Accountable Tracing Signatures from Lattices.

Group signatures allow users of a group to sign messages anonymously in the name of the group, while incorporating a tracing mechanism to revoke anonymity and identify the signer of any message. Since its introduction by Chaum and van Heyst (EUROCRYPT 1991), numerous proposals have been put forward, yielding various improvements on security, efficiency and functionality. However, a drawback of traditional group signatures is that the opening authority is given too much power, i.e., he can indiscriminately revoke anonymity and there is no mechanism to keep him accountable. To overcome this problem, Kohlweiss and Miers (PoPET 2015) introduced the notion of accountable tracing signatures ((mathsf {ATS})) - an enhanced group signature variant in which the opening authority is kept accountable for his actions. Kohlweiss and Miers demonstrated a generic construction of (mathsf {ATS}) and put forward a concrete instantiation based on number-theoretic assumptions. To the best of our knowledge, no other (mathsf {ATS}) scheme has been known, and the problem of instantiating (mathsf {ATS}) under post-quantum assumptions, e.g., lattices, remains open to date.