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Private Alpha

Sign together. Everyone keeps the proof.

Document Signing, Decentralized.

Sign together. Everyone keeps the proof.

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Invite-only during the alpha. The people who sign need no account.

Verify a ceremony

Each signer adds their face, in order, closing the ring.

A partnership deal, a sale, a loan between friends: three of you need to sign. Each of you gets the document and signs from your phone. In the end it's like a contract made in three originals: everyone walks away with their own.

The server never receives your document, only its fingerprint.

Your browser reads the file and sends COSigna a 64-character fingerprint. Faces are end-to-end encrypted; no biometric template is ever computed. How the server stays blind →

Each signer checks the document, then adds their face to the one before.

Signers go in an order set in advance. Each device confirms the document is byte-for-byte the one the previous signer approved; the signer recognizes that person's photo, then takes their own with the document's code in frame. Identity is declared, never verified by us. The story →

The certificate verifies offline, without us.

Each sealed ceremony is anchored to Bitcoin via OpenTimestamps. The offline verifier is one HTML file you can keep and run in ten years. How the proof lasts →

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Invite-only during the alpha. The people who sign need no account.
COSigna — patent EP3665600B1 · US11531746B2 · FR3070079B1
Report bug COSigna — a Cryptographic Ring of Mutual Consent · The ring is strong because the loop is closed. The ring is strong because the loop is closed. COSigna