Efficient attributes for anonymous credentials

Abstract

We extend the Camenisch-Lysyanskaya anonymous credential system such that selective disclosure of attributes becomes highly efficient. The resulting system significantly improves upon existing approaches, which suffer from a linear complexity in the total number of attributes. This limitation makes them unfit for many practical applications, such as electronic identity cards. Our system can incorporate an arbitrary number of binary and finite-set attributes without significant performance impact. Our approach folds all such attributes in a single attribute base and, thus, boosts the efficiency of all proofs of possession. The core idea is to encode discrete binary and finite-set attribute values as prime numbers. We use the divisibility property for efficient proofs of their presence or absence. We additionally contribute efficient methods for conjunctions and disjunctions. The system builds on the Strong-RSA assumption alone. We demonstrate the applicability and performance improvements of our method in realistic application scenarios, such as, electronic identity cards and complex/structured credentials. Our method has crucial advantages in devices with restricted computational capabilities, such as smartcards and cell phones.