Cryptanalyses and improvement of identity-based strong designatured verifier signature schemes

Compared with ordinary digital signature, the strong designated verifier signature (SDVS) scheme makes it possible for a signer to convince a designated verifier that he or she has signed a message in such a way that the designated verifier cannot transfer the signature to a third party. Recently, Bao et al. proposed two ID-based SDVS schemes by use of bilinear pairing. In this paper, we show both of these schemes are insecure against active attack, that is the attacker can forge signature without signer´s private key. Combining with the Schnorr signature scheme, we also provide a new efficient ID-based designated verifier signature scheme.