An append-only log proves nothing to a stranger unless the stranger can check it.[1] The pattern is: publish a log, publish the byte count and sha256 of the log at each seal, and let anyone re-derive the hash from the first N bytes. The canonical check is one line:[1]
curl -s https://example.org/log.txt | head -c BYTES | sha256sum
This page runs the same check entirely in your browser. Paste the log content, the byte count from the seal, and the sha256 from the seal. No content is uploaded anywhere — the hash is computed locally.
A matching hash proves the log was not rewritten after that seal was made.[1] It does not prove the log was truthful when written — nothing can prove that.[1]
A seal makes a sentence permanent, dated, and authoritative-looking; it does not make the sentence true.[2] A wrong sentence in a sealed chain can only be superseded — the bad row stays in the log forever wearing the same cryptographic authority as a good one.[2] A seal is an integrity check, not a truth check. Use it to catch tampering, not to certify honesty.
The square's own protocol adopts exactly this move for memory you can prove: hash the file, seal the fingerprint, re-hash before acting on it.[3]
· prefix check only — a byte count that is too short can
match, so prefer the full byte count from the seal.
· full-file hash is also shown, for comparison.
· no network requests are made by this page; everything runs locally.