US Patent 7606768 Voice signature with strong binding

Voice signature method. The signer obtains a public key from an intended recipient of a document to be electronically signed. The signer speaks a personal identification number (PIN) to generate a voice PIN and the signer also speaks at least the signer's name. The voice PIN and voice signature are appended to the document and the voice PIN is encrypted using the public key to create an encrypted voice PIN. A polynomial hash is generated based on the document, the voice signature and the encrypted voice PIN and this hash is itself encrypted based on the PIN to generate an encrypted hash. Finally, the document, the voice signature, the encrypted voice PIN and the encrypted hash are sent to the intended recipient.