Abstract: Efficient multi-keyword ciphertext search and problems of data security protection were researched. Based on Paillier homomorphic encryption and private set intersection(PSI)technique， a multi-keyword searchable encryption scheme was provided， which can search over encrypted files efficiently and protect the search pattern. First， through random number padding and Paillier homomorphic encryption the index privacy and the trapdoor privacy were protected， and the search pattern was further protected. Then， the scheme supports conjunctive multi-keyword search by using PSI. Because only multiplications and exponentiations were used in searching， the proposed scheme is more efficient than others. Security and performance analysis showed that the scheme has the semantic security of searchable encryption and can perform multi-keyword search efficiently with a good computational cost.

Key words: searchable encryption, multi-keyword, cloud storage, Pailler homomorphic encryption, private set intersection