Group Undeniable Signatures

A group undeniable signature scheme is proposed in which each group member can sign on behalf of the group without revealing his or her identity and the verification of a signature can only be done with the cooperation of the group manager. For business applications, group undeniable signatures can be used to validate price lists, press release or digital contracts when the signatures are commercially sensitive or valuable to a competitor. If a group is falsely accused of having signed a particular signature, the manager should have the ability to prove his innocence. In case of a later dispute, the manager can track down which member signed the signature. Our scheme can be proven to be unforgeable, signature-simulatable and coalition-resistant. The confirmation and denial protocols are also zero-knowledge. Furthermore, the time, space and communication complexity are independent of the group size. Key-Words: Group signature, Undeniable signature, Signature of knowledge, Unforgeability, Coalition resistance.