How to Win the Clonewars: Efficient Periodic n-Times Anonymous Authentication

Jan Camensich, Susan Hohenberger, Markulf Kohlweiss, Anna Lysyanskaya, Mira Belenkiy

ACM CCS |

Published by Association for Computing Machinery, Inc.

We create a credential system that lets a user anonymously authenticate at most n times in a single time period. A user withdraws a dispenser of n e-tokens. She shows an e-token to a verifier to authenticate herself; each e-token can be used only once, however, the dispenser automatically refreshes every time period. The only prior solution to this problem, due to Damgård et al. [29], uses protocols that are a factor of k slower for the user and verifier, where k is the security parameter. Damgård et al. also only support one authentication per time period, while we support n. Because our construction is based on e-cash, we can use existing techniques to identify a cheating user, trace all of her e-tokens, and revoke her dispensers. We also offer a new anonymity service: glitch protection for basically honest users who (occasionally) reuse e-tokens. The verifier can always recognize a reused e-token; however, we preserve the anonymity of users who do not reuse e-tokens too often.