Unlike masked with analog chaotic sequence, digital information is masked with binary chaotic sequence with a method proposed by U. Parlitz and S. Ergezinger (Phys. Lett. 198A (1994) 146). It is demonstrated by numerical simulations that both security and robustness of this communication method are improved. When considered as digital communication, the method is very robust to transmission errors. PACS numbers: 05.45.+b, 43.72.+q Key words: communication, binary (analog) chaotic sequence, robust, security Vol. 29P e is estimated with respect to p for p = 0 ~ 0.4, again with a random message sequence of K = 3 x 10 5 bits. It is found that no error of message is detected when p < 0.32. The result for p > 0.32 is plotted in Fig. 3, which shows that P e follows a power law P e -