Abstract: The account book of blockchain is open and transparent to realize the traceability and verifiability of transactions. However, this makes the privacy of blockchain users be an urgent problem. In order to solve the problem of transaction amount and identity exposure of both parties in alliance chain transaction, a privacy protection method of alliance chain based on group signature and homomorphic encryption is proposed. This method can protect the identity of the payee and the privacy of the transaction amount on the premise of meeting the traceability and verifiability of the transaction. In this scheme, the concept of group in group signature is combined with the alliance chain properly and we propose the concept of partial identity anonymity to make the user identity anonymous to other secondary nodes but verifiable to the primary nodes. Then the additive homomorphism property of Paillier homomorphism encryption is used to verify the legitimacy of the transaction and protect the privacy of the transaction amount. A four-step verification method for the main nodes is proposed, and through verifying the group signature, account ownership and the validity of the transaction amount, it realizes the supervision of the main nodes on the legality of the transaction. Through analysis, the scheme can resist tamper attacks and public key replacement attacks, and the transaction legitimacy is verified to be reasonable. Finally, by comparing with other schemes, the calculation cost of this scheme is reasonable.

Key words: alliance blockchain, identity privacy, transaction amount privacy, group signature, Paillier homomorphism encryption