadata as parameters according to
       [RFC8941] section 4.1.1.2 in the "Signature" HTTP header field any order, skipping fields that does
       are not have a corresponding
   member in available:

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

       *  "keyid": Verification 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.

   Note that the HTTP message's "Signature-Input" HTTP header field MUST
   be ignored.

4.3.  Examples

   The following "inner-list" serialization is a non-normative example used instead of "Signature-Input" and
   "Signature" HTTP header fields representing the signature "sf-
   list" serialization in
   Figure 2:

   Signature-Input: sig1=(*request-target, *created, host, date,
       cache-control, x-empty-header, x-example); keyId="test-key-a";
       alg=hs2019; created=1402170695; expires=1402170995
   Signature: sig1=:K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUe
       Zx/Kdrq32DrfakQ6bPsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibe
       oHyqU/yCjphSmEdd7WD+zrchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4
       CaB8X/I5/+HLZLGvDiezqi6/7p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg
       1Q7MpWYZs0soHjttq0uLIA3DIbQfLiIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZg
       FquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==:

   Since order to facilitate this value's inclusion in
   the "Signature-Input" and "Signature" are both defined header's dictionary, as
   Dictionary Structured Headers, they can discussed in
   Section 4.1.

   The Table 6 values would be used to easily include
   multiple signatures within the same HTTP message.  For example, serialized as follows:

("@request-target" "host" "date" "cache-control" "x-empty-header" "x-example"); keyid="test-key-a"; alg="hs2019"; created=1402170695; expires=1402170995

3.2.  Creating a
   signer may include multiple signatures signing the same content with
   different keys and/or algorithms Signature

   In order to support verifiers with different
   capabilities, or create a reverse proxy may include information about the
   client in header fields when forwarding the request to signature, a service
   host, signer completes the following
   process:

   1.  Choose key material and may also include a signature over those fields algorithm, and set metadata properties
       Section 3.2.1

   2.  Create the
   client's signature. Signature Input Section 3.2.2

   3.  Sign the Signature Input Section 3.2.3

   The following is a non-normative example sections describe each of
   header fields a reverse proxy might add to a forwarded request that
   contains the signature these steps in detail.

3.2.1.  Choose and Set Signature Metadata Properties

   1.  The signer chooses an HTTP Signature Algorithm from those
       registered in the above example:

   X-Forwarded-For: 192.0.2.123
   Signature-Input: reverse_proxy_sig=(*created, host, date,
       signature:sig1, x-forwarded-for); keyId="test-key-a";
       alg=hs2019; created=1402170695; expires=1402170695.25
   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 defined by
       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] document, and shall follow sets the template presented in
   Section 5.1.1.

5.1.1.  Registration Template signature's Algorithm Name

      An identifier for the HTTP Signature Algorithm. property to
       that value.  The name signer 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. choose an algorithm marked
       "Deprecated".  The identifier MUST be unique
      within the context of the registry.

   Status

      A brief text description of mechanism by which the status signer chooses an
       algorithm is out of the algorithm. scope for this document.

   2.  The
      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as signer chooses key material to the reason use for
      the status.

   Description

      A description of the algorithm used to sign the signing string
      when generating an HTTP Message Signature, or instructions on how and
       verification, and sets the signature's Verification Key Material
       property to determine that algorithm.  When the description specifies an
      algorithm, it key material required for verification.  The
       signer MUST include a reference to choose key material that is appropriate for the document or
      documents
       signature's Algorithm, and that define conforms to any requirements
       defined by the algorithm.

5.1.2.  Initial Contents

   (( MS: The references in this section are problematic Algorithm, such as many key size or format.  The
       mechanism by which the signer chooses key material is out of
       scope for this document.

   3.  The signer sets the
   specifications that they refer signature's Creation Time property to are too implementation specific,
   rather than just pointing the
       current time.

   4.  The signer sets the signature's Expiration Time property to the proper signature and hashing
   specifications.  A better approach might be just specifying
       time at which the signature and hashing function specifications, leaving implementers is to connect the dots (which are not that hard expire, or to connect). ))

5.1.2.1.  hs2019

   Algorithm Name

      "hs2019"

   Status

      active

   Description

      Derived from metadata associated with keyId.  Recommend support
      for:

      *  RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]

      *  HMAC [RFC2104] using SHA-512 [RFC6234]

      *  ECDSA using curve P-256 DSS [FIPS186-4] and SHA-512 [RFC6234]

      *  Ed25519ph, Ed25519ctx, and Ed25519 [RFC8032]

5.1.2.2.  rsa-sha1

   Algorithm Name

      "rsa-sha1"

   Status

      Deprecated; SHA-1 not secure.

   Description

      RSASSA-PKCS1-v1_5 [RFC8017] using SHA-1 [RFC6234]

5.1.2.3.  rsa-sha256

   Algorithm Name

      "rsa-sha256"

   Status

      Deprecated; specifying signature algorithm enables attack vector.

   Description

      RSASSA-PKCS1-v1_5 [RFC8017] using SHA-256 [RFC6234]

5.1.2.4.  hmac-sha256

   Algorithm Name

      "hmac-sha256"

   Status

      Deprecated; specifying signature algorithm enables attack vector.

   Description

      HMAC [RFC2104] using SHA-256 [RFC6234]

5.1.2.5.  ecdsa-sha256

   Algorithm Name

      "ecdsa-sha256"

   Status

      Deprecated; specifying signature algorithm enables attack vector.

   Description

      ECDSA using curve P-256 DSS [FIPS186-4] and SHA-256 [RFC6234]

5.2.  HTTP Signature Metadata Parameters Registry

   This document defines undefined if the
       signature will not expire.

   5.  The signer creates an ordered list of content identifiers
       representing the "Signature-Input" Structured Header, whose
   member values may have parameters containing metadata about a message
   signature.  IANA is asked to create content and maintain a new registry
   titled "HTTP Signature Metadata Parameters" signature metadata to record be
       covered by the signature, and maintain assigns this list as the set
       signature's Covered Content.

       *  Each identifier MUST be one of parameters those defined for use with member values in Section 2.

       *  This list MUST NOT be empty, as this would result in creating
          a signature over the
   "Signature-Input" Structured Header.  Initial values for empty string.

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

       *  Signers SHOULD include a date stamp, such as the "date"
          header.  Alternatively, the "created" signature metadata
          parameter can fulfil this
   registry are given role.

       *  Further guidance on what to include in Section 5.2.2.  Future assignments this list and
   modifications to existing assignments are to be made through in what
          order is out of scope for this document.  However, the
   Expert Review registration policy [RFC8126] list
          order is significant and shall follow once established for a given
          signature it MUST be preserved for that signature.

       *  Note that the
   template presented signature metadata is not included in Section 5.2.1.

5.2.1.  Registration Template

5.2.2.  Initial Contents

   The table below contains the initial contents
          explicit list of covered content identifiers since its value
          is always covered.

   For example, given the following HTTP Signature
   Metadata Parameters Registry.  Each row in the 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 represents presents a
   distinct entry in the registry.

