Identity-Based Chameleon Hash Scheme Without Key Exposure

The notion of chameleon hash function without key exposure plays an important role in designing chameleon signatures. However, all of the existing key-exposure free chameleon hash schemes are presented in the setting of certificate-based systems. In 2004, Ateniese and de Medeiros questioned whether there is an efficient construction for identity-based chameleon hashing without key exposure. In this paper, the authors propose the foist identity-based chameleon hash scheme without key exposure based on the three-trapdoor mechanism, which provides an affirmative answer to the open problem.