Provided are a block chain transaction privacy protection method and system. The method comprises: establishing a transaction group between nodes of a block chain system, a user creating an account on a node, and the node generating public and private key information of the account and then joining the group; a transaction request node using a broadcast encryption algorithm to encrypt transaction information, signing the encrypted transaction information using a group signature algorithm, and then broadcasting the transaction information that has been subjected to encryption and the group signature; and a common non-accounting node verifying and broadcasting the transaction information, an accounting node decrypting the transaction information and executing a smart contract to carry out accounting processing, and carrying out broadcasting encryption on the transaction information and then recording same in a public ledger, wherein saved data may only be opened by the accounting node, the transaction request node and an administration node. The present invention uses a broadcasting encryption algorithm and a group signature technology method, so as to solve the problem of privacy protection in a block chain system and ensure the traceability of a transaction at the same time.
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