           +=========+========+================================+
           | Name non-normative example of metadata
   values that a signer may choose:

        +==============+=========================================+
        | Status Property     | Reference(s) Value                                   |
           +=========+========+================================+
        +==============+=========================================+
        | alg Algorithm    | Active hs2019                                  | Section 4.1.1 of this document
        +--------------+-----------------------------------------+
        |
           +---------+--------+--------------------------------+ Covered      | created "@request-target", "host", "date",      | Active
        | Section 4.1.1 of this document Content      |
           +---------+--------+--------------------------------+ "cache-control", "x-emptyheader",       | expires
        | Active              | Section 4.1.1 of this document "x-example", "x-dictionary;key=b",      |
           +---------+--------+--------------------------------+
        | keyId              | Active "x-dictionary;key=a", "x-list;prefix=3" | Section 4.1.1 of this document
        +--------------+-----------------------------------------+
        |
           +---------+--------+--------------------------------+

              Table 6: Initial contents of the HTTP Signature
                       Metadata Parameters Registry.

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/info/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/info/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/info/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/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase Creation     | 1402174295                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Expiration   | 1402174595                              |
        | Time         |                                         |
        +--------------+-----------------------------------------+
        | Verification | The public key provided in RFC
              2119              |
        | Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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

   [StructuredFields]
              "Structured Field Vaues identified by the    |
        |              | "keyid" value "test-key-a".             |
        +--------------+-----------------------------------------+

              Table 6: Non-normative example metadata values

3.2.2.  Create the Signature Input

   The Signature Input is a US-ASCII string containing the content that
   will be signed.  To create it, the signer or verifier concatenates
   together entries for HTTP", 2020,
              <https://datatracker.ietf.org/doc/draft-ietf-httpbis-
              header-structure>.

7.2.  Informative References

   [RFC3230]  Mogul, J. and A. Van Hoff, "Instance Digests each identifier in HTTP",
              RFC 3230, DOI 10.17487/RFC3230, January 2002,
              <https://www.rfc-editor.org/info/rfc3230>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [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/info/rfc3986>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/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/info/rfc6234>.

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

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC7541]  Peon, R. and H. Ruellan, "HPACK: Header Compression for
              HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
              <https://www.rfc-editor.org/info/rfc7541>.

   [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/info/rfc8017>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [RFC8126]  Cotton, M., Leiba, B., signature's Covered
   Content in the order it occurs in the list, with each entry separated
   by a newline ""\n"".  An identifier's entry is a "sf-string" followed
   with a colon "":"", a space "" "", and T. Narten, "Guidelines the identifier's canonicalized
   value.

   The signer or verifier then includes the signature metadata specialty
   field "@signature-params" as the last entry in the covered content,
   separated by a newline ""\n"".  Section 2.4.2

   If Covered Content contains an identifier for
              Writing a header field that is
   malformed or is not present in the message, the implementation MUST
   produce an IANA Considerations Section error.

   If Covered Content contains an identifier for a Dictionary member
   that references a header field using the "key" parameter that is not
   present, is malformed in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/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/info/rfc8446>.

   [WP-HTTP-Sig-Audit]
              "Security Considerations the message, or is not a Dictionary
   Structured Field, the implementation MUST produce an error.  If the
   header field value does not contain the specified member, the
   implementation MUST produce an error.

   If Covered Content contains an identifier for HTTP Signatures", 2013,
              <https://web-payments.org/specs/source/http-signatures-
              audit/>.

Appendix A.  Examples

A.1. a List Prefix that
   references a header field using the "prefix" parameter that is not
   present, is malformed in the message, or is not a List Structured
   Field, the implementation MUST produce an error.  If the header field
   value contains fewer than the specified number of members, the
   implementation MUST produce an error.

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

"@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 Keys

   This section provides cryptographic keys that are referenced in 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=b "x-list";prefix=3); keyid="test-key-a"; alg="hs2019"; created=1402170695; expires=1402170995

           Figure 1: Non-normative example signatures throughout this document.  These keys MUST NOT be
   used for any purpose other than testing.

A.1.1.  Example Key RSA test Signature Input

3.2.3.  Sign the Signature Input

   The following key is a 2048-bit RSA public signer signs the Signature Input using the signing algorithm
   described by the signature's Algorithm property, and private the key pair:

   -----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-----

A.2.  Example keyId Values material
   chosen by the signer.  The table below maps signer then encodes the result of that
   operation as a base 64-encoded string [RFC4648].  This string is the
   signature value.

   For the non-normative example "keyId" values to associated algorithms
   and/or keys.  These are Signature metadata in Section 3.2.1 and
   Signature Input in Figure 1, the corresponding signature value is:

   K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUeZx/Kdrq32DrfakQ6b
   PsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibeoHyqU/yCjphSmEdd7WD+z
   rchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4CaB8X/I5/+HLZLGvDiezqi6/7
   p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg1Q7MpWYZs0soHjttq0uLIA3DIbQfL
   iIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZgFquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==

              Figure 2: Non-normative example mappings signature value

3.3.  Verifying a Signature

   In order to verify a signature, a verifier MUST:

   1.  Examine the signature's metadata 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
       header fields or other content are valid only within required to be covered by the
       signature.

   2.  Use the received HTTP message and the context of examples signature's metadata to
       recreate the Signature Input, using the process described in examples within
       Section 3.2.2.  The value of the "@signature-params" input is the
       value of the signature input header field for this signature, not
       including the signature's label.

   3.  Use the signature's Algorithm and Verification Key Material with
       the recreated Signing Input to verify the signature value.

   A signature with a Creation Time that is in the future documents or an
   Expiration Time that reference this section.  Unless otherwise specified, within is in the
   context of examples it should past MUST NOT be assumed processed.

   The verifier MUST ensure that a signature's Algorithm is appropriate
   for the key material the signer and verifier
   understand these "keyId" mappings.  These "keyId" values are not
   reserved, and deployments are free to will use them, with these
   associations or others.

     +============+=================================+================+
     | keyId      | to verify the signature.
   If the Algorithm                       | Verification   |
     |            |                                 | Key            |
     +============+=================================+================+
     | test-key-a | "hs2019", using RSASSA-PSS      | The public is not appropriate for the key |
     |            | [RFC8017] and SHA-512 [RFC6234] | specified material (for
   example, if it is the wrong size, or in   |
     |            |                                 | Appendix A.1.1 |
     +------------+---------------------------------+----------------+
     | test-key-b | rsa-sha256                      | the wrong format), the
   signature MUST NOT be processed.

3.3.1.  Enforcing Application Requirements

   The public key |
     |            |                                 | verification requirements specified in   |
     |            |                                 | Appendix A.1.1 |
     +------------+---------------------------------+----------------+

                                  Table 7

A.3.  Test Cases

   This section provides 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 that may of additional requirements an application
   might define are:

   *  Requiring a specific set of header fields to be used as test
   cases 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 validate implementation correctness.  These examples be of a certain size (e.g., 2048 bits vs. 1024
      bits).

