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OC Stamp

Create a stamp

Prove who signed a file, and when. The file never leaves your browser: only its SHA-256 is signed.

Step 1: What you are stamping

Any file. Your browser computes its SHA-256; the file never leaves this tab.

Drop a file here, or choose one

Large files hash in a few seconds.

It stays in your browser. Only its hash is signed.

Step 2: Who signs

A Bitcoin address whose wallet can sign a message (BIP-322). No keys are stored.

In step 3 you sign with a browser wallet, or paste a signature from any wallet.

Step 3: Sign it

Add a file and choose who signs first.