algovoi-rfc9421-a2a

A2A per-message signing adapter binding the AlgoVoi RFC 9421 signer, verifier, and keyid resolver to the A2A message envelope. Thin glue over three shipped, hardened primitives; no new cryptography.

• Signs and verifies A2A JSON-RPC requests with RFC 9421 (HTTP Message Signatures) + RFC 9530 (Content-Digest) over application/a2a+json.
• Resolves the signer keyid with the SSRF-guarded algovoi-rfc9421-keyid resolver (did:key / did:web / HTTPS).
• Enforces the Sprint A hardening: replay window, single-use nonce, tag anti cross-protocol reuse, and an algorithm allow-list.

Layers

This is the per-message signature layer (does this specific request come from the key holder). It is orthogonal to A2A AgentCard signing (spec 8.4, JWS over the card document) and composes with it.

Trust boundary

Verifying a signature proves the request was signed by the holder of the key that keyid resolves to. It does not by itself prove the sender's identity; that binding is a policy decision the caller owns, normally via the agent's 8.4-signed AgentCard. verify_a2a_request therefore requires expected_keyid, an authorize_keyid predicate, or an explicit require_keyid_authorization=False opt-out. It will not silently trust an attacker-chosen keyid.

Install

pip install algovoi-rfc9421-a2a

Apache-2.0.