Three party signing protocol providing non-linkability

A three-party signing method that protects the privacy of the signer and prevents verifiers from colluding to cross-link information signed by the signer, the method comprising the steps of:

• generating by a sender A a value M1 containing information identifying the sender A to a trusted third party T, information identifying an intended receiver B to the trusted third party T, information specifying data D, a signature S1 on at least a sub-portion of M1 containing at least the information specifying the data D;
• sending by A the value M1 containing the information specifying the data D with the signature S1 to the trusted third party T;
• validating by T the value M1, and if the value M1 is validated, then generating by T a psuedonymous identifier A1 for the sender A and a value M2 containing psuedonymous identifier A1 permitting A's psuedonymous identity to be determined by the receiver B, a copy of the information specifying the data D, a copy of A's signature S1 encrypted in a key that will allow only the trusted third party T to decrypt and recover it, a copy of T's signature S2 on at least a sub-portion of the value M2 containing at least a copy of the information specifying the data D that sender A provided to trusted third party T in value M1;
• sending by T the value M2 to the A, who in turn sends M2 to the intended receiver B, or else sending by T the value M2 directly to B;
• and
• validating by B the value M2, and if the value M2 is valid, then B is assured that A's signature S1 generated on data D was also valid, in which case B can trust that A did indeed sign D, even though B does not verify A's signature directly, or even “see” A's signature.

A three-party signing method that protects the privacy of the signer and prevents verifiers from colluding to cross-link information signed by the signer, the method comprising the steps of:

• creating and transmitting protocol information between a sender A, a trusted third party T and an intended receiver B, which includes generating and verifying of digital signatures S1 for the sender A and S2 for the trusted third party T in a manner that prevents the signature S1 from being cross-linked to data signed by the sender A;
• escrowing the protocol information;
• and
• resolving disputes between the sender A and the receiver B using an impartial party IP which accesses the escrowed protocol information.