   Application-specific requirements are
   based on expected and encouraged.  When
   an application defines additional requirements, it MUST enforce them
   during 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"}

A.3.1.  Signature Generation

A.3.1.1.  hs2019 signature over minimal recommended content

   This presents metadata for a Signature using "hs2019", over minimum
   recommended data verification process, and signature verification
   MUST fail if the signature does not conform to sign:

           +==============+===================================+
           | Property     | Value                             |
           +==============+===================================+
           | Algorithm    | "hs2019", using RSASSA-PSS        |
           |              | [RFC8017] using SHA-512 [RFC6234] |
           +--------------+-----------------------------------+
           | Covered      | *created, *request-target         |
           | Content      |                                   |
           +--------------+-----------------------------------+
           | Creation     | 8:51:35 PM GMT, June 7th, 2014    |
           | Time         |                                   |
           +--------------+-----------------------------------+
           | Expiration   | Undefined                         |
           | Time         |                                   |
           +--------------+-----------------------------------+
           | Verification | The public key specified the application's
   requirements.

   Applications MUST enforce the requirements defined in       |
           | Key Material | Appendix A.1.1.                   |
           +--------------+-----------------------------------+

                                 Table 8

   The Signature Input is:

   *created: 1402170695
   *request-target: post /foo?param=value&pet=dog

   The signature value is:

   QaVaWYfF2da6tG66Xtd0GrVFChJ0fOWUe/C6kaYESPiYYwnMH9egOgyKqgLLY9NQJFk7b
   QY834sHEUwjS5ByEBaO3QNwIvqEY1qAAU/2MX14tc9Yn7ELBnaaNHaHkV3xVO9KIuLT7V
   6e4OUuGb1axfbXpMgPEql6CEFrn6K95CLuuKP5/gOEcBtmJp5L58gN4VvZrk2OVA6U971
   YiEDNuDa4CwMcQMvcGssbc/L3OULTUffD/1VcPtdGImP2uvVQntpT8b2lBeBpfh8MuaV2
   vtzidyBYFtAUoYhRWO8+ntqA1q2OK4LMjM2XgDScSVWvGdVd459A0wI9lRlnPap3zg==

   A possible this document.
   Regardless of use case, applications MUST NOT accept signatures that
   do not conform to these requirements.

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 containing fields, both defined
   within this specification.  The "Signature" HTTP header field
   contains signature is:

   Signature-Input: sig1=(*created, *request-target);
       keyId="test-key-a"; created=1402170695
   Signature: sig1=:QaVaWYfF2da6tG66Xtd0GrVFChJ0fOWUe/C6kaYESPiYYwnMH9eg
       OgyKqgLLY9NQJFk7bQY834sHEUwjS5ByEBaO3QNwIvqEY1qAAU/2MX14tc9Yn7ELB
       naaNHaHkV3xVO9KIuLT7V6e4OUuGb1axfbXpMgPEql6CEFrn6K95CLuuKP5/gOEcB
       tmJp5L58gN4VvZrk2OVA6U971YiEDNuDa4CwMcQMvcGssbc/L3OULTUffD/1VcPtd
       GImP2uvVQntpT8b2lBeBpfh8MuaV2vtzidyBYFtAUoYhRWO8+ntqA1q2OK4LMjM2X
       gDScSVWvGdVd459A0wI9lRlnPap3zg==:

A.3.1.2.  hs2019 values, while the "Signature-Input" HTTP header
   field identifies the Covered Content and metadata that describe how
   each signature covering all was generated.

4.1.  The 'Signature-Input' HTTP Header

   The "Signature-Input" HTTP header fields

   This presents 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 Signature using "hs2019" single message signature.  The member's name is an
   identifier that covers all
   header fields in uniquely identifies the request:

         +==============+========================================+
         | Property     | Value                                  |
         +==============+========================================+
         | Algorithm    | "hs2019", using RSASSA-PSS [RFC8017]   |
         |              | using SHA-512 [RFC6234]                |
         +--------------+----------------------------------------+
         | Covered      | *created, *request-target, host, date, |
         | Content      | content-type, digest, content-length   |
         +--------------+----------------------------------------+
         | Creation     | 8:51:35 PM GMT, June 7th, 2014         |
         | Time         |                                        |
         +--------------+----------------------------------------+
         | Expiration   | Undefined                              |
         | Time         |                                        |
         +--------------+----------------------------------------+
         | Verification | message signature within the
   context of the HTTP message.  The public key specified member's value is the serialization
   of the covered content including all signature metadata parameters,
   described in            |
         | Key Material | Appendix A.1.1.                        |
         +--------------+----------------------------------------+

                                  Table 9

   The Signature Input is:

   *created: 1402170695
   *request-target: post /foo?param=value&pet=dog
   host: example.com
   date: Tue, 07 Jun 2014 20:51:35 GMT
   content-type: application/json
   digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   content-length: 18

   The Section 3.1.

  Signature-Input: sig1=("@request-target" "host" "date"
      "cache-control" "x-empty-header" "x-example"); keyid="test-key-a";
      alg="hs2019"; created=1402170695; expires=1402170995

   To facilitate signature value is:

   B24UG4FaiE2kSXBNKV4DA91J+mElAhS3mncrgyteAye1GKMpmzt8jkHNjoudtqw3GngGY
   3n0mmwjdfn1eA6nAjgeHwl0WXced5tONcCPNzLswqPOiobGeA5y4WE8iBveel30OKYVel
   0lZ1OnXOmN5TIEIIPo9LrE+LzZis6A0HA1FRMtKgKGhT3N965pkqfhKbq/V48kpJKT8+c
   Zs0TOn4HFMG+OIy6c9ofSBrXD68yxP6QYTz6xH0GMWawLyPLYR52j3I05fK1ylAb6K0ox
   PxzQ5nwrLD+mUVPZ9rDs1En6fmOX9xfkZTblG/5D+s1fHHs9dDXCOVkT5dLS8DjdIA==

   A possible validation, the "Signature-Input" and "Signature" header containing this MUST
   contain the same serialization value used in generating the signature is:

   Signature-Input: sig1=(*request-target, *created, host, date,
           content-type, digest, content-length); keyId="test-key-a";
       alg=hs2019; created=1402170695
   Signature: sig1=:B24UG4FaiE2kSXBNKV4DA91J+mElAhS3mncrgyteAye1GKMpmzt8
       jkHNjoudtqw3GngGY3n0mmwjdfn1eA6nAjgeHwl0WXced5tONcCPNzLswqPOiobGe
       A5y4WE8iBveel30OKYVel0lZ1OnXOmN5TIEIIPo9LrE+LzZis6A0HA1FRMtKgKGhT
       3N965pkqfhKbq/V48kpJKT8+cZs0TOn4HFMG+OIy6c9ofSBrXD68yxP6QYTz6xH0G
       MWawLyPLYR52j3I05fK1ylAb6K0oxPxzQ5nwrLD+mUVPZ9rDs1En6fmOX9xfkZTbl
       G/5D+s1fHHs9dDXCOVkT5dLS8DjdIA==:

A.3.2.  Signature Verification

A.3.2.1.  Minimal Required Signature
   input.

