QHSE: An efficient privacy-preserving scheme for blockchain-based transactions

摘要

As bitcoin has drawn a lot of attention, people have developed various cryptocurrencies based on blockchain framework. The decentralization feature of blockchain makes the transaction information public in the cryptocurrency. It is possible to expose the user's privacy. Therefore, it is necessary to design an efficient and secure scheme to hide transaction information and guarantee that the transaction is carried out normally. In this paper, we propose a quasi-homomorphic symmetric encryption (QHSE) scheme to conceal the transaction amounts in cryptocurrency based on blockchain. For each transaction, transaction participants employ Diffie-Hellman key exchange protocol to generate the specific transaction key as the symmetric key of QHSE. That is, each transaction has a distinct transaction key. Even if the transaction key of one transaction is leaked, other transactions will not reveal any private information, which guarantees the atomicity and stability of the transactions. To achieve the interoperability of different symmetric key, we design a KeyUp algorithm which enables the calculations between different ciphertexts. Combined with KeyUp, we also construct several operation algorithms (Multiplication, Addition, Comparison), so that transactions can be performed and verified normally in the ciphertext state. We prove that the proposed QHSE will not leak any private information to unauthorized parties, and demonstrate the utility and efficiency of QHSE from theoretical and experimental aspects.