Abstract: A new method for public key cryptosystem and digital signature scheme is suggested. The system employs computations in zn. Where n is an integer number of a composite modulus. There are similarity with the most widely used digital signatures and public cryptosystem such as RSA and ElGamal schemes, regarding the mathematical background. Concerning calculation needs the new approach is unchangeable and, it is more efficient compare with the best known schemes, when measured with both public and private calculations.