  In 1998, M. S. Baptista proposed a chaotic cryptosystem