Efficient Cca-Secure Cdh Based Kem Balanced Between Ciphertext And Key

In this paper we construct an efficient CCA-secure key encapsulation scheme in the standard model. The new scheme is based on the computational Diffie-Hellman assumption and the twinning technique; which has been widely discussed in recent years. Compared with previous schemes of the same kind, the new scheme is more generic, and offers a simple approach for reconciling ciphertext length and key size by altering a parameter. Choosing a reasonable value for the parameter, a balance between the ciphertext length and key size could be achieved.