Hard invalidation of electronic signatures

Abstract

We present a new concept for invalidating electronic signatures which, in many situations, seem to be better suited for real business and society applications. We do not rely on an administrative invalidation process executed separately for each single signing key and based on certificate revocation lists. Instead, all signatures created with a certain group are invalidated by a certain event. We propose a hard invalidation via releasing of the inherent cryptographic proof value–instead of soft invalidation via revoking certificates which leaves intact the cryptographic strength of signatures (even if legal validity is partially lost). We present concrete efficient realizations of our ideas based on verifiable encryption, trapdoor discrete logarithm groups and ring signatures.