crovia-seal (Python reference)

Reference implementation of Crovia Seal v1.

Install

pip install -e .
# for tests
pip install -e ".[test]"

Smoke test (reproduces a signed Seal end-to-end)

python examples/demo_hp.py

Test suite

pytest -v

Covers:

• test_canonical.py — CSC-1 canonicalization determinism, every edge case: controls, non-ASCII, supplementary-plane code points, JS-safe integer bounds, float rejection, duplicate-key detection, UTF-16 key sort order.
• test_seal.py — happy path: structural shape, round-trip verify, pinned vs unpinned verification, chain composition, optional fields (checks, anchor).
• test_tamper.py — adversarial vectors: every field tamper must be detected, downgrade attempts on version/algorithm/domain must be detected, cross-protocol signature replay must fail, key substitution with signature rewrite is detected only by pinned verification (as specified).

Public API

from crovia_seal import (
    generate_issuer_key, load_issuer_key, load_public_key,
    emit_seal, verify_seal,
    compute_payload, compute_seal_hash,
    canonicalize,
    VerifyResult,
    CroviaSealError, CanonicalizationError, SchemaError, VerificationError, ChainError,
)

Dependencies

• cryptography — for Ed25519. Widely audited, maintained by PyCA.
• Python stdlib only otherwise (hashlib, base64, secrets, re, dataclasses).

No network, no file I/O, no randomness outside key and nonce generation.

Threat model

See ../../SPEC.md §9 for the full threat model. Summary:

• Signature replay across protocols: prevented by domain separation.
• JSON malleability: eliminated by CSC-1.
• Field tampering: all non-signature fields are covered by the signature.
• Version downgrade: seal_version is inside the signed payload.
• Key substitution: mitigated by pinned-key verification (issuer_pubkey_hex).
• Chain rollback: issuer hash chain is append-only and fork-detectable.

License

Apache 2.0. Specification text is additionally CC0 (see ../../LICENSE).