In this paper, the international data encryption algorithm is applied to design the symmetric cryptosystem based on chaotic signals. Ciphertext are masked by means of the tent map. Plaintext could be recovered to the original signals through chaos synchronization. Since the H/sub /spl infin// controller is robust, it can restrain effects of different initial values and variant system parameters between the transmitter and the receiver. To synchronize the tent map between the transmitter and the receiver, the controller is designed using H/sub /spl infin// methodology. At last, the tent map cryptosystem are structured by combining the international data encryption algorithm and chaos synchronization and applied to the encryption of voice and picture. Computer simulations demonstrate that the cryptosystem based on cryptography and chaotic masking could promote the performance of information security.