HTTP Message Signatures Directory

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Table of Contents

1. Introduction

[HTTP-MESSAGE-SIGNATURES] allow a signer to generate a signature over an HTTP message, and a verifier to validate it. The specification assumes verifiers have prior knowledge of signers' key material, requiring out-of-band key distribution mechanisms. This creates deployment friction and limits the ability to dynamically verify signatures from previously unknown signers.¶

This document defines: 1. A standardized key directory format based on JWKS for publishing HTTP Message Signatures keys 2. A well-known URI location for discovering these key directories 3. A new HTTP header field enabling in-band key directory location discovery¶

Together, these mechanisms enable key distribution and discovery for HTTP Message Signatures cryptographic material.¶

2. Conventions and Definitions

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.¶

3. Configuration

The key directory is served as a JSON Web Key Set (JWKS) as defined in Section 5 of [JWK]. The "alg" parameter are restricted to algorithm registered against HTTP Signature Algorithms Section of [HTTP-MESSAGE-SIGNATURES-IANA]¶

The directory SHOULD be server over HTTPS. The directory MUST be served with media type application/http-message-signatures-directory.¶

Client application SHOULD validate the directory format and reject malformed entries.¶

4. HTTP Method Context Signature-Agent

A service sending signed requests as defined in [HTTP-MESSAGE-SIGNATURES] MAY include a Signature-Agent header field to communicate its signing key directory. This header field contains a URI allowing retrieval of an HTTP Message Signatures Directory as defined in Section 3.¶

Signature-Agent = sf-string   ; Section 3.3.3 of {{STRUCTURED-HEADERS}}

5. Security Considerations

6. Privacy Considerations

Key directories enable discovery of signing keys which may reveal information about the signing entity. Implementers should consider:¶

7. IANA Considerations

This section contains considerations for IANA.¶

8. References

Appendix A. Examples

GET /.well-known/bar HTTP/1.1
Host: example.com
Accept: application/http-message-signatures-directory

HTTP/1.1 200 OK
Content-Type: application/http-message-signatures-directory
Cache-Control: max-age=86400
{
  "keys": {
    "kty": "OKP",
    "crv": "Ed25519",
    "kid": "NFcWBst6DXG-N35nHdzMrioWntdzNZghQSkjHNMMSjw",
    "x": "JrQLj5P_89iXES9-vFgrIy29clF9CC_oPPsw3c5D0bs",
    "use": "sig",
    "nbf": 1712793600,
    "exp": 1715385600
  }
}

POST /foo?param=Value&Pet=dog HTTP/1.1
Host: example.com
Signature-Agent: https://directory.test
{"hello": "world"}

HTTP/1.1 200 OK
{"message": "good dog"}

Acknowledgments

TODO acknowledge.¶

Author's Address