Policy-based chameleon hash functions have been widely proposed for its use in blockchain rewriting systems. They allow anyone
to create a mutable transaction associated with an access policy, while an authorized user who possesses sufficient rewriting
privileges from a trusted authority satisfying the access policy can rewrite the mutable transaction. However, existing chameleon
hash functions lack certain fundamental security guarantees, including forward security and backward security. In this paper, we
introduce a new primitive called forward/backward-secure policy-based chameleon hash (FB-PCH for short). We present a practical
instantiation. We prove that the proposed scheme achieves forward/backward-secure collision-resistance, and show its practicality
through implementation and evaluation analysis.
