An Efficient CPA-Secure Encryption Scheme with Equality Test

In this paper, we propose a CPA-Secure encryption scheme with equality test. Unlike other public key solutions, in our scheme, only the data owner can encrypt the message and get the comparable ciphertext, and only the tester with token who can perform the equality test. Our encryption scheme is based on multiplicative homomorphism of ElGamal Encryption and Non Interactive Zero Knowledge proof of Discrete Log. We proof that the proposed scheme is OW-CPA security under the attack of the adversary who has equality test token, and IND-CPA security under the attack of adversary who can not test the equality. The proposed scheme only suppose to compare two ciphertexts encrypted by same user, though it is less of flexibility, it is efficient and more suitable for data outsourcing scenario.