verifyum

Prove that a file existed, unchanged, at a point in time. The file never leaves your machine: only a domain-separated commitment is sent.

pip install verifyum
verifyum stamp contract.pdf
verifyum verify contract.pdf

stamp writes contract.pdf.verifyum.json beside the file. That receipt holds the nonce, which is the only thing tying your file to its public proof, and which Verifyum never has. Losing it loses the link for good.

Treat it like a key. The file is created with mode 0600, which POSIX honours and Windows ignores, so writing it does not make it private: do not commit it and do not sync it anywhere you would not put a credential.

verify recomputes the commitment from the bytes and the receipt and checks it against the public record. verifyum witness contract.pdf additionally walks the Merkle path to the checkpoint and checks the service signature.

Exit codes: 0 all good, 1 a check failed, 2 usage or file error, 3 the service was unavailable, which is worth retrying.

It also works as a library:

from verifyum import anchor_file, verify, verify_witness

Standard library only, Python 3.10 or later. The protocol, the witness layer and independent verifiers in six languages are at https://github.com/aisenseapi/verifyum-verify

It proves the bytes existed and have not changed. It does not prove authorship, ownership, or that anything in the file is true.

MIT.