In recent years, blockchain has attracted attention for its use in cryptocurrencies such as Bitcoin.Because of its structure, once a transaction is registered in a blockchain, it is held permanently and cannot be modified again.Policy-based Chameleon Hash (PCH) proposed by Derler et al. enables the modification of transactions in blockchains.It allows the creator of a transaction to set an access policy, i.e., who can modify it.Another user can rewrite the transaction only if he or she has attributes that satisfy the access policy.However, PCH has a feature that a user who loses an access previlege can abuse the key to modify the transaction.In this paper, we propose Revocable Policy-based Chameleon Hash (R-PCH), which provides additional security to existing PCHs by allowing revocation of a user who has lost the
access privilege and preventing key abuse.