HTTP                                                     A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                          J. Richer, Ed.
Expires: 25 May 2023                                 Bespoke Engineering
                                                               M. Sporny
                                                          Digital Bazaar
                                                        21 November 2022


                        HTTP Message Signatures
                draft-ietf-httpbis-message-signatures-15

Abstract

   This document describes a mechanism for creating, encoding, and
   verifying digital signatures or message authentication codes over
   components of an HTTP message.  This mechanism supports use cases
   where the full HTTP message may not be known to the signer, and where
   the message may be transformed (e.g., by intermediaries) before
   reaching the verifier.  This document also describes a means for
   requesting that a signature be applied to a subsequent HTTP message
   in an ongoing HTTP exchange.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-httpbis-message-
   signatures/.

   Discussion of this document takes place on the HTTP Working Group
   mailing list (mailto:ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/.  Working Group
   information can be found at https://httpwg.org/.

   Source for this draft and an issue tracker can be found at
   https://github.com/httpwg/http-extensions/labels/signatures.

Status of This Memo

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

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



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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   This Internet-Draft will expire on 25 May 2023.

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   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   6
     1.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   8
     1.3.  HTTP Message Transformations  . . . . . . . . . . . . . .   9
     1.4.  Application of HTTP Message Signatures  . . . . . . . . .  10
   2.  HTTP Message Components . . . . . . . . . . . . . . . . . . .  12
     2.1.  HTTP Fields . . . . . . . . . . . . . . . . . . . . . . .  13
       2.1.1.  Strict Serialization of HTTP Structured Fields  . . .  16
       2.1.2.  Dictionary Structured Field Members . . . . . . . . .  17
       2.1.3.  Binary-wrapped HTTP Fields  . . . . . . . . . . . . .  18
       2.1.4.  Trailer Fields  . . . . . . . . . . . . . . . . . . .  19
     2.2.  Derived Components  . . . . . . . . . . . . . . . . . . .  20
       2.2.1.  Method  . . . . . . . . . . . . . . . . . . . . . . .  22
       2.2.2.  Target URI  . . . . . . . . . . . . . . . . . . . . .  22
       2.2.3.  Authority . . . . . . . . . . . . . . . . . . . . . .  23
       2.2.4.  Scheme  . . . . . . . . . . . . . . . . . . . . . . .  23
       2.2.5.  Request Target  . . . . . . . . . . . . . . . . . . .  24
       2.2.6.  Path  . . . . . . . . . . . . . . . . . . . . . . . .  25
       2.2.7.  Query . . . . . . . . . . . . . . . . . . . . . . . .  26
       2.2.8.  Query Parameters  . . . . . . . . . . . . . . . . . .  27
       2.2.9.  Status Code . . . . . . . . . . . . . . . . . . . . .  28
     2.3.  Signature Parameters  . . . . . . . . . . . . . . . . . .  28
     2.4.  Request-Response Signature Binding  . . . . . . . . . . .  30
     2.5.  Creating the Signature Base . . . . . . . . . . . . . . .  33
   3.  HTTP Message Signatures . . . . . . . . . . . . . . . . . . .  37



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     3.1.  Creating a Signature  . . . . . . . . . . . . . . . . . .  37
     3.2.  Verifying a Signature . . . . . . . . . . . . . . . . . .  39
       3.2.1.  Enforcing Application Requirements  . . . . . . . . .  42
     3.3.  Signature Algorithms  . . . . . . . . . . . . . . . . . .  43
       3.3.1.  RSASSA-PSS using SHA-512  . . . . . . . . . . . . . .  43
       3.3.2.  RSASSA-PKCS1-v1_5 using SHA-256 . . . . . . . . . . .  44
       3.3.3.  HMAC using SHA-256  . . . . . . . . . . . . . . . . .  44
       3.3.4.  ECDSA using curve P-256 DSS and SHA-256 . . . . . . .  45
       3.3.5.  ECDSA using curve P-384 DSS and SHA-384 . . . . . . .  46
       3.3.6.  EdDSA using curve edwards25519  . . . . . . . . . . .  46
       3.3.7.  JSON Web Signature (JWS) algorithms . . . . . . . . .  47
   4.  Including a Message Signature in a Message  . . . . . . . . .  47
     4.1.  The Signature-Input HTTP Field  . . . . . . . . . . . . .  48
     4.2.  The Signature HTTP Field  . . . . . . . . . . . . . . . .  49
     4.3.  Multiple Signatures . . . . . . . . . . . . . . . . . . .  49
   5.  Requesting Signatures . . . . . . . . . . . . . . . . . . . .  52
     5.1.  The Accept-Signature Field  . . . . . . . . . . . . . . .  53
     5.2.  Processing an Accept-Signature  . . . . . . . . . . . . .  54
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  55
     6.1.  HTTP Field Name Registration  . . . . . . . . . . . . . .  55
     6.2.  HTTP Signature Algorithms Registry  . . . . . . . . . . .  55
       6.2.1.  Registration Template . . . . . . . . . . . . . . . .  56
       6.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  56
     6.3.  HTTP Signature Metadata Parameters Registry . . . . . . .  57
       6.3.1.  Registration Template . . . . . . . . . . . . . . . .  57
       6.3.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  57
     6.4.  HTTP Signature Derived Component Names Registry . . . . .  58
       6.4.1.  Registration Template . . . . . . . . . . . . . . . .  58
       6.4.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  59
     6.5.  HTTP Signature Component Parameters Registry  . . . . . .  60
       6.5.1.  Registration Template . . . . . . . . . . . . . . . .  61
       6.5.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  61
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  62
     7.1.  General Considerations  . . . . . . . . . . . . . . . . .  63
       7.1.1.  Skipping Signature Verification . . . . . . . . . . .  63
       7.1.2.  Use of TLS  . . . . . . . . . . . . . . . . . . . . .  63
     7.2.  Message Processing and Selection  . . . . . . . . . . . .  63
       7.2.1.  Insufficient Coverage . . . . . . . . . . . . . . . .  64
       7.2.2.  Signature Replay  . . . . . . . . . . . . . . . . . .  64
       7.2.3.  Choosing Message Components . . . . . . . . . . . . .  65
       7.2.4.  Choosing Signature Parameters and Derived Components
               over HTTP Fields  . . . . . . . . . . . . . . . . . .  65
       7.2.5.  Signature Labels  . . . . . . . . . . . . . . . . . .  66
       7.2.6.  Multiple Signature Confusion  . . . . . . . . . . . .  66
       7.2.7.  Collision of Application-Specific Signature Tag . . .  67
       7.2.8.  Message Content . . . . . . . . . . . . . . . . . . .  67
     7.3.  Cryptographic Considerations  . . . . . . . . . . . . . .  68
       7.3.1.  Cryptography and Signature Collision  . . . . . . . .  68



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       7.3.2.  Key Theft . . . . . . . . . . . . . . . . . . . . . .  69
       7.3.3.  Symmetric Cryptography  . . . . . . . . . . . . . . .  69
       7.3.4.  Key Specification Mix-Up  . . . . . . . . . . . . . .  70
       7.3.5.  Non-deterministic Signature Primitives  . . . . . . .  70
       7.3.6.  Key and Algorithm Specification Downgrades  . . . . .  70
     7.4.  Matching Covered Components to Message  . . . . . . . . .  71
       7.4.1.  Modification of Required Message Parameters . . . . .  71
       7.4.2.  Mismatch of Signature Parameters from Message . . . .  71
       7.4.3.  Message Component Source and Context  . . . . . . . .  72
       7.4.4.  Multiple Message Component Contexts . . . . . . . . .  73
     7.5.  HTTP Processing . . . . . . . . . . . . . . . . . . . . .  73
       7.5.1.  Confusing HTTP Field Names for Derived Component
               Names . . . . . . . . . . . . . . . . . . . . . . . .  73
       7.5.2.  Semantically Equivalent Field Values  . . . . . . . .  74
       7.5.3.  Parsing Structured Field Values . . . . . . . . . . .  75
       7.5.4.  HTTP Versions and Component Ambiguity . . . . . . . .  75
       7.5.5.  Canonicalization Attacks  . . . . . . . . . . . . . .  76
       7.5.6.  Non-List Field Values . . . . . . . . . . . . . . . .  76
       7.5.7.  Padding Attacks with Multiple Field Values  . . . . .  77
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  78
     8.1.  Identification through Keys . . . . . . . . . . . . . . .  78
     8.2.  Signatures do not provide confidentiality . . . . . . . .  78
     8.3.  Oracles . . . . . . . . . . . . . . . . . . . . . . . . .  79
     8.4.  Required Content  . . . . . . . . . . . . . . . . . . . .  79
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  79
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  79
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  81
   Appendix A.  Detecting HTTP Message Signatures  . . . . . . . . .  82
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  82
     B.1.  Example Keys  . . . . . . . . . . . . . . . . . . . . . .  83
       B.1.1.  Example Key RSA test  . . . . . . . . . . . . . . . .  83
       B.1.2.  Example RSA PSS Key . . . . . . . . . . . . . . . . .  85
       B.1.3.  Example ECC P-256 Test Key  . . . . . . . . . . . . .  87
       B.1.4.  Example Ed25519 Test Key  . . . . . . . . . . . . . .  88
       B.1.5.  Example Shared Secret . . . . . . . . . . . . . . . .  89
     B.2.  Test Cases  . . . . . . . . . . . . . . . . . . . . . . .  89
       B.2.1.  Minimal Signature Using rsa-pss-sha512  . . . . . . .  90
       B.2.2.  Selective Covered Components using rsa-pss-sha512 . .  91
       B.2.3.  Full Coverage using rsa-pss-sha512  . . . . . . . . .  92
       B.2.4.  Signing a Response using ecdsa-p256-sha256  . . . . .  93
       B.2.5.  Signing a Request using hmac-sha256 . . . . . . . . .  93
       B.2.6.  Signing a Request using ed25519 . . . . . . . . . . .  94
     B.3.  TLS-Terminating Proxies . . . . . . . . . . . . . . . . .  95
     B.4.  HTTP Message Transformations  . . . . . . . . . . . . . .  97
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . . 100
   Document History  . . . . . . . . . . . . . . . . . . . . . . . . 100
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 105




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1.  Introduction

   Message integrity and authenticity are security properties that are
   critical to the secure operation of many HTTP applications.
   Application developers typically rely on the transport layer to
   provide these properties, by operating their application over [TLS].
   However, TLS only guarantees these properties over a single TLS
   connection, and the path between client and application may be
   composed of multiple independent TLS connections (for example, if the
   application is hosted behind a TLS-terminating gateway or if the
   client is behind a TLS Inspection appliance).  In such cases, TLS
   cannot guarantee end-to-end message integrity or authenticity between
   the client and application.  Additionally, some operating
   environments present obstacles that make it impractical to use TLS,
   or to use features necessary to provide message authenticity.
   Furthermore, some applications require the binding of an application-
   level key to the HTTP message, separate from any TLS certificates in
   use.  Consequently, while TLS can meet message integrity and
   authenticity needs for many HTTP-based applications, it is not a
   universal solution.

   This document defines a mechanism for providing end-to-end integrity
   and authenticity for components of an HTTP message.  The mechanism
   allows applications to create digital signatures or message
   authentication codes (MACs) over only the components of the message
   that are meaningful and appropriate for the application.  Strict
   canonicalization rules ensure that the verifier can verify the
   signature even if the message has been transformed in any of the many
   ways permitted by HTTP.

   The signing mechanism described in this document consists of three
   parts:

   *  A common nomenclature and canonicalization rule set for the
      different protocol elements and other components of HTTP messages,
      used to create the signature base.

   *  Algorithms for generating and verifying signatures over HTTP
      message components using this signature base through application
      of cryptographic primitives.

   *  A mechanism for attaching a signature and related metadata to an
      HTTP message, and for parsing attached signatures and metadata
      from HTTP messages.  To facilitate this, this document defines the
      "Signature-Input" and "Signature" fields.






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   This document also provides a mechanism for negotiation the use of
   signatures in one or more subsequent messages via the "Accept-
   Signature" field.  This optional negotiation mechanism can be used
   along with opportunistic or application-driven message signatures by
   either party.

1.1.  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", "target
   URI", "gateway", "header field", "intermediary", "request target",
   "trailer field", "sender", "method", and "recipient" are used as
   defined in [HTTP].

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

   This document uses the following terminology from Section 3 of
   [STRUCTURED-FIELDS] to specify data types: List, Inner List,
   Dictionary, Item, String, Integer, Byte Sequence, and Boolean.

   This document defines several string constructions using [ABNF] and
   uses the following ABNF rules: VCHAR, SP, DQUOTE, LF.  This document
   uses the following ABNF rules from [STRUCTURED-FIELDS]: sf-string,
   inner-list, parameters.  This document uses the following ABNF rules
   from [HTTP]: field-content.

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

   HTTP Message Signature:
      A digital signature or keyed MAC that covers one or more portions
      of an HTTP message.  Note that a given HTTP Message can contain
      multiple HTTP Message Signatures.

   Signer:





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      The entity that is generating or has generated an HTTP Message
      Signature.  Note that multiple entities can act as signers and
      apply separate HTTP Message Signatures to a given HTTP Message.

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

   HTTP Message Component:
      A portion of an HTTP message that is capable of being covered by
      an HTTP Message Signature.

   Derived Component:
      An HTTP Message Component derived from the HTTP message through
      the use of a specified algorithm or process.  See Section 2.2.

   HTTP Message Component Name:
      A string that identifies an HTTP Message Component's source, such
      as a field name or derived component name.

   HTTP Message Component Identifier:
      The combination of an HTTP Message Component Name and any
      parameters that uniquely identifies a specific HTTP Message
      Component in respect to a particular HTTP Message Signature and
      the HTTP Message it applies to.

   HTTP Message Component Value:
      The value associated with a given component identifier within the
      context of a particular HTTP Message.  Component values are
      derived from the HTTP Message and are usually subject to a
      canonicalization process.

   Covered Components:
      An ordered set of HTTP message component identifiers for fields
      (Section 2.1) and derived components (Section 2.2) that indicates
      the set of message components covered by the signature, never
      including the @signature-params identifier itself.  The order of
      this set is preserved and communicated between the signer and
      verifier to facilitate reconstruction of the signature base.

   Signature Base:
      The sequence of bytes generated by the signer and verifier using
      the covered components set and the HTTP Message.  The signature
      base is processed by the cryptographic algorithm to produce or
      verify the HTTP Message Signature.




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   HTTP Message Signature Algorithm:
      A cryptographic algorithm that describes the signing and
      verification process for the signature, defined in terms of the
      HTTP_SIGN and HTTP_VERIFY primitives described in Section 3.3.

   Key Material:
      The key material required to create or verify the signature.  The
      key material is often identified with an explicit key identifier,
      allowing the signer to indicate to the verifier which key was
      used.

   Creation Time:
      A timestamp representing the point in time that the signature was
      generated, as asserted by the signer.

   Expiration Time:
      A timestamp representing the point in time after which the
      signature should no longer be accepted by the verifier, as
      asserted by the signer.

   Target Message:
      The HTTP message to which an HTTP Message Signature is applied.

   Signature Context:
      The data source from which the HTTP Message Component Values are
      drawn.  The context includes the target message and any additional
      information the signer or verifier might have, such as the full
      target URI of a request or the related request message for a
      response.

   The term "Unix time" is defined by [POSIX.1], Section 4.16
   (http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
   V1_chap04.html#tag_04_16).

   This document contains non-normative examples of partial and complete
   HTTP messages.  Some examples use a single trailing backslash \ to
   indicate line wrapping for long values, as per [RFC8792].  The \
   character and leading spaces on wrapped lines are not part of the
   value.

1.2.  Requirements

   HTTP permits and sometimes requires intermediaries to transform
   messages in a variety of ways.  This can result in a recipient
   receiving a message that is not bitwise-equivalent to the message
   that was originally sent.  In such a case, the recipient will be
   unable to verify integrity protections over the raw bytes of the
   sender's HTTP message, as verifying digital signatures or MACs



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   requires both signer and verifier to have the exact same signature
   base.  Since the exact raw bytes of the message cannot be relied upon
   as a reliable source for a signature base, the signer and verifier
   have to independently create the signature base from their respective
   versions of the message, via a mechanism that is resilient to safe
   changes that do not alter the meaning of the message.

   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 message
   content, the method, or a particular header field) is relevant.
   Thus, a general purpose solution needs to provide signers with some
   degree of control over which message components are signed.

   HTTP applications may be running in environments that do not provide
   complete access to or control over HTTP messages (such as a web
   browser's JavaScript environment), or may be using libraries that
   abstract away the details of the protocol (such as the Java
   HTTPClient library (https://openjdk.java.net/groups/net/httpclient/
   intro.html)).  These applications need to be able to generate and
   verify signatures despite incomplete knowledge of the HTTP message.

1.3.  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 could occur under HTTP, provided as
   context:

   *  Re-ordering of fields with different field names (Section 5.3 of
      [HTTP]).

   *  Combination of fields with the same field name (Section 5.2 of
      [HTTP]).

   *  Removal of fields listed in the Connection header field
      (Section 7.6.1 of [HTTP]).

   *  Addition of fields that indicate control options (Section 7.6.1 of
      [HTTP]).

   *  Addition or removal of a transfer coding (Section 7.7 of [HTTP]).

   *  Addition of fields such as Via (Section 7.6.3 of [HTTP]) and
      Forwarded (Section 4 of [RFC7239]).



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

   *  Changes in casing (e.g., "Origin" to "origin") of any case-
      insensitive components such as field names, request URI scheme, or
      host.

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

   *  Addition or removal of obs-folds from field values.

   *  Changes to the request target and authority that when applied
      together do not result in a change to the message's target URI, as
      defined in Section 7.1 of [HTTP].

   We can identify these types of transformations as ones that should
   not prevent signature verification, even when performed on message
   components covered by the signature.  Additionally, all changes to
   components not covered by the signature should not prevent signature
   verification.

   Some examples of these kinds of transformations, and the effect they
   have on the message signature, are found in Appendix B.4.

1.4.  Application of HTTP Message Signatures

   HTTP Message Signatures are designed to be a general-purpose security
   mechanism applicable in a wide variety of circumstances and
   applications.  In order to properly and safely apply HTTP Message
   Signatures, an application or profile of this specification MUST
   specify all of the following items:

   *  The set of component identifiers (Section 2) and signature
      parameters (Section 2.3) that are expected and required to be
      included in the covered components list.  For example, an
      authorization protocol could mandate that the Authorization field
      be covered to protect the authorization credentials and mandate
      the signature parameters contain a created parameter, while an API
      expecting semantically relevant HTTP message content could require
      the Content-Digest field defined in [DIGEST] to be present and
      covered as well as mandate a value for tag that is specific to the
      API being protected.








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   *  A means of retrieving the key material used to verify the
      signature.  An application will usually use the keyid parameter of
      the signature parameters (Section 2.3) and define rules for
      resolving a key from there, though the appropriate key could be
      known from other means such as pre-registration of a signer's key.

   *  A means of determining the signature algorithm used to verify the
      signature is appropriate for the key material.  For example, the
      process could use the alg parameter of the signature parameters
      (Section 2.3) to state the algorithm explicitly, derive the
      algorithm from the key material, or use some pre-configured
      algorithm agreed upon by the signer and verifier.

   *  A means of determining that a given key and algorithm presented in
      the request are appropriate for the request being made.  For
      example, a server expecting only ECDSA signatures should know to
      reject any RSA signatures, or a server expecting asymmetric
      cryptography should know to reject any symmetric cryptography.

   *  A means of determining the context for derivation of message
      components from an HTTP message and its application context.
      While this is normally the target HTTP message itself, the context
      could include additional information known to the application,
      such as an external host name.

   When choosing these parameters, an application of HTTP message
   signatures has to ensure that the verifier will have access to all
   required information needed to re-create the signature base.  For
   example, a server behind a reverse proxy would need to know the
   original request URI to make use of the derived component @target-
   uri, even though the apparent target URI would be changed by the
   reverse proxy (see also Section 7.4.3).  Additionally, an application
   using signatures in responses would need to ensure that clients
   receiving signed responses have access to all the signed portions of
   the message, including any portions of the request that were signed
   by the server using the related-response parameter.

   The details of this kind of profiling are the purview of the
   application and outside the scope of this specification, however some
   additional considerations are discussed in Section 7.  In particular,
   when choosing the required set of component identifiers, care has to
   be taken to make sure that the coverage is sufficient for the
   application, as discussed in Section 7.2.1 and Section 7.2.8.








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2.  HTTP Message Components

   In order to allow signers and verifiers to establish which components
   are covered by a signature, this document defines component
   identifiers for components covered by an HTTP Message Signature, a
   set of rules for deriving and canonicalizing the values associated
   with these component identifiers from the HTTP Message, and the means
   for combining these canonicalized values into a signature base.

