An encryption approach to digital communication by using spatiotemporal chaos synchronization is proposed. Two one-way coupled map lattice (OCOML) systems driven by a chaotic signal are synchronized. The chaotic outputs of the OCOML systems serve as the encryption and decryption keys and the main secret key is a set of coupling parameters of the OCOML. The advantages of the cryptosystem are its high communication efficiency, higher level of security and easy implementation by software. An example of duplex real-time voice communication between two computer users is described.