Privacy-preserving database system

A database system includes a server, index server and client. In one embodiment the server randomly permutes the order of database records. The server provides to the index server an array of encryption keys by generating a random encryption key corresponding to each permuted database record. The server encrypts each permuted database record with its corresponding encryption key. The index server computes and encrypts a sum of each encryption key and a corresponding random mask and sends a permuted array of masked keys to the server. The index server provides to the client an encrypted database record, and the mask and key corresponding to the encrypted record. The client sends the encrypted sum of the mask and key to the server. The server decrypts the masked key with a public key and sends the decrypted key to the client. The client then recovers the record key and decrypts the record.