   The signature context for deriving these values MUST be accessible to
   both the signer and the verifier of the message.  The context MUST be
   the same across all components in a given signature.  For example, it
   would be an error to use a the raw query string for the @query
   derived component but combined query and form parameters for the
   @query-param derived component.  For more considerations of the
   message component context, see Section 7.4.3.

   A component identifier is composed of a component name and any
   parameters associated with that name.  Each component name is either
   an HTTP field name (Section 2.1) or a registered derived component
   name (Section 2.2).  The possible parameters for a component
   identifier are dependent on the component identifier, and a registry
   cataloging all possible parameters is defined in Section 6.3.

   Within a single list of covered components, each component identifier
   MUST occur only once.  One component identifier is distinct from
   another if either the component name or its parameters differ.
   Multiple component identifiers having the same component name MAY be
   included if they have parameters that make them distinct.  The order
   of parameters MUST be preserved when processing a component
   identifier (such as when parsing during verification), but the order
   of parameters is not significant when comparing two component
   identifiers for equality.  That is to say, "foo";bar;baz cannot be in
   the same message as "foo";baz;bar, since these two component
   identifiers are equivalent, but a system processing one form is not
   allowed to transform it into the other form.

   The component value associated with a component identifier is defined
   by the identifier itself.  Component values MUST NOT contain newline
   (\n) characters.  Some HTTP message components can undergo
   transformations that change the bitwise value without altering the
   meaning of the component's value (for example, when combining field
   values).  Message component values must therefore be canonicalized
   before they are signed, to ensure that a signature can be verified
   despite such intermediary transformations.  This document defines
   rules for each component identifier that transform the identifier's
   associated component value into such a canonical form.




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   The following sections define component identifier names, their
   parameters, their associated values, and the canonicalization rules
   for their values.  The method for combining message components into
   the signature base is defined in Section 2.5.

2.1.  HTTP Fields

   The component name for an HTTP field is the lowercased form of its
   field name as defined in Section 5.1 of [HTTP].  While HTTP field
   names are case-insensitive, implementations MUST use lowercased field
   names (e.g., content-type, date, etag) when using them as component
   names.

   The component value for an HTTP field is the field value for the
   named field as defined in Section 5.5 of [HTTP].  The field value
   MUST be taken from the named header field of the target message
   unless this behavior is overridden by additional parameters and
   rules, such as the req and tr flags, below.

   Unless overridden by additional parameters and rules, HTTP field
   values MUST be combined into a single value as defined in Section 5.2
   of [HTTP] to create the component value.  Specifically, HTTP fields
   sent as multiple fields MUST be combined using a single comma (",")
   and a single space (" ") between each item.  Note that intermediaries
   are allowed to combine values of HTTP fields with any amount of
   whitespace between the commas, and if this behavior is not accounted
   for by the verifier, the signature can fail since the signer and
   verifier will be see a different component value in their respective
   signature bases.  For robustness, it is RECOMMENDED that signed
   messages include only a single instance of any field covered under
   the signature, particularly with the value for any list-based fields
   serialized using the algorithm below.  This approach increases the
   chances of the field value remaining untouched through
   intermediaries.  Where that approach is not possible and multiple
   instances of a field need to be sent separately, it is RECOMMENDED
   that signers and verifiers process any list-based fields by parsing
   out individual field values and combining them based on the strict
   algorithm below, to counter possible intermediary behavior.  When the
   field in question is a structured field of tyle List or Dictionary,
   this effect can be accomplished more directly by using the strict
   structured field serialization of the field value, as described in
   Section 2.1.1.

   Note that some HTTP fields, such as Set-Cookie [COOKIE], do not
   follow a syntax that allows for combination of field values in this
   manner (such that the combined output is unambiguous from multiple
   inputs).  Even though the component value is never parsed by the
   message signature process and used only as part of the signature base



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   in Section 2.5, caution needs to be taken when including such fields
   in signatures since the combined value could be ambiguous.  The bs
   parameter defined in Section 2.1.3 provides a method for wrapping
   such problematic fields.  See Section 7.5.6 for more discussion of
   this issue.

   If the correctly combined value is not directly available for a given
   field by an implementation, the following algorithm will produce
   canonicalized results for list-based fields:

   1.  Create an ordered list of the field values of each instance of
       the field in the message, in the order that they occur (or will
       occur) in the message.  If necessary, separate individual values
       found in a field instance.

   2.  Strip leading and trailing whitespace from each item in the list.
       Note that since HTTP field values are not allowed to contain
       leading and trailing whitespace, this will be a no-op in a
       compliant implementation.

   3.  Remove any obsolete line-folding within the line and replace it
       with a single space (" "), as discussed in Section 5.2 of
       [HTTP1].  Note that this behavior is specific to [HTTP1] and does
       not apply to other versions of the HTTP specification which do
       not allow internal line folding.

   4.  Concatenate the list of values together with a single comma (",")
       and a single space (" ") between each item.

   The resulting string is the component value for the field.

   Note that some HTTP fields have values with multiple valid
   serializations that have equivalent semantics, such as allow case-
   insensitive values that intermediaries could change.  Applications
   signing and processing such fields MUST consider how to handle the
   values of such fields to ensure that the signer and verifier can
   derive the same value, as discussed in Section 7.5.2.

   Following are non-normative examples of component values for header
   fields, given the following example HTTP message fragment:











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   Host: www.example.com
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   X-OWS-Header:   Leading and trailing whitespace.
   X-Obs-Fold-Header: Obsolete
       line folding.
   Cache-Control: max-age=60
   Cache-Control:    must-revalidate
   Example-Dict:  a=1,    b=2;x=1;y=2,   c=(a   b   c)

   The following example shows the component values for these example
   header fields, presented using the signature base format defined in
   in Section 2.5:

   "host": www.example.com
   "date": Tue, 20 Apr 2021 02:07:56 GMT
   "x-ows-header": Leading and trailing whitespace.
   "x-obs-fold-header": Obsolete line folding.
   "cache-control": max-age=60, must-revalidate
   "example-dict": a=1,    b=2;x=1;y=2,   c=(a   b   c)

   Since empty HTTP fields are allowed, they can also be signed when
   present in a message.  The canonicalized value is the empty string.
   This means that the following empty header:

   NOTE: '\' line wrapping per RFC 8792

   X-Empty-Header: \

   Is serialized by the signature base generation algorithm
   (Section 2.5) with an empty string value following the colon and
   space added after the content identifier.

   NOTE: '\' line wrapping per RFC 8792

   "x-empty-header": \

   Note: the trailing spaces in these values are shown here using the
   line wrapping algorithm in [RFC8792] due to limitations in the
   document format that strips trailing spaces from diagrams.

   Any HTTP field component identifiers MAY have the following
   parameters in specific circumstances, each described in detail in
   their own sections:

   sf  A boolean flag indicating that the component value is serialized
      using strict encoding of the structured field value.
      Section 2.1.1




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   key  A string parameter used to select a single member value from a
      Dictionary structured field.  Section 2.1.2

   bs  A boolean flag indicating that individual field values are
      encoded using Byte Sequence data structures before being combined
      into the component value.  Section 2.1.3

   req  A boolean flag for signed responses indicating that the
      component value is derived from the request that triggered this
      response message and not from the response message directly.  Note
      that this parameter can also be applied to any derived component
      identifiers that target the request.  Section 2.4

   tr  A boolean flag indicating that the field value is taken from the
      trailers of the message as defined in Section 6.5 of [HTTP].  If
      this flag is absent, the field value is taken from the headers of
      the message as defined in Section 6.3 of [HTTP].  Section 2.1.4

   Multiple parameters MAY be specified together, though some
   combinations are redundant or incompatible.  For example, the sf
   parameter's functionality is already covered when the key parameter
   is used on a dictionary item, since key requires strict serialization
   of the value.  The bs parameter, which requires the raw field values
   from the message, is not compatible with use of the sf or key
   parameters, which require the parsed data structures of the field
   values after combination.

   Additional parameters can be defined in the registry established in
   Section 6.3.

2.1.1.  Strict Serialization of HTTP Structured Fields

   If the value of an HTTP field is known by the application to be a
   structured field ([STRUCTURED-FIELDS]), and the expected type of the
   structured field is known, the signer MAY include the sf parameter in
   the component identifier.  If this parameter is included with a
   component identifier, the HTTP field value MUST be serialized using
   the rules specified in Section 4 of [STRUCTURED-FIELDS] applicable to
   the type of the HTTP field.  Note that this process will replace any
   optional internal whitespace with a single space character, among
   other potential transformations of the value.

   If multiple field values occur within a message, these values MUST be
   combined into a single List or Dictionary structure before
   serialization.

   For example, the following dictionary field is a valid serialization:




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   Example-Dict:  a=1,    b=2;x=1;y=2,   c=(a   b   c)

   If included in the signature base without parameters, its value would
   be:

   "example-dict": a=1,    b=2;x=1;y=2,   c=(a   b   c)

   However, if the sf parameter is added, the value is re-serialized as
   follows:

   "example-dict";sf: a=1, b=2;x=1;y=2, c=(a b c)

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

2.1.2.  Dictionary Structured Field Members

   If a given field is known by the application to be a Dictionary
   structured field, an individual member in the value of that
   Dictionary is identified by using the parameter key and the
   Dictionary member key as a String value.

   If multiple field values occur within a message, these values MUST be
   combined into a single Dictionary structure before serialization.

   An individual member value of a Dictionary Structured Field is
   canonicalized by applying the serialization algorithm described in
   Section 4.1.2 of [STRUCTURED-FIELDS] on the member_value and its
   parameters, not including the dictionary key itself.  Specifically,
   the value is serialized as an Item or Inner List (the two possible
   values of a Dictionary member).

   Each parameterized key for a given field MUST NOT appear more than
   once in the signature base.  Parameterized keys MAY appear in any
   order in the signature base, regardless of the order they occur in
   the source Dictionary.

   If a Dictionary key is named as a covered component but it does not
   occur in the Dictionary, this MUST cause an error in the signature
   base generation.

   Following are non-normative examples of canonicalized values for
   Dictionary structured field members given the following example
   header field, whose value is known by the application to be a
   Dictionary:

   Example-Dict:  a=1, b=2;x=1;y=2, c=(a   b    c), d





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   The following example shows canonicalized values for different
   component identifiers of this field, presented using the signature
   base format discussed in Section 2.5:

   "example-dict";key="a": 1
   "example-dict";key="d": ?1
   "example-dict";key="b": 2;x=1;y=2
   "example-dict";key="c": (a b c)

   Note that the value for key="c" has been re-serialized according to
   the strict member_value algorithm, and the value for key="d" has been
   serialized as a Boolean value.

2.1.3.  Binary-wrapped HTTP Fields

   If the value of the the HTTP field in question is known by the
   application to cause problems with serialization, particularly with
   the combination of multiple values into a single line as discussed in
   Section 7.5.6, the signer SHOULD include the bs parameter in a
   component identifier to indicate the values of the fields need to be
   wrapped as binary structures before being combined.

   If this parameter is included with a component identifier, the
   component value MUST be calculated using the following algorithm:

   1.  Let the input be the ordered set of values for a field, in the
       order they appear in the message.

   2.  Create an empty List for accumulating processed field values.

   3.  For each field value in the set:

       1.  Strip leading and trailing whitespace from the field value.
           Note that since HTTP field values are not allowed to contain
           leading and trailing whitespace, this will be a no-op in a
           compliant implementation.

       2.  Remove any obsolete line-folding within the line and replace
           it with a single space (" "), as discussed in Section 5.2 of
           [HTTP1].  Note that this behavior is specific to [HTTP1] and
           does not apply to other versions of the HTTP specification.

       3.  Encode the bytes of the resulting field value's ASCII
           representation as a Byte Sequence.

       4.  Add the Byte Sequence to the List accumulator.

   4.  The intermediate result is a List of Byte Sequence values.



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   5.  Follow the strict serialization of a List as described in
       Section 4.1.1 of [STRUCTURED-FIELDS] and return this output.

   For example, the following field with internal commas prevents the
   distinct field values from being safely combined:

   Example-Header: value, with, lots
   Example-Header: of, commas

   In our example, the same field can be sent with a semantically
   different single value:

   Example-Header: value, with, lots, of, commas

   Both of these versions are treated differently by the application.
   however, if included in the signature base without parameters, the
   component value would be the same in both cases:

   "example-header": value, with, lots, of, commas

   However, if the bs parameter is added, the two separate instances are
   encoded and serialized as follows:

   "example-header";bs: :dmFsdWUsIHdpdGgsIGxvdHM=:, :b2YsIGNvbW1hcw==:

   For the single-instance field above, the encoding with the bs
   parameter is:

   "example-header";bs: :dmFsdWUsIHdpdGgsIGxvdHMsIG9mLCBjb21tYXM=:

   This component value is distinct from the multiple-instance field
   above, preventing a collision which could potentially be exploited.

2.1.4.  Trailer Fields

   If the signer wants to include a trailer field in the signature, the
   signer MUST include the tr boolean parameter to indicate the value
   MUST be taken from the trailer fields and not from the header fields.

   For example, given the following message:











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   HTTP/1.1 200 OK
   Content-Type: text/plain
   Transfer-Encoding: chunked
   Trailer: Expires

   4
   HTTP
   7
   Message
   a
   Signatures
   0
   Expires: Wed, 9 Nov 2022 07:28:00 GMT

   The signer decides to add both the Trailer header field as well as
   the Expires trailer to the signature base, along with the status code
   derived component:

   "@status": 200
   "trailer": Expires
   "expires";tr: Wed, 9 Nov 2022 07:28:00 GMT

   If a field is available as both a header and trailer in a message,
   both values MAY be signed, but the values MUST be signed separately.
   The values of header fields and trailer fields of the same name MUST
   NOT be combined for purposes of the signature.

   Since trailer fields could be merged into the header fields or
   dropped entirely by intermediaries as per Section 6.5.1 of [HTTP], it
   is NOT RECOMMENDED to include trailers in the signature unless the
   signer knows that the verifier will have access to the values of the
   trailers as sent.

2.2.  Derived Components

   In addition to HTTP fields, there are a number of different
   components that can be derived from the control data, signature
   context, or other aspects of the HTTP message being signed.  Such
   derived components can be included in the signature base by defining
   a component name, possible parameters, message target, and the
   derivation method for its component value.

   Derived component names MUST start with the "at" @ character.  This
   differentiates derived component names from HTTP field names, which
   cannot contain the @ character as per Section 5.1 of [HTTP].
   Processors of HTTP Message Signatures MUST treat derived component
   names separately from field names, as discussed in Section 7.5.1.




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   This specification defines the following derived components:

   @method  The method used for a request.  (Section 2.2.1)

   @target-uri  The full target URI for a request.  (Section 2.2.2)

   @authority  The authority of the target URI for a request.
      (Section 2.2.3)

   @scheme  The scheme of the target URI for a request.  (Section 2.2.4)

   @request-target  The request target.  (Section 2.2.5)

   @path  The absolute path portion of the target URI for a request.
      (Section 2.2.6)

   @query  The query portion of the target URI for a request.
      (Section 2.2.7)

   @query-param  A parsed query parameter of the target URI for a
      request.  (Section 2.2.8)

   @status  The status code for a response.  (Section 2.2.9).

   Additional derived component names are defined in the HTTP Signatures
   Derived Component Name Registry.  (Section 6.4)

   Derived component values are taken from the context of the target
   message for the signature.  This context includes information about
   the message itself, such as its control data, as well as any
   additional state and context held by the signer or verifier.  In
   particular, when signing a response, the signer can include any
   derived components from the originating request by using the
   request-response signature binding parameter (Section 2.4).

   request:  Values derived from and results applied to an HTTP request
      message as described in Section 3.4 of [HTTP].  If the target
      message of the signature is a response, using the req parameter
      allows a request-targeted derived component to be included in the
      signature (see Section 2.4).

   response:  Values derived from and results applied to an HTTP
      response message as described in Section 3.4 of [HTTP].

   A derived component definition MUST define all target message types
   to which it can be applied.





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   Derived component values MUST be limited to printable characters and
   spaces and MUST NOT contain any newline characters.  Derived
   component values MUST NOT start or end with whitespace characters.

2.2.1.  Method

   The @method derived component refers to the HTTP method of a request
   message.  The component value is canonicalized by taking the value of
   the method as a string.  Note that the method name is case-sensitive
   as per [HTTP], Section 9.1, and conventionally standardized method
   names are uppercase US-ASCII.

   For example, the following request message:

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

   Would result in the following @method component value:

   POST

   And the following signature base line:

   "@method": POST

2.2.2.  Target URI

   The @target-uri derived component refers to the target URI of a
   request message.  The component value is the full absolute target URI
   of the request, potentially assembled from all available parts
   including the authority and request target as described in [HTTP],
   Section 7.1.

   For example, the following message sent over HTTPS:

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

   Would result in the following @target-uri component value:

   https://www.example.com/path?param=value

   And the following signature base line:

   "@target-uri": https://www.example.com/path?param=value






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2.2.3.  Authority

   The @authority derived component refers to the authority component of
   the target URI of the HTTP request message, as defined in [HTTP],
   Section 7.2.  In HTTP 1.1, this is usually conveyed using the Host
   header, while in HTTP 2 and HTTP 3 it is conveyed using the
   :authority pseudo-header.  The value is the fully-qualified authority
   component of the request, comprised of the host and, optionally, port
   of the request target, as a string.  The component value MUST be
   normalized according to the rules in [HTTP], Section 4.2.3.  Namely,
   the host name is normalized to lowercase and the default port is
   omitted.

   For example, the following request message:

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

   Would result in the following @authority component value:

   www.example.com

   And the following signature base line:

   "@authority": www.example.com

   The @authority derived component SHOULD be used instead of signing
   the Host header directly, see Section 7.2.4.

2.2.4.  Scheme

   The @scheme derived component refers to the scheme of the target URL
   of the HTTP request message.  The component value is the scheme as a
   lowercase string as defined in [HTTP], Section 4.2.  While the scheme
   itself is case-insensitive, it MUST be normalized to lowercase for
   inclusion in the signature base.

   For example, the following request message requested over plain HTTP:

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

   Would result in the following @scheme component value:

   http

   And the following signature base line:




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   "@scheme": http

2.2.5.  Request Target

   The @request-target derived component refers to the full request
   target of the HTTP request message, as defined in [HTTP],
   Section 7.1.  The component value of the request target can take
   different forms, depending on the type of request, as described
   below.

   For HTTP 1.1, the component value is equivalent to the request target
   portion of the request line.  However, this value is more difficult
   to reliably construct in other versions of HTTP.  Therefore, it is
   NOT RECOMMENDED that this component be used when versions of HTTP
   other than 1.1 might be in use.

   The origin form value is combination of the absolute path and query
   components of the request URL.  For example, the following request
   message:

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

   Would result in the following @request-target component value:

   /path?param=value

   And the following signature base line:

   "@request-target": /path?param=value

   The following request to an HTTP proxy with the absolute-form value,
   containing the fully qualified target URI:

   GET https://www.example.com/path?param=value HTTP/1.1

   Would result in the following @request-target component value:

   https://www.example.com/path?param=value

   And the following signature base line:

   "@request-target": https://www.example.com/path?param=value

   The following CONNECT request with an authority-form value,
   containing the host and port of the target:





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   CONNECT www.example.com:80 HTTP/1.1
   Host: www.example.com

   Would result in the following @request-target component value:

   www.example.com:80

   And the following signature base line:

   "@request-target": www.example.com:80

   The following OPTIONS request message with the asterisk-form value,
   containing a single asterisk * character:

   OPTIONS * HTTP/1.1
   Host: www.example.com

   Would result in the following @request-target component value:

   *

   And the following signature base line:

   "@request-target": *

2.2.6.  Path

   The @path derived component refers to the target path of the HTTP
   request message.  The component value is the absolute path of the
   request target defined by [URI], with no query component and no
   trailing ? character.  The value is normalized according to the rules
   in [HTTP], Section 4.2.3.  Namely, an empty path string is normalized
   as a single slash / character.  Path components are represented by
   their values before decoding any percent-encoded octets, as described
   in the simple string comparison rules in Section 6.2.1 of [URI].

   For example, the following request message:

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

   Would result in the following @path component value:

   /path

   And the following signature base line:

   "@path": /path



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2.2.7.  Query

   The @query derived component refers to the query component of the
   HTTP request message.  The component value is the entire normalized
   query string defined by [URI], including the leading ? character.
   The value is read using the simple string comparison rules in
   Section 6.2.1 of [URI].  Namely, percent-encoded octets are not
   decoded.