4.2.  The 'Signature' HTTP Header

   This presents a "Signature-Input" and

   The "Signature" HTTP header field is a Dictionary Structured Header
   [RFC8941] containing
   only zero or more message signatures generated from
   content within the minimal required parameters:

   Signature-Input: sig1=(); keyId="test-key-a"; created=1402170695
   Signature: sig1=:cxieW5ZKV9R9A70+Ua1A/1FCvVayuE6Z77wDGNVFSiluSzR9TYFV
       vwUjeU6CTYUdbOByGMCee5q1eWWUOM8BIH04Si6VndEHjQVdHqshAtNJk2Quzs6WC
       2DkV0vysOhBSvFZuLZvtCmXRQfYGTGhZqGwq/AAmFbt5WNLQtDrEe0ErveEKBfaz+
       IJ35zhaj+dun71YZ82b/CRfO6fSSt8VXeJuvdqUuVPWqjgJD4n9mgZpZFGBaDdPiw
       pfbVZHzcHrumFJeFHWXH64a+c5GN+TWlP8NPg2zFdEc/joMymBiRelq236WGm5VvV
       9a22RW2/yLmaU/uwf9v40yGR/I1NRA==:

   The corresponding HTTP message.  Each member's name is a signature metadata derived from this header field
   is:

      +=================+==========================================+
      | Property        | Value                                    |
      +=================+==========================================+
      | Algorithm       | "hs2019", using RSASSA-PSS using SHA-256 |
      +-----------------+------------------------------------------+
      | Covered Content | *created                                 |
      +-----------------+------------------------------------------+
      | Creation Time   | 8:51:35 PM GMT, June 7th, 2014           |
      +-----------------+------------------------------------------+
      | Expiration Time | Undefined                                |
      +-----------------+------------------------------------------+
      | Verification    | The public key specified
   identifier that is present as a member name in              |
      | Key Material    | Appendix A.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 10

   The corresponding Signature Input is:

   *created: 1402170695

A.3.2.2.  Minimal Recommended Signature the "Signature-Input"
   Structured Header

   This presents within the HTTP message.  Each member's value is a "Signature-Input" and "Signature" header
   Byte Sequence containing
   only the minimal required and recommended parameters:

   Signature-Input: sig1=(); alg=hs2019; keyId="test-key-a";
       created=1402170695
   Signature: sig1=:cxieW5ZKV9R9A70+Ua1A/1FCvVayuE6Z77wDGNVFSiluSzR9TYFV
       vwUjeU6CTYUdbOByGMCee5q1eWWUOM8BIH04Si6VndEHjQVdHqshAtNJk2Quzs6WC
       2DkV0vysOhBSvFZuLZvtCmXRQfYGTGhZqGwq/AAmFbt5WNLQtDrEe0ErveEKBfaz+
       IJ35zhaj+dun71YZ82b/CRfO6fSSt8VXeJuvdqUuVPWqjgJD4n9mgZpZFGBaDdPiw
       pfbVZHzcHrumFJeFHWXH64a+c5GN+TWlP8NPg2zFdEc/joMymBiRelq236WGm5VvV
       9a22RW2/yLmaU/uwf9v40yGR/I1NRA==:

   The corresponding signature metadata derived from this header field
   is:

      +=================+==========================================+
      | Property        | Value                                    |
      +=================+==========================================+
      | Algorithm       | "hs2019", using RSASSA-PSS using SHA-512 |
      +-----------------+------------------------------------------+
      | Covered Content | *created                                 |
      +-----------------+------------------------------------------+
      | Creation Time   | 8:51:35 PM GMT, June 7th, 2014           |
      +-----------------+------------------------------------------+
      | Expiration Time | Undefined                                |
      +-----------------+------------------------------------------+
      | Verification    | The public key specified value for the message
   signature identified by the member name.  Any member in              |
      | Key Material    | Appendix A.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 11

   The the
   "Signature" HTTP header field that does not have a corresponding Signature Input is:

   *created: 1402170695

A.3.2.3.  Minimal Signature Header using rsa-sha256

   This presents
   member in the HTTP message's "Signature-Input" HTTP header field MUST
   be ignored.

  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 minimal non-normative example of "Signature-Input" and
   "Signature" HTTP header for 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="hs2019"; created=1402170695; expires=1402170995
   Signature: sig1=:K2qGT5srn2OGbOIDzQ6kYT+ruaycnDAAUpKv+ePFfD0RAxn/1BUe\
       Zx/Kdrq32DrfakQ6bPsvB9aqZqognNT6be4olHROIkeV879RrsrObury8L9SCEibe\
       oHyqU/yCjphSmEdd7WD+zrchK57quskKwRefy2iEC5S2uAH0EPyOZKWlvbKmKu5q4\
       CaB8X/I5/+HLZLGvDiezqi6/7p2Gngf5hwZ0lSdy39vyNMaaAT0tKo6nuVw0S1MVg\
       1Q7MpWYZs0soHjttq0uLIA3DIbQfLiIvK6/l0BdWTU7+2uQj7lBkQAsFZHoA96ZZg\
       FquQrXRlmYOh+Hx5D9fJkXcXe5tmAg==:

   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 using over those fields and the "rsa-sha256" algorithm:

   Signature: sig1=(date); alg=rsa-sha256; keyId="test-key-b"
   Signature: sig1=:HtXycCl97RBVkZi66ADKnC9c5eSSlb57GnQ4KFqNZplOpNfxqk62
       JzZ484jXgLvoOTRaKfR4hwyxlcyb+BWkVasApQovBSdit9Ml/YmN2IvJDPncrlhPD
       VDv36Z9/DiSO+RNHD7iLXugdXo1+MGRimW1RmYdenl/ITeb7rjfLZ4b9VNnLFtVWw
       rjhAiwIqeLjodVImzVc5srrk19HMZNuUejK6I3/MyN3+3U8tIRW4LWzx6ZgGZUaEE
       P0aBlBkt7Fj0Tt5/P5HNW/Sa/m8smxbOHnwzAJDa10PyjzdIbywlnWIIWtZKPPsoV
       oKVopUWEU3TNhpWmaVhFrUL/O6SN3w==:
   client's signature.  The corresponding signature metadata derived from this following is a non-normative example of
   header field
   is:

         +===========================+==========================+
         | Property                  | Value                    |
         +===========================+==========================+
         | Algorithm                 | rsa-sha256               |
         +---------------------------+--------------------------+
         | Covered Content           | date                     |
         +---------------------------+--------------------------+
         | Creation Time             | Undefined                |
         +---------------------------+--------------------------+
         | Expiration Time           | Undefined                |
         +---------------------------+--------------------------+
         | Verification Key Material | The public key specified |
         |                           | fields a reverse proxy might add to a forwarded request that
   contains the signature in Appendix A.1.1.       |
         +---------------------------+--------------------------+

                                 Table 12

   The corresponding 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="hs2019"; 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 Input is:

   date: Tue, 07 Jun 2014 20:51:35 GMT

Appendix B.  Topics Algorithms Registry

   This document defines HTTP Signature Algorithms, for Working Group Discussion

   _RFC EDITOR: please remove this section before publication_

   The draft has known issues that will need which IANA is
   asked to be addressed during
   development, create and these issues have been enumerated but not addressed
   in maintain a new registry titled "HTTP Signature
   Algorithms".  Initial values for this version.  Topics registry are not listed given in any particular order.

B.1.  Issues
B.1.1.  Confusing guidance on algorithm
   Section 5.1.2.  Future assignments and key identification

   The current draft encourages determining modifications to existing
   assignment are to be made through the Algorithm metadata
   property from Expert Review registration
   policy [RFC8126] and shall follow the "keyId" field, both template presented in the guidance
   Section 5.1.1.

