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


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

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 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
   is a work-in-progress and not yet suitable for deployment.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 May 2021.




Backman, et al.            Expires 21 May 2021                  [Page 1]


Internet-Draft            Signing HTTP Messages            November 2020


Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Discussion . . . . . . . . . . . . . . . . .   5
     1.2.  HTTP Message Transformations  . . . . . . . . . . . . . .   5
     1.3.  Safe Transformations  . . . . . . . . . . . . . . . . . .   6
     1.4.  Conventions and Terminology . . . . . . . . . . . . . . .   7
   2.  Identifying and Canonicalizing Content  . . . . . . . . . . .   8
     2.1.  HTTP Header Fields  . . . . . . . . . . . . . . . . . . .   8
       2.1.1.  Canonicalization Examples . . . . . . . . . . . . . .   9
     2.2.  Dictionary Structured Field Members . . . . . . . . . . .   9
       2.2.1.  Canonicalization Examples . . . . . . . . . . . . . .  10
     2.3.  List Prefixes . . . . . . . . . . . . . . . . . . . . . .  10
       2.3.1.  Canonicalization Examples . . . . . . . . . . . . . .  10
     2.4.  Signature Creation Time . . . . . . . . . . . . . . . . .  11
     2.5.  Signature Expiration Time . . . . . . . . . . . . . . . .  11
     2.6.  Target Endpoint . . . . . . . . . . . . . . . . . . . . .  11
       2.6.1.  Canonicalization Examples . . . . . . . . . . . . . .  12
   3.  HTTP Message Signatures . . . . . . . . . . . . . . . . . . .  12
     3.1.  Signature Metadata  . . . . . . . . . . . . . . . . . . .  13
     3.2.  Creating a Signature  . . . . . . . . . . . . . . . . . .  13
       3.2.1.  Choose and Set Signature Metadata Properties  . . . .  14
       3.2.2.  Create the Signature Input  . . . . . . . . . . . . .  16
       3.2.3.  Sign the Signature Input  . . . . . . . . . . . . . .  17
     3.3.  Verifying a Signature . . . . . . . . . . . . . . . . . .  17
       3.3.1.  Enforcing Application Requirements  . . . . . . . . .  18
   4.  Including a Message Signature in a Message  . . . . . . . . .  19
     4.1.  The 'Signature-Input' HTTP Header . . . . . . . . . . . .  19
       4.1.1.  Metadata Parameters . . . . . . . . . . . . . . . . .  19
     4.2.  The 'Signature' HTTP Header . . . . . . . . . . . . . . .  20
     4.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  20
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     5.1.  HTTP Signature Algorithms Registry  . . . . . . . . . . .  21
       5.1.1.  Registration Template . . . . . . . . . . . . . . . .  21



Backman, et al.            Expires 21 May 2021                  [Page 2]


Internet-Draft            Signing HTTP Messages            November 2020


       5.1.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  22
     5.2.  HTTP Signature Metadata Parameters Registry . . . . . . .  24
       5.2.1.  Registration Template . . . . . . . . . . . . . . . .  24
       5.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  24
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  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  . . . . . . . . . . . . . . . .  29
       A.3.2.  Signature Verification  . . . . . . . . . . . . . . .  32
   Appendix B.  Topics for Working Group Discussion  . . . . . . . .  34
     B.1.  Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  34
       B.1.1.  Confusing guidance on algorithm and key
               identification  . . . . . . . . . . . . . . . . . . .  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  . . . . . . . . . . . . . . . . .  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  . . . . . . . . . . . . . . . . . . . .  36
       B.1.8.  Multiple Set-Cookie headers are not well supported  .  36
       B.1.9.  Covered Content list is not signed  . . . . . . . . .  37
       B.1.10. Algorithm is not signed . . . . . . . . . . . . . . .  37
       B.1.11. Verification key identifier is not signed . . . . . .  37
       B.1.12. Max values, precision for Integer String and Decimal
               String not defined  . . . . . . . . . . . . . . . . .  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  . . . . . . . . . . . . . . . . . . . . .  37
       B.1.15. Should require lowercased header field names as
               identifiers . . . . . . . . . . . . . . . . . . . . .  37
       B.1.16. Reconcile Date header and Creation Time . . . . . . .  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



Backman, et al.            Expires 21 May 2021                  [Page 3]


Internet-Draft            Signing HTTP Messages            November 2020


     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.





