Provably secure certificateless proxy signature scheme in the standard model

Certificateless public key cryptography was introduced to solve the key escrow problem in identity-based cryptography and eliminate the use of certificates. As an extension of proxy signature in the certificateless setting, certificateless proxy signature has attracted much attention and many schemes have been proposed recently. So far, only one certificateless proxy signature scheme without using the random oracles was found in the literature. Unfortunately, cryptanalysis shows that it suffers from some security drawbacks and fails in achieving the existential unforgeability. To overcome the security weaknesses in this scheme, we newly propose a certificateless proxy signature scheme without random oracles. In the standard model, we strictly prove it to be existentially unforgeable against chosen message attacks. Compared with previous certificateless proxy signature scheme without random oracles, the new scheme offers stronger security while enjoying better performance.