Analysis and Improvement of Certificateless signature and Proxy re-signature schemes

Certificateless cryptography avoids the key escrow problem in identity-based crytosystems and certificate management in traditional public-key crytosystems, it has been researched by many scholars and many certificateless signature schemes have been proposed. However, most of them exist some security drawbacks and are insecure for some kinds of attacks. In this paper, we analyze two certificateless signature schemes and one proxy re-signature scheme proposed by some scholars recently. And we show that these schemes are insecure and also present the detailed attack steps. In order to overcome this problem, we also address some improved schemes which have the same or better performance than the original schemes.