Concrete Chosen-Ciphertext Secure Encryption from Subgroup Membership Problems

Using three previously studied subgroup membership problems, we obtain new concrete encryption schemes secure against adaptive chosen-ciphertext attack in the standard model, from the Cramer-Shoup and Kurosawa-Desmedt constructions. The schemes obtained are quite efficient. In fact, the Cramer-Shoup derived schemes are more efficient than the previous schemes from this construction, including the Cramer-Shoup cryptosystem, when long messages are considered. The hybrid variants are even more efficient, with a smaller number of exponentiations and a shorter ciphertext than the Kurosawa-Desmedt Decisional Diffie-Hellman based scheme.