Revocable Policy-Based Chameleon Hash

Policy-based chameleon hash (PCH) is a cryptographic building block which finds increasing practical applications. Given a message and an access policy, for any chameleon hash generated by a PCH scheme, a chameleon trapdoor holder whose rewriting privileges satisfy the access policy can amend the underlying message without affecting the hash value. In practice, it is necessary to revoke the rewriting privileges of a trapdoor holder due to various reasons, such as change of positions, compromise of credentials, or malicious behaviours. In this paper, we introduce the notion of revocable PCH (RPCH) and formally define its security. We instantiate a concrete RPCH construction by putting forward a practical revocable attribute-based encryption (RABE) scheme which is adaptively secure under a standard assumption on prime-order pairing groups. As application examples, we show how to effectively integrate RPCH into mutable blockchain and sanitizable signature for revoking the rewriting privileges of any chameleon trapdoor holders. We implement our RPCH scheme and evaluate its performance to demonstrate its efficiency.