   For example, the following request message:

   POST /path?param=value&foo=bar&baz=bat%2Dman HTTP/1.1
   Host: www.example.com

   Would result in the following @query component value:

   ?param=value&foo=bar&baz=bat%2Dman

   And the following signature base line:

   "@query": ?param=value&foo=bar&baz=bat%2Dman

   The following request message:

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

   Would result in the following @query component value:

   ?queryString

   And the following signature base line:

   "@query": ?queryString

   If the query string is absent from the request message, the value is
   the leading ? character alone:

   ?

   Resulting in the following signature base line:

   "@query": ?








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2.2.8.  Query Parameters

   If a request target URI uses HTML form parameters in the query string
   as defined in HTMLURL, Section 5 [HTMLURL], the @query-param derived
   component allows addressing of individual query parameters.  The
   query parameters MUST be parsed according to HTMLURL, Section 5.1
   [HTMLURL], resulting in a list of (nameString, valueString) tuples.
   The REQUIRED name parameter of each component identifier contains the
   nameString of a single query parameter as a String value.  Several
   different named query parameters MAY be included in the covered
   components.  Single named parameters MAY occur in any order in the
   covered components.

   The component value of a single named parameter is the valueString of
   the named query parameter defined by HTMLURL, Section 5.1 [HTMLURL],
   which is the value after percent-encoded octets are decoded.  Note
   that this value does not include any leading ? characters, equals
   sign =, or separating & characters.  Named query parameters with an
   empty valueString are included with an empty string as the component
   value.

   If a query parameter is named as a covered component but it does not
   occur in the query parameters, this MUST cause an error in the
   signature base generation.

   For example for the following request:

   POST /path?param=value&foo=bar&baz=batman&qux= HTTP/1.1
   Host: www.example.com

   Indicating the baz, qux and param named query parameters would result
   in the following @query-param component values:

   _baz_: batman

   _qux_: an empty string

   _param_: value

   And the following signature base lines:

   NOTE: '\' line wrapping per RFC 8792

   "@query-param";name="baz": batman
   "@query-param";name="qux": \

   "@query-param";name="param": value




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   If a parameter name occurs multiple times in a request, all parameter
   values of that name MUST be included in separate signature base lines
   in the order in which the parameters occur in the target URI.  Note
   that in some implementations, the order of parsed query parameters is
   not stable, and this situation could lead to unexpected results.  If
   multiple parameters are common within an application, it is
   RECOMMENDED to sign the entire query string using the @query
   component identifier defined in Section 2.2.7.

2.2.9.  Status Code

   The @status derived component refers to the three-digit numeric HTTP
   status code of a response message as defined in [HTTP], Section 15.
   The component value is the serialized three-digit integer of the HTTP
   status code, with no descriptive text.

   For example, the following response message:

   HTTP/1.1 200 OK
   Date: Fri, 26 Mar 2010 00:05:00 GMT

   Would result in the following @status component value:

   200

   And the following signature base line:

   "@status": 200

   The @status component identifier MUST NOT be used in a request
   message.

2.3.  Signature Parameters

   HTTP Message Signatures have metadata properties that provide
   information regarding the signature's generation and verification,
   consisting of the ordered set of covered components and the ordered
   set of parameters including a timestamp of signature creation,
   identifiers for verification key material, and other utilities.  This
   metadata is represented by a special derived component for signature
   parameters, and it is treated slightly differently from other derived
   components.  Specifically, the signature parameters message component
   is REQUIRED as the last line of the signature base (Section 2.5), and
   the component identifier MUST NOT be enumerated within the set of
   covered components for any signature, including itself.

   The signature parameters component name is @signature-params.




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   The signature parameters component value is the serialization of the
   signature parameters for this signature, including the covered
   components ordered set with all associated parameters.  These
   parameters include any of the following:

   *  created: Creation time as an Integer UNIX timestamp value.  Sub-
      second precision is not supported.  Inclusion of this parameter is
      RECOMMENDED.

   *  expires: Expiration time as an Integer UNIX timestamp value.  Sub-
      second precision is not supported.

   *  nonce: A random unique value generated for this signature as a
      String value.

   *  alg: The HTTP message signature algorithm from the HTTP Message
      Signature Algorithm Registry, as a String value.

   *  keyid: The identifier for the key material as a String value.

   *  tag: An application-specific tag for the signature as a String
      value.  This value is used by applications to help identify
      signatures relevant for specific applications or protocols.

   Additional parameters can be defined in the HTTP Signature Parameters
   Registry (Section 6.3.2).  Note that there is no general ordering to
   the parameters, but once an ordering is chosen for a given set of
   parameters, it cannot be changed without altering the signature
   parameters value.

   The signature parameters component value is serialized as a
   parameterized Inner List using the rules in Section 4 of
   [STRUCTURED-FIELDS] as follows:

   1.  Let the output be an empty string.

   2.  Determine an order for the component identifiers of the covered
       components, not including the @signature-params component
       identifier itself.  Once this order is chosen, it cannot be
       changed.  This order MUST be the same order as used in creating
       the signature base (Section 2.5).










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   3.  Serialize the component identifiers of the covered components,
       including all parameters, as an ordered Inner List of String
       values according to Section 4.1.1.1 of [STRUCTURED-FIELDS] and
       append this to the output.  Note that the component identifiers
       can include their own parameters, and these parameters are
       ordered sets.  Once an order is chosen for a component's
       parameters, the order cannot be changed.

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

   5.  Append the parameters to the Inner List in order according to
       Section 4.1.1.2 of [STRUCTURED-FIELDS], skipping parameters that
       are not available or not used for this message signature.

   6.  The output contains the signature parameters component value.

   Note that the Inner List serialization from Section 4.1.1.1 of
   [STRUCTURED-FIELDS] is used for the covered component value instead
   of the List serialization from Section 4.1.1 of [STRUCTURED-FIELDS]
   in order to facilitate parallelism with this value's inclusion in the
   Signature-Input field, as discussed in Section 4.1.

   This example shows the serialized component value for the parameters
   of an example message signature:

   NOTE: '\' line wrapping per RFC 8792

   ("@target-uri" "@authority" "date" "cache-control")\
     ;keyid="test-key-rsa-pss";alg="rsa-pss-sha512";\
     created=1618884475;expires=1618884775

   Note that an HTTP message could contain multiple signatures
   (Section 4.3), but only the signature parameters used for a single
   signature are included in a given signature parameters entry.

2.4.  Request-Response Signature Binding

   When a request message results in a signed response message, the
   signer can include portions of the request message in the signature
   base by adding the req parameter to the component identifier.

   req  A boolean flag indicating that the component value is derived
      from the request that triggered this response message and not from
      the response message directly.






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   This parameter can be applied to both HTTP fields and derived
   components that target the request, with the same semantics.  The
   component value for a message component using this parameter is
   calculated in the same manner as it is normally, but data is pulled
   from the request message instead of the target response message to
   which the signature is applied.

   Note that the same component name MAY be included with and without
   the req parameter in a single signature base, indicating the same
   named component from both the request and response message.

   The req parameter MAY be combined with other parameters as
   appropriate for the component identifier, such as the key parameter
   for a dictionary field.

   For example, when serving a response for this signed request:

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18
   Signature-Input: sig1=("@method" "@authority" "@path" \
     "content-digest" "content-length" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature:  sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
     RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
     c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
     jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
     TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
     jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:

   {"hello": "world"}

   This would result in the following unsigned response message:

   HTTP/1.1 503 Service Unavailable
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Length: 62

   {"busy": true, "message": "Your call is very important to us"}





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   To cryptographically link the response to the request, the server
   signs the response with its own key and includes the method,
   authority, and the signature value sig1 from the request in the
   covered components of the response.  The signature base for this
   example is:

   NOTE: '\' line wrapping per RFC 8792

   "@status": 503
   "content-length": 62
   "content-type": application/json
   "signature";req;key="sig1": :LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziC\
     LuD8r5MW9S0RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY\
     /UkBIS1M8Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE\
     3IpWINTEzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9Hd\
     bD2Tr65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3\
     LZElYyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
   "@authority";req: example.com
   "@method";req: POST
   "@signature-params": ("@status" "content-length" "content-type" \
     "signature";req;key="sig1" "@authority";req "@method";req)\
     ;created=1618884479;keyid="test-key-ecc-p256"

   The signed response message is:

   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 503 Service Unavailable
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Length: 62
   Signature-Input: reqres=("@status" "content-length" "content-type" \
     "signature";req;key="sig1" "@authority";req "@method";req)\
     ;created=1618884479;keyid="test-key-ecc-p256"
   Signature: reqres=:mh17P4TbYYBmBwsXPT4nsyVzW4Rp9Fb8WcvnfqKCQLoMvzOB\
     LD/n32tL/GPW6XE5GAS5bdsg1khK6lBzV1Cx/Q==:

   {"busy": true, "message": "Your call is very important to us"}

   Since the request's signature value itself is not repeated in the
   response, the requester MUST keep the original signature value around
   long enough to validate the signature of the response that uses this
   component identifier.








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   Note that the ECDSA algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.

   The req parameter MUST NOT be used in a signature that targets a
   request message.

2.5.  Creating the Signature Base

   The signature base is a US-ASCII string containing the canonicalized
   HTTP message components covered by the signature.  The input to the
   signature base creation algorithm is the ordered set of covered
   component identifiers and their associated values, along with any
   additional signature parameters discussed in Section 2.3.

   Component identifiers are serialized using the production grammar
   defined by [STRUCTURED-FIELDS], Section 4.  The component identifier
   has a component name, which is a String Item value serialized using
   the sf-string ABNF rule.  The component identifier MAY also include
   defined parameters which are serialized using the parameters ABNF
   rule.  The signature parameters line defined in Section 2.3 follows
   this same pattern, but the component identifier is a String Item with
   a fixed value and no parameters, and the component value is always an
   Inner List with optional parameters.

   Note that this means the serialization of the component name itself
   is encased in double quotes, with parameters following as a
   semicolon-separated list, such as "cache-control", "@authority",
   "@signature-params", or "example-dictionary";key="foo".

   The output is the ordered set of bytes that form the signature base,
   which conforms to the following ABNF:

   signature-base = *( signature-base-line LF ) signature-params-line
   signature-base-line = component-identifier ":" SP
       ( derived-component-value / field-content ) ; no obs-fold
   component-identifier = component-name parameters
   component-name = sf-string
   derived-component-value = *( VCHAR / SP )
   signature-params-line = DQUOTE "@signature-params" DQUOTE
        ":" SP inner-list








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   To create the signature base, the signer or verifier concatenates
   together entries for each component identifier in the signature's
   covered components (including their parameters) using the following
   algorithm.  All errors produced as described immediately MUST fail
   the algorithm with no signature output base output.

   1.  Let the output be an empty string.

   2.  For each message component item in the covered components set (in
       order):

       1.  Append the component identifier for the covered component
           serialized according to the component-identifier ABNF rule.
           Note that this serialization places the component name in
           double quotes and appends any parameters outside of the
           quotes.

       2.  Append a single colon :

       3.  Append a single space " "

       4.  Determine the component value for the component identifier.

           *  If the component identifier has a parameter that is not
              understood, produce an error.

           *  If the component identifier has several incompatible
              parameters, such as bs and sf, produce an error.

           *  If the component identifier contains the req parameter and
              the target message is a request, produce an error.

           *  If the component identifier contains the req parameter and
              the target message is a response, the context for the
              component value is the related request message of the
              target response message.  Otherwise, the context for the
              component value is the target message.

           *  If the component name starts with an "at" character (@),
              derive the component's value from the message according to
              the specific rules defined for the derived component, as
              in Section 2.2, including processing of any known valid
              parameters.  If the derived component name is unknown or
              the value cannot be derived, produce an error.

           *  If the component name does not start with an "at"
              character (@), canonicalize the HTTP field value as
              described in Section 2.1, including processing of any



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              known valid parameters.  If the field cannot be found in
              the message, or the value cannot be obtained in the
              context, produce an error.

       5.  Append the covered component's canonicalized component value.

       6.  Append a single newline \n

   3.  Append the signature parameters component (Section 2.3) according
       to the signature-params-line rule as follows:

       1.  Append the component identifier for the signature parameters
           serialized according to the component-identifier rule, i.e.
           the exact value "@signature-params" (including double quotes)

       2.  Append a single colon :

       3.  Append a single space " "

       4.  Append the signature parameters' canonicalized component
           value as defined in Section 2.3, i.e. an Inner List
           structured field value with parameters

   4.  Return the output string.

   If covered components reference a component identifier that cannot be
   resolved to a component value in the message, the implementation MUST
   produce an error and not create a signature base.  Such situations
   are included but not limited to:

   *  The signer or verifier does not understand the derived component
      name.

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

   *  The component identifier includes a parameter that is unknown or
      does not apply to the component identifier to which it is
      attached.

   *  The component identifier indicates that a structured field
      serialization is used (via the sf parameter), but the field in
      question is known to not be a structured field or the type of
      structured field is not known to the implementation.

   *  The component identifier is a dictionary member identifier that
      references a field that is not present in the message, is not a
      Dictionary Structured Field, or whose value is malformed.



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   *  The component identifier is a dictionary member identifier or a
      named query parameter identifier that references a member that is
      not present in the component value, or whose value is malformed.
      E.g., the identifier is "example-dict";key="c" and the value of
      the Example-Dict header field is a=1, b=2, which does not have the
      c value.

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

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18

   {"hello": "world"}

   The covered components consist of the @method, @authority, and @path
   derived components followed by the Content-Digest, Content-Length,
   and Content-Type HTTP header fields, in order.  The signature
   parameters consist of a creation timestamp of 1618884473 and a key
   identifier of test-key-rsa-pss.  Note that no explicit alg parameter
   is given here since the verifier is known by the application to use
   the RSA PSS algorithm based on the identified key.  The signature
   base for this message with these parameters is:

   NOTE: '\' line wrapping per RFC 8792

   "@method": POST
   "@authority": example.com
   "@path": /foo
   "content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
     +TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   "content-length": 18
   "content-type": application/json
   "@signature-params": ("@method" "@authority" "@path" \
     "content-digest" "content-length" "content-type")\
     ;created=1618884473;keyid="test-key-rsa-pss"

               Figure 1: Non-normative example Signature Base






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   Note that the example signature base here, or anywhere else within
   this specification, does not include the final newline that ends the
   displayed example.

3.  HTTP Message Signatures

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

3.1.  Creating a Signature

   Creation of an HTTP message signature is a process that takes as its
   input the signature context (including the target message) and the
   requirements for the application.  The output is a signature value
   and set of signature parameters that can be communicated to the
   verifier by adding them to the message.

   In order to create a signature, a signer MUST follow the following
   algorithm:

   1.  The signer chooses an HTTP signature algorithm and key material
       for signing.  The signer MUST choose key material that is
       appropriate for the signature's algorithm, and that conforms to
       any requirements defined by the algorithm, such as key size or
       format.  The mechanism by which the signer chooses the algorithm
       and key material is out of scope for this document.

   2.  The signer sets the signature's creation time to the current
       time.

   3.  If applicable, the signer sets the signature's expiration time
       property to the time at which the signature is to expire.  The
       expiration is a hint to the verifier, expressing the time at
       which the signer is no longer willing to vouch for the safety of
       the signature.

   4.  The signer creates an ordered set of component identifiers
       representing the message components to be covered by the
       signature, and attaches signature metadata parameters to this
       set.  The serialized value of this is later used as the value of
       the Signature-Input field as described in Section 4.1.





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       *  Once an order of covered components is chosen, the order MUST
          NOT change for the life of the signature.

       *  Each covered component identifier MUST be either an HTTP field
          in the signature context Section 2.1 or a derived component
          listed in Section 2.2 or its associated registry.

       *  Signers of a request SHOULD include some or all of the message
          control data in the covered components, such as the @method,
          @authority, @target-uri, or some combination thereof.

       *  Signers SHOULD include the created signature metadata
          parameter to indicate when the signature was created.

       *  The @signature-params derived component identifier MUST NOT be
          listed in the list of covered component identifiers.  The
          derived component is required to always be the last line in
          the signature base, ensuring that a signature always covers
          its own metadata and the metadata cannot be substituted.

       *  Further guidance on what to include in this set and in what
          order is out of scope for this document.

   5.  The signer creates the signature base using these parameters and
       the signature base creation algorithm.  (Section 2.5)

   6.  The signer uses the HTTP_SIGN primitive function to sign the
       signature base with the chosen signing algorithm using the key
       material chosen by the signer.  The HTTP_SIGN primitive and
       several concrete applications of signing algorithms are defined
       in in Section 3.3.

   7.  The byte array output of the signature function is the HTTP
       message signature output value to be included in the Signature
       field as defined in Section 4.2.

   For example, given the HTTP message and signature parameters in the
   example in Section 2.5, the example signature base is signed with the
   test-key-rsa-pss key in Appendix B.1.2 and the RSA PSS algorithm
   described in Section 3.3.1, giving the following message signature
   output value, encoded in Base64:










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   NOTE: '\' line wrapping per RFC 8792

   HIbjHC5rS0BYaa9v4QfD4193TORw7u9edguPh0AW3dMq9WImrlFrCGUDih47vAxi4L2\
   YRZ3XMJc1uOKk/J0ZmZ+wcta4nKIgBkKq0rM9hs3CQyxXGxHLMCy8uqK488o+9jrptQ\
   +xFPHK7a9sRL1IXNaagCNN3ZxJsYapFj+JXbmaI5rtAdSfSvzPuBCh+ARHBmWuNo1Uz\
   VVdHXrl8ePL4cccqlazIJdC4QEjrF+Sn4IxBQzTZsL9y9TP5FsZYzHvDqbInkTNigBc\
   E9cKOYNFCn4D/WM7F6TNuZO9EgtzepLWcjTymlHzK7aXq6Am6sfOrpIC49yXjj3ae6H\
   RalVc/g==

              Figure 2: Non-normative example signature value

   Note that the RSA PSS algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.

3.2.  Verifying a Signature

   Verification of an HTTP message signature is a process that takes as
   its input the signature context (including the target message,
   particularly its Signature and Signature-Input fields) and the
   requirements for the application.  The output of the verification is
   either a positive verification or an error.

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

   1.  Parse the Signature and Signature-Input fields as described in
       Section 4.1 and Section 4.2, and extract the signatures to be
       verified.

       1.  If there is more than one signature value present, determine
           which signature should be processed for this message based on
           the policy and configuration of the verifier.  If an
           applicable signature is not found, produce an error.

       2.  If the chosen Signature value does not have a corresponding
           Signature-Input value, produce an error.

   2.  Parse the values of the chosen Signature-Input field as a
       parameterized Inner List to get the ordered list of covered
       components and the signature parameters for the signature to be
       verified.

   3.  Parse the value of the corresponding Signature field to get the
       byte array value of the signature to be verified.




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   4.  Examine the signature parameters to confirm that the signature
       meets the requirements described in this document, as well as any
       additional requirements defined by the application such as which
       message components are required to be covered by the signature.
       (Section 3.2.1)

   5.  Determine the verification key material for this signature.  If
       the key material is known through external means such as static
       configuration or external protocol negotiation, the verifier will
       use that.  If the key is identified in the signature parameters,
       the verifier will dereference this to appropriate key material to
       use with the signature.  The verifier has to determine the
       trustworthiness of the key material for the context in which the
       signature is presented.  If a key is identified that the verifier
       does not know, does not trust for this request, or does not match
       something preconfigured, the verification MUST fail.

   6.  Determine the algorithm to apply for verification:

       1.  If the algorithm is known through external means such as
           static configuration or external protocol negotiation, the
           verifier will use this algorithm.

       2.  If the algorithm can be determined from the keying material,
           such as through an algorithm field on the key value itself,
           the verifier will use this algorithm.

       3.  If the algorithm is explicitly stated in the signature
           parameters using a value from the HTTP Message Signatures
           registry, the verifier will use the referenced algorithm.

       4.  If the algorithm is specified in more than one location, such
           as through static configuration and the algorithm signature
           parameter, or the algorithm signature parameter and from the
           key material itself, the resolved algorithms MUST be the
           same.  If the algorithms are not the same, the verifier MUST
           fail the verification.

   7.  Use the received HTTP message and the parsed signature parameters
       to re-create the signature base, using the algorithm defined in
       Section 2.5.  The value of the @signature-params input is the
       value of the Signature-Input field for this signature serialized
       according to the rules described in Section 2.3.  Note that this
       does not include the signature's label from the Signature-Input
       field.






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   8.  If the key material is appropriate for the algorithm, apply the
       appropriate HTTP_VERIFY cryptographic verification algorithm to
       the signature, recalculated signature base, key material,
       signature value.  The HTTP_VERIFY primitive and several concrete
       algorithms are defined in Section 3.3.

