An Accumulator-Based Revocation in Delegatable Anonymous Credentials

For privacy-enhancing user authentication, anonymous credential system was proposed. In the system, a user is issued a credential on attributes from an issuer, and the user can anonymously prove the ownership of the credential. As the extension, a delegatable anonymous credential (DAC) system was proposed. In the DAC system, the owner of a credential can hierarchically delegate it to another entity, who can also issue a credential to lower entities. Since intermediate issuers in the chaining credentials can be hidden, the DAC system is considered to be applied to a permissioned blockchain. Furthermore, to enable the revocation of credentials, a revocable DAC system was proposed. However, in the previously proposed revocable DAC system, an issuer, who manages the user group, has to issue the non-revocation credentials to all non-revoked users at every epoch, and thus the issuer can be in a bottleneck and the communication cost is high. In this paper, we propose a revocable DAC system using an accumulator. In the proposed system, only a single accumulator and the credential on the accumulator are published at every epoch. Thus there is no bottleneck of the issuer and the communication cost is very low.