How to verify a certificate

A certificate is self-contained. Four checks, none of which needs this server: (1) the SHA-256 of your file equals the digest; (2) the SHA-256 of the canonical JSON of the payload equals payload_sha256; (3) the entry hash equals SHA-256 of prev_hash, payload_sha256 and recorded_at joined by newlines; (4) the Ed25519 signature over the entry hash (as ASCII) verifies with the published public key. Optionally, verify the .ots proof against the digest with the OpenTimestamps client for the Bitcoin anchor. The offline script below does all four with no dependencies.

Offline verification script (Python 3, no dependencies)

curl -O https://valaxia.ro/verify.py
python3 verify.py certificate.json my_file.pdf
# optional, Bitcoin anchor:  pip install opentimestamps-client && ots verify -d <digest> proof.ots

Server public key (Ed25519, hex): b38e884aad6129652ef85db29f941d9eeb89faa20aec4d1f0523b371367d16e5