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

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

   For example, verifying the signature with the key sig1 of the
   following message with the test-key-rsa-pss key in Appendix B.1.2 and
   the RSA PSS algorithm described in Section 3.3.1:

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18
   Signature-Input: sig1=("@method" "@authority" "@path" \
     "content-digest" "content-length" "content-type")\
     ;created=1618884473;keyid="test-key-rsa-pss"
   Signature: sig1=:HIbjHC5rS0BYaa9v4QfD4193TORw7u9edguPh0AW3dMq9WImrl\
     FrCGUDih47vAxi4L2YRZ3XMJc1uOKk/J0ZmZ+wcta4nKIgBkKq0rM9hs3CQyxXGxH\
     LMCy8uqK488o+9jrptQ+xFPHK7a9sRL1IXNaagCNN3ZxJsYapFj+JXbmaI5rtAdSf\
     SvzPuBCh+ARHBmWuNo1UzVVdHXrl8ePL4cccqlazIJdC4QEjrF+Sn4IxBQzTZsL9y\
     9TP5FsZYzHvDqbInkTNigBcE9cKOYNFCn4D/WM7F6TNuZO9EgtzepLWcjTymlHzK7\
     aXq6Am6sfOrpIC49yXjj3ae6HRalVc/g==:

   {"hello": "world"}

   With the additional requirements that at least the method, authority,
   path, content-digest, content-length, and content-type be signed, and
   that the signature creation timestamp is recent enough at the time of
   verification, the verification passes.










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3.2.1.  Enforcing Application Requirements

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

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

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

   *  Enforcing a maximum signature age from the time of the created
      time stamp.

   *  Rejection of signatures past the expiration time in the expires
      time stamp.  Note that the expiration time is a hint from the
      signer and that a verifier can always reject a signature ahead of
      its expiration time.

   *  Prohibition of certain signature metadata parameters, such as
      runtime algorithm signaling with the alg parameter when the
      algorithm is determined from the key information.

   *  Ensuring successful dereferencing of the keyid parameter to valid
      and appropriate key material.

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

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

   *  Enforcing uniqueness of the nonce parameter.

   *  Requiring an application-specific value for the tag parameter.

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

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



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3.3.  Signature Algorithms

   An HTTP Message signature MUST use a cryptographic digital signature
   or MAC method that is appropriate for the key material, environment,
   and needs of the signer and verifier.  This specification does not
   strictly limit the available signature algorithms, and any signature
   algorithm that meets these basic requirements MAY be used by an
   application of HTTP message signatures.

   Each signing method HTTP_SIGN takes as its input the signature base
   defined in Section 2.5 as a byte array (M), the signing key material
   (Ks), and outputs the signature output as a byte array (S):

   HTTP_SIGN (M, Ks)  ->  S

   Each verification method HTTP_VERIFY takes as its input the re-
   generated signature base defined in Section 2.5 as a byte array (M),
   the verification key material (Kv), and the presented signature to be
   verified as a byte array (S) and outputs the verification result (V)
   as a boolean:

   HTTP_VERIFY (M, Kv, S) -> V

   The following sections contain several common signature algorithms
   and demonstrates how these cryptographic primitives map to the
   HTTP_SIGN and HTTP_VERIFY definitions here.  Which method to use can
   be communicated through the explicit algorithm signature parameter
   alg defined in Section 2.3, by reference to the key material, or
   through mutual agreement between the signer and verifier.  Signature
   algorithms selected using the alg parameter MUST use values from the
   HTTP Message Signature Algorithms Registry (Section 6.2).

3.3.1.  RSASSA-PSS using SHA-512

   To sign using this algorithm, the signer applies the RSASSA-PSS-SIGN
   (K, M) function defined in [RFC8017] with the signer's private
   signing key (K) and the signature base (M) (Section 2.5).  The mask
   generation function is MGF1 as specified in [RFC8017] with a hash
   function of SHA-512 [RFC6234].  The salt length (sLen) is 64 bytes.
   The hash function (Hash) SHA-512 [RFC6234] is applied to the
   signature base to create the digest content to which the digital
   signature is applied.  The resulting signed content byte array (S) is
   the HTTP message signature output used in Section 3.1.

   To verify using this algorithm, the verifier applies the RSASSA-PSS-
   VERIFY ((n, e), M, S) function [RFC8017] using the public key portion
   of the verification key material ((n, e)) and the signature base (M)
   re-created as described in Section 3.2.  The mask generation function



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   is MGF1 as specified in [RFC8017] with a hash function of SHA-512
   [RFC6234].  The salt length (sLen) is 64 bytes.  The hash function
   (Hash) SHA-512 [RFC6234] is applied to the signature base to create
   the digest content to which the verification function is applied.
   The verifier extracts the HTTP message signature to be verified (S)
   as described in Section 3.2.  The results of the verification
   function indicate if the signature presented is valid.

   Note that the output of RSA PSS algorithms are non-deterministic, and
   therefore it is not correct to re-calculate a new signature on the
   signature base and compare the results to an existing signature.
   Instead, the verification algorithm defined here needs to be used.
   See Section 7.3.5.

   Use of this algorithm can be indicated at runtime using the rsa-pss-
   sha512 value for the alg signature parameter.

3.3.2.  RSASSA-PKCS1-v1_5 using SHA-256

   To sign using this algorithm, the signer applies the RSASSA-
   PKCS1-V1_5-SIGN (K, M) function defined in [RFC8017] with the
   signer's private signing key (K) and the signature base (M)
   (Section 2.5).  The hash SHA-256 [RFC6234] is applied to the
   signature base to create the digest content to which the digital
   signature is applied.  The resulting signed content byte array (S) is
   the HTTP message signature output used in Section 3.1.

   To verify using this algorithm, the verifier applies the RSASSA-
   PKCS1-V1_5-VERIFY ((n, e), M, S) function [RFC8017] using the public
   key portion of the verification key material ((n, e)) and the
   signature base (M) re-created as described in Section 3.2.  The hash
   function SHA-256 [RFC6234] is applied to the signature base to create
   the digest content to which the verification function is applied.
   The verifier extracts the HTTP message signature to be verified (S)
   as described in Section 3.2.  The results of the verification
   function indicate if the signature presented is valid.

   Use of this algorithm can be indicated at runtime using the rsa-
   v1_5-sha256 value for the alg signature parameter.

3.3.3.  HMAC using SHA-256

   To sign and verify using this algorithm, the signer applies the HMAC
   function [RFC2104] with the shared signing key (K) and the signature
   base (text) (Section 2.5).  The hash function SHA-256 [RFC6234] is
   applied to the signature base to create the digest content to which
   the HMAC is applied, giving the signature result.




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   For signing, the resulting value is the HTTP message signature output
   used in Section 3.1.

   For verification, the verifier extracts the HTTP message signature to
   be verified (S) as described in Section 3.2.  The output of the HMAC
   function is compared bytewise to the value of the HTTP message
   signature, and the results of the comparison determine the validity
   of the signature presented.

   Use of this algorithm can be indicated at runtime using the hmac-
   sha256 value for the alg signature parameter.

3.3.4.  ECDSA using curve P-256 DSS and SHA-256

   To sign using this algorithm, the signer applies the ECDSA algorithm
   defined in [FIPS186-4] using curve P-256 with the signer's private
   signing key and the signature base (Section 2.5).  The hash SHA-256
   [RFC6234] is applied to the signature base to create the digest
   content to which the digital signature is applied, (M).  The
   signature algorithm returns two integer values, r and s.  These are
   both encoded as big-endian unsigned integers, zero-padded to
   32-octets each.  These encoded values are concatenated into a single
   64-octet array consisting of the encoded value of r followed by the
   encoded value of s.  The resulting concatenation of (r, s) is byte
   array of the HTTP message signature output used in Section 3.1.

   To verify using this algorithm, the verifier applies the ECDSA
   algorithm defined in [FIPS186-4] using the public key portion of the
   verification key material and the signature base re-created as
   described in Section 3.2.  The hash function SHA-256 [RFC6234] is
   applied to the signature base to create the digest content to which
   the signature verification function is applied, (M).  The verifier
   extracts the HTTP message signature to be verified (S) as described
   in Section 3.2.  This value is a 64-octet array consisting of the
   encoded values of r and s concatenated in order.  These are both
   encoded in big-endian unsigned integers, zero-padded to 32-octets
   each.  The resulting signature value (r, s) is used as input to the
   signature verification function.  The results of the verification
   function indicate if the signature presented is valid.

   Note that the output of ECDSA algorithms are non-deterministic, and
   therefore it is not correct to re-calculate a new signature on the
   signature base and compare the results to an existing signature.
   Instead, the verification algorithm defined here needs to be used.
   See Section 7.3.5.

   Use of this algorithm can be indicated at runtime using the ecdsa-
   p256-sha256 value for the alg signature parameter.



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3.3.5.  ECDSA using curve P-384 DSS and SHA-384

   To sign using this algorithm, the signer applies the ECDSA algorithm
   defined in [FIPS186-4] using curve P-384 with the signer's private
   signing key and the signature base (Section 2.5).  The hash SHA-384
   [RFC6234] is applied to the signature base to create the digest
   content to which the digital signature is applied, (M).  The
   signature algorithm returns two integer values, r and s.  These are
   both encoded as big-endian unsigned integers, zero-padded to
   48-octets each.  These encoded values are concatenated into a single
   96-octet array consisting of the encoded value of r followed by the
   encoded value of s.  The resulting concatenation of (r, s) is byte
   array of the HTTP message signature output used in Section 3.1.

   To verify using this algorithm, the verifier applies the ECDSA
   algorithm defined in [FIPS186-4] using the public key portion of the
   verification key material and the signature base re-created as
   described in Section 3.2.  The hash function SHA-384 [RFC6234] is
   applied to the signature base to create the digest content to which
   the signature verification function is applied, (M).  The verifier
   extracts the HTTP message signature to be verified (S) as described
   in Section 3.2.  This value is a 96-octet array consisting of the
   encoded values of r and s concatenated in order.  These are both
   encoded in big-endian unsigned integers, zero-padded to 48-octets
   each.  The resulting signature value (r, s) is used as input to the
   signature verification function.  The results of the verification
   function indicate if the signature presented is valid.

   Note that the output of ECDSA algorithms are non-deterministic, and
   therefore it is not correct to re-calculate a new signature on the
   signature base and compare the results to an existing signature.
   Instead, the verification algorithm defined here needs to be used.
   See Section 7.3.5.

   Use of this algorithm can be indicated at runtime using the ecdsa-
   p384-sha384 value for the alg signature parameter.

3.3.6.  EdDSA using curve edwards25519

   To sign using this algorithm, the signer applies the Ed25519
   algorithm defined in Section 5.1.6 of [RFC8032] with the signer's
   private signing key and the signature base (Section 2.5).  The
   signature base is taken as the input message (M) with no pre-hash
   function.  The signature is a 64-octet concatenation of R and S as
   specified in Section 5.1.6 of [RFC8032], and this is taken as a byte
   array for the HTTP message signature output used in Section 3.1.





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   To verify using this algorithm, the signer applies the Ed25519
   algorithm defined in Section 5.1.7 of [RFC8032] using the public key
   portion of the verification key material (A) and the signature base
   re-created as described in Section 3.2.  The signature base is taken
   as the input message (M) with no pre-hash function.  The signature to
   be verified is processed as the 64-octet concatenation of R and S as
   specified in Section 5.1.7 of [RFC8032].  The results of the
   verification function indicate if the signature presented is valid.

   Use of this algorithm can be indicated at runtime using the ed25519
   value for the alg signature parameter.

3.3.7.  JSON Web Signature (JWS) algorithms

   If the signing algorithm is a JOSE signing algorithm from the JSON
   Web Signature and Encryption Algorithms Registry established by
   [RFC7518], the JWS algorithm definition determines the signature and
   hashing algorithms to apply for both signing and verification.

   For both signing and verification, the HTTP messages signature base
   (Section 2.5) is used as the entire "JWS Signing Input".  The JOSE
   Header defined in [RFC7517] is not used, and the signature base is
   not first encoded in Base64 before applying the algorithm.  The
   output of the JWS signature is taken as a byte array prior to the
   Base64url encoding used in JOSE.

   The JWS algorithm MUST NOT be none and MUST NOT be any algorithm with
   a JOSE Implementation Requirement of Prohibited.

   JWA algorithm values from the JSON Web Signature and Encryption
   Algorithms Registry are not included as signature parameters.
   Typically, the JWS algorithm can be signaled using JSON Web Keys or
   other mechanisms common to JOSE implementations.  In fact, and JWA
   algorithm values are not registered in the HTTP Message Signature
   Algorithms Registry (Section 6.2), and so the explicit alg signature
   parameter is not used at all when using JOSE signing algorithms.

4.  Including a Message Signature in a Message

   HTTP message signatures can be included within an HTTP message via
   the Signature-Input and Signature fields, both defined within this
   specification.

   The Signature-Input field identifies the covered components and
   parameters that describe how the signature was generated, while the
   Signature field contains the signature value.  Each field MAY contain
   multiple labeled values.




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   An HTTP message signature is identified by a label within an HTTP
   message.  This label MUST be unique within a given HTTP message and
   MUST be used in both the Signature-Input and Signature fields.  The
   label is chosen by the signer, except where a specific label is
   dictated by protocol negotiations such as described in Section 5.

   An HTTP message signature MUST use both Signature-Input and Signature
   fields and each field MUST contain the same labels.  The presence of
   a label in one field but not in the other is an error.

4.1.  The Signature-Input HTTP Field

   The Signature-Input field is a Dictionary structured field defined in
   Section 3.2 of [STRUCTURED-FIELDS] containing the metadata for one or
   more message signatures generated from components within the HTTP
   message.  Each member describes a single message signature.  The
   member's key is the label that uniquely identifies the message
   signature within the context of the HTTP message.  The member's value
   is the serialization of the covered components Inner List plus all
   signature metadata parameters identified by the label.

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig1=("@method" "@target-uri" "@authority" \
     "content-digest" "cache-control");\
     created=1618884475;keyid="test-key-rsa-pss"

   To facilitate signature validation, the Signature-Input field value
   MUST contain the same serialized value used in generating the
   signature base's @signature-params value defined in Section 2.3.
   Note that in a structured field value, list order and parameter order
   have to be preserved.

   The signer MAY include the Signature-Input field as a trailer to
   facilitate signing a message after its content has been processed by
   the signer.  However, since intermediaries are allowed to drop
   trailers as per [HTTP], it is RECOMMENDED that the Signature-Input
   field be included only as a header to avoid signatures being
   inadvertently stripped from a message.

   Multiple Signature-Input fields MAY be included in a single HTTP
   message.  The signature labels MUST be unique across all field
   values.








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4.2.  The Signature HTTP Field

   The Signature field is a Dictionary structured field defined in
   Section 3.2 of [STRUCTURED-FIELDS] containing one or more message
   signatures generated from components and context of the HTTP message.
   The member's key is the label that uniquely identifies the message
   signature within the context of the HTTP message.  The member's value
   is a Byte Sequence containing the signature value for the message
   signature identified by the label.

   NOTE: '\' line wrapping per RFC 8792

   Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
     1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCiHz\
     C87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW84jS8\
     gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53r58Rmp\
     Z+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCVRj05NrxA\
     BNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:

   The signer MAY include the Signature field as a trailer to facilitate
   signing a message after its content has been processed by the signer.
   However, since intermediaries are allowed to drop trailers as per
   [HTTP], it is RECOMMENDED that the Signature field be included only
   as a header to avoid signatures being inadvertently stripped from a
   message.

   Multiple Signature fields MAY be included in a single HTTP message.
   The signature labels MUST be unique across all field values.

4.3.  Multiple Signatures

   Multiple distinct signatures MAY be included in a single message.
   Each distinct signature MUST have a unique label.  These multiple
   signatures could be added all by the same signer or could come from
   several different signers.  For example, a signer may include
   multiple signatures signing the same message components with
   different keys or algorithms to support verifiers with different
   capabilities, or a reverse proxy may include information about the
   client in fields when forwarding the request to a service host,
   including a signature over the client's original signature values.

   The following non-normative example starts with a signed request from
   the client.  A reverse proxy takes this request validates the
   client's signature.







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   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18
   Signature-Input: sig1=("@method" "@authority" "@path" \
     "content-digest" "content-length" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature:  sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
     RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
     c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
     jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
     TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
     jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:

   {"hello": "world"}

   The proxy then alters the message before forwarding it on to the
   origin server, changing the target host and adding the Forwarded
   header field defined in [RFC7239].

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: origin.host.internal.example
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18
   Forwarded: for=192.0.2.123
   Signature-Input: sig1=("@method" "@authority" "@path" \
     "content-digest" "content-length" "content-type")\
     ;created=1618884475;keyid="test-key-rsa-pss"
   Signature:  sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
     RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8Br\
     c8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINTEzpx\
     jqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr65+BXe\
     TG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZElYyUKaAI\
     jZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:

   {"hello": "world"}





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   The proxy includes the client's signature value under the label sig1,
   which the proxy signs in addition to the Forwarded field.  Note that
   since the client's signature already covers the client's Signature-
   Input value for sig1, this value is transitively covered by the
   proxy's signature and need not be added explicitly.  The proxy
   identifies its own key and algorithm and, in this example, includes
   an expiration for the signature to indicate to downstream systems
   that the proxy will not vouch for this signed message past this short
   time window.  This results in a signature base of:

   NOTE: '\' line wrapping per RFC 8792

   "signature";key="sig1": :LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8\
     r5MW9S0RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkB\
     IS1M8Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpW\
     INTEzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2T\
     r65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZEl\
     YyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:
   "forwarded": for=192.0.2.123
   "@signature-params": ("signature";key="sig1" "forwarded")\
     ;created=1618884480;expires=1618884540;keyid="test-key-rsa"\
     ;alg="rsa-v1_5-sha256"

   And a signature output value of:

   NOTE: '\' line wrapping per RFC 8792

   G1WLTL4/9PGSKEQbSAMypZNk+I2dpLJ6qvl2JISahlP31OO/QEUd8/HdO2O7vYLi5k3\
   JIiAK3UPK4U+kvJZyIUidsiXlzRI+Y2se3SGo0D8dLfhG95bKr6ukYXl60QHpsGRTfS\
   iwdtvYKXGpKNrMlISJYd+oGrGRyI9gbCy0aFhc6I/okIMLeK4g9PgzpC3YTwhUQ98KI\
   BNLWHgREfBgJxjPbxFlsgJ9ykPviLj8GKJ81HwsK3XM9P7WaS7fMGOt8h1kSqgkZQB9\
   YqiIo+WhHvJa7iPy8QrYFKzx9BBEY6AwfStZAsXXz3LobZseyxsYcLJLs8rY0wVA9NP\
   sxKrHGA==

   These values are added to the HTTP request message by the proxy.  The
   original signature is included under the identifier sig1, and the
   reverse proxy's signature is included under the label proxy_sig.  The
   proxy uses the key test-key-rsa to create its signature using the
   rsa-v1_5-sha256 signature algorithm, while the client's original
   signature was made using the key id of test-key-rsa-pss and an RSA
   PSS signature algorithm.










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   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: origin.host.internal.example
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18
   Forwarded: for=192.0.2.123
   Signature-Input: sig1=("@method" "@authority" "@path" \
       "content-digest" "content-length" "content-type")\
       ;created=1618884475;keyid="test-key-rsa-pss", \
     proxy_sig=("signature";key="sig1" "forwarded")\
       ;created=1618884480;expires=1618884540;keyid="test-key-rsa"\
       ;alg="rsa-v1_5-sha256"
   Signature:  sig1=:LAH8BjcfcOcLojiuOBFWn0P5keD3xAOuJRGziCLuD8r5MW9S0\
       RoXXLzLSRfGY/3SF8kVIkHjE13SEFdTo4Af/fJ/Pu9wheqoLVdwXyY/UkBIS1M8\
       Brc8IODsn5DFIrG0IrburbLi0uCc+E2ZIIb6HbUJ+o+jP58JelMTe0QE3IpWINT\
       EzpxjqDf5/Df+InHCAkQCTuKsamjWXUpyOT1Wkxi7YPVNOjW4MfNuTZ9HdbD2Tr\
       65+BXeTG9ZS/9SWuXAc+BZ8WyPz0QRz//ec3uWXd7bYYODSjRAxHqX+S1ag3LZE\
       lYyUKaAIjZ8MGOt4gXEwCSLDv/zqxZeWLj/PDkn6w==:, \
     proxy_sig=:G1WLTL4/9PGSKEQbSAMypZNk+I2dpLJ6qvl2JISahlP31OO/QEUd8/\
       HdO2O7vYLi5k3JIiAK3UPK4U+kvJZyIUidsiXlzRI+Y2se3SGo0D8dLfhG95bKr\
       6ukYXl60QHpsGRTfSiwdtvYKXGpKNrMlISJYd+oGrGRyI9gbCy0aFhc6I/okIML\
       eK4g9PgzpC3YTwhUQ98KIBNLWHgREfBgJxjPbxFlsgJ9ykPviLj8GKJ81HwsK3X\
       M9P7WaS7fMGOt8h1kSqgkZQB9YqiIo+WhHvJa7iPy8QrYFKzx9BBEY6AwfStZAs\
       XXz3LobZseyxsYcLJLs8rY0wVA9NPsxKrHGA==:

   {"hello": "world"}

   The proxy's signature and the client's original signature can be
   verified independently for the same message, based on the needs of
   the application.  Since the proxy's signature covers the client
   signature, the backend service fronted by the proxy can trust that
   the proxy has validated the incoming signature.

