Round Optimal Blind Signatures

Sanjam Garg (1), Vanishree Rao (1), Amit Sahai (1), Dominique Schröder (2) and Dominique Unruh (3)
(1) University of California, Los Angeles USA; (2) University of Maryland, USA; and (3) University of Tartu, Estonia

Abstract. Constructing round-optimal blind signatures in the standard model has been a long standing open problem. In particular, Fischlin and Schröder recently ruled out a large class of three-move blind signatures in the standard model (Eurocrypt’10). In particular, their result shows that finding security proofs for the well-known blind signature schemes by Chaum, and by Pointcheval and Stern in the standard model via black-box reductions is hard. In this work we propose the first round-optimal, i.e., two-move, blind signature scheme in the standard model (i.e., without assuming random oracles or the existence of a common reference string). Our scheme relies on the Decisional Diffie Hellman assumption and the existence of sub-exponentially hard 1-to-1 one way functions. This scheme is also secure in the concurrent setting.