A Bilinear Spontaneous Anonymous Threshold Signature for Ad Hoc Groups

We present an adaptive chosen-plaintext cryptanalysis of Boneh, et al.\u27s bilinear spontaneous anonymous ad hoc group signature. Then we present a patch, and an extension to a threshold version complete with a security proof in the random oracle model (ROM)

Democratic Group Signatures with Threshold Traceability

Recently, democratic group signatures(DGSs) particularly catch our attention due to their great flexibilities, \emph{i.e}., \emph{no group manager}, \emph{anonymity}, and \emph{individual traceability}. In existing DGS schemes, individual traceability says that any member in the group can reveal the actual signer\u27s 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 $(t, n)$-\emph{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