5.  Requesting Signatures

   While a signer is free to attach a signature to a request or response
   without prompting, it is often desirable for a potential verifier to
   signal that it expects a signature from a potential signer using the
   Accept-Signature field.

   When the Accept-Signature field is sent in an HTTP request message,
   the field indicates that the client desires the server to sign the
   response using the identified parameters, and the target message is
   the response to this request.  All responses from resources that



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   support such signature negotiation SHOULD either be uncacheable or
   contain a Vary header field that lists Accept-Signature, in order to
   prevent a cache from returning a response with a signature intended
   for a different request.

   When the Accept-Signature field is used in an HTTP response message,
   the field indicates that the server desires the client to sign its
   next request to the server with the identified parameters, and the
   target message is the client's next request.  The client can choose
   to also continue signing future requests to the same server in the
   same way.

   The target message of an Accept-Signature field MUST include all
   labeled signatures indicated in the Accept-Header signature, each
   covering the same identified components of the Accept-Signature
   field.

   The sender of an Accept-Signature field MUST include only identifiers
   that are appropriate for the type of the target message.  For
   example, if the target message is a request, the covered components
   can not include the @status component identifier.

5.1.  The Accept-Signature Field

   The Accept-Signature field is a Dictionary structured field defined
   in Section 3.2 of [STRUCTURED-FIELDS] containing the metadata for one
   or more requested message signatures to be generated from message
   components of the target HTTP message.  Each member describes a
   single message signature.  The member's name is label that uniquely
   identifies the requested message signature within the context of the
   target HTTP message.  The member's value is the serialization of the
   desired covered components of the target message, including any
   allowed signature metadata parameters, using the serialization
   process defined in Section 2.3.

   NOTE: '\' line wrapping per RFC 8792

   Accept-Signature: sig1=("@method" "@target-uri" "@authority" \
     "content-digest" "cache-control");\
     keyid="test-key-rsa-pss"

   The requested signature MAY include parameters, such as a desired
   algorithm or key identifier.  These parameters MUST NOT include
   parameters that the signer is expected to generate, such as the
   created parameter.






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5.2.  Processing an Accept-Signature

   The receiver of an Accept-Signature field fulfills that header as
   follows:

   1.  Parse the field value as a Dictionary

   2.  For each member of the dictionary:

       1.  The key is taken as the label of the output signature as
           specified in Section 4.1

       2.  Parse the value of the member to obtain the set of covered
           component identifiers

       3.  Determine that the covered components are applicable to the
           target message.  If not, the process fails and returns an
           error.

       4.  Process the requested parameters, such as the signing
           algorithm and key material.  If any requested parameters
           cannot be fulfilled, or if the requested parameters conflict
           with those deemed appropriate to the target message, the
           process fails and returns an error.

       5.  Select and generate any additional parameters necessary for
           completing the signature

       6.  Create the HTTP message signature over the target message

       7.  Create the Signature-Input and Signature values and associate
           them with the label

   3.  Optionally create any additional Signature-Input and Signature
       values, with unique labels not found in the Accept-Signature
       field

   4.  Combine all labeled Signature-Input and Signature values and
       attach both fields to the target message

   Note that by this process, a signature applied to a target message
   MUST have the same label, MUST have the same set of covered
   component, and MAY have additional parameters.  Also note that the
   target message MAY include additional signatures not specified by the
   Accept-Signature field.






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6.  IANA Considerations

   IANA is asked to update one registry and create four new registries,
   according to the following sections.

6.1.  HTTP Field Name Registration

   IANA is asked to update the "Hypertext Transfer Protocol (HTTP) Field
   Name Registry" registry ([HTTP]) according to the table below:

        +==================+===========+=========================+
        | Field Name       | Status    | Reference               |
        +==================+===========+=========================+
        | Signature-Input  | permanent | Section 4.1 of RFC nnnn |
        +------------------+-----------+-------------------------+
        | Signature        | permanent | Section 4.2 of RFC nnnn |
        +------------------+-----------+-------------------------+
        | Accept-Signature | permanent | Section 5.1 of RFC nnnn |
        +------------------+-----------+-------------------------+

                                 Table 1

6.2.  HTTP Signature Algorithms Registry

   This document defines HTTP Signature Algorithms, for which IANA is
   asked to create and maintain a new registry titled "HTTP Signature
   Algorithms".  Initial values for this registry are given in
   Section 6.2.2.  Future assignments and modifications to existing
   assignment are to be made through the Expert Review registration
   policy [RFC8126] and shall follow the template presented in
   Section 6.2.1.

   Algorithms referenced by algorithm identifiers have to be fully
   defined with all parameters fixed.  Algorithm identifiers in this
   registry are to be interpreted as whole string values and not as a
   combination of parts.  That is to say, it is expected that
   implementors understand rsa-pss-sha512 as referring to one specific
   algorithm with its hash, mask, and salt values set as defined here.
   Implementors do not parse out the rsa, pss, and sha512 portions of
   the identifier to determine parameters of the signing algorithm from
   the string, and the registry of one combination of parameters does
   not imply the registration of other combinations.

   Algorithms added to this registry MUST NOT be aliases for other
   entries in the registry.






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6.2.1.  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.

   Description:
      A brief description of the algorithm used to sign the signature
      base.

   Status:
      A brief text description of the status of the algorithm.  The
      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as to the reason for
      the status.

   Specification document(s):
      Reference to the document(s) that specify the algorithm,
      preferably including a URI that can be used to retrieve a copy of
      the document(s).  An indication of the relevant sections may also
      be included but is not required.

6.2.2.  Initial Contents

    +===================+===================+========+===============+
    | Algorithm Name    | Description       | Status | Specification |
    |                   |                   |        | document(s)   |
    +===================+===================+========+===============+
    | rsa-pss-sha512    | RSASSA-PSS using  | Active | Section 3.3.1 |
    |                   | SHA-512           |        | of RFC nnnn   |
    +-------------------+-------------------+--------+---------------+
    | rsa-v1_5-sha256   | RSASSA-PKCS1-v1_5 | Active | Section 3.3.2 |
    |                   | using SHA-256     |        | of RFC nnnn   |
    +-------------------+-------------------+--------+---------------+
    | hmac-sha256       | HMAC using        | Active | Section 3.3.3 |
    |                   | SHA-256           |        | of RFC nnnn   |
    +-------------------+-------------------+--------+---------------+
    | ecdsa-p256-sha256 | ECDSA using curve | Active | Section 3.3.4 |
    |                   | P-256 DSS and     |        | of RFC nnnn   |
    |                   | SHA-256           |        |               |
    +-------------------+-------------------+--------+---------------+
    | ecdsa-p384-sha384 | ECDSA using curve | Active | Section 3.3.5 |
    |                   | P-384 DSS and     |        | of RFC nnnn   |
    |                   | SHA-384           |        |               |
    +-------------------+-------------------+--------+---------------+



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    | ed25519           | Edwards Curve DSA | Active | Section 3.3.6 |
    |                   | using curve       |        | of RFC nnnn   |
    |                   | edwards25519      |        |               |
    +-------------------+-------------------+--------+---------------+

        Table 2: Initial contents of the HTTP Signature Algorithms
                                Registry.

6.3.  HTTP Signature Metadata Parameters Registry

   This document defines the signature parameters structure in
   Section 2.3, which may have parameters containing metadata about a
   message signature.  IANA is asked to create and maintain a new
   registry titled "HTTP Signature Metadata Parameters" to record and
   maintain the set of parameters defined for use with member values in
   the signature parameters structure.  Initial values for this registry
   are given in Section 6.3.2.  Future assignments and modifications to
   existing assignments are to be made through the Expert Review
   registration policy [RFC8126] and shall follow the template presented
   in Section 6.3.1.

6.3.1.  Registration Template

   Name:
      An identifier for the HTTP signature metadata parameter.  The name
      MUST be an ASCII string that conforms to the key ABNF rule defined
      in Section 3.1.2 of [STRUCTURED-FIELDS] and SHOULD NOT exceed 20
      characters in length.  The identifier MUST be unique within the
      context of the registry.

   Description:
      A brief description of the metadata parameter and what it
      represents.

   Specification document(s):
      Reference to the document(s) that specify the parameter,
      preferably including a URI that can be used to retrieve a copy of
      the document(s).  An indication of the relevant sections may also
      be included but is not required.

6.3.2.  Initial Contents

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






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        +=========+===============================+===============+
        | Name    | Description                   | Specification |
        |         |                               | document(s)   |
        +=========+===============================+===============+
        | alg     | Explicitly declared signature | Section 2.3   |
        |         | algorithm                     | of RFC nnnn   |
        +---------+-------------------------------+---------------+
        | created | Timestamp of signature        | Section 2.3   |
        |         | creation                      | of RFC nnnn   |
        +---------+-------------------------------+---------------+
        | expires | Timestamp of proposed         | Section 2.3   |
        |         | signature expiration          | of RFC nnnn   |
        +---------+-------------------------------+---------------+
        | keyid   | Key identifier for the        | Section 2.3   |
        |         | signing and verification keys | of RFC nnnn   |
        |         | used to create this signature |               |
        +---------+-------------------------------+---------------+
        | nonce   | A single-use nonce value      | Section 2.3   |
        |         |                               | of RFC nnnn   |
        +---------+-------------------------------+---------------+
        | tag     | An application-specific tag   | Section 2.3   |
        |         | for a signature               | of RFC nnnn   |
        +---------+-------------------------------+---------------+

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

6.4.  HTTP Signature Derived Component Names Registry

   This document defines a method for canonicalizing HTTP message
   components, including components that can be derived from the context
   of the HTTP message outside of the HTTP fields.  These derived
   components are identified by a unique string, known as the component
   name.  Component names for derived components always start with the
   "@" (at) symbol to distinguish them from HTTP header fields.  IANA is
   asked to create and maintain a new registry typed "HTTP Signature
   Derived Component Names" to record and maintain the set of non-field
   component names and the methods to produce their associated component
   values.  Initial values for this registry are given in Section 6.4.2.
   Future assignments and modifications to existing assignments are to
   be made through the Expert Review registration policy [RFC8126] and
   shall follow the template presented in Section 6.4.1.

6.4.1.  Registration Template

   Name:





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      A name for the HTTP derived component.  The name MUST begin with
      the "@" character followed by an ASCII string consisting only of
      lower-case characters ("a" - "z"), digits ("0" - "9"), and hyphens
      ("-"), and SHOULD NOT exceed 20 characters in length.  The name
      MUST be unique within the context of the registry.

   Description:
      A description of the derived component.

   Status:
      A brief text description of the status of the algorithm.  The
      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as to the reason for
      the status.

   Target:
      The valid message targets for the derived parameter.  MUST be one
      of the values "Request", "Response", or "Request, Response".  The
      semantics of these are defined in Section 2.2.

   Specification document(s):
      Reference to the document(s) that specify the derived component,
      preferably including a URI that can be used to retrieve a copy of
      the document(s).  An indication of the relevant sections may also
      be included but is not required.

6.4.2.  Initial Contents

   The table below contains the initial contents of the HTTP Signature
   Derived Component Names Registry.

   +===================+==============+======+========+===============+
   | Name              | Description  |Status|Target  | Specification |
   |                   |              |      |        | document(s)   |
   +===================+==============+======+========+===============+
   | @signature-params | Reserved for |Active|Request,| Section 2.3   |
   |                   | signature    |      |Response| of RFC nnnn   |
   |                   | parameters   |      |        |               |
   |                   | line in      |      |        |               |
   |                   | signature    |      |        |               |
   |                   | base         |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @method           | The HTTP     |Active|Request | Section 2.2.1 |
   |                   | request      |      |        | of RFC nnnn   |
   |                   | method       |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @authority        | The HTTP     |Active|Request | Section 2.2.3 |
   |                   | authority,   |      |        | of RFC nnnn   |



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   |                   | or target    |      |        |               |
   |                   | host         |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @scheme           | The URI      |Active|Request | Section 2.2.4 |
   |                   | scheme of    |      |        | of RFC nnnn   |
   |                   | the request  |      |        |               |
   |                   | URI          |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @target-uri       | The full     |Active|Request | Section 2.2.2 |
   |                   | target URI   |      |        | of RFC nnnn   |
   |                   | of the       |      |        |               |
   |                   | request      |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @request-target   | The request  |Active|Request | Section 2.2.5 |
   |                   | target of    |      |        | of RFC nnnn   |
   |                   | the request  |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @path             | The full     |Active|Request | Section 2.2.6 |
   |                   | path of the  |      |        | of RFC nnnn   |
   |                   | request URI  |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @query            | The full     |Active|Request | Section 2.2.7 |
   |                   | query of the |      |        | of RFC nnnn   |
   |                   | request URI  |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @query-param      | A single     |Active|Request | Section 2.2.8 |
   |                   | named query  |      |        | of RFC nnnn   |
   |                   | parameter    |      |        |               |
   +-------------------+--------------+------+--------+---------------+
   | @status           | The status   |Active|Response| Section 2.2.9 |
   |                   | code of the  |      |        | of RFC nnnn   |
   |                   | response     |      |        |               |
   +-------------------+--------------+------+--------+---------------+

         Table 4: Initial contents of the HTTP Signature Derived
                        Component Names Registry.

6.5.  HTTP Signature Component Parameters Registry

   This document defines several kinds of component identifiers, some of
   which can be parameterized in specific circumstances to provide
   unique modified behavior.  IANA is asked to create and maintain a new
   registry typed "HTTP Signature Component Parameters" to record and
   maintain the set of parameters names, the component identifiers they
   are associated with, and the modifications these parameters make to
   the component value.  Definitions of parameters MUST define the
   targets to which they apply (such as specific field types, derived
   components, or contexts) and any incompatibilities with other



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   parameters known at the time of definition.  Initial values for this
   registry are given in Section 6.5.2.  Future assignments and
   modifications to existing assignments are to be made through the
   Expert Review registration policy [RFC8126] and shall follow the
   template presented in Section 6.5.1.

6.5.1.  Registration Template

   Name:
      A name for the parameter.  The name MUST be an ASCII string that
      conforms to the key ABNF rule defined in Section 3.1.2 of
      [STRUCTURED-FIELDS] and SHOULD NOT exceed 20 characters in length.
      The name MUST be unique within the context of the registry.

   Description:
      A description of the parameter's function.

   Status:
      A brief text description of the status of the parameter.  The
      description MUST begin with one of "Active" or "Deprecated", and
      MAY provide further context or explanation as to the reason for
      the status.

   Specification document(s):
      Reference to the document(s) that specify the derived component,
      preferably including a URI that can be used to retrieve a copy of
      the document(s).  An indication of the relevant sections may also
      be included but is not required.

6.5.2.  Initial Contents

   The table below contains the initial contents of the HTTP Signature
   Derived Component Names Registry.


















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     +======+==============================+========+===============+
     | Name | Description                  | Status | Specification |
     |      |                              |        | document(s)   |
     +======+==============================+========+===============+
     | sf   | Strict structured field      | Active | Section 2.1.1 |
     |      | serialization                |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+
     | key  | Single key value of          | Active | Section 2.1.2 |
     |      | dictionary structured fields |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+
     | bs   | Byte Sequence wrapping       | Active | Section 2.1.3 |
     |      | indicator                    |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+
     | tr   | Trailer                      | Active | Section 2.1.4 |
     |      |                              |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+
     | req  | Related request indicator    | Active | Section 2.2.4 |
     |      |                              |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+
     | name | Single named query parameter | Active | Section 2.2.8 |
     |      |                              |        | of RFC nnnn   |
     +------+------------------------------+--------+---------------+

        Table 5: Initial contents of the HTTP Signature Component
                           Parameters Registry.

7.  Security Considerations

   In order for an HTTP message to be considered _covered_ by a
   signature, all of the following conditions have to be true:

   *  a signature is expected or allowed on the message by the verifier

   *  the signature exists on the message

   *  the signature is verified against the identified key material and
      algorithm

   *  the key material and algorithm are appropriate for the context of
      the message

   *  the signature is within expected time boundaries

   *  the signature covers the expected content, including any critical
      components

   *  the list of covered components is applicable to the context of the
      message



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   In addition to the application requirement definitions listed in
   Section 1.4, the following security considerations provide discussion
   and context to the requirements of creating and verifying signatures
   on HTTP messages.

7.1.  General Considerations

7.1.1.  Skipping Signature Verification

   HTTP Message Signatures only provide security if the signature is
   verified by the verifier.  Since the message to which the signature
   is attached remains a valid HTTP message without the signature
   fields, it is possible for a verifier to ignore the output of the
   verification function and still process the message.  Common reasons
   for this could be relaxed requirements in a development environment
   or a temporary suspension of enforcing verification during debugging
   an overall system.  Such temporary suspensions are difficult to
   detect under positive-example testing since a good signature will
   always trigger a valid response whether or not it has been checked.

   To detect this, verifiers should be tested using both valid and
   invalid signatures, ensuring that the invalid signature fails as
   expected.

7.1.2.  Use of TLS

   The use of HTTP Message Signatures does not negate the need for TLS
   or its equivalent to protect information in transit.  Message
   signatures provide message integrity over the covered message
   components but do not provide any confidentiality for the
   communication between parties.

   TLS provides such confidentiality between the TLS endpoints.  As part
   of this, TLS also protects the signature data itself from being
   captured by an attacker, which is an important step in preventing
   signature replay (Section 7.2.2).

   When TLS is used, it needs to be deployed according to the
   recommendations in [BCP195].

7.2.  Message Processing and Selection










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7.2.1.  Insufficient Coverage

   Any portions of the message not covered by the signature are
   susceptible to modification by an attacker without affecting the
   signature.  An attacker can take advantage of this by introducing or
   modifying a header field or other message component that will change
   the processing of the message but will not be covered by the
   signature.  Such an altered message would still pass signature
   verification, but when the verifier processes the message as a whole,
   the unsigned content injected by the attacker would subvert the trust
   conveyed by the valid signature and change the outcome of processing
   the message.

   To combat this, an application of this specification should require
   as much of the message as possible to be signed, within the limits of
   the application and deployment.  The verifier should only trust
   message components that have been signed.  Verifiers could also strip
   out any sensitive unsigned portions of the message before processing
   of the message continues.

7.2.2.  Signature Replay

   Since HTTP Message Signatures allows sub-portions of the HTTP message
   to be signed, it is possible for two different HTTP messages to
   validate against the same signature.  The most extreme form of this
   would be a signature over no message components.  If such a signature
   were intercepted, it could be replayed at will by an attacker,
   attached to any HTTP message.  Even with sufficient component
   coverage, a given signature could be applied to two similar HTTP
   messages, allowing a message to be replayed by an attacker with the
   signature intact.

   To counteract these kinds of attacks, it's first important for the
   signer to cover sufficient portions of the message to differentiate
   it from other messages.  In addition, the signature can use the nonce
   signature parameter to provide a per-message unique value to allow
   the verifier to detect replay of the signature itself if a nonce
   value is repeated.  Furthermore, the signer can provide a timestamp
   for when the signature was created and a time at which the signer
   considers the signature to be expired, limiting the utility of a
   captured signature value.

   If a verifier wants to trigger a new signature from a signer, it can
   send the Accept-Signature header field with a new nonce parameter.
   An attacker that is simply replaying a signature would not be able to
   generate a new signature with the chosen nonce value.





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7.2.3.  Choosing Message Components

   Applications of HTTP Message Signatures need to decide which message
   components will be covered by the signature.  Depending on the
   application, some components could be expected to be changed by
   intermediaries prior to the signature's verification.  If these
   components are covered, such changes would, by design, break the
   signature.

   However, the HTTP Message Signature standard allows for flexibility
   in determining which components are signed precisely so that a given
   application can choose the appropriate portions of the message that
   need to be signed, avoiding problematic components.  For example, a
   web application framework that relies on rewriting query parameters
   might avoid use of the @query derived component in favor of sub-
   indexing the query value using @query-param derived components
   instead.