5.1.1.  Registration Template

   Algorithm Name:
      An identifier for the use HTTP Signature Algorithm.  The name MUST be
      an ASCII string consisting only of
   "algorithm" and "keyId", lower-case characters (""a"" -
      ""z""), digits (""0"" - ""9""), and the definition for the "hs2019"
   algorithm hyphens (""-""), and deprecation of the other algorithms SHOULD
      NOT exceed 20 characters in the registry. length.  The current state arose from concern that a malicious party could
   change identifier MUST be unique
      within the value context of the "algorithm" parameter, potentially tricking
   the verifier into accepting a signature that would not have been
   verified under the actual parameter.

   Punting algorithm identification into "keyId" hurts interoperability,
   since we aren't defining the syntax or semantics registry.

   Status:
      A brief text description of "keyId".  It
   actually goes against that claim, as we are dictating that the
   signing algorithm must be specified by "keyId" or derivable from it.
   It also renders the algorithm registry essentially useless.  Instead status of this approach, we can protect against manipulation the algorithm.  The
      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as to the
   Signature header field by adding support reason for (and possibly mandating)
   including Signature metadata within the Signature Input.

B.1.2.  Lack of definition of keyId hurts interoperability

   The current text leaves
      the format and semantics status.

   Description:
      A description of "keyId"
   completely up to the implementation.  This is primarily due algorithm used to sign the
   fact that most implementers of Cavage have extensive investment in
   key distribution and management, and just need to plug signing string
      when generating an identifier
   into HTTP Message Signature, or instructions on how
      to determine that algorithm.  When the header.  We should support those cases, but we also need description specifies an
      algorithm, it MUST include a reference to
   provide guidance for the developer document or
      documents that doesn't have define the algorithm.

5.1.2.  Initial Contents

   (( MS: The references in this section are problematic as many of the
   specifications that and just
   wants they refer to know how are too implementation specific,
   rather than just pointing to identify a key.  It may the proper signature and hashing
   specifications.  A better approach might be enough to punt this just specifying the
   signature and hashing function specifications, leaving implementers
   to profiling specs, but this needs connect the dots (which are not that hard to be explored more.

B.1.3. connect). ))

5.1.2.1.  hs2019

   Algorithm Registry duplicates work of JWA

   [RFC7518] already defines an IANA registry for cryptographic
   algorithms. Name:
      "hs2019"

   Status:
      active

   Description:
      Derived from metadata associated with keyid.  Recommend support
      for:

      *  RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]

      *  HMAC [RFC2104] using SHA-512 [RFC6234]

      *  ECDSA using curve P-256 DSS [FIPS186-4] and SHA-512 [RFC6234]

      *  Ed25519ph, Ed25519ctx, and Ed25519 [RFC8032]

5.1.2.2.  rsa-sha1

   Algorithm Name:
      "rsa-sha1"

   Status:
      Deprecated; SHA-1 not secure.

   Description:
      RSASSA-PKCS1-v1_5 [RFC8017] using SHA-1 [RFC6234]

5.1.2.3.  rsa-sha256

   Algorithm Name:
      "rsa-sha256"

   Status:
      Deprecated; specifying signature algorithm enables attack vector.

   Description:
      RSASSA-PKCS1-v1_5 [RFC8017] using SHA-256 [RFC6234]

5.1.2.4.  hmac-sha256

   Algorithm Name:
      "hmac-sha256"

   Status:
      Deprecated; specifying signature algorithm enables attack vector.

   Description:
      HMAC [RFC2104] using SHA-256 [RFC6234]

5.1.2.5.  ecdsa-sha256

   Algorithm Name:
      "ecdsa-sha256"

   Status:
      Deprecated; specifying signature algorithm enables attack vector.

   Description:
      ECDSA using curve P-256 DSS [FIPS186-4] and SHA-256 [RFC6234]

5.2.  HTTP Signature Metadata Parameters Registry

   This wasn't used by Cavage out of concerns document defines the "Signature-Input" Structured Header, whose
   member values may have parameters containing metadata about
   complexity of JOSE, and issues with JWE a message
   signature.  IANA is asked to create and JWS being too flexible,
   leading maintain a new registry
   titled "HTTP Signature Metadata Parameters" to insecure combinations record and maintain
   the set of options.  Using JWA's definitions
   does not need to mean we're using JOSE, however.  We should look at
   if/how we can leverage JWA's work without introducing too many sharp
   edges parameters defined for implementers.

   In any use of JWS algorithms, with member values in the
   "Signature-Input" Structured Header.  Initial values for this spec would define a way
   registry are given in Section 5.2.2.  Future assignments and
   modifications to create
   the JWS Signing Input string existing assignments are to be applied to made through the algorithm.  It
   should be noted that this is incompatible with JWS itself, which
   requires
   Expert Review registration policy [RFC8126] and shall follow the inclusion of a structured header
   template presented in Section 5.2.1.

5.2.1.  Registration Template

5.2.2.  Initial Contents

   The table below contains the signature input.

   A possible approach is to incorporate all elements initial contents of the JWA
   signature algorithm registry into this spec using a prefix or other
   marker, such as "jws-RS256" for the RSA 256 JSON Web HTTP Signature
   algorithm.

B.1.4.  Algorithm Registry should not be initialized with deprecated
        entries

   The initial entries in this document reflect those
   Metadata Parameters Registry.  Each row in Cavage.  The
   ones that are marked deprecated were done so because of the issue
   explained table represents a
   distinct entry in Appendix B.1.1, with the possible exception registry.

            +=========+========+==============================+
            | Name    | Status | Reference(s)                 |
            +=========+========+==============================+
            | alg     | Active | Section 3.1 of this document |
            +---------+--------+------------------------------+
            | created | Active | Section 3.1 of this document |
            +---------+--------+------------------------------+
            | expires | Active | Section 3.1 of this document |
            +---------+--------+------------------------------+
            | keyid   | Active | Section 3.1 of this document |
            +---------+--------+------------------------------+

              Table 7: Initial contents of "rsa-
   sha1".  We should probably just remove that one.

B.1.5.  No percent-encoding normalization of path/query

   See: issue #26 (https://github.com/w3c-dvcg/http-signatures/
   issues/26)

   The canonicalization rules the HTTP Signature
                       Metadata Parameters Registry.

5.3.  HTTP Signature Specialty Content Identifiers Registry

   This document defines a method for "*request-target" do not perform
   handle minor, semantically meaningless differences in percent-
   encoding, such canonicalizing HTTP message
   content, including content that verification could fail if an intermediary
   normalizes can be generated from the effective request URI prior to forwarding context of
   the message.

   At HTTP message outside of the HTTP headers.  This content is
   identified by a minimum, they should be case unique key.  IANA is asked to create and percent-encoding normalized as
   described in sections 6.2.2.1 maintain a
   new registry typed "HTTP Signature Specialty Content Identifiers" to
   record and 6.2.2.2 maintain the set of [RFC3986].

B.1.6.  Misleading name for headers parameter

   The Covered Content list contains non-header content identifiers and
   their canonicalization method.  Initial values for more than just
   headers, so the "header" parameter name is no longer appropriate.
   Some alternatives: "content", "signed-content", "covered-content".

