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"

}'

2. Fetch the receipt

curl https://defaultverifier.com/settlement-witness/receipt/

Note: use the `receipt_id` from the returned receipt

3. Verify locally (Node)

cd examples/node-verify

node verify.js receipt.json jwks.json

Examples

Node.js verification example:

examples/node-verify/

Python verification example:

examples/verify_receipt_python.py

Usage:

python3 examples/verify_receipt_python.py

API Endpoints

Create Receipt

POST /settlement-witness

Submits a task verification request and returns a signed SAR receipt.

Retrieve Receipt

GET /settlement-witness/receipt/{receipt_id}

Note: Use the `receipt_id` from the returned receipt (sha256:...) for retrieval.

Returns a previously issued receipt.

Wallet Receipt Explorer

GET /settlement-witness/receipts?wallet={address}

Returns recent receipts associated with a wallet address.

The public explorer is available at:

https://defaultverifier.com/explorer

This interface allows browsing recent receipts and wallet-indexed delivery history.

Public Verification Keys

https://defaultverifier.com/.well-known/jwks.json

Alternative (SAR protocol reference):

https://defaultverifier.com/.well-known/sar-keys.json

Used to verify Ed25519 signatures for receipts.

Key Registry

https://defaultverifier.com/.well-known/sar-keys.json

Registry of verifier public keys referenced by `verifier_kid`.