Date Added: Oct 2012
Concurrent signatures provide a way to exchange digital signature among parties in an efficient and fair manner. To the best of the authors' knowledge, all the existing solutions can only be proven secure in the random oracle model. How to build an efficient concurrent signature scheme in the standard model has remained as an open problem since its introduction in 2004. In this paper, they answer the problem affirmatively. Base on a novel idea, they propose a new concurrent signature construction, the security of which does not rely on the random oracle assumption. Their idea stems from an attempt of achieving a strong ambiguity feature that anyone should be able to produce indistinguishable ambiguous signatures by just using public information available in the system.