   Some components are expected to be changed by intermediaries and
   ought not to be signed under most circumstance.  The Via and
   Forwarded header fields, for example, are expected to be manipulated
   by proxies and other middle-boxes, including replacing or entirely
   dropping existing values.  These fields should not be covered by the
   signature except in very limited and tightly-coupled scenarios.

   Additional considerations for choosing signature aspects are
   discussed in Section 1.4.

7.2.4.  Choosing Signature Parameters and Derived Components over HTTP
        Fields

   Some HTTP fields have values and interpretations that are similar to
   HTTP signature parameters or derived components.  In most cases, it
   is more desirable to sign the non-field alternative.  In particular,
   the following fields should usually not be included in the signature
   unless the application specifically requires it:

   "date"  The "date" field value represents the timestamp of the HTTP
      message.  However, the creation time of the signature itself is
      encoded in the created signature parameter.  These two values can
      be different, depending on how the signature and the HTTP message
      are created and serialized.  Applications processing signatures
      for valid time windows should use the created signature parameter
      for such calculations.  An application could also put limits on
      how much skew there is between the "date" field and the created
      signature parameter, in order to limit the application of a
      generated signature to different HTTP messages.  See also
      Section 7.2.2 and Section 7.2.1.



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   "host"  The "host" header field is specific to HTTP 1.1, and its
      functionality is subsumed by the "@authority" derived component,
      defined in Section 2.2.3.  In order to preserve the value across
      different HTTP versions, applications should always use the
      "@authority" derived component.  See also Section 7.5.4.

7.2.5.  Signature Labels

   HTTP Message Signature values are identified in the Signature and
   Signature-Input field values by unique labels.  These labels are
   chosen only when attaching the signature values to the message and
   are not accounted for in the signing process.  An intermediary is
   allowed to re-label an existing signature when processing the
   message.

   Therefore, applications should not rely on specific labels being
   present, and applications should not put semantic meaning on the
   labels themselves.  Instead, additional signature parameters can be
   used to convey whatever additional meaning is required to be attached
   to and covered by the signature.  In particular, the tag parameter
   can be used to define an application-specific value as described in
   Section 7.2.7.

7.2.6.  Multiple Signature Confusion

   Since multiple signatures can be applied to one message
   (Section 4.3), it is possible for an attacker to attach their own
   signature to a captured message without modifying existing
   signatures.  This new signature could be completely valid based on
   the attacker's key, or it could be an invalid signature for any
   number of reasons.  Each of these situations need to be accounted
   for.

   A verifier processing a set of valid signatures needs to account for
   all of the signers, identified by the signing keys.  Only signatures
   from expected signers should be accepted, regardless of the
   cryptographic validity of the signature itself.

   A verifier processing a set of signatures on a message also needs to
   determine what to do when one or more of the signatures are not
   valid.  If a message is accepted when at least one signature is
   valid, then a verifier could drop all invalid signatures from the
   request before processing the message further.  Alternatively, if the
   verifier rejects a message for a single invalid signature, an
   attacker could use this to deny service to otherwise valid messages
   by injecting invalid signatures alongside the valid ones.





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7.2.7.  Collision of Application-Specific Signature Tag

   Multiple applications and protocols could apply HTTP signatures on
   the same message simultaneously.  In fact, this is a desired feature
   in many circumstances as described in Section 4.3.  A naive verifier
   could become confused in processing multiple signatures, either
   accepting or rejecting a message based on an unrelated or irrelevant
   signature.  In order to help an application select which signatures
   apply to its own processing, the application can declare a specific
   value for the tag signature parameter as defined in Section 2.3.  For
   example, a signature targeting an application gateway could require
   tag="app-gateway" as part of the signature parameters for that
   application.

   The use of the tag parameter does not prevent an attacker from also
   using the same value as a target application, since the parameter's
   value is public and otherwise unrestricted.  As a consequence, a
   verifier should only use value of the tag parameter to limit which
   signatures to check.  Each signature still needs to be examined by
   the verifier to ensure that sufficient coverage is provided, as
   discussed in Section 7.2.1.

7.2.8.  Message Content

   On its own, this specification does not provide coverage for the
   content of an HTTP message under the signature, either in request or
   response.  However, [DIGEST] defines a set of fields that allow a
   cryptographic digest of the content to be represented in a field.
   Once this field is created, it can be included just like any other
   field as defined in Section 2.1.

   For example, in the following response message:

   HTTP/1.1 200 OK
   Content-Type: application/json

   {"hello": "world"}

   The digest of the content can be added to the Content-Digest field as
   follows:











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   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 200 OK
   Content-Type: application/json
   Content-Digest: \
     sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:

   {"hello": "world"}

   This field can be included in a signature base just like any other
   field along with the basic signature parameters:

   "@status": 200
   "content-digest": \
     sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
   "@signature-input": ("@status" "content-digest")

   From here, the signing process proceeds as usual.

   Upon verification, it is important that the verifier validate not
   only the signature but also the value of the Content-Digest field
   itself against the actual received content.  Unless the verifier
   performs this step, it would be possible for an attacker to
   substitute the message content but leave the Content-Digest field
   value untouched to pass the signature.  Since only the field value is
   covered by the signature directly, checking only the signature is not
   sufficient protection against such a substitution attack.

   As discussed in [DIGEST], the value of the Content-Digest field is
   dependent on the content encoding of the message.  If an intermediary
   changes the content encoding, the resulting Content-Digest value
   would change, which would in turn invalidate the signature.  Any
   intermediary performing such an action would need to apply a new
   signature with the updated Content-Digest field value, similar to the
   reverse proxy use case discussed in Section 4.3.

7.3.  Cryptographic Considerations

7.3.1.  Cryptography and Signature Collision

   The HTTP Message Signatures specification does not define any of its
   own cryptographic primitives, and instead relies on other
   specifications to define such elements.  If the signature algorithm
   or key used to process the signature base is vulnerable to any
   attacks, the resulting signature will also be susceptible to these
   same attacks.





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   A common attack against signature systems is to force a signature
   collision, where the same signature value successfully verifies
   against multiple different inputs.  Since this specification relies
   on reconstruction of the signature base from an HTTP message, and the
   list of components signed is fixed in the signature, it is difficult
   but not impossible for an attacker to effect such a collision.  An
   attacker would need to manipulate the HTTP message and its covered
   message components in order to make the collision effective.

   To counter this, only vetted keys and signature algorithms should be
   used to sign HTTP messages.  The HTTP Message Signatures Algorithm
   Registry is one source of trusted signature algorithms for
   applications to apply to their messages.

   While it is possible for an attacker to substitute the signature
   parameters value or the signature value separately, the signature
   base generation algorithm (Section 2.5) always covers the signature
   parameters as the final value in the signature base using a
   deterministic serialization method.  This step strongly binds the
   signature base with the signature value in a way that makes it much
   more difficult for an attacker to perform a partial substitution on
   the signature bases.

7.3.2.  Key Theft

   A foundational assumption of signature-based cryptographic systems is
   that the signing key is not compromised by an attacker.  If the keys
   used to sign the message are exfiltrated or stolen, the attacker will
   be able to generate their own signatures using those keys.  As a
   consequence, signers have to protect any signing key material from
   exfiltration, capture, and use by an attacker.

   To combat this, signers can rotate keys over time to limit the amount
   of time stolen keys are useful.  Signers can also use key escrow and
   storage systems to limit the attack surface against keys.
   Furthermore, the use of asymmetric signing algorithms exposes key
   material less than the use of symmetric signing algorithms
   (Section 7.3.3).

7.3.3.  Symmetric Cryptography

   The HTTP Message Signatures specification allows for both asymmetric
   and symmetric cryptography to be applied to HTTP messages.  By its
   nature, symmetric cryptographic methods require the same key material
   to be known by both the signer and verifier.  This effectively means
   that a verifier is capable of generating a valid signature, since
   they have access to the same key material.  An attacker that is able
   to compromise a verifier would be able to then impersonate a signer.



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   Where possible, asymmetric methods or secure key agreement mechanisms
   should be used in order to avoid this type of attack.  When symmetric
   methods are used, distribution of the key material needs to be
   protected by the overall system.  One technique for this is the use
   of separate cryptographic modules that separate the verification
   process (and therefore the key material) from other code, minimizing
   the vulnerable attack surface.  Another technique is the use of key
   derivation functions that allow the signer and verifier to agree on
   unique keys for each message without having to share the key values
   directly.

   Additionally, if symmetric algorithms are allowed within a system,
   special care must be taken to avoid key downgrade attacks
   (Section 7.3.6).

7.3.4.  Key Specification Mix-Up

   The existence of a valid signature on an HTTP message is not
   sufficient to prove that the message has been signed by the
   appropriate party.  It is up to the verifier to ensure that a given
   key and algorithm are appropriate for the message in question.  If
   the verifier does not perform such a step, an attacker could
   substitute their own signature using their own key on a message and
   force a verifier to accept and process it.  To combat this, the
   verifier needs to ensure that not only does the signature validate
   for a message, but that the key and algorithm used are appropriate.

7.3.5.  Non-deterministic Signature Primitives

   Some cryptographic primitives such as RSA PSS and ECDSA have non-
   deterministic outputs, which include some amount of entropy within
   the algorithm.  For such algorithms, multiple signatures generated in
   succession will not match.  A lazy implementation of a verifier could
   ignore this distinction and simply check for the same value being
   created by re-signing the signature base.  Such an implementation
   would work for deterministic algorithms such as HMAC and EdDSA but
   fail to verify valid signatures made using non-deterministic
   algorithms.  It is therefore important that a verifier always use the
   correctly-defined verification function for the algorithm in question
   and not do a simple comparison.

7.3.6.  Key and Algorithm Specification Downgrades

   Applications of this specification need to protect against key
   specification downgrade attacks.  For example, the same RSA key can
   be used for both RSA-PSS and RSA v1.5 signatures.  If an application
   expects a key to only be used with RSA-PSS, it needs to reject
   signatures for that key using the weaker RSA 1.5 specification.



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   Another example of a downgrade attack occurs when an asymmetric
   algorithm is expected, such as RSA-PSS, but an attacker substitutes a
   signature using symmetric algorithm, such as HMAC.  A naive verifier
   implementation could use the value of the public RSA key as the input
   to the HMAC verification function.  Since the public key is known to
   the attacker, this would allow the attacker to create a valid HMAC
   signature against this known key.  To prevent this, the verifier
   needs to ensure that both the key material and the algorithm are
   appropriate for the usage in question.  Additionally, while this
   specification does allow runtime specification of the algorithm using
   the alg signature parameter, applications are encouraged to use other
   mechanisms such as static configuration or higher protocol-level
   algorithm specification instead, preventing an attacker from
   substituting the algorithm specified.

7.4.  Matching Covered Components to Message

7.4.1.  Modification of Required Message Parameters

   An attacker could effectively deny a service by modifying an
   otherwise benign signature parameter or signed message component.
   While rejecting a modified message is the desired behavior,
   consistently failing signatures could lead to the verifier turning
   off signature checking in order to make systems work again (see
   Section 7.1.1), or to the application minimizing the signed component
   requirements.

   If such failures are common within an application, the signer and
   verifier should compare their generated signature bases with each
   other to determine which part of the message is being modified.  If
   an expected modification is found, the signer and verifier can agree
   on an alternative set of requirements that will pass.  However, the
   signer and verifier should not remove the requirement to sign the
   modified component when it is suspected an attacker is modifying the
   component.

7.4.2.  Mismatch of Signature Parameters from Message

   The verifier needs to make sure that the signed message components
   match those in the message itself.  For example, the @method derived
   component requires that the value within the signature base be the
   same as the HTTP method used when presenting this message.  This
   specification encourages this by requiring the verifier to derive the
   signature base from the message, but lazy cacheing or conveyance of a
   raw signature base to a processing subsystem could lead to downstream
   verifiers accepting a message that does not match the presented
   signature.




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   To counter this, the component that generates the signature base
   needs to be trusted by both the signer and verifier within a system.

7.4.3.  Message Component Source and Context

   The context for deriving message component values includes the HTTP
   Message itself, any associated messages (such as the request that
   triggered a response), and additional information that the signer or
   verifier has access to.  Both signers and verifiers need to take
   carefully consider the source of all information when creating
   component values for the signature base and take care not to take
   information from untrusted sources.  Otherwise, an attacker could
   leverage such a loosely-defined message context to inject their own
   values into the signature base string, overriding or corrupting the
   intended values.

   For example, in most situations, the target URI of the message is
   defined in [HTTP], Section 7.1.  However, let's say that there is an
   application that requires signing of the @authority of the incoming
   request, but the application doing the processing is behind a reverse
   proxy.  Such an application would expect a change in the @authority
   value, and it could be configured to know the external target URI as
   seen by the client on the other side of the proxy.  This application
   would use this configured value as its target URI for the purposes of
   deriving message component values such as @authority instead of using
   the target URI of the incoming message.

   This approach is not without problems, as a misconfigured system
   could accept signed requests intended for different components in the
   system.  For this scenario, an intermediary could instead add its own
   signature to be verified by the application directly, as demonstrated
   in Section 4.3.  This alternative approach requires a more active
   intermediary but relies less on the target application knowing
   external configuration values.

   For another example, Section 2.4 defines a method for signing
   response messages but including portions of the request message that
   triggered the response.  In this case, the context for component
   value calculation is the combination of the response and request
   message, not just the single message to which the signature is
   applied.  For this feature, the req flag allows both signer to
   explicitly signal which part of the context is being sourced for a
   component identifier's value.  Implementations need to ensure that
   only the intended message is being referred to for each component,
   otherwise an attacker could attempt to subvert a signature by
   manipulating one side or the other.





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7.4.4.  Multiple Message Component Contexts

   It is possible that the context for deriving message component values
   could be distinct for each signature present within a single message.
   This is particularly the case when proxies mutate messages and
   include signatures over the mutated values, in addition to any
   existing signatures.  For example, a reverse proxy can replace a
   public hostname in a request to a service with the hostname for the
   individual service host that it is forwarding the request on to.  If
   both the client and the reverse proxy add signatures covering
   @authority, the service host will see two signatures on the request,
   each signing different values for the @authority message component,
   reflecting the change to that component as the message made its way
   from the client to the service host.

   In such a case, it's common for the internal service to verify only
   one of the signatures or to use externally-configured information, as
   discussed in Section 7.4.3.  However, a verifier processing both
   signatures has to use a different message component context for each
   signature, since the component value for the @authority component
   will be different for each signature.  Verifiers like this need to be
   aware of both the reverse proxy's context for incoming messages as
   well as the target service's context for the message coming from the
   reverse proxy.  The verifier needs to take particular care to apply
   the correct context to the correct signature, otherwise an attacker
   could use knowledge of this complex setup to confuse the inputs to
   the verifier.

   Such verifiers also need to ensure that any differences in message
   component contexts between signatures are expected and permitted.
   For example, in the above scenario, the reverse proxy could include
   the original hostname in a Forwarded header field, and sign
   @authority, forwarded, and the client's entry in the signature field.
   The verifier can use the hostname from the Forwarded header field to
   confirm that the hostname was transformed as expected.

7.5.  HTTP Processing

7.5.1.  Confusing HTTP Field Names for Derived Component Names

   The definition of HTTP field names does not allow for the use of the
   @ character anywhere in the name.  As such, since all derived
   component names start with the @ character, these namespaces should
   be completely separate.  However, some HTTP implementations are not
   sufficiently strict about the characters accepted in HTTP field
   names.  In such implementations, a sender (or attacker) could inject
   a header field starting with an @ character and have it passed
   through to the application code.  These invalid header fields could



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   be used to override a portion of the derived message content and
   substitute an arbitrary value, providing a potential place for an
   attacker to mount a signature collision (Section 7.3.1) attack or
   other functional substitution attack (such as using the signature
   from a GET request on a crafted POST request).

   To combat this, when selecting values for a message component, if the
   component name starts with the @ character, it needs to be processed
   as a derived component and never taken as a fields.  Only if the
   component name does not start with the @ character can it be taken
   from the fields of the message.  The algorithm discussed in
   Section 2.5 provides a safe order of operations.

7.5.2.  Semantically Equivalent Field Values

   The signature base generation algorithm (Section 2.5) uses the value
   of an HTTP field as its component value.  In the common case, this
   amounts to taking the actual bytes of the field value as the
   component value for both the signer and verifier.  However, some
   field values allow for transformation of the values in semantically
   equivalent ways that alter the bytes used in the value itself.  For
   example, a field definition can declare some or all of its value to
   be case-insensitive, or to have special handling of internal
   whitespace characters.  Other fields have expected transformations
   from intermediaries, such as the removal of comments in the Via
   header field.  In such cases, a verifier could be tripped up by using
   the equivalent transformed field value, which would differ from the
   byte value used by the signer.  The verifier would have have a
   difficult time finding this class of errors since the value of the
   field is still acceptable for the application, but the actual bytes
   required by the signature base would not match.

   When processing such fields, the signer and verifier have to agree
   how to handle such transformations, if at all.  One option is to not
   sign problematic fields, but care must be taken to ensure that there
   is still sufficient signature coverage (Section 7.2.1) for the
   application.  Another option is to define an application-specific
   canonicalization value for the field before it is added to the HTTP
   message, such as to always remove internal comments before signing,
   or to always transform values to lowercase.  Since these
   transformations are applied prior to the field being used as input to
   the signature base generation algorithm, the signature base will
   still simply contain the byte value of the field as it appears within
   the message.  If the transformations were to be applied after the
   value is extracted from the message but before it is added to the
   signature base, different attack surfaces such as value substitution
   attacks could be launched against the application.  All application-
   specific additional rules are outside the scope of this



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   specification, and by their very nature these transformations would
   harm interoperability of the implementation outside of this specific
   application.  It is recommended that applications avoid the use of
   such additional rules wherever possible.

7.5.3.  Parsing Structured Field Values

   Several parts of this specification rely on the parsing of structured
   field values [STRUCTURED-FIELDS].  In particular, normalization of
   HTTP structured field values (Section 2.1.1), referencing members of
   a dictionary structured field (Section 2.1.2), and processing the
   @signature-input value when verifying a signature (Section 3.2).
   While structured field values are designed to be relatively simple to
   parse, a naive or broken implementation of such a parser could lead
   to subtle attack surfaces being exposed in the implementation.

   For example, if a buggy parser of the @signature-input value does not
   enforce proper closing of quotes around string values within the list
   of component identifiers, an attacker could take advantage of this
   and inject additional content into the signature base through
   manipulating the Signature-Input field value on a message.

   To counteract this, implementations should use fully compliant and
   trusted parsers for all structured field processing, both on the
   signer and verifier side.

7.5.4.  HTTP Versions and Component Ambiguity

   Some message components are expressed in different ways across HTTP
   versions.  For example, the authority of the request target is sent
   using the Host header field in HTTP 1.1 but with the :authority
   pseudo-header in HTTP 2.  If a signer sends an HTTP 1.1 message and
   signs the Host field, but the message is translated to HTTP 2 before
   it reaches the verifier, the signature will not validate as the Host
   header field could be dropped.

   It is for this reason that HTTP Message Signatures defines a set of
   derived components that define a single way to get value in question,
   such as the @authority derived component (Section 2.2.3) in lieu of
   the Host header field.  Applications should therefore prefer derived
   components for such options where possible.










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7.5.5.  Canonicalization Attacks

   Any ambiguity in the generation of the signature base could provide
   an attacker with leverage to substitute or break a signature on a
   message.  Some message component values, particularly HTTP field
   values, are potentially susceptible to broken implementations that
   could lead to unexpected and insecure behavior.  Naive
   implementations of this specification might implement HTTP field
   processing by taking the single value of a field and using it as the
   direct component value without processing it appropriately.

   For example, if the handling of obs-fold field values does not remove
   the internal line folding and whitespace, additional newlines could
   be introduced into the signature base by the signer, providing a
   potential place for an attacker to mount a signature collision
   (Section 7.3.1) attack.  Alternatively, if header fields that appear
   multiple times are not joined into a single string value, as is
   required by this specification, similar attacks can be mounted as a
   signed component value would show up in the signature base more than
   once and could be substituted or otherwise attacked in this way.

   To counter this, the entire field value processing algorithm needs to
   be implemented by all implementations of signers and verifiers.

7.5.6.  Non-List Field Values

   When an HTTP field occurs multiple times in a single message, these
   values need to be combined into a single one-line string value to be
   included in the HTTP signature base, as described in Section 2.5.
   Not all HTTP fields can be combined into a single value in this way
   and still be a valid value for the field.  For the purposes of
   generating the signature base, the message component value is never
   meant to be read back out of the signature base string or used in the
   application.  Therefore it is considered best practice to treat the
   signature base generation algorithm separately from processing the
   field values by the application, particularly for fields that are
   known to have this property.  If the field values that are being
   signed do not validate, the signed message should also be rejected.

