Forward-Secure Blind Signature Scheme Based on the Strong RSA Assumption

Key exposure problem turns out to be very serious in security services. For example, in electronic cash, the problem is very severe since money is directly involved. In other applications of cryptography, it is also a devastating attack. Forward security is the first security notion addressing the this issue. Roughly speaking, forward secrecy is aimed to protect validity of the all usage before key exposure. In this paper, we investigate the key exposure problem in blind signature (with application to electronic cash in mind). We then propose a blind signature scheme which guarantees forward security. Our scheme is constructed from the provably secure Okamoto-Guillou-Quisquater (OGQ for short) blind signature scheme. Using forking lemma proposed by Pointcheval and Stern [4], we can show the equivalence between existence of a forger with feasibility of solving the strong RSA problem. In addition, our scheme introduces no significant communication overhead comparing with OGQ