| As a distributed database,the blockchain has the characteristics of decentralization and non-tampering.The blockchain is supported by cryptography technology,which can store data securely and effectively reduce the cost of trust.However,the existing blockchain system has weak performance in data management,and only supports related queries with transaction hash as a key.The query method is single and inefficient,and cannot meet the query needs of users.In addition,the blockchain data is public and fully visible to users in the system,and the user’s privacy cannot be guaranteed.For some industries with high privacy protection requirements,the secure storage of data cannot be satisfied,which limits the application expansion of the blockchain.Although traditional encryption technology can ensure the confidentiality of data,it cannot meet the diversified needs of data.Encrypting the data will make the features that support plaintext retrieval disappear,and it is more difficult to perform effective retrieval in the ciphertext state.The searchable encryption technology supports retrieval in the ciphertext state,which can effectively solve the problems of blockchain data retrieval and privacy protection.However,due to the low retrieval efficiency of the blockchain system itself,encrypting the data will further reduce the retrieval efficiency of the data on the blockchain.Our research mainly focuses on the insufficiency of blockchain data query efficiency and privacy protection.The specific work is as follows:(1)Aiming at the problems of single and low efficiency of blockchain data search,we propose an index structure of account transaction chain based on sub-chain query.In the blockchain system,the transaction chain of the active account is long,and it is still difficult to retrieve the target transaction in a large number of account transactions.For this,we divide the transaction chain into sub-chains,and convert the query of the transaction chain into sub-chain query.When querying the early history records of an account,it has high retrieval efficiency.(2)In view of the openness and transparency of blockchain data and the inability to guarantee user privacy,we designed a blockchain data search scheme based on public key searchable encryption.The data is encrypted with searchable encryption technology to ensure user privacy and the ciphertext on the chain can be retrieved.In order to defend against keyword guessing attack(KGA)and chosen plaintext attack(CPA)by external adversaries,we design a secure retrieval scheme with encrypted trapdoor and obfuscated output.Aiming at the low efficiency of ciphertext retrieval on the chain,the Kw-chain index is constructed by using keyword ciphertext,which improves the ciphertext retrieval efficiency.(3)In view of the difficulties of data security and sharing brought about by traditional medical data management methods,we combined blockchain technology to design a blockchain-based electronic medical record storage and sharing model.In order to improve the retrieval efficiency of EMR,an EMR-chain index structure was designed using patient ID. |
