Public key cryptosystem based on two cryptographic assumptions

A new fast public key cryptosystem is proposed, which is based on two dissimilar number-theoretic hard problems, namely the simultaneous Diophantine approximation problem and integer factorisation problem. The adversary has to solve the two hard problems simultaneously to recover the plaintext according to their knowledge about the public keys and the cipher-text. Therefore, the scheme is expected to gain a high level of security. The newly-designed public key cryptosystem is efficient with respect to encryption and decryption. The encryption of this system is about three times faster than that of RSA, and the decryption is six times faster than that of RSA. The cipher-text expansion of the system is about 8:3.