Cryptanalysis of a Certificate-Based on Signature Scheme

Certificate-based cryptosystem combines the advantage of both traditional public key cryptosystem and identity based cryptosystem as it avoids the usage of certificates and resolves the key escrow problem. Recently, Liu et al. proposed a short and efficient certificate-based signature scheme and showed that the scheme was secure in the random oracles. In this paper, we show that Liu et al.'s certificate-based signature scheme is universally forgeable by a Type I adversary who models an uncertified entity and can replace the public keys of entities at will, but is not allowed to obtain the target user's certificate. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Harbin University of Science and Technology.