Insecurity of A Key-Policy Attribute Based Encryption Scheme With Equality Test

Attribute-based encryption is a popular cryptographic technology to protect the privacy of clients' data in cloud computing. In order to make the scheme have the functionality of comparing ciphertext, Zhu et al. combined concepts of key-policy attributed-based encryption with public key encryption with equality test and proposed key-policy attributed-based encryption with equality test. They defined its security model and put forward a scheme from bilinear pairing. In this paper, we first use two methods to show that their scheme is not secure for one-way under chosen ciphertext attack. Next, we show that the scheme is not secure for a test under chosen ciphertext attack defined in their paper yet. Finally, we point out the definition of a test under chosen ciphertext attack is very strong, which causes no scheme to satisfy the model.