Backman, et al.            Expires 21 May 2021                  [Page 4]


Internet-Draft            Signing HTTP Messages            November 2020


   *  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).




Backman, et al.            Expires 21 May 2021                  [Page 5]


Internet-Draft            Signing HTTP Messages            November 2020


   *  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" and "Host" header field that when
      applied together do not result in a change to the message's
      effective request URI, as defined in Section 5.5 of [MESSAGING].

   Additionally, all changes to content not covered by the signature are
   considered safe.






Backman, et al.            Expires 21 May 2021                  [Page 6]


Internet-Draft            Signing HTTP Messages            November 2020


1.4.  Conventions and Terminology

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

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

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

   For brevity, the term "signature" on its own is used in this document
   to refer to both digital signatures and keyed MACs.  Similarly, the
   verb "sign" refers to the generation of either a digital signature or
   keyed MAC over a given input string.  The qualified term "digital
   signature" refers specifically to the output of an asymmetric
   cryptographic signing operation.

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

   Decimal String

      An Integer String optionally concatenated with a period "."
      followed by a second Integer String, representing a positive real
      number expressed in base 10.  The first Integer String represents
      the integral portion of the number, 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
      can reference. ))

   Integer String

      A US-ASCII string of one or more digits "0-9", representing a
      positive integer in base 10. (( Editor's note: There's got to be a
      definition for this that we can reference. ))

   Signer

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

   Verifier



Backman, et al.            Expires 21 May 2021                  [Page 7]


Internet-Draft            Signing HTTP Messages            November 2020


      An entity that is verifying or has verified an HTTP Message
      Signature against an HTTP Message.  Note that an HTTP Message
      Signature may be verified multiple times, potentially by different
      entities.

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

2.  Identifying and Canonicalizing Content

   In order to allow signers and verifiers to establish which content is
   covered by a signature, this document defines content identifiers for
   signature metadata and discrete pieces of message content that may be
   covered by an HTTP Message Signature.

   Some content within HTTP messages may undergo transformations that
   change the bitwise value without altering meaning of the content (for
   example, the merging together of header fields with the same name).
   Message content must therefore be canonicalized before it is signed,
   to ensure that a signature can be verified despite such innocuous
   transformations.  This document defines rules for each content
   identifier that transform the identifier's associated content into
   such a canonical form.

   The following sections define content identifiers, their associated
   content, and their canonicalization rules.

2.1.  HTTP Header Fields

   An HTTP header 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 content identifiers.

   An HTTP header field value is canonicalized as follows:

   1.  Create an ordered list of the field values of each instance of
       the header field in the message, in the order that they occur (or
       will occur) in the message.

   2.  Strip leading and trailing whitespace from each item in the list.

   3.  Concatenate the list items together, with a comma "," and space "
       " between each item.  The resulting string is the canonicalized
       value.



Backman, et al.            Expires 21 May 2021                  [Page 8]


Internet-Draft            Signing HTTP Messages            November 2020


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

         +===================+==================================+
         | Header Field      | Canonicalized Value              |
         +===================+==================================+
         | cache-control     | max-age=60, must-revalidate      |
         +-------------------+----------------------------------+
         | date              | Tue, 07 Jun 2014 20:51:35 GMT    |
         +-------------------+----------------------------------+
         | server            | www.example.com                  |
         +-------------------+----------------------------------+
         | x-empty-header    |                                  |
         +-------------------+----------------------------------+
         | x-obs-fold-header | Obsolete line folding.           |
         +-------------------+----------------------------------+
         | x-ows-header      | Leading and trailing whitespace. |
         +-------------------+----------------------------------+

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

2.2.  Dictionary Structured Field Members

   An individual member in the value of a Dictionary Structured Field is
   identified by the lowercased field name, followed by a semicolon
   "":"", followed by the member name.  An individual member in the
   value of a Dictionary Structured Field is canonicalized by applying
   the serialization algorithm described in Section 4.1.2 of
   [StructuredFields] on a Dictionary containing only that member.






Backman, et al.            Expires 21 May 2021                  [Page 9]


Internet-Draft            Signing HTTP Messages            November 2020


2.2.1.  Canonicalization Examples

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

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

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

               +====================+=====================+
               | 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 of
                   Dictionary member canonicalization.

