Day four of our how-to week turns to the other side of a signature: checking one. A logo and a signature image prove nothing on their own, because both can be copied into any PDF. These five checks tell a genuine signed document from a changed copy.
1. Drop the PDF on a verifier
Attest's verifier is free and open source, and it needs no account. The file is fingerprinted on your device and never uploaded. Try it at attest.datahubz.com/verify.
2. Read each check
The verifier checks the original document, each signer's passkey signature and entries, the record anchored on Base, and the pages you see, which it re-makes from what was signed. A genuine copy passes every check.
3. Change one word and the check fails
If a single word on the pages was changed, the pages no longer match what was signed, and the verifier says so: "The pages you see aren't what was signed."
4. Scan the code on any stamp
Every signature carries a stamp with a QR code. Scanning it opens the agreement's live certificate, which re-checks every signature and reads the anchor from Base in your own browser.
5. Check it without us
The verifier is inside every signed copy. Save it, open it on any computer and drop the PDF on it: it works offline, apart from the on-chain checks, which it reads from a public Base node. The answer comes from the cryptography, not from Attest.
The step-by-step verification guide explains each check and what a failure means.
Attest is part of the Horizen ecosystem on Base, and its zero-knowledge proofs are verified on zkVerify.