B.1.7.  Changes to whitespace this registry are
   given in header field values break verification

   Some header field values contain RWS, OWS, and/or BWS.  Since the
   header field value canonicalization rules do not address whitespace,
   changes to it (e.g., removing OWS or BWS or replacing strings of RWS
   with a single space) can cause verification Section 5.3.2.  Future assignments and modifications to fail.

B.1.8.  Multiple Set-Cookie headers
   existing assignments are not well supported

   The Set-Cookie header can occur multiple times but does not adhere to be made through the list syntax, Expert Review
   registration policy [RFC8126] and thus is not well supported by shall follow the header field
   value concatenation rules.

B.1.9.  Covered Content list is not signed template presented
   in Section 5.3.1.

5.3.1.  Registration Template

5.3.2.  Initial Contents

   The Covered Content list should be part table below contains the initial contents of the HTTP Signature Input, to
   protect against malicious changes.

B.1.10.  Algorithm is not signed

   The Algorithm should be part
   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 Input, Specialty
                       Content Identifiers Registry.

6.  Security Considerations

   (( TODO: need to protect
   against malicious changes.

B.1.11.  Verification key identifier is 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

   The Verification key identifier (e.g., the value used for the "keyId"
   parameter) should be part a given use case. ))

   There are a number of the Signature Input, security considerations to protect against
   malicious changes.

B.1.12.  Max values, precision 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 Integer String use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [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 Decimal String not
         defined

   The definitions P-H. Kamp, "Structured Field Values for Integer String
              HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
              <https://www.rfc-editor.org/rfc/rfc8941>.

   [SEMANTICS]
              Fielding, R., Ed. and Decimal String do not specify
   a maximum value.  The definition for Decimal String (used to provide
   sub-second precision for Expiration Time) does not define minimum or
   maximum precision requirements.  It should set a sane requirement
   here (e.g., MUST support up to 3 decimal places J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and no more).

B.1.13.  keyId parameter value could break list syntax

   The "keyId" parameter value needs to be constrained so as to not
   break list syntax (e.g., by containing a comma).

B.1.14.  Creation Time 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 Expiration Time do not allow 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>.

   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
              "PKCS #1: RSA Cryptography Specifications Version 2.2",
              RFC 8017, DOI 10.17487/RFC8017, November 2016,
              <https://www.rfc-editor.org/rfc/rfc8017>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/rfc/rfc8032>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for clock skew

   The processing instructions
              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 Creation Time and Expiration Time
   imply that verifiers are not permitted HTTP Signatures", 2013,
              <https://web-payments.org/specs/source/http-signatures-
              audit/>.

Appendix A.  Detecting HTTP Message Signatures

   There have been many attempts to account for clock skew
   during signature verification.

B.1.15.  Should require lowercased header field names as identifiers

   The current text allows mixed-case create signed HTTP messages in the
   past, including other non-standard definitions of the "Signature"
   header field names when they are
   being used as content identifiers.  This within this specification.  It is unnecessary, as header
   field names are case-insensitive, recommended that
   developers wishing to support both this specification and creates opportunity for
   incompatibility.  Instead, content identifiers should always be
   lowercase.

B.1.16.  Reconcile Date header other
   historial drafts do so carefully and Creation Time

   The draft deliberately, as
   incompatibilities between this specification and various versions of
   other drafts could lead to problems.

   It is missing guidance on if/how recommended that implementers first detect and validate the Date
   "Signature-Input" header relates to
   signature Creation Time.  There are cases where they may be
   different, such as if a signature was pre-created.  Should Creation
   Time default defined in this specification to the value detect that
   this standard is in use and not an alternative.  If the Date "Signature-
   Input" header if the "created"
   parameter is not specified?

B.1.17.  Remove algorithm-specific rules for content identifiers

   The rules that restrict when the signer present, all "Signature" headers can or must include certain
   identifiers appear to be related 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:

   -----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 pseudo-revving context of the Cavage
   draft examples in examples within this and future documents
   that happened when reference this section.  Unless otherwise specified, within the "hs2019" algorithm was introduced.  We
   should drop these rules, as
   context of examples it can be expected that anyone
   implementing this draft will support all content identifiers.

B.1.18.  Add guidance for signing compressed headers

   The draft should provide guidance on how to sign headers when
   [RFC7541] is used.  This guidance might be as simple as "sign the
   uncompressed header field value."

B.1.19.  Transformations to Via header field value break verification

   Intermediaries are permitted to strip comments from assumed that the "Via" header
   field value, signer and consolidate related sequences of entries.  The
   canonicalization rules do not account for verifier
   understand these changes, and thus
   they cause signature verification to fail if the "Via" header is
   signed.  At the very least, guidance on signing or not signing "Via"
   headers needs to be included.

B.1.20.  Case changes to case-insensitive header field values break
         verification

   Some header field "keyid" mappings.  These "keyid" values are case-insensitive, in whole not
   reserved, and deployments are free to use them, with these
   associations or others.

     +============+=================================+================+
     | keyid      | Algorithm                       | Verification   |
     |            |                                 | Key            |
     +============+=================================+================+
     | test-key-a | "hs2019", using RSASSA-PSS      | The public key |
     |            | [RFC8017] and SHA-512 [RFC6234] | specified in part.   |
     |            |                                 | Appendix B.1.1 |
     +------------+---------------------------------+----------------+
     | test-key-b | rsa-sha256                      | The canonicalization rules do not account for this, thus a case
   change to a covered header field value causes verification to fail.

B.1.21.  Need more examples for Signature header

   Add more public key |
     |            |                                 | specified in   |
     |            |                                 | Appendix B.1.1 |
     +------------+---------------------------------+----------------+

                                  Table 9

B.3.  Test Cases

   This section provides non-normative examples showing different cases e.g, where "created" or
   "expires" are not present.

B.1.22.  Expiration not needed

   In many cases, putting the expiration of the signature into the hands
   of the signer opens up more options for failures than necessary.
   Instead of the "expires", any verifier can use the "created" field
   and an internal lifetime or offset to calculate expiration.  We
   should consider dropping the "expires" field.

B.2.  Features

B.2.1.  Define more content identifiers

   It should that may be possible used as test
   cases to independently include 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 Generation

B.3.1.1.  hs2019 signature over minimal recommended content
   and

   This presents metadata properties in Covered Content:

   *  The signature's Algorithm

   *  The signature's Covered Content

   *  The value used for the "keyId" parameter

   *  Request method

   *  Individual components of the effective request URI: scheme,
      authority, path, query

   *  Status code

   *  Request body (currently supported via Digest header [RFC3230] )

B.2.2.  Multiple signature support

   (( Editor's note: I believe this use case is theoretical.  Please let
   me know if this is a use case you have. ))

   There may be scenarios where attaching multiple signatures to a
   single message is useful:

   *  A gateway attaches a signature Signature using "hs2019", over headers it adds (e.g.,
      "Forwarded") to messages already signed by the user agent.

   *  A signer attaches two signatures signed by different keys, minimum
   recommended data to be
      verified by different entities.

