QWED A2A architecture for agent verification

Pipeline overview

Every inter-agent message flows through five deterministic stages:

Stage	Component	What it does
1. Schema	Pydantic `AgentMessage`	Validates sender/receiver IDs, payload type, timestamp, optional signature
2. Trust	`TrustBoundary`	Checks blocklists, allowlists, pair blocks, rate limits — deny-all by default
3. Engine	`_route_to_engine()`	Routes to `finance_guard`, `logic_guard`, `code_guard`, or `passthrough`
4. Attestation	`A2ACryptoService`	Signs the verdict with ES256 JWT — includes payload hash, trace ID, engine used
5. Verdict	`VerificationVerdict`	Returns `forwarded` or `blocked` with reason, attestation, and audit trace

Full verification sequence

Component relationship

Trust boundary evaluation

The trust boundary evaluates every request through a strict sequence. Note that allowlist checks happen before rate-limit allocation to prevent map-spray attacks.

Engine routing

The interceptor routes payloads based on payload_type:

PayloadType	Engine	Verification	Precision
`financial_transaction`	`finance_guard`	Decimal arithmetic — recomputes totals from line items	`Decimal("0.01")` tolerance
`logic_assertion`	`logic_guard`	Set-based contradiction detection (P AND NOT P)	Deterministic, sorted output
`code_execution`	`code_guard`	Case-insensitive regex for `eval`, `exec`, `subprocess`, `os.system`, etc.	Import/alias detection
`general` / `data_query`	`passthrough`	No verification — forwarded immediately	N/A

Data model

JWT attestation structure

Every verdict includes a signed JWT with this payload:

{
  "iss": "did:qwed:a2a:local",
  "sub": "sha256:abc123...",
  "iat": 1711411200,
  "exp": 1711497600,
  "jti": "a2a_demo_001",
  "qwed_a2a": {
    "version": "1.0",
    "verdict": "forwarded",
    "engine": "finance_guard",
    "sender": "procurement-agent",
    "receiver": "treasury-agent"
  }
}

The sub claim is a SHA-256 hash of the original payload, making the attestation tamper-evident. Any modification to the payload invalidates the hash match.

Overview

Core Components

Guides

QWED A2A architecture for agent verification

Pipeline overview

Full verification sequence

Component relationship

Trust boundary evaluation

Engine routing

Data model

JWT attestation structure

​Pipeline overview

​Full verification sequence

​Component relationship

​Trust boundary evaluation

​Engine routing

​Data model

​JWT attestation structure

Pipeline overview

Full verification sequence

Component relationship

Trust boundary evaluation

Engine routing

Data model

JWT attestation structure