tersign (Python)

Tersign — the evidence layer for the agent economy. This package is the verification-first Python SDK: zero dependencies, standard library only — the verify path a tribunal, examiner, or CI job can run with nothing installed.

python3 -m tersign verify receipt.json            # offline — no network, ever
python3 -m tersign verify 0x<digest> --ledger …   # chain lookup (explicit network)

from tersign import verify_receipt, digest_of, chain_link_digest, verify_link, verify_commitment

result = verify_receipt(signed_receipt)        # {'valid': True, 'signer': '0x…', 'digest': '0x…'}

What it covers (v0.1):

• RFC 8785 (JCS) canonical form + the Tersign artifact digest (keccak256(utf8(JCS(v)))) and chain-link constructor — byte-compatible with the TypeScript reference, pinned by shared cross-implementation vectors.
• EIP-712 recovery for the upstream x402 receipt domain (the merged offer-receipt extension) — pure-python secp256k1, canonical low-s only.
• Counter-signature verification (verify_link): EIP-191 over the raw 32-byte chain-link digest, recovered against the published ledger signer (https://tersign.ai/v1/ledger).
• Chain commitment recompute (verify_commitment): since 2026-08-28 each anchor stamps a chain commitment — an accumulator over every counter-signed link — so one anchored digest covers the whole prefix; rows anchored earlier bind the head record only and say so (subjectSchema).

Issuing/signing lives in the TypeScript SDK (npm tersign); this package is the independent second implementation of the verification surface — cross-implementation by construction. Frozen evidence bundles (tersign-evidence-bundle-v1) ship their own copy of this verify core inside the artifact, so bundle verification never depends on an install.

No console script on purpose: the tersign bin name belongs to the npm package; the Python surface is python3 -m tersign.