Module dpop 

DPoP (Demonstration of Proof-of-Possession) for Chio tool invocations.

A DPoP proof is a signed canonical JSON object that binds a single tool invocation to the agent’s keypair. It prevents stolen-token replay by requiring the agent to prove possession of the private key corresponding to capability.subject on every invocation.

Proof fields:

• schema: constant "chio.dpop_proof.v1"
• capability_id: token ID of the capability being invoked
• tool_server: server_id of the target tool server
• tool_name: name of the tool being called
• action_hash: SHA-256 hash of the serialized tool arguments
• nonce: caller-chosen random string (replay prevention)
• issued_at: Unix seconds when the proof was created
• agent_key: hex-encoded public key of the signer (Ed25519 by default; p256: / p384: prefix under the FIPS crypto path)

Verification steps (in order):

1. Schema check – must equal DPOP_SCHEMA
2. Sender constraint – agent_key must equal capability.subject
3. Binding fields – capability_id, tool_server, tool_name, action_hash all match
4. Freshness – issued_at + proof_ttl_secs >= now and issued_at <= now + max_clock_skew_secs
5. Signature – verified through the signing backend negotiated between agent and kernel; dispatches off the algorithm carried by agent_key and the proof’s signature field
6. Nonce replay – nonce must not have been seen within the TTL window

Structs

DpopConfig

Configuration for DPoP proof verification.

DpopNonceStore

In-memory LRU nonce replay store.

DpopProof

A signed DPoP proof ready for transmission.

DpopProofBody

The signable body of a DPoP proof.

Constants

DPOP_SCHEMA

Schema identifier for Chio DPoP proofs.

Functions

is_supported_dpop_schema

verify_dpop_proof

Verify a DPoP proof against the given capability and invocation context.