Abstract: Encrypted database scheme about outsourced data confidentiality and user privacy was researched， and a scheme of multi-layer nested database encryption for multiple users was proposed. A data encryption scheme was also proposed based on onion model to perform nested encryption on outsourced data by applying multi-layer theory with a variety of data encryption algorithms to guarantee data confidentiality and to work with SQL queries in different types. Meanwhile， user privacy protection scheme was proposed based on single server private information retrieval(PIR)to enable users to send SQL queries with sensitive data and protect the privacy of users when accessing the database， realizing user anonymous query. The security analysis results show that the scheme protects data confidentiality and user privacy. An evaluation result tested with a benchmark tool Sysbench demonstrates its well query processing efficiency， throughput and robustness.

Key words: outsourced data, onion encryption model, database encryption, private information retrieval(PIR), privacy protection