A digital communication system based on the use of chaotic carriers is disclosed. For each symbol to be sent, the transmitter sends a reference chaotic signal followed by a transformed version of the reference chaotic signal. For different symbols, different transformations are performed. Also, the transformations are designed such that the transformed versions of the reference chaotic signal do not resemble the original reference chaotic signal. As a consequence, little information can be deduced by inspecting the frequency spectrum of the transmitted signal. Moreover, even if the communication could be detected, it is difficult to decode the messages because there are numerous transformations possible.