Public Key Cryptography

The magic ink signature recently proposed in [11] is a blind signature which allows “unblinding” of a signature by authorities to establish what is known as audit trail and anonymity revocation in case of criminal activities. In [11] as well as in all the previous fair blind signature schemes (e. g., [2] and [10]), trustees need to search a database maintained by signers to obtain a transcript of the corresponding signing protocol instance in order to trace the signature receiver. In other words, to establish anonymity revocation, the trustees need to know some information which was produced in the signing stage and kept by the signers. This is clearly not convenient for the anonymity revocation in certain applications. In this paper, we propose a new type of magic ink signature scheme. The novel feature of the new scheme is that anonymity revocation is made transcript irrelevant. That is, the trustee can revoke a receiver’s anonymity based solely on the information embedded in a signature, not on any additional information; therefore, it is possible that the trustee revoke the anonymity without the help from the signer, therefore, without the signer knowing who is being traced.