   If an HTTP field allows for unquoted commas within its values,
   combining multiple field values can lead to a situation where two
   semantically different messages produce the same line in a signature
   base.  For example, take the following hypothetical header field with
   an internal comma in its syntax, here used to define two separate
   lists of values:

   Example-Header: value, with, lots
   Example-Header: of, commas



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   For this header field, sending all of these values as a single field
   value results in a single list of values:

   Example-Header: value, with, lots, of, commas

   Both of these messages would create the following line in the
   signature base:

   "example-header": value, with, lots, of, commas

   Since two semantically distinct inputs can create the same output in
   the signature base, special care has to be taken when handling such
   values.

   Specifically, the Set-Cookie field [COOKIE] defines an internal
   syntax that does not conform to the List syntax in
   [STRUCTURED-FIELDS].  In particular some portions allow unquoted
   commas, and the field is typically sent as multiple separate field
   lines with distinct values when sending multiple cookies.  When
   multiple Set-Cookie fields are sent in the same message, it is not
   generally possible to combine these into a single line and be able to
   parse and use the results, as discussed in [HTTP], Section 5.3.
   Therefore, all the cookies need to be processed from their separate
   header values, without being combined, while the signature base needs
   to be processed from the special combined value generated solely for
   this purpose.  If the cookie value is invalid, the signed message
   ought to be rejected as this is a possible padding attack as
   described in Section 7.5.7.

   To deal with this, an application can choose to limit signing of
   problematic fields like Set-Cookie, such as including the field in a
   signature only when a single field value is present and the results
   would be unambiguous.  Similar caution needs to be taken with all
   fields that could have non-deterministic mappings into the signature
   base.  Signers can also make use of the bs parameter to armor such
   fields, as described in Section 2.1.3.

7.5.7.  Padding Attacks with Multiple Field Values

   Since HTTP field values need to be combined in a single string value
   to be included in the HTTP signature base, as described in
   Section 2.5, it is possible for an attacker to inject an additional
   value for a given field and add this to the signature base of the
   verifier.

   In most circumstances, this causes the signature validation to fail
   as expected, since the new signature base value will not match the
   one used by the signer to create the signature.  However, it is



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   theoretically possible for the attacker to inject both a garbage
   value to a field and a desired value to another field in order to
   force a particular input.  This is a variation of the collision
   attack described in Section 7.3.1, where the attacker accomplishes
   their change in the message by adding to existing field values.

   To counter this, an application needs to validate the content of the
   fields covered in the signature in addition to ensuring that the
   signature itself validates.  With such protections, the attacker's
   padding attack would be rejected by the field value processor, even
   in the case where the attacker could force a signature collision.

8.  Privacy Considerations

8.1.  Identification through Keys

   If a signer uses the same key with multiple verifiers, or uses the
   same key over time with a single verifier, the ongoing use of that
   key can be used to track the signer throughout the set of verifiers
   that messages are sent to.  Since cryptographic keys are meant to be
   functionally unique, the use of the same key over time is a strong
   indicator that it is the same party signing multiple messages.

   In many applications, this is a desirable trait, and it allows HTTP
   Message Signatures to be used as part of authenticating the signer to
   the verifier.  However, it could be unintentional tracking that a
   signer might not be aware of.  To counter this kind of tracking, a
   signer can use a different key for each verifier that it is in
   communication with.  Sometimes, a signer could also rotate their key
   when sending messages to a given verifier.  These approaches do not
   negate the need for other anti-tracking techniques to be applied as
   necessary.

8.2.  Signatures do not provide confidentiality

   HTTP Message Signatures do not provide confidentiality of any of the
   information protected by the signature.  The content of the HTTP
   message, including the value of all fields and the value of the
   signature itself, is presented in plaintext to any party with access
   to the message.

   To provide confidentiality at the transport level, TLS or its
   equivalent can be used as discussed in Section 7.1.2.








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8.3.  Oracles

   It is important to balance the need for providing useful feedback to
   developers on error conditions without providing additional
   information to an attacker.  For example, a naive but helpful server
   implementation might try to indicate the required key identifier
   needed for requesting a resource.  If someone knows who controls that
   key, a correlation can be made between the resource's existence and
   the party identified by the key.  Access to such information could be
   used by an attacker as a means to target the legitimate owner of the
   resource for further attacks.

8.4.  Required Content

   A core design tenet of this specification is that all message
   components covered by the signature need to be available to the
   verifier in order to recreate the signature base and verify the
   signature.  As a consequence, if an application of this specification
   requires that a particular field be signed, the verifier will need
   access to the value of that field.

   For example, in some complex systems with intermediary processors
   this could cause the surprising behavior of an intermediary not being
   able to remove privacy-sensitive information from a message before
   forwarding it on for processing, for fear of breaking the signature.
   A possible mitigation for this specific situation would be for the
   intermediary to verify the signature itself, then modifying the
   message to remove the privacy-sensitive information.  The
   intermediary can add its own signature at this point to signal to the
   next destination that the incoming signature was validated, as is
   shown in the example in Section 4.3.

9.  References

9.1.  Normative References

   [ABNF]     Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5234>.

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

   [HTMLURL]  "URL (Living Standard)", 2021,
              <https://url.spec.whatwg.org/>.



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   [HTTP]     Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [HTTP1]    Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
              June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.

   [POSIX.1]  "The Open Group Base Specifications Issue 7, 2018
              edition", 2018,
              <https://pubs.opengroup.org/onlinepubs/9699919799/>.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/rfc/rfc2104>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/rfc/rfc6234>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7517>.

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

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

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






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

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

   [URI]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

9.2.  Informative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, May 2015.

              Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", BCP 195, RFC 8996, March 2021.

              <https://www.rfc-editor.org/info/bcp195>

   [CLIENT-CERT]
              Campbell, B. and M. Bishop, "Client-Cert HTTP Header
              Field", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-client-cert-field-03, 19 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              client-cert-field-03>.

   [COOKIE]   Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,
              <https://www.rfc-editor.org/rfc/rfc6265>.

   [DIGEST]   Polli, R. and L. Pardue, "Digest Fields", Work in
              Progress, Internet-Draft, draft-ietf-httpbis-digest-
              headers-10, 19 June 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              digest-headers-10>.

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





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   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

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

   [TLS]      Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

Appendix A.  Detecting HTTP Message Signatures

   There have been many attempts to create signed HTTP messages in the
   past, including other non-standardized definitions of the Signature
   field, which is used within this specification.  It is recommended
   that developers wishing to support both this specification and other
   historical drafts do so carefully and deliberately, as
   incompatibilities between this specification and various versions of
   other drafts could lead to unexpected problems.

   It is recommended that implementers first detect and validate the
   Signature-Input field defined in this specification to detect that
   this standard is in use and not an alternative.  If the Signature-
   Input field is present, all Signature fields can be parsed and
   interpreted in the context of this specification.

Appendix B.  Examples

   The following non-normative examples are provided as a means of
   testing implementations of HTTP Message Signatures.  The signed
   messages given can be used to create the signature base with the
   stated parameters, creating signatures using the stated algorithms
   and keys.

   The private keys given can be used to generate signatures, though
   since several of the demonstrated algorithms are nondeterministic,
   the results of a signature are expected to be different from the
   exact bytes of the examples.  The public keys given can be used to
   validate all signed examples.








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B.1.  Example Keys

   This section provides cryptographic keys that are referenced in
   example signatures throughout this document.  These keys MUST NOT be
   used for any purpose other than testing.

   The key identifiers for each key are used throughout the examples in
   this specification.  It is assumed for these examples that the signer
   and verifier can unambiguously dereference all key identifiers used
   here, and that the keys and algorithms used are appropriate for the
   context in which the signature is presented.

   The components for each private key in PEM format can be displayed by
   executing the following OpenSSL command:

   openssl pkey -text

   This command was tested with all the example keys on OpenSSL version
   1.1.1m.  Note that some systems cannot produce or use all of these
   keys directly, and may require additional processing.  All keys are
   also made available in JWK format.

B.1.1.  Example Key RSA test

   The following key is a 2048-bit RSA public and private key pair,
   referred to in this document as test-key-rsa.  This key is encoded in
   PEM Format, with no encryption.
























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   -----BEGIN RSA PUBLIC KEY-----
   MIIBCgKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsPBRrw
   WEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsdJKFq
   MGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75jfZg
   kne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKIlE0P
   uKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZSFlQ
   PSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQAB
   -----END RSA PUBLIC KEY-----

   -----BEGIN RSA PRIVATE KEY-----
   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-----

   The same public and private keypair in JWK format:













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   NOTE: '\' line wrapping per RFC 8792

   {
     "kty": "RSA",
     "kid": "test-key-rsa",
     "p": "sqeUJmqXE3LP8tYoIjMIAKiTm9o6psPlc8CrLI9CH0UbuaA2JCOMcCNq8Sy\
     YbTqgnWlB9ZfcAm_cFpA8tYci9m5vYK8HNxQr-8FS3Qo8N9RJ8d0U5CswDzMYfRgh\
     AfUGwmlWj5hp1pQzAuhwbOXFtxKHVsMPhz1IBtF9Y8jvgqgYHLbmyiu1mw",
     "q": "vSlgXQbvHzWmuUBFRHAejRh_naQTDV3GnH4lcRHuFBFZCSLn82xQS2_7xFO\
     qfabqq17kNcvKfzdvWpGxxJ2cILAq0pZS6DmrZlvBU4IkK2ZHCac_XfWVZFh-PrsH\
     _EnVkDpfcYR_iw1F40C1q5w8R6WBHaew3SAp",
     "d": "b8lm5JZ2hUduLnq-OAKCSODeWQ7Uqs7eet2bqeuAD0_2po-PG4qhZoo7VwF\
     CUTWlJan9wqdxiAPlbEQKkCdFRcbakbjN2TMJjMCHWL5zfgvqhmgeyKsrqg1wSce9\
     7J1_Mkvn3fh6CbqnwNb6bVFDvTJS3i5FzRhKiv6rUsYm8ZAdF4XRaYkFkeuHPl7rc\
     -ruUTSAjC4GovxIxoDJFe0r4kbFmkiZOr40e8RZYK7T1IKrSvzfxx5AjnlK_OZOTC\
     q0L7wBPbMW-IxmQpFCjpI-yuoi3FlZG3LaLNrBMXQF_lLZUDHs77q3fAGxDWwum2h\
     KBfdBuUQtjlqwjQlgXPsskQ",
     "e": "AQAB",
     "qi": "PkbARLOwU_LcZrQy9mmfcPoQlAuCyeu1Q9nH7PYSnbHTFzmiud4Hl8bIXU\
     9a0_58blDoOl3PctF-b4rAEJYUpCODu5PFyN6uEFYRg-YQwpjBMkXk8Eb39128ctA\
     RB40Lx8caDhRdTyaEedIG3cQDXSpAl9EOzXkzfx4bZxjAHU9mkMdJwOcMDQ",
     "dp": "aiodZsrWpi8HFfZfeRs8OS_0L5x6WBl3Y9btoZgsIeruc9uZ8NXTIdxaM6\
     FdnyNEyOYA1VH94tDYR-xEt1br1ud_dkPslLV_Aac7d7EaYc7cdkb7oC9t6sphVg0\
     dqE0UTDlOwBxBYMtGmQbJsFzGpmjzVgKqWqJ3B947li2U7t63HXEvKprY2w",
     "dq": "b0DzpSMb5p42dcQgOTU8Mr4S6JOEhRr_YjErMkpaXUEqvZ3jEB9HRmcRi5\
     Gtt4NBiBMiY6V9br8a5gjEpiAQoIUcWokBMAYjEeurU8M6JLBd3YaZVVjISaFmdty\
     nwLFoQxCh6_EC1rSywwrfDpSwO29S9i8Xbaap",
     "n": "hAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsPBRrwWEBnez6\
     d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsdJKFqMGmXCQvE\
     G7YemcxDTRPxAleIAgYYRjTSd_QBwVW9OwNFhekro3RtlinV0a75jfZgkne_YiktS\
     vLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKIlE0PuKxI4T-HIa\
     Fpv8-rdV6eUgOrB2xeI1dSFFn_nnv5OoZJEIB-VmuKn3DCUcCZSFlQPSXSfBDiUGh\
     wOw76WuSSsf1D4b_vLoJ10w"
   }

B.1.2.  Example RSA PSS Key

   The following key is a 2048-bit RSA public and private key pair,
   referred to in this document as test-key-rsa-pss.  This key is PCKS#8
   encoded in PEM format, with no encryption.











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   -----BEGIN PUBLIC KEY-----
   MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAr4tmm3r20Wd/PbqvP1s2
   +QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvMs8ct+Lh1GH45x28Rw3Ry53mm+
   oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95AndTrifbIFPNU8PPMO7OyrFAHq
   gDsznjPFmTOtCEcN2Z1FpWgchwuYLPL+Wokqltd11nqqzi+bJ9cvSKADYdUAAN5W
   Utzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSyZYoA485mqcO0GVAdVw9lq4
   aOT9v6d+nb4bnNkQVklLQ3fVAvJm+xdDOp9LCNCN48V2pnDOkFV6+U9nV5oyc6XI
   2wIDAQAB
   -----END PUBLIC KEY-----

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

   The same public and private keypair in JWK format:











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   {
     "kty": "RSA",
     "kid": "test-key-rsa-pss",
     "p": "5V-6ISI5yEaCFXm-fk1EM2xwAWekePVCAyvr9QbTlFOCZwt9WwjUjhtKRus\
     i5Uq-IYZ_tq2WRE4As4b_FHEMtp2AER43IcvmXPqKFBoUktVDS7dThIHrsnRi1U7d\
     HqVdwiMEMe5jxKNgnsKLpnq-4NyhoS6OeWu1SFozG9J9xQk",
     "q": "w-wIde17W5Y0Cphp3ZZ0uM8OUq1AkrV2IKauqYHaDxAT32EM4ci2MMER2nI\
     UEo4g_42lW0zYouFFqONwv0-HyOsgPpdSqKRC5WLgn0VXabjaNcy6KhNPXeJ0Agtq\
     diDwPeJ2_L_eKwNWQ43RfdQBUquAwSd7SEmmQ8sViqB628M",
     "d": "lAfIqfpCYomVShfAKnwf2lD9I0wKjkHsCtZCif4kAlwQqqW6N-tIL3bdOR-\
     VWf0Q1ZBIDtpO91UrG7pansyrPERbNrRJlPiYEyPTHkCT1nD-l2isuiyGLNBNnFoK\
     fBgA4KAbPJZQatFIV9Cn34JSHnpN5-2ehreGBYHtkwHFtlmzeF3yu5bqRcqOhx8lk\
     YmBzDAEUFyyXjknU5-WjAT9DzuG0MpOTkcU1EnjnIjyVBZLUB5Lxm8puyq8hH8B_E\
     5LNC-1oc8j-tDy98UvRTTiYvZvs87cGCFxg0LijNhg7CE3g9piNqB6DzMgA9MHSOw\
     cElVtfKdYfo4H3OHZXsSmEQ",
     "e": "AQAB",
     "qi": "jRAqfYi_tKCjhP9eM0N2XaRlNeoYCTx06GlSLD8d0zc4ZZuEePY10LMGWI\
     6Y_JC0CvvvQYhNa9sAj4hFjIVLsWeTplVVUezGO1ofLW4kYWVpnMpHgAY1pRM4kyz\
     o1p3MKYY8DE1BA4KqhSOfhdGs6Ov3Dfj0migZeE7Fu7yc7Fc",
     "dp": "otDolkxtJ7Sk8gmRJqZCGx6GAvlGznWJfibXPv6xgUAl-G83dD84YgcNGn\
     oeMxRzEekfDtT5LVMRPF4_AoucsqPqHDyOdfb-dlGBYfOBVxj6w-xF5HE0lV_4J-H\
     rI63Od9fTSn4lY5d1JjyCVJIcnBEAyiD6EUZbUBh23vDzRcE",
     "dq": "iZE1S6CpqmBoQDxOsXGQmaeBdhoCqkDSJhEDuS_dLhBq88FQa0UkcE1QvO\
     K3J2Q21VnfDqGBx7SH1hOFOj-cpz45kNluB832ztxDvnHQ9AIA7h_HY_3VD6YPMNR\
     VN4bfSYS3abdLR0Z7jsmInGJ9X0_fA0E2tkZIgXeas5EFU0M",
     "n": "r4tmm3r20Wd_PbqvP1s2-QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvM\
     s8ct-Lh1GH45x28Rw3Ry53mm-oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95An\
     dTrifbIFPNU8PPMO7OyrFAHqgDsznjPFmTOtCEcN2Z1FpWgchwuYLPL-Wokqltd11\
     nqqzi-bJ9cvSKADYdUAAN5WUtzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSy\
     ZYoA485mqcO0GVAdVw9lq4aOT9v6d-nb4bnNkQVklLQ3fVAvJm-xdDOp9LCNCN48V\
     2pnDOkFV6-U9nV5oyc6XI2w"
   }

B.1.3.  Example ECC P-256 Test Key

   The following key is a public and private elliptical curve key pair
   over the curve P-256, referred to in this document as `test-key-ecc-
   p256.  This key is encoded in PEM format, with no encryption.











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

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

   The same public and private keypair in JWK format:

   {
     "kty": "EC",
     "crv": "P-256",
     "kid": "test-key-ecc-p256",
     "d": "UpuF81l-kOxbjf7T4mNSv0r5tN67Gim7rnf6EFpcYDs",
     "x": "qIVYZVLCrPZHGHjP17CTW0_-D9Lfw0EkjqF7xB4FivA",
     "y": "Mc4nN9LTDOBhfoUeg8Ye9WedFRhnZXZJA12Qp0zZ6F0"
   }

B.1.4.  Example Ed25519 Test Key

   The following key is an elliptical curve key over the Edwards curve
   ed25519, referred to in this document as test-key-ed25519.  This key
   is PCKS#8 encoded in PEM format, with no encryption.

   -----BEGIN PUBLIC KEY-----
   MCowBQYDK2VwAyEAJrQLj5P/89iXES9+vFgrIy29clF9CC/oPPsw3c5D0bs=
   -----END PUBLIC KEY-----

   -----BEGIN PRIVATE KEY-----
   MC4CAQAwBQYDK2VwBCIEIJ+DYvh6SEqVTm50DFtMDoQikTmiCqirVv9mWG9qfSnF
   -----END PRIVATE KEY-----

   The same public and private keypair in JWK format:

   {
     "kty": "OKP",
     "crv": "Ed25519",
     "kid": "test-key-ed25519",
     "d": "n4Ni-HpISpVObnQMW0wOhCKROaIKqKtW_2ZYb2p9KcU",
     "x": "JrQLj5P_89iXES9-vFgrIy29clF9CC_oPPsw3c5D0bs"
   }






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B.1.5.  Example Shared Secret

   The following shared secret is 64 randomly-generated bytes encoded in
   Base64, referred to in this document as test-shared-secret.

   NOTE: '\' line wrapping per RFC 8792

   uzvJfB4u3N0Jy4T7NZ75MDVcr8zSTInedJtkgcu46YW4XByzNJjxBdtjUkdJPBt\
     bmHhIDi6pcl8jsasjlTMtDQ==

B.2.  Test Cases

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

   For requests, this test-request message is used:

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+T\
     aPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   Content-Length: 18

   {"hello": "world"}

   For responses, this test-response message is used:

   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 200 OK
   Date: Tue, 20 Apr 2021 02:07:56 GMT
   Content-Type: application/json
   Content-Digest: sha-512=:JlEy2bfUz7WrWIjc1qV6KVLpdr/7L5/L4h7Sxvh6sN\
     HpDQWDCL+GauFQWcZBvVDhiyOnAQsxzZFYwi0wDH+1pw==:
   Content-Length: 23

   {"message": "good dog"}









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

   This example presents a minimal signature using the rsa-pss-sha512
   algorithm over test-request, covering none of the components of the
   HTTP message, but providing a timestamped signature proof of
   possession of the key with a signer-provided nonce.

