Efficient Chosen Ciphertext Secure Public Key Cryptosystem from the ID-Based Encryption of Waters

In Eurocrypt 2004, Canetti, Halevi and Katz proposed a method for constructing Chosen Ciphertext secure ( ie., CCA secure) public key encryption from any Selective-ID secure ID-Based Encryption (IBE). However, this method needs one time signature and thus adds noticeable overhead to the underling scheme. In this paper, a new CCA secure public key cryptosystem is constructed from the Adaptive-ID secure IBE scheme proposed by Waters. Here, the identity is the hash of the first two parts of the ciphertext, and the bilinear map is used to test the ciphertext validity. The proposal is much more efficient than those obtained from the general CHK method. The security of the new scheme is proved under the standard Decisional Bilinear Diffie-Hellman (DBDH) assumption.