Democratic Group Signatures with Threshold Traceability

Recently, democratic group signatures(DGSs) particularly catch our attention due to their great flexibilities, i.e., no group manager, anonymity, and individual traceability. In existing DGS schemes, individual traceability says that any member in the group can reveal the actual signer’s identity from a given signature. In this paper, we formally describe the definition of DGS, revisit its security notions by strengthening the requirement for the property of traceability, and present a concrete DGS construction with (t, n)-threshold traceability which combines the concepts of group signatures and of threshold cryptography. The idea behind the (t, n)-threshold traceability is to distribute between n group members the capability of tracing the actual signer such that any subset of not less than t members can jointly reconstruct a secret and reveal the identity of the signer while preserving security even in the presence of an active adversary which can corrupt up to t− 1 group members.