A Secure Chameleon Hash Function without Key Exposure from Pairings

Chameleon signatures are based on well established hash-and-sign paradigm, where a chameleon hash function is used to compute the cryptographic message digest, and becomes an important building block. The chameleon hash function is a trapdoor one-way hash function with some special properties, and plays an important role in constructing chameleon signature. In the paper, we propose a new chameleon hash scheme which enjoys some advantages of the previous schemes: collision-resistant, semantic security, and key-exposure freeness. At the same time, we show that the recipient’s trapdoor information will never be compromised under the assumption of q-SDH+CDH problem which is a new security assumption