Group Signature Library (GSSLib) is a Java library (GSS library) and part of the PRISMACLOUD FLEXAUTH cryptographic tool that supports group signature schemes, a variant of signature schemes which help to enhance the privacy of the signers. In particular in group signatures a group manager can set up a group so that every member of this group can anonymously generate a signature on behalf of the group. In addition there is an opening authority which can revoke the anonymity of the users in case of misbehaviour.