   This could be addressed by changing the sign:

           +==============+===================================+
           | Property     | Value                             |
           +==============+===================================+
           | Algorithm    | "hs2019", using RSASSA-PSS        |
           |              | [RFC8017] using SHA-512 [RFC6234] |
           +--------------+-----------------------------------+
           | Covered      | @request-target                   |
           | Content      |                                   |
           +--------------+-----------------------------------+
           | Creation     | 8:51:35 PM GMT, June 7th, 2014    |
           | Time         |                                   |
           +--------------+-----------------------------------+
           | Expiration   | Undefined                         |
           | Time         |                                   |
           +--------------+-----------------------------------+
           | Verification | The public key specified in       |
           | Key Material | Appendix B.1.1.                   |
           +--------------+-----------------------------------+

                                 Table 10

   The Signature header syntax to
   accept a list of parameter sets for a single signature, e.g., by
   separating parameters with "";"" instead of "","".  It may also be
   necessary to include a Input is:

"@request-target": post /foo?param=value&pet=dog
"@signature-params": ("@request-target"); keyid="test-key-a"; created=1402170695

   The signature identifier parameter.

B.2.3.  Support for incremental signing of header field value list items

   (( Editor's note: I believe this use case is theoretical.  Please let
   me know if this is a use case you have. ))

   Currently, signing a is:

   QaVaWYfF2da6tG66Xtd0GrVFChJ0fOWUe/C6kaYESPiYYwnMH9egOgyKqgLLY9NQJFk7b
   QY834sHEUwjS5ByEBaO3QNwIvqEY1qAAU/2MX14tc9Yn7ELBnaaNHaHkV3xVO9KIuLT7V
   6e4OUuGb1axfbXpMgPEql6CEFrn6K95CLuuKP5/gOEcBtmJp5L58gN4VvZrk2OVA6U971
   YiEDNuDa4CwMcQMvcGssbc/L3OULTUffD/1VcPtdGImP2uvVQntpT8b2lBeBpfh8MuaV2
   vtzidyBYFtAUoYhRWO8+ntqA1q2OK4LMjM2XgDScSVWvGdVd459A0wI9lRlnPap3zg==

   A possible "Signature-Input" and "Signature" header field value is all-or-nothing: either the
   entire value is signed, or none of it is.  For containing this
   signature is:

   # NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@request-target");
       keyid="test-key-a"; created=1402170695
   Signature: sig1=:QaVaWYfF2da6tG66Xtd0GrVFChJ0fOWUe/C6kaYESPiYYwnMH9eg\
       OgyKqgLLY9NQJFk7bQY834sHEUwjS5ByEBaO3QNwIvqEY1qAAU/2MX14tc9Yn7ELB\
       naaNHaHkV3xVO9KIuLT7V6e4OUuGb1axfbXpMgPEql6CEFrn6K95CLuuKP5/gOEcB\
       tmJp5L58gN4VvZrk2OVA6U971YiEDNuDa4CwMcQMvcGssbc/L3OULTUffD/1VcPtd\
       GImP2uvVQntpT8b2lBeBpfh8MuaV2vtzidyBYFtAUoYhRWO8+ntqA1q2OK4LMjM2X\
       gDScSVWvGdVd459A0wI9lRlnPap3zg==:

B.3.1.2.  hs2019 signature covering all header fields

   This presents metadata for a Signature using "hs2019" that use
   list syntax, it would be useful to be able to specify which items covers all
   header fields in the list are signed. request:

       +==============+============================================+
       | Property     | Value                                      |
       +==============+============================================+
       | Algorithm    | "hs2019", using RSASSA-PSS [RFC8017] using |
       |              | SHA-512 [RFC6234]                          |
       +--------------+--------------------------------------------+
       | Covered      | "@request-target", "host", "date",         |
       | Content      | "content-type", "digest", "content-length" |
       +--------------+--------------------------------------------+
       | Creation     | 8:51:35 PM GMT, June 7th, 2014             |
       | Time         |                                            |
       +--------------+--------------------------------------------+
       | Expiration   | Undefined                                  |
       | Time         |                                            |
       +--------------+--------------------------------------------+
       | Verification | The public key specified in                |
       | Key Material | Appendix B.1.1.                            |
       +--------------+--------------------------------------------+

                                  Table 11

   The Signature Input is:

"@request-target": post /foo?param=value&pet=dog
"host": example.com
"date": Tue, 07 Jun 2014 20:51:35 GMT
"content-type": application/json
"digest": SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
"content-length": 18
"@signature-params": ("@request-target" "host" "date" "content-type" "digest" "content-length"); keyid="test-key-a"; alg="hs2019"; created=1402170695

   The signature value is:

   B24UG4FaiE2kSXBNKV4DA91J+mElAhS3mncrgyteAye1GKMpmzt8jkHNjoudtqw3GngGY
   3n0mmwjdfn1eA6nAjgeHwl0WXced5tONcCPNzLswqPOiobGeA5y4WE8iBveel30OKYVel
   0lZ1OnXOmN5TIEIIPo9LrE+LzZis6A0HA1FRMtKgKGhT3N965pkqfhKbq/V48kpJKT8+c
   Zs0TOn4HFMG+OIy6c9ofSBrXD68yxP6QYTz6xH0GMWawLyPLYR52j3I05fK1ylAb6K0ox
   PxzQ5nwrLD+mUVPZ9rDs1En6fmOX9xfkZTblG/5D+s1fHHs9dDXCOVkT5dLS8DjdIA==

   A simple approach that allowed the signer to indicate the list size
   at signing time would allow possible "Signature-Input" and "Signature" header containing this
   signature is:

   # NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@request-target" "host" "date"
           "content-type" "digest" "content-length"); keyid="test-key-a";
       alg="hs2019"; created=1402170695
   Signature: sig1=:B24UG4FaiE2kSXBNKV4DA91J+mElAhS3mncrgyteAye1GKMpmzt8\
       jkHNjoudtqw3GngGY3n0mmwjdfn1eA6nAjgeHwl0WXced5tONcCPNzLswqPOiobGe\
       A5y4WE8iBveel30OKYVel0lZ1OnXOmN5TIEIIPo9LrE+LzZis6A0HA1FRMtKgKGhT\
       3N965pkqfhKbq/V48kpJKT8+cZs0TOn4HFMG+OIy6c9ofSBrXD68yxP6QYTz6xH0G\
       MWawLyPLYR52j3I05fK1ylAb6K0oxPxzQ5nwrLD+mUVPZ9rDs1En6fmOX9xfkZTbl\
       G/5D+s1fHHs9dDXCOVkT5dLS8DjdIA==:

B.3.2.  Signature Verification

B.3.2.1.  Minimal Required Signature Header

   This presents a signer to sign "Signature-Input" and "Signature" header fields that are
   may be appended to by intermediaries as the message makes its way to containing
   only the recipient.  Specifying list size minimal required parameters:

   # NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=(); keyid="test-key-a"; created=1402170695
   Signature: sig1=:cxieW5ZKV9R9A70+Ua1A/1FCvVayuE6Z77wDGNVFSiluSzR9TYFV\
       vwUjeU6CTYUdbOByGMCee5q1eWWUOM8BIH04Si6VndEHjQVdHqshAtNJk2Quzs6WC\
       2DkV0vysOhBSvFZuLZvtCmXRQfYGTGhZqGwq/AAmFbt5WNLQtDrEe0ErveEKBfaz+\
       IJ35zhaj+dun71YZ82b/CRfO6fSSt8VXeJuvdqUuVPWqjgJD4n9mgZpZFGBaDdPiw\
       pfbVZHzcHrumFJeFHWXH64a+c5GN+TWlP8NPg2zFdEc/joMymBiRelq236WGm5VvV\
       9a22RW2/yLmaU/uwf9v40yGR/I1NRA==:

   The corresponding signature metadata derived from this header field
   is:

      +=================+==========================================+
      | Property        | Value                                    |
      +=================+==========================================+
      | Algorithm       | "hs2019", using RSASSA-PSS using SHA-256 |
      +-----------------+------------------------------------------+
      | Covered Content | ``                                       |
      +-----------------+------------------------------------------+
      | Creation Time   | 8:51:35 PM GMT, June 7th, 2014           |
      +-----------------+------------------------------------------+
      | Expiration Time | Undefined                                |
      +-----------------+------------------------------------------+
      | Verification    | The public key specified in terms of number of items
   could introduce risks of list syntax is not strictly adhered to
   (e.g., a malicious party crafts              |
      | Key Material    | Appendix B.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 12

   The corresponding Signature Input is:

"@signature-params": sig1=(); alg="hs2019"; keyid="test-key-a"; created=1402170695

B.3.2.2.  Minimal Recommended Signature Header

   This presents a value that gets parsed by the
   application as 5 items, but by the verifier as 4).  Specifying list
   size in number of octets might address this, but more exploration is
   required.

B.2.4.  Support expected authority changes

   In some cases, the authority of "Signature-Input" and "Signature" header containing
   only the effective request URI may be
   expected to change, for example minimal required and recommended parameters:

   # NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=(); alg="hs2019"; keyid="test-key-a";
       created=1402170695
   Signature: sig1=:cxieW5ZKV9R9A70+Ua1A/1FCvVayuE6Z77wDGNVFSiluSzR9TYFV\
       vwUjeU6CTYUdbOByGMCee5q1eWWUOM8BIH04Si6VndEHjQVdHqshAtNJk2Quzs6WC\
       2DkV0vysOhBSvFZuLZvtCmXRQfYGTGhZqGwq/AAmFbt5WNLQtDrEe0ErveEKBfaz+\
       IJ35zhaj+dun71YZ82b/CRfO6fSSt8VXeJuvdqUuVPWqjgJD4n9mgZpZFGBaDdPiw\
       pfbVZHzcHrumFJeFHWXH64a+c5GN+TWlP8NPg2zFdEc/joMymBiRelq236WGm5VvV\
       9a22RW2/yLmaU/uwf9v40yGR/I1NRA==:

   The corresponding signature metadata derived from "public-service-
   name.example.com" to "service-host-1.public-service-
   name.example.com". this header field
   is:

      +=================+==========================================+
      | Property        | Value                                    |
      +=================+==========================================+
      | Algorithm       | "hs2019", using RSASSA-PSS using SHA-512 |
      +-----------------+------------------------------------------+
      | Covered Content | ``                                       |
      +-----------------+------------------------------------------+
      | Creation Time   | 8:51:35 PM GMT, June 7th, 2014           |
      +-----------------+------------------------------------------+
      | Expiration Time | Undefined                                |
      +-----------------+------------------------------------------+
      | Verification    | The public key specified in              |
      | Key Material    | Appendix B.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 13

   The corresponding Signature Input is:

   "@signature-params": sig1=(); alg="rsa-sha256"; keyid="test-key-b"

B.3.2.3.  Minimal Signature Header using rsa-sha256

   This is commonly the case for services that are
   hosted behind a load-balancing gateway, where the client sends
   requests to presents a publicly known domain name for the service, minimal "Signature-Input" and these
   requests are transformed by the gateway into requests to specific
   hosts in "Signature" header for
   a signature using the service fleet.

   One possible way to handle "rsa-sha256" algorithm:

   # NOTE: '\' line wrapping per RFC 8792

   Signature: sig1=("date"); alg=rsa-sha256; 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 would be to special-case the Host header field to allow verifier to substitute a known expected value,
   or a value provided
   is:

         +===========================+==========================+
         | Property                  | Value                    |
         +===========================+==========================+
         | Algorithm                 | rsa-sha256               |
         +---------------------------+--------------------------+
         | Covered Content           | date                     |
         +---------------------------+--------------------------+
         | Creation Time             | Undefined                |
         +---------------------------+--------------------------+
         | Expiration Time           | Undefined                |
         +---------------------------+--------------------------+
         | Verification Key Material | The public key specified |
         |                           | in another header field (e.g., "Via") when
   generating the Appendix B.1.1.       |
         +---------------------------+--------------------------+

                                 Table 14

   The corresponding Signature Input, provided that the verifier also
   recognizes the real value in the "Host" header.  Alternatively, this
   logic could apply to an "(audience)" content identifier.

B.2.5.  Support for signing specific cookies

   A signer may only wish to sign one or a few cookies, for example if
   the website requires its authentication state cookie to be signed,
   but also sets other cookies (e.g., for analytics, ad tracking, etc.) Input is:

   "date": Tue, 07 Jun 2014 20:51:35 GMT
   "@signature-params": ("date"); alg=rsa-sha256; keyid="test-key-b"

Acknowledgements

   This specification is was initially based on the draft-cavage-http-signatures draft-cavage-http-
   signatures internet draft.  The editor 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

      -  Since -01 -02

      -  -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:member-name". ""x-dictionary-field";key=member-name".

         o  Defined content identifiers for first N members of a List,
            e.g., "x-list-field:4". ""x-list-field":prefix=4".

         o  Fixed up examples.

         o  Updated introduction now that it's adopted.

         o  Defined specialty content identifiers and a means to extend
            them.

         o  Required signature parameters to be included in signature.

         o  Added guidance on backwards compatibility, detection, and
            use of signature methods.

      -  -01

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

         o  Added real example values for Creation Time and Expiration
            Time.

         o  Minor editorial corrections and readability improvements.

      -  -00

         o  Initialized from draft-richanna-http-message-signatures-00,
            following adoption by the working group.

   *  draft-richanna-http-message-signatures

      -  -00

         o  Converted to xml2rfc v3 and reformatted to comply with RFC
            style guides.

         o  Removed Signature auth-scheme definition and related
            content.

         o  Removed conflicting normative requirements for use of
            algorithm parameter.  Now MUST NOT be relied upon.

         o  Removed Extensions appendix.

         o  Rewrote abstract and introduction to explain context and
            need, and challenges inherent in signing HTTP messages.

         o  Rewrote and heavily expanded algorithm definition, retaining
            normative requirements.

         o  Added definitions for key terms, referenced RFC 7230 for
            HTTP terms.

         o  Added examples for canonicalization and signature generation
            steps.

         o  Rewrote Signature header definition, retaining normative
            requirements.

         o  Added default values for algorithm and expires parameters.

         o  Rewrote HTTP Signature Algorithms registry definition.
            Added change control policy and registry template.  Removed
            suggested URI.

         o  Added IANA HTTP Signature Parameter registry.

         o  Added additional normative and informative references.

         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/