Chaotic cryptology has been widely investigated recently. This paper analyzes the security pitfalls existing in digital chaotic stream ciphers, which work on the well characterized one-dimensional(1-D) chaotic systems. As a practical solution to these problems caused by 1-D chaotic systems, a chaotic keystream generator using nonlinear digital filters with
-D uniform distribution is proposed. To improve system security further and overcome the effects of finite wordlength, the coupling method with parameter perturbing is considered. Detailed theoretical analyses show that it has perfect cryptographic properties, and can be used to construct stream ciphers with higher security than other 1-D chaotic ciphers. Finally, some numeric experiments are made and the experimental results coincide well with the theoretical analyses.