2.3.  List Prefixes

   A prefix of a List Structured Field consisting of the first N members
   in the field's value (where N is an integer greater than 0 and less
   than or equal to the number of members in the List) is identified by
   the lowercased field name, followed by a semicolon "":"", followed by
   N expressed as an Integer String.  A list prefix is canonicalized by
   applying the serialization algorithm described in Section 4.1.1 of
   [StructuredFields] on a List containing only the first N members as
   specified in the list prefix, in the order they appear in the
   original List.

2.3.1.  Canonicalization Examples

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

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

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




Backman, et al.            Expires 21 May 2021                 [Page 10]


Internet-Draft            Signing HTTP Messages            November 2020


               +====================+=====================+
               | 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 as the number of seconds since
   the Epoch, 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

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

   Its canonicalized value is a Decimal String containing the
   signature's Expiration Time expressed as the number of seconds since
   the Epoch, 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 of the effective request URI, is identified by the
   "*request-target" identifier.



Backman, et al.            Expires 21 May 2021                 [Page 11]


Internet-Draft            Signing HTTP Messages            November 2020


   Its value is canonicalized as follows:

   1.  Take the lowercased HTTP method of the message.

   2.  Append a space " ".

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

2.6.1.  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 of "*request-target"
                             canonicalization.

3.  HTTP Message Signatures

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




Backman, et al.            Expires 21 May 2021                 [Page 12]


Internet-Draft            Signing HTTP Messages            November 2020


3.1.  Signature Metadata

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

   Algorithm

      An HTTP Signature Algorithm defined in the HTTP Signature
      Algorithms Registry defined in this document.  It describes the
      signing and verification algorithms for the signature.

   Creation Time

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

   Covered Content

      An ordered list of content identifiers (Section 2) that indicates
      the metadata and message content that is covered by the signature.
      The order of identifiers in this list affects signature generation
      and verification, and therefore MUST be preserved.

   Expiration Time

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

   Verification Key Material

      The key material required to verify the signature.

3.2.  Creating a Signature

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

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

   2.  Create the Signature Input Section 3.2.2

   3.  Sign the Signature Input Section 3.2.3




Backman, et al.            Expires 21 May 2021                 [Page 13]


Internet-Draft            Signing HTTP Messages            November 2020


   The following sections describe each of 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 HTTP Signature Algorithms Registry defined by
       this document, and sets the signature's Algorithm property to
       that value.  The signer MUST NOT choose an algorithm marked
       "Deprecated".  The mechanism by which the signer chooses an
       algorithm is out of scope for this document.

   2.  The signer chooses key material to use for signing and
       verification, and sets the signature's Verification Key Material
       property to the key material required for verification.  The
       signer MUST choose key material that is appropriate for the
       signature's Algorithm, and that conforms to any requirements
       defined by the Algorithm, such as key size or format.  The
       mechanism by which the signer chooses key material is out of
       scope for this document.

   3.  The signer sets the signature's Creation Time property to the
       current time.

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

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

       *  Each identifier MUST be one of those defined in Section 2.

       *  This list MUST NOT be empty, as this would result in creating
          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" in the list.

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







Backman, et al.            Expires 21 May 2021                 [Page 14]


Internet-Draft            Signing HTTP Messages            November 2020


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

   For example, given the following HTTP message:

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

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

     +==============+================================================+
     | Property     | Value                                          |
     +==============+================================================+
     | Algorithm    | hs2019                                         |
     +--------------+------------------------------------------------+
     | Covered      | "*request-target", "*created", "host", "date", |
     | Content      | "cache-contol", "x-emptyheader", "x-example",  |
     |              | "x-dictionary:b", "x-dictionary:a", "x-list:3" |
     +--------------+------------------------------------------------+
     | Creation     | 1402174295                                     |
     | Time         |                                                |
     +--------------+------------------------------------------------+
     | Expiration   | 1402174595                                     |
     | Time         |                                                |
     +--------------+------------------------------------------------+
     | Verification | The public key provided in Appendix A.1.1 and  |
     | Key Material | identified by the "keyId" value "test-key-a".  |
     +--------------+------------------------------------------------+

               Table 5: Non-normative example metadata values










Backman, et al.            Expires 21 May 2021                 [Page 15]


Internet-Draft            Signing HTTP Messages            November 2020


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 a US-ASCII string consisting of the
   lowercased identifier followed with a colon "":"", a space "" "", and
   the identifier's canonicalized 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 is
   not present or malformed in the message, 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 in
   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 a List Prefix that
   references a header field 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 5, the
   corresponding Signature Input is:













Backman, et al.            Expires 21 May 2021                 [Page 16]


Internet-Draft            Signing HTTP Messages            November 2020


   *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 header with some whitespace.
   x-dictionary: b=2
   x-dictionary: a=1
   x-list: (a, b, c)

              Figure 1: Non-normative example Signature Input

3.2.3.  Sign the Signature Input

   The signer signs the Signature Input using the signing algorithm
   described by the signature's Algorithm property, and the key material
   chosen by the signer.  The 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 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 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 required to be covered by the
       signature.

