A generic construction for universally-convertible undeniable signatures
Undeniable signatures are classic digital signatures which are not universally verifiable and can only be verified with the help of the signer. Its extended version, convertible undeniable signatures, equips the signer with the additional ability to make his undeniable signatures universally verifiable whenever required. A selectively-convertible undeniable signature scheme allows the signer to convert a single signature into a universally verifiable signature by releasing a selective proof in a later time, while “universally-convertible” refers to the case where the signer has the additional ability to generate a universal proof which can finally convert all his undeniable signatures into universally verifiable signatures. In this paper, we propose a generic construction for universally-convertible undeniable signatures. Our construction is based on three building blocks: a strongly unforgeable classic signature scheme, a selectively-convertible undeniable signature scheme and a collision-resistant hash function. Formal proofs guarantee that our construction has a tight security reduction to the underlying security assumptions. As one of the applications of our generic construction, one can obtain the first provable secure universally-convertible undeniable signature scheme in the standard model.