A speculative design for combining visual signatures with SoundLinks-embedded audio to create a fraud-resistant, human-verifiable digital signature.

🧩 Concept

• Visual mark: a handwritten or stylus signature (image).
• Audio clip: signer speaks a short phrase (e.g., “I, N. Kovac, sign this document on Aug 21, 2025”).
• SoundLinks DID: embedded inaudibly in the audio, tied to blockchain.
• Bind hash: SHA-256(docHash || visualSigHash || SDID) links all three together.

Result: A multi-modal signature (sight + sound + crypto).

🛠 How It Works

Signing Flow

1. Document hash is computed.
2. Signer draws a visual signature.
3. Signer records an audio phrase → SoundLinks SDK embeds SDID.
4. bind = hash(docHash + visualSigHash + SDID).
5. Optionally, bind is also signed via PKI.
6. Bundle is registered on blockchain/registry and packaged into the PDF/ZIP.

Verification Flow

1. Recompute doc + visual sig hashes.
2. Extract SDID from audio and validate watermark.