   2.  Use the received HTTP message and the signature's metadata to
       recreate the Signature Input, using the process described in
       Section 3.2.2.

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



Backman, et al.            Expires 21 May 2021                 [Page 17]


Internet-Draft            Signing HTTP Messages            November 2020


   A signature with a Creation Time that is in the future or an
   Expiration Time that is in the past MUST NOT be processed.

   The verifier MUST ensure that a signature's Algorithm is appropriate
   for the key material the verifier will use to verify the signature.
   If the Algorithm is not appropriate for the key material (for
   example, if it is the wrong size, or in the wrong format), the
   signature MUST NOT be processed.

3.3.1.  Enforcing Application Requirements

   The verification requirements specified in this document are intended
   as a baseline set of restrictions that are generally applicable to
   all use cases.  Applications using HTTP Message Signatures MAY impose
   requirements above and beyond those specified by this document, as
   appropriate for their use case.

   Some non-normative examples of additional requirements an application
   might define are:

   *  Requiring a specific set of header fields to be signed (e.g.,
      Authorization, Digest).

   *  Enforcing a maximum signature age.

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

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

   Application-specific requirements are expected and encouraged.  When
   an application defines additional requirements, it MUST enforce them
   during the signature verification process, and signature verification
   MUST fail if the signature does not conform to the application's
   requirements.

   Applications MUST enforce the requirements defined in this document.
   Regardless of use case, applications MUST NOT accept signatures that
   do not conform to these requirements.











Backman, et al.            Expires 21 May 2021                 [Page 18]


Internet-Draft            Signing HTTP Messages            November 2020


4.  Including a Message Signature in a Message

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

4.1.  The 'Signature-Input' HTTP Header

   The "Signature-Input" HTTP header field is a Dictionary Structured
   Header [StructuredFields] containing the metadata for zero or more
   message signatures generated from content within the HTTP message.
   Each member describes a single message signature.  The member's name
   is an identifier that uniquely identifies the message signature
   within the context of the HTTP message.  The member's value is the
   message signature's Covered Content, expressed as a List of Tokens.
   Further signature metadata is expressed in parameters on the member
   value, as described below.

4.1.1.  Metadata Parameters

   The parameters on each "Signature-Input" member value contain
   metadata about the signature.  Each parameter name MUST be a
   parameter name registered in the IANA HTTP Signatures Metadata
   Parameters Registry 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 this document.  Verifiers MUST
      determine the signature's Algorithm from the "keyId" parameter
      rather than from "alg".  If "alg" is provided 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 the
      signature's Creation Time, expressed as the canonicalized value of
      the "*created" content identifier, as defined in Section 2.  If
      not specified, the signature's Creation Time is undefined.  This



Backman, et al.            Expires 21 May 2021                 [Page 19]


Internet-Draft            Signing HTTP Messages            November 2020


      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 Expiration Time, expressed as the canonicalized value
      of the "*expires" content identifier, as defined in Section 2.  If
      the signature does not have an Expiration Time, this parameter
      MUST be omitted.  If not specified, the signature's Expiration
      Time is undefined.

   keyId

      REQUIRED.  The "keyId" parameter is a String whose value can be
      used by a verifier to identify and/or obtain the signature's
      Verification Key Material.  Further format and semantics of this
      value are out of scope for this document.

4.2.  The 'Signature' HTTP Header

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

4.3.  Examples

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



Backman, et al.            Expires 21 May 2021                 [Page 20]


Internet-Draft            Signing HTTP Messages            November 2020


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

   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 this registry are given in
   Section 5.1.2.  Future assignments and modifications to existing
   assignment are to be made through the Expert Review registration
   policy [RFC8126] and shall follow the template presented in
   Section 5.1.1.

