Decentralized Attribute-Based Credentials with Short Attribute Proofs from DualRing

An attribute-based credential (ABC) system, which is an extension from anonymous credential (AC) system, allows a user to anonymously prove selected attributes in a credential which is issued from an issuer. A decentralized ABC system was proposed, where a public ledger such as blockchain certifies user’s attributes in the form of a commitment, instead of a trusted issuer. In the previously proposed decentralized ABC system, the attribute proof is inefficient, since the verification of an RSA-based accumulator is proved by an inefficient proof of knowledge on double discrete logs. Furthermore, the RSA-based accumulator needs a trusted setup for public parameters. On the other hand, an efficient (blacklistable) ring signature scheme without using trusted setup was proposed. In the scheme, an efficient ring signature scheme called DualRing is used, where the signature size is O(log N) and the signing/verification costs are O(N), for the number N of public keys used for anonymization. The (blacklistable) ring signature scheme can be applied to (blacklistable) AC system, but it is not an ABC system. In this paper, we propose a decentralized ABC system from DualRing, where the proof data size is O(log N) for the number N of commitments used for anonymization, and the proof generation and verification costs are O(N), without using trusted setup.