EMT: Extended Merkle Tree Structure for Inserted Data Redaction in Permissioned Blockchain

Inserted data redaction is an important and hot security topic for permissioned blockchain. However, existing redactable schemes have two problems: (i) Uncaptured Change: Transaction-level redaction schemes modify both user-inserted data and system-generated transaction data, making it difficult to capture the changes in system-generated transactions data; (ii) Unexpected Spread: When the redaction process deletes harmful data, the consensus process may take a long time, resulting in unexpected spread of harmful data. Instead of eliminating the influence of the harmful data, it promotes its spread. To tackle these problems, we propose an Extended Merkle Tree (EMT) structure for inserted data redaction in permissioned blockchain. EMT separates the system-generated transaction data from user-inserted data, ensuring that only the inserted data can be modified during redaction. Furthermore, we design an EMT-based blockchain ledger and develop a smart contract to implement the inserted data redaction. We prove that our redaction scheme preserves the core security features of blockchain and implements redaction operations in Hyperledger Fabric. The experimental results show that our EMT-based blockchain scheme is capable of redacting the harmful inserted data while incurring less than 5% overhead compared to current permissioned blockchains.