PROBLEM TO BE SOLVED: To provide a digital signature technique safety using a standard model and reducing the length of signature, in a group signature. SOLUTION: A content provision service system (group signature system) 2 for members includes: a group index management device 40 for executing a group member index generation step (S1); a group management device 10 for executing a set-up step (S3) and a joining step (S4); a group member device (signature generating device) 20 for executing a signature generation step (S5); and a signature verification device 30 for executing a signature verification step (S7), and the group index management device 40 executes an open step (S10). COPYRIGHT: (C)2010,JPO&INPIT