Certificateless threshold cryptosystem secure against chosen-ciphertext attack

This paper proposes the first certificateless threshold decryption scheme which avoids both the single point of failure in the distributed networks and the inherent key escrow problem in identity-based cryptosystem. The scheme is secure against threshold chosen-ciphertext attack. It tolerates the Type I adversary that can replace public key and the Type II adversary that has access to the system’s master key. The formal proof of security is presented in the random oracle model, assuming some underlying problems closely related to the Bilinear Diffie-Hellman Problem are computationally hard.