Abstract
Chameleon Hash Function (CH) is a hash function with a public and secret key pair. CH is collision-resistant for users without a secret key, while users with a secret key can find collisions in hash values. Chameleon Hash has been used in various cryptographic schemes, including online/offline signatures by Shamir et al. and blockchain modification by Ateniese et al. However, once the secret key is exposed in CH, its collision resistance is lost, and the security of all existing CH-based methods cannot be guaranteed. In this paper, we propose a generic Forward-Secure CH scheme, capable of converting any given CH into a Forward-Secure CH (FSCH) through the implementation of forward-secure encryption techniques. The security of the proposed protocol is reduced to Forward-Secure collision resistance, meaning that even if the current secret key is compromised, it ensures that collisions involving past hash values cannot be exploited or detected.