Paper 2019/1269 Original: eprint.iacr.org/2019/1269 ↗

Repudiable Ring Signature: Stronger Security and Logarithmic-Size

Abstract

Ring signatures allow a person to generate a signature on behalf of an ad hoc group, and can hide the true identity of the signer among the group. Repudiable ring signatures are the more strongly defined ring signatures, which can allow every non-signer to prove to others that the signature was not generated by himself. This paper has two main areas of focus. First, we propose a new requirement for repudiable ring signatures, which is that no one can forge a valid repudiation for others. Second, as a breakthrough, we present the first logarithmic-size repudiable ring signatures which do not rely on a trusted setup or the random oracle model. Specifically, our scheme can be instantiated from standard assumptions and the size of signatures and repudiations only grows logarithmically in the number of ring members. Besides, our scheme also provides a new construction of logarithmic-size standard ring signatures.