DefaultVerifier — SAR Verification Infrastructure

SAR (Settlement Attestation Receipt) is a verification protocol that produces cryptographically signed receipts proving whether an AI agent completed a task according to its specification.

DefaultVerifier is a live SAR verifier implementation with a public receipt registry, metrics API, and explorer.

If it matters—Verify it.

Architecture

Understand the SAR stack and verification model:

👉 SAR Architecture

Example Response

{ "witness": "SettlementWitness", "witness_version": "v0", "task_id": "example", "verifier_endpoint": "https://defaultverifier.com/verify", "witness_timestamp": "2026-01-01T00:00:00Z", "receipt_id": "...", "receipt": { "profile": "settlement-witness-verified-v0.2", "task_id_hash": "sha256:...", "verdict": "PASS", "reason_code": "CONDITION_SATISFIED", "ts": "...", "verifier_kid": "...", "counterparty": "0xABC...", "receipt_id": "sha256:...", "sig": "base64url:..." },

"_ext": { "agent_id": "0x123:demo" } }

Notes

the receipt payload is issued under the settlement-witness-verified-v0.2 profile; verdicts are PASS, FAIL, or INDETERMINATE
when counterparty is present, it is included in signature scope and in receipt_id derivation
retired signer keys remain valid for verifying receipts they historically signed; verifier_kid in a receipt is historical evidence and is never rewritten
current signer lifecycle (which kid is active vs. retired) is published at https://defaultverifier.com/.well-known/sar-keys.json — treat that endpoint, not this README, as the source of truth for which key is currently active
this behavior is implemented and publicly verifiable via the live receipt and key endpoints

SAR Compatibility: This implementation follows SAR verification semantics, with an extended signed payload when counterparty is present.

Demo

Run a full end-to-end verification in ~2 minutes: DEMO.md

Quick Start

1. Create a receipt

curl -X POST https://defaultverifier.com/settlement-witness
-H 'content-type: application/json'
-d '{ "task_id":"quickstart-001", "spec":{"checks":[{"kind":"field_equals","inputs":{"output_path":"$.result"},"expected":"hello"}]}, "output":{"result":"hello"}, "counterparty":"0x1234567890abcdef1234567890abcdef12345678" }'