   The corresponding signature base is:

   NOTE: '\' line wrapping per RFC 8792

   "@signature-params": ();created=1618884473;keyid="test-key-rsa-pss"\
     ;nonce="b3k2pp5k7z-50gnwp.yemd"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the signature label sig-b21:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b21=();created=1618884473\
     ;keyid="test-key-rsa-pss";nonce="b3k2pp5k7z-50gnwp.yemd"
   Signature: sig-b21=:d2pmTvmbncD3xQm8E9ZV2828BjQWGgiwAaw5bAkgibUopem\
     LJcWDy/lkbbHAve4cRAtx31Iq786U7it++wgGxbtRxf8Udx7zFZsckzXaJMkA7ChG\
     52eSkFxykJeNqsrWH5S+oxNFlD4dzVuwe8DhTSja8xxbR/Z2cOGdCbzR72rgFWhzx\
     2VjBqJzsPLMIQKhO4DGezXehhWwE56YCE+O6c0mKZsfxVrogUvA4HELjVKWmAvtl6\
     UnCh8jYzuVG5WSb/QEVPnP5TmcAnLH1g+s++v6d4s8m0gCw1fV5/SITLq9mhho8K3\
     +7EPYTU8IU1bLhdxO5Nyt8C8ssinQ98Xw9Q==:

   Note that since the covered components list is empty, this signature
   could be applied by an attacker to an unrelated HTTP message.  In
   this example, the nonce parameter is included to prevent the same
   signature from being replayed more than once, but if an attacker
   intercepts the signature and prevents its delivery to the verifier,
   the attacker could apply this signature to another message.
   Therefore, use of an empty covered components set is discouraged.
   See Section 7.2.1 for more discussion.

   Note that the RSA PSS algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.









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B.2.2.  Selective Covered Components using rsa-pss-sha512

   This example covers additional components (the authority, the
   Content-Digest header field, and a single named query parameter) in
   test-request using the rsa-pss-sha512 algorithm.  This example also
   adds a tag parameter with the application-specific value of header-
   example.

   The corresponding signature base is:

   NOTE: '\' line wrapping per RFC 8792

   "@authority": example.com
   "content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
     +TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   "@query-param";name="Pet": dog
   "@signature-params": ("@authority" "content-digest" \
     "@query-param";name="Pet")\
     ;created=1618884473;keyid="test-key-rsa-pss"\
     ;tag="header-example"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the label sig-b22:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b22=("@authority" "content-digest" \
     "@query-param";name="Pet");created=1618884473\
     ;keyid="test-key-rsa-pss";tag="header-example"
   Signature: sig-b22=:LjbtqUbfmvjj5C5kr1Ugj4PmLYvx9wVjZvD9GsTT4F7GrcQ\
     EdJzgI9qHxICagShLRiLMlAJjtq6N4CDfKtjvuJyE5qH7KT8UCMkSowOB4+ECxCmT\
     8rtAmj/0PIXxi0A0nxKyB09RNrCQibbUjsLS/2YyFYXEu4TRJQzRw1rLEuEfY17SA\
     RYhpTlaqwZVtR8NV7+4UKkjqpcAoFqWFQh62s7Cl+H2fjBSpqfZUJcsIk4N6wiKYd\
     4je2U/lankenQ99PZfB4jY3I5rSV2DSBVkSFsURIjYErOs0tFTQosMTAoxk//0RoK\
     UqiYY8Bh0aaUEb0rQl3/XaVe4bXTugEjHSw==:

   Note that the RSA PSS algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.










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

   This example covers all applicable message components in test-request
   (including the content type and length) plus many derived components,
   again using the rsa-pss-sha512 algorithm.  Note that the Host header
   field is not covered because the @authority derived component is
   included instead.

   The corresponding signature base is:

   NOTE: '\' line wrapping per RFC 8792

   "date": Tue, 20 Apr 2021 02:07:55 GMT
   "@method": POST
   "@path": /foo
   "@query": ?param=Value&Pet=dog
   "@authority": example.com
   "content-type": application/json
   "content-digest": sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX\
     +TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew==:
   "content-length": 18
   "@signature-params": ("date" "@method" "@path" "@query" \
     "@authority" "content-type" "content-digest" "content-length")\
     ;created=1618884473;keyid="test-key-rsa-pss"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the label sig-b23:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b23=("date" "@method" "@path" "@query" \
     "@authority" "content-type" "content-digest" "content-length")\
     ;created=1618884473;keyid="test-key-rsa-pss"
   Signature: sig-b23=:bbN8oArOxYoyylQQUU6QYwrTuaxLwjAC9fbY2F6SVWvh0yB\
     iMIRGOnMYwZ/5MR6fb0Kh1rIRASVxFkeGt683+qRpRRU5p2voTp768ZrCUb38K0fU\
     xN0O0iC59DzYx8DFll5GmydPxSmme9v6ULbMFkl+V5B1TP/yPViV7KsLNmvKiLJH1\
     pFkh/aYA2HXXZzNBXmIkoQoLd7YfW91kE9o/CCoC1xMy7JA1ipwvKvfrs65ldmlu9\
     bpG6A9BmzhuzF8Eim5f8ui9eH8LZH896+QIF61ka39VBrohr9iyMUJpvRX2Zbhl5Z\
     JzSRxpJyoEZAFL2FUo5fTIztsDZKEgM4cUA==:

   Note in this example that the value of the Date header and the value
   of the created signature parameter need not be the same.  This is due
   to the fact that the Date header is added when creating the HTTP
   Message and the created parameter is populated when creating the
   signature over that message, and these two times could vary.  If the
   Date header is covered by the signature, it is up to the verifier to
   determine whether its value has to match that of the created
   parameter or not.  See Section 7.2.4 for more discussion.



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   Note that the RSA PSS algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.

B.2.4.  Signing a Response using ecdsa-p256-sha256

   This example covers portions of the test-response response message
   using the ecdsa-p256-sha256 algorithm and the key test-key-ecc-p256.

   The corresponding signature base is:

   NOTE: '\' line wrapping per RFC 8792

   "@status": 200
   "content-type": application/json
   "content-digest": sha-512=:mEWXIS7MaLRuGgxOBdODa3xqM1XdEvxoYhvlCFJ4\
     1QJgJc4GTsPp29l5oGX69wWdXymyU0rjJuahq4l5aGgfLQ==:
   "content-length": 23
   "@signature-params": ("@status" "content-type" "content-digest" \
     "content-length");created=1618884473;keyid="test-key-ecc-p256"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the label sig-b24:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b24=("@status" "content-type" \
     "content-digest" "content-length");created=1618884473\
     ;keyid="test-key-ecc-p256"
   Signature: sig-b24=:wNmSUAhwb5LxtOtOpNa6W5xj067m5hFrj0XQ4fvpaCLx0NK\
     ocgPquLgyahnzDnDAUy5eCdlYUEkLIj+32oiasw==:

   Note that the ECDSA algorithm in use here is non-deterministic,
   meaning a different signature value will be created every time the
   algorithm is run.  The signature value provided here can be validated
   against the given keys, but newly-generated signature values are not
   expected to match the example.  See Section 7.3.5.

B.2.5.  Signing a Request using hmac-sha256

   This example covers portions of the test-request using the hmac-
   sha256 algorithm and the secret test-shared-secret.

   The corresponding signature base is:





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   NOTE: '\' line wrapping per RFC 8792

   "date": Tue, 20 Apr 2021 02:07:55 GMT
   "@authority": example.com
   "content-type": application/json
   "@signature-params": ("date" "@authority" "content-type")\
     ;created=1618884473;keyid="test-shared-secret"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the label sig-b25:

   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b25=("date" "@authority" "content-type")\
     ;created=1618884473;keyid="test-shared-secret"
   Signature: sig-b25=:pxcQw6G3AjtMBQjwo8XzkZf/bws5LelbaMk5rGIGtE8=:

   Before using symmetric signatures in practice, see the discussion of
   the security tradeoffs in Section 7.3.3.

B.2.6.  Signing a Request using ed25519

   This example covers portions of the test-request using the ed25519
   algorithm and the key test-key-ed25519.

   The corresponding signature base is:

   NOTE: '\' line wrapping per RFC 8792

   "date": Tue, 20 Apr 2021 02:07:55 GMT
   "@method": POST
   "@path": /foo
   "@authority": example.com
   "content-type": application/json
   "content-length": 18
   "@signature-params": ("date" "@method" "@path" "@authority" \
     "content-type" "content-length");created=1618884473\
     ;keyid="test-key-ed25519"

   This results in the following Signature-Input and Signature header
   fields being added to the message under the label sig-b26:










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   NOTE: '\' line wrapping per RFC 8792

   Signature-Input: sig-b26=("date" "@method" "@path" "@authority" \
     "content-type" "content-length");created=1618884473\
     ;keyid="test-key-ed25519"
   Signature: sig-b26=:wqcAqbmYJ2ji2glfAMaRy4gruYYnx2nEFN2HN6jrnDnQCK1\
     u02Gb04v9EDgwUPiu4A0w6vuQv5lIp5WPpBKRCw==:

B.3.  TLS-Terminating Proxies

   In this example, there is a TLS-terminating reverse proxy sitting in
   front of the resource.  The client does not sign the request but
   instead uses mutual TLS to make its call.  The terminating proxy
   validates the TLS stream and injects a Client-Cert header according
   to [CLIENT-CERT], and then applies a signature to this field.  By
   signing this header field, a reverse proxy can not only attest to its
   own validation of the initial request's TLS parameters but also
   authenticate itself to the backend system independently of the
   client's actions.

   The client makes the following request to the TLS terminating proxy
   using mutual TLS:

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Length: 18

   {"hello": "world"}

   The proxy processes the TLS connection and extracts the client's TLS
   certificate to a Client-Cert header field and passes it along to the
   internal service hosted at service.internal.example.  This results in
   the following unsigned request:
















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   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: service.internal.example
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Length: 18
   Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
     BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
     AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
     wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
     C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
     R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
     8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
     4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
     bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:

   {"hello": "world"}

   Without a signature, the internal service would need to trust that
   the incoming connection has the right information.  By signing the
   Client-Cert header and other portions of the internal request, the
   internal service can be assured that the correct party, the trusted
   proxy, has processed the request and presented it to the correct
   service.  The proxy's signature base consists of the following:

   NOTE: '\' line wrapping per RFC 8792

   "@path": /foo
   "@query": ?param=Value&Pet=dog
   "@method": POST
   "@authority": service.internal.example
   "client-cert": :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQ\
     KDBJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBD\
     QTAeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDM\
     FkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXm\
     ckC8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQY\
     DVR0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8B\
     Af8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQ\
     GV4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0\
     Q6bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
   "@signature-params": ("@path" "@query" "@method" "@authority" \
     "client-cert");created=1618884473;keyid="test-key-ecc-p256"

   This results in the following signature:






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   xVMHVpawaAC/0SbHrKRs9i8I3eOs5RtTMGCWXm/9nvZzoHsIg6Mce9315T6xoklyy0y\
   zhD9ah4JHRwMLOgmizw==

   Which results in the following signed request sent from the proxy to
   the internal service with the proxy's signature under the label ttrp:

   NOTE: '\' line wrapping per RFC 8792

   POST /foo?param=Value&Pet=dog HTTP/1.1
   Host: service.internal.example
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Content-Type: application/json
   Content-Length: 18
   Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
     BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
     AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
     wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
     C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
     R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
     8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
     4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
     bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
   Signature-Input: ttrp=("@path" "@query" "@method" "@authority" \
     "client-cert");created=1618884473;keyid="test-key-ecc-p256"
   Signature: ttrp=:xVMHVpawaAC/0SbHrKRs9i8I3eOs5RtTMGCWXm/9nvZzoHsIg6\
     Mce9315T6xoklyy0yzhD9ah4JHRwMLOgmizw==:

   {"hello": "world"}

   The internal service can validate the proxy's signature and therefore
   be able to trust that the client's certificate has been appropriately
   processed.

B.4.  HTTP Message Transformations

   The HTTP protocol allows intermediaries and applications to transform
   an HTTP message without affecting the semantics of the message
   itself.  HTTP message signatures are designed to be robust against
   many of these transformations in different circumstances.

   For example, the following HTTP request message has been signed using
   the ed25519 algorithm and the key test-key-ed25519.







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   GET /demo?name1=Value1&Name2=value2 HTTP/1.1
   Host: example.org
   Date: Fri, 15 Jul 2022 14:24:55 GMT
   Accept: application/json
   Accept: */*
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:

   The signature base string for this message is:

   "@method": GET
   "@path": /demo
   "@authority": example.org
   "accept": application/json, */*
   "@signature-params": ("@method" "@path" "@authority" "accept")\
     ;created=1618884473;keyid="test-key-ed25519"

   The following message has been altered by adding the Accept-Language
   header as well as adding a query parameter.  However, since neither
   the Accept-Language header nor the query are covered by the
   signature, the same signature is still valid:

   NOTE: '\' line wrapping per RFC 8792

   GET /demo?name1=Value1&Name2=value2&param=added HTTP/1.1
   Host: example.org
   Date: Fri, 15 Jul 2022 14:24:55 GMT
   Accept: application/json
   Accept: */*
   Accept-Language: en-US,en;q=0.5
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:

   The following message has been altered by removing the Date header,
   adding a Referer header, and collapsing the Accept header into a
   single line.  The Date and Referrer headers are not covered by the
   signature, and the collapsing of the Accept header is an allowed
   transformation that is already accounted for by the canonicalization
   algorithm for HTTP field values.  The same signature is still valid:






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   GET /demo?name1=Value1&Name2=value2 HTTP/1.1
   Host: example.org
   Referer: https://developer.example.org/demo
   Accept: application/json, */*
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:

   The following message has been altered by re-ordering the field
   values of the original message, but not re-ordering the individual
   Accept headers.  The same signature is still valid:

   NOTE: '\' line wrapping per RFC 8792

   GET /demo?name1=Value1&Name2=value2 HTTP/1.1
   Accept: application/json
   Accept: */*
   Date: Fri, 15 Jul 2022 14:24:55 GMT
   Host: example.org
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:

   The following message has been altered by changing the method to POST
   and the authority to "example.com" (inside the Host header).  Since
   both the method and authority are covered by the signature, the same
   signature is NOT still valid:

   NOTE: '\' line wrapping per RFC 8792

   POST /demo?name1=Value1&Name2=value2 HTTP/1.1
   Host: example.com
   Date: Fri, 15 Jul 2022 14:24:55 GMT
   Accept: application/json
   Accept: */*
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:








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   The following message has been altered by changing the order of the
   two instances of the Accept header.  Since the order of fields with
   the same name is semantically significant in HTTP, this changes the
   value used in the signature base, and the same signature is NOT still
   valid:

   NOTE: '\' line wrapping per RFC 8792

   GET /demo?name1=Value1&Name2=value2 HTTP/1.1
   Host: example.org
   Date: Fri, 15 Jul 2022 14:24:55 GMT
   Accept: */*
   Accept: application/json
   Signature-Input: transform=("@method" "@path" "@authority" \
     "accept");created=1618884473;keyid="test-key-ed25519"
   Signature: transform=:ZT1kooQsEHpZ0I1IjCqtQppOmIqlJPeo7DHR3SoMn0s5J\
     Z1eRGS0A+vyYP9t/LXlh5QMFFQ6cpLt2m0pmj3NDA==:

Acknowledgements

   This specification was initially based on the draft-cavage-http-
   signatures internet draft.  The editors would like to thank the
   authors of that draft, Mark Cavage and Manu Sporny, for their work on
   that draft and their continuing contributions.  The specification
   also includes contributions from the draft-oauth-signed-http-request
   internet draft and other similar efforts.

   The editors would also like to thank the following individuals for
   feedback, insight, and implementation of this draft and its
   predecessors (in alphabetical order): Mark Adamcin, Mark Allen, Paul
   Annesley, Karl Böhlmark, Stéphane Bortzmeyer, Sarven Capadisli, Liam
   Dennehy, Stephen Farrell, Phillip Hallam-Baker, Tyler Ham, Eric
   Holmes, Andrey Kislyuk, Adam Knight, Dave Lehn, Dave Longley, Ilari
   Liusvaara, James H.  Manger, Kathleen Moriarty, Mark Nottingham, Yoav
   Nir, Adrian Palmer, Lucas Pardue, Roberto Polli, Julian Reschke,
   Michael Richardson, Wojciech Rygielski, Rich Salz, Adam Scarr, Cory
   J.  Slep, Dirk Stein, Henry Story, Lukasz Szewc, Chris Webber, and
   Jeffrey Yasskin.

Document History

   _RFC EDITOR: please remove this section before publication_

   *  draft-ietf-httpbis-message-signatures

      -  -14

         o  Target raw non-decoded values for "@query" and "@path".



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         o  Add method for signing trailers.

         o  Call out potential issues of list-based field values.

         o  Update IANA registry for header fields.

         o  Call out potential issues with Content-Digest in example.

         o  Add JWK formats for all keys.

      -  -13

         o  Renamed "context" parameter to "tag".

         o  Added discussion on messages with multiple known contexts.

      -  -12

         o  Added "context" parameter.

         o  Added set of safe transformation examples.

         o  Added ECDSA over P-384.

         o  Expanded definiton of message component source context.

         o  Sorted security considerations into categories.

      -  -11

         o  Added ABNF references, coalesced ABNF rules.

         o  Editorial and formatting fixes.

         o  Update examples.

         o  Added Byte Sequence field value wrapping.

      -  -10

         o  Removed "related response" and "@request-response" in favor
            of generic "req" parameter.

         o  Editorial fixes to comply with HTTP extension style
            guidelines.

         o  Add security consideration on message content.




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      -  -09

         o  Explained key formats better.

         o  Removed "host" and "date" from most examples.

         o  Fixed query component generation.

         o  Renamed "signature input" and "signature input string" to
            "signature base".

         o  Added consideration for semantically equivalent field
            values.

      -  -08

         o  Editorial fixes.

         o  Changed "specialty component" to "derived component".

         o  Expanded signature input generation and ABNF rules.

         o  Added Ed25519 algorithm.

         o  Clarified encoding of ECDSA signature.

         o  Clarified use of non-deterministic algorithms.

      -  -07

         o  Added security and privacy considerations.

         o  Added pointers to algorithm values from definition sections.

         o  Expanded IANA registry sections.

         o  Clarified that the signing and verification algorithms take
            application requirements as inputs.

         o  Defined "signature targets" of request, response, and
            related-response for specialty components.

      -  -06

         o  Updated language for message components, including
            identifiers and values.





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         o  Clarified that Signature-Input and Signature are fields
            which can be used as headers or trailers.

         o  Add "Accept-Signature" field and semantics for signature
            negotiation.

         o  Define new specialty content identifiers, re-defined
            request-target identifier.

         o  Added request-response binding.

      -  -05

         o  Remove list prefixes.

         o  Clarify signature algorithm parameters.

         o  Update and fix examples.

         o  Add examples for ECC and HMAC.

      -  -04

         o  Moved signature component definitions up to intro.

         o  Created formal function definitions for algorithms to
            fulfill.

         o  Updated all examples.

         o  Added nonce parameter field.

      -  -03

         o  Clarified signing and verification processes.

         o  Updated algorithm and key selection method.

         o  Clearly defined core algorithm set.

         o  Defined JOSE signature mapping process.

         o  Removed legacy signature methods.

         o  Define signature parameters separately from "signature"
            object model.





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         o  Define serialization values for signature-input header based
            on signature input.

      -  -02

         o  Removed editorial comments on document sources.

         o  Removed in-document issues list in favor of tracked issues.

         o  Replaced unstructured Signature header with Signature-Input
            and Signature Dictionary Structured Header Fields.

         o  Defined content identifiers for individual Dictionary
            members, e.g., "x-dictionary-field";key=member-name.

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

         o  Fixed up examples.

         o  Updated introduction now that it's adopted.

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

         o  Required signature parameters to be included in signature.

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

      -  -01

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

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

         o  Minor editorial corrections and readability improvements.

      -  -00

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

   *  draft-richanna-http-message-signatures

      -  -00



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

         o  Removed Signature auth-scheme definition and related
            content.

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

         o  Removed Extensions appendix.

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

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

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

         o  Added examples for canonicalization and signature generation
            steps.

         o  Rewrote Signature header definition, retaining normative
            requirements.

         o  Added default values for algorithm and expires parameters.

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

         o  Added IANA HTTP Signature Parameter registry.

         o  Added additional normative and informative references.

         o  Added Topics for Working Group Discussion section, to be
            removed prior to publication as an RFC.

Authors' Addresses

   Annabelle Backman (editor)
   Amazon
   P.O. Box 81226
   Seattle, WA 98108-1226
   United States of America
   Email: richanna@amazon.com
   URI:   https://www.amazon.com/



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   Justin Richer (editor)
   Bespoke Engineering
   Email: ietf@justin.richer.org
   URI:   https://bspk.io/


   Manu Sporny
   Digital Bazaar
   203 Roanoke Street W.
   Blacksburg, VA 24060
   United States of America
   Email: msporny@digitalbazaar.com
   URI:   https://manu.sporny.org/






































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