Resource-efficient anonymous group identification

We present a system, named Homage, for verifying that a person is a member of some group without anyone, not even the issuing body, being able to determine their identity. Homage provides a strong disincentive to people against their passing on their membership-proving information to others. The computation and data transfer required axe unaffected by the number of members, and are low enough to be appropriate for smart card implementations. The anonymity of Homage is based on the assumption that the Diffie-Hellman decision problem is hard. This paper does not prove that forgery is impossible, although it does provide strong evidence that this is the case.