Efficient blacklistable anonymous credential system with reputation using a pairing‐based accumulator

As privacy‐enhancing authentications without any TTP (Trusted Third Party), blacklistable anonymous credential systems with reputation have been proposed. However, the previous systems have the efficiency problem: The authentication data size is O (L) or O ( K ) , where L is the reputation list, and K is the size of a window indicating the most recent K authentications of the user. Therefore, the previous systems suffer from O (L) or O ( K ) ‐size data in each authentication. In addition, the authentication needs the computation of O (L) or O ( K ) exponentiations. In this paper, an efficient blacklistable anonymous credential system with reputation is proposed. In our system, the data size of the authentication is O ( 1 ) . Furthermore, although the computational costs in the authentication depend on some parameters, the parameter‐related costs are only multiplications instead of exponentiations. Compared to the previously proposed blacklistable system FARB with the constant computational and communication costs, our system has the advantage that the clear/redeem protocol only has to be executed every interval instead of every session. For constructing our system, we newly introduce the concept of an accumulator for reputation, and propose an efficient construction.