摘要：Chameleon signatures are based on the well established hash-and-sign paradigm, where a chameleon hash function is used to compute the cryptographic message digest. Chameleon signatures simultaneously provide the properties of non-repudiation and non-transferability for the signed message. However, the initial constructions of chameleon signatures suffer from the problem of key exposure of chameleon hashing. Recently, some specific constructions of key-exposure free chameleon hashing are presented in the setting of certificate-based systems, but few works are done in identity-based systems. In this paper, we first analyse the hierarchical identity-based chameleon hash (HIBCH) and key-exposure free identity-based chameleon hash schemes (IBCH) proposed by Bao et al. in 2011 and then propose two improved schemes from bilinear pairings, with the idea of hierarchical key distribution. Moreover, we analyse the security and efficiency of our proposed schemes.
关键词：Chameleon hash;Key exposure;Identity based system