5.1.1.  Registration Template

   Algorithm Name

      An identifier for the HTTP Signature Algorithm.  The name MUST be
      an ASCII string consisting only of lower-case characters (""a"" -
      ""z""), digits (""0"" - ""9""), and hyphens (""-""), and SHOULD
      NOT exceed 20 characters in length.  The identifier MUST be unique
      within the context of the registry.

   Status

      A brief text description of the status of the algorithm.  The



Backman, et al.            Expires 21 May 2021                 [Page 21]


Internet-Draft            Signing HTTP Messages            November 2020


      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as to the reason for
      the status.

   Description

      A description of the algorithm used to sign the signing string
      when generating an HTTP Message Signature, or instructions on how
      to determine that algorithm.  When the description specifies an
      algorithm, it MUST include a reference to the document or
      documents that define the algorithm.

5.1.2.  Initial Contents

   (( MS: The references in this section are problematic as many of the
   specifications that they refer to are too implementation specific,
   rather than just pointing to the proper signature and hashing
   specifications.  A better approach might be just specifying the
   signature and hashing function specifications, leaving implementers
   to connect the dots (which are not that hard 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]




Backman, et al.            Expires 21 May 2021                 [Page 22]


Internet-Draft            Signing HTTP Messages            November 2020


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"




Backman, et al.            Expires 21 May 2021                 [Page 23]


Internet-Draft            Signing HTTP Messages            November 2020


   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 the "Signature-Input" Structured Header, whose
   member values may have parameters containing metadata about a message
   signature.  IANA is asked to create and maintain a new registry
   titled "HTTP Signature Metadata Parameters" to record and maintain
   the set of parameters defined for use with member values in the
   "Signature-Input" Structured Header.  Initial values for this
   registry are given in Section 5.2.2.  Future assignments and
   modifications to existing assignments are to be made through the
   Expert Review registration policy [RFC8126] and shall follow the
   template presented in Section 5.2.1.

5.2.1.  Registration Template

5.2.2.  Initial Contents

   The table below contains the initial contents of the HTTP Signature
   Metadata Parameters Registry.  Each row in the table represents a
   distinct entry in the registry.

           +=========+========+================================+
           | Name    | Status | Reference(s)                   |
           +=========+========+================================+
           | alg     | Active | Section 4.1.1 of this document |
           +---------+--------+--------------------------------+
           | created | Active | Section 4.1.1 of this document |
           +---------+--------+--------------------------------+
           | expires | Active | Section 4.1.1 of this document |
           +---------+--------+--------------------------------+
           | keyId   | Active | Section 4.1.1 of this document |
           +---------+--------+--------------------------------+

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








Backman, et al.            Expires 21 May 2021                 [Page 24]


Internet-Draft            Signing HTTP Messages            November 2020


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>.




Backman, et al.            Expires 21 May 2021                 [Page 25]


Internet-Draft            Signing HTTP Messages            November 2020


   [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/info/rfc8174>.

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

   [StructuredFields]
              "Structured Field Vaues 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 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>.





Backman, et al.            Expires 21 May 2021                 [Page 26]


Internet-Draft            Signing HTTP Messages            November 2020


   [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., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/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 for HTTP Signatures", 2013,
              <https://web-payments.org/specs/source/http-signatures-
              audit/>.

Appendix A.  Examples

A.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.

A.1.1.  Example Key RSA test

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












Backman, et al.            Expires 21 May 2021                 [Page 27]


Internet-Draft            Signing HTTP Messages            November 2020


   -----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

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




Backman, et al.            Expires 21 May 2021                 [Page 28]


Internet-Draft            Signing HTTP Messages            November 2020


     +============+=================================+================+
     | keyId      | Algorithm                       | Verification   |
     |            |                                 | Key            |
     +============+=================================+================+
     | test-key-a | "hs2019", using RSASSA-PSS      | The public key |
     |            | [RFC8017] and SHA-512 [RFC6234] | specified in   |
     |            |                                 | Appendix A.1.1 |
     +------------+---------------------------------+----------------+
     | test-key-b | rsa-sha256                      | The public key |
     |            |                                 | specified in   |
     |            |                                 | Appendix A.1.1 |
     +------------+---------------------------------+----------------+

                                  Table 7

A.3.  Test Cases

   This section provides non-normative examples that may be used as test
   cases to validate implementation correctness.  These examples are
   based on the following HTTP message:

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

   {"hello": "world"}

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 to sign:















Backman, et al.            Expires 21 May 2021                 [Page 29]


Internet-Draft            Signing HTTP Messages            November 2020


           +==============+===================================+
           | 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 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 "Signature-Input" and "Signature" header containing this
   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==:






Backman, et al.            Expires 21 May 2021                 [Page 30]


Internet-Draft            Signing HTTP Messages            November 2020


A.3.1.2.  hs2019 signature covering all header fields

   This presents metadata for a Signature using "hs2019" that covers all
   header fields in 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 | The public key specified 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 signature value is:

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

   A possible "Signature-Input" and "Signature" header containing this
   signature is:





Backman, et al.            Expires 21 May 2021                 [Page 31]


Internet-Draft            Signing HTTP Messages            November 2020


   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 Header

   This presents a "Signature-Input" and "Signature" header containing
   only 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 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 in              |
      | Key Material    | Appendix A.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 10

   The corresponding Signature Input is:

   *created: 1402170695



Backman, et al.            Expires 21 May 2021                 [Page 32]


Internet-Draft            Signing HTTP Messages            November 2020


A.3.2.2.  Minimal Recommended Signature Header

   This presents a "Signature-Input" and "Signature" header 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 in              |
      | Key Material    | Appendix A.1.1.                          |
      +-----------------+------------------------------------------+

                                 Table 11

   The corresponding Signature Input is:

   *created: 1402170695

A.3.2.3.  Minimal Signature Header using rsa-sha256

   This presents a minimal "Signature-Input" and "Signature" header for
   a signature using the "rsa-sha256" algorithm:









Backman, et al.            Expires 21 May 2021                 [Page 33]


Internet-Draft            Signing HTTP Messages            November 2020


   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 header field
   is:

         +===========================+==========================+
         | Property                  | Value                    |
         +===========================+==========================+
         | Algorithm                 | rsa-sha256               |
         +---------------------------+--------------------------+
         | Covered Content           | date                     |
         +---------------------------+--------------------------+
         | Creation Time             | Undefined                |
         +---------------------------+--------------------------+
         | Expiration Time           | Undefined                |
         +---------------------------+--------------------------+
         | Verification Key Material | The public key specified |
         |                           | in Appendix A.1.1.       |
         +---------------------------+--------------------------+

                                 Table 12

   The corresponding Signature Input is:

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

Appendix B.  Topics for Working Group Discussion

   _RFC EDITOR: please remove this section before publication_

   The draft has known issues that will need to be addressed during
   development, and these issues have been enumerated but not addressed
   in this version.  Topics are not listed in any particular order.

B.1.  Issues










Backman, et al.            Expires 21 May 2021                 [Page 34]


Internet-Draft            Signing HTTP Messages            November 2020


B.1.1.  Confusing guidance on algorithm and key identification

   The current draft encourages determining the Algorithm metadata
   property from the "keyId" field, both in the guidance for the use of
   "algorithm" and "keyId", and the definition for the "hs2019"
   algorithm and deprecation of the other algorithms in the registry.
   The current state arose from concern that a malicious party could
   change the value 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 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
   of this approach, we can protect against manipulation of the
   Signature header field by adding support 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 of "keyId"
   completely up to the implementation.  This is primarily due to the
   fact that most implementers of Cavage have extensive investment in
   key distribution and management, and just need to plug an identifier
   into the header.  We should support those cases, but we also need to
   provide guidance for the developer that doesn't have that and just
   wants to know how to identify a key.  It may be enough to punt this
   to profiling specs, but this needs to be explored more.

B.1.3.  Algorithm Registry duplicates work of JWA

   [RFC7518] already defines an IANA registry for cryptographic
   algorithms.  This wasn't used by Cavage out of concerns about
   complexity of JOSE, and issues with JWE and JWS being too flexible,
   leading to insecure combinations 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 for implementers.

   In any use of JWS algorithms, this spec would define a way to create
   the JWS Signing Input string to be applied to the algorithm.  It
   should be noted that this is incompatible with JWS itself, which
   requires the inclusion of a structured header in the signature input.






Backman, et al.            Expires 21 May 2021                 [Page 35]


Internet-Draft            Signing HTTP Messages            November 2020


   A possible approach is to incorporate all elements 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 Signature
   algorithm.

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

   The initial entries in this document reflect those in Cavage.  The
   ones that are marked deprecated were done so because of the issue
   explained in Appendix B.1.1, with the possible exception 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 for "*request-target" do not perform
   handle minor, semantically meaningless differences in percent-
   encoding, such that verification could fail if an intermediary
   normalizes the effective request URI prior to forwarding the message.

   At a minimum, they should be case and percent-encoding normalized as
   described in sections 6.2.2.1 and 6.2.2.2 of [RFC3986].

B.1.6.  Misleading name for headers parameter

   The Covered Content list contains identifiers 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 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 to fail.

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

   The Set-Cookie header can occur multiple times but does not adhere to
   the list syntax, and thus is not well supported by the header field
   value concatenation rules.







Backman, et al.            Expires 21 May 2021                 [Page 36]


Internet-Draft            Signing HTTP Messages            November 2020


B.1.9.  Covered Content list is not signed

   The Covered Content list should be part of the Signature Input, to
   protect against malicious changes.

B.1.10.  Algorithm is not signed

   The Algorithm should be part of the Signature Input, to protect
   against malicious changes.

B.1.11.  Verification key identifier is not signed

   The Verification key identifier (e.g., the value used for the "keyId"
   parameter) should be part of the Signature Input, to protect against
   malicious changes.

B.1.12.  Max values, precision for Integer String and Decimal String not
         defined

   The definitions for Integer String 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 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 and Expiration Time do not allow for clock skew

   The processing instructions for Creation Time and Expiration Time
   imply that verifiers are not permitted 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 header field names when they are
   being used as content identifiers.  This is unnecessary, as header
   field names are case-insensitive, and creates opportunity for
   incompatibility.  Instead, content identifiers should always be
   lowercase.








Backman, et al.            Expires 21 May 2021                 [Page 37]


Internet-Draft            Signing HTTP Messages            November 2020


B.1.16.  Reconcile Date header and Creation Time

   The draft is missing guidance on if/how the Date 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 to the value in the Date 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 can or must include certain
   identifiers appear to be related to the pseudo-revving of the Cavage
   draft that happened when the "hs2019" algorithm was introduced.  We
   should drop these rules, as 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 the "Via" header
   field value, and consolidate related sequences of entries.  The
   canonicalization rules do not account for 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 values are case-insensitive, in whole or in part.
   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 examples showing different cases e.g, where "created" or
   "expires" are not present.









Backman, et al.            Expires 21 May 2021                 [Page 38]


Internet-Draft            Signing HTTP Messages            November 2020


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 be possible to independently include the following content
   and 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 over headers it adds (e.g.,
      "Forwarded") to messages already signed by the user agent.

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

   This could be addressed by changing 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 signature identifier parameter.



Backman, et al.            Expires 21 May 2021                 [Page 39]


Internet-Draft            Signing HTTP Messages            November 2020


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 header field value is all-or-nothing: either the
   entire value is signed, or none of it is.  For header fields that use
   list syntax, it would be useful to be able to specify which items in
   the list are signed.

   A simple approach that allowed the signer to indicate the list size
   at signing time would allow a signer to sign header fields that are
   may be appended to by intermediaries as the message makes its way to
   the recipient.  Specifying list size in terms of number of items
   could introduce risks of list syntax is not strictly adhered to
   (e.g., a malicious party crafts 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 the effective request URI may be
   expected to change, for example from "public-service-
   name.example.com" to "service-host-1.public-service-
   name.example.com".  This is commonly the case for services that are
   hosted behind a load-balancing gateway, where the client sends
   requests to a publicly known domain name for the service, and these
   requests are transformed by the gateway into requests to specific
   hosts in the service fleet.

   One possible way to handle this would be to special-case the Host
   header field to allow verifier to substitute a known expected value,
   or a value provided in another header field (e.g., "Via") when
   generating the 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.)








Backman, et al.            Expires 21 May 2021                 [Page 40]


Internet-Draft            Signing HTTP Messages            November 2020


Acknowledgements

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

         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".

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

         o  Fixed up examples.

         o  Updated introduction now that it's adopted.

      -  -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.



Backman, et al.            Expires 21 May 2021                 [Page 41]


Internet-Draft            Signing HTTP Messages            November 2020


      -  -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.




Backman, et al.            Expires 21 May 2021                 [Page 42]


Internet-Draft            Signing HTTP Messages            November 2020


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/
























Backman, et al.            Expires 21 May 2021                 [Page 43]