Unique group signatures

We initiate the study of unique group signature such that signatures of the same message by the same user will always have a large common component (i.e., unique identifier). It enables an efficient detection algorithm, revealing the identities of illegal users, which is fundamentally different from previous primitives. We present a number of unique group signature schemes (without random oracles) under a variety of security models that extend the standard security models of ordinary group signatures. Our work is a beneficial step towards mitigating the well-known group signature paradox, and it also has many other interesting applications and efficiency implications.