Paper 2016/662

Practical Round-Optimal Blind Signatures in the Standard Model from Weaker Assumptions

Georg Fuchsbauer, Christian Hanser, Chethan Kamath, and Daniel Slamanig

Abstract

At Crypto'15 Fuchsbauer, Hanser and Slamanig (FHS) presented the first standard-model construction of efficient round-optimal blind signatures that does not require complexity leveraging. It is conceptually simple and builds on the primitive of structure-preserving signatures on equivalence classes (SPS-EQ). FHS prove the unforgeability of their scheme assuming EUF-CMA security of the SPS-EQ scheme and hardness of a version of the DH inversion problem. Blindness under adversarially chosen keys is proven under an interactive variant of the DDH assumption. We propose a variant of their scheme whose blindness can be proven under a non-interactive assumption, namely a variant of the bilinear DDH assumption. We moreover prove its unforgeability assuming only unforgeability of the underlying SPS-EQ but no additional assumptions as needed for the FHS scheme.