Fast Harn Cryptosystem Using N-adic Expansion

An improved Harn cryptosystem that has the same security as the original one is proposed using n-adic expansion.The proposed cryptosystem only needs one time encryption and decryption as well as solving a system of linear equations modulo n when a large message with t blocks is encrypted,while the originalcryptosystem needs t times RSA and ElGamal encryption and decryption repeatedly,so the proposed cryptosystem has more efficiency when the number of message blocks t is large.