Discrete logarithm based chameleon hashing and signatures without key exposure

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 key exposure problem of chameleon hashing. This creates a strong disincentive for the recipient to compute hash collisions, partially undermining the concept of non-transferability. Recently, some constructions of discrete logarithm based chameleon hashing and signatures without key exposure are presented, while in the setting of gap Diffie–Hellman groups with pairings.In this paper, we propose the first key-exposure free chameleon hash and signature scheme based on discrete logarithm systems, without using the gap Diffie–Hellman groups. This provides more flexible constructions of efficient key-exposure free chameleon hash and signature schemes. Moreover, one distinguishing advantage of the resulting chameleon signature scheme is that the property of “message hiding” or “message recovery” can be achieved freely by the signer, i.e., the signer can efficiently prove which message was the original one if he desires.