Efficient Identity-Committable Signature and Group-Oriented Ring Signature Schemes

The identity of “Deep Throat”, a pseudonym of the information source in the Watergate scandal, remained mysterious for more than three decades. In 2005, an ex-FBI official claimed that he was the anonymous source. Nevertheless, some are still inconvinced. In this paper, we introduce a new notion of identity-committable signatures (ICS) to ensure the anonymity of “Deep Throat” inside a group. A member of an organization can sign a message on behalf of himself (regular signature) or the organization (identitycommitted signature). In the latter case, the signer’s identity is hidden from anyone, and can be opened by himself only. We describe the requirements of ICS and give the formal definition of it. Then we extend the notion of ICS to group-oriented ring signatures (GRS) which further allow the signer to hide his identity behind multiple groups. Since the signer can include the whole members of a group at a time, our GRS scheme is more efficient and practical than general ring signature schemes. Finally, we provide concrete constructions of ICS and GRS with information-theoretic anonymity, that is, the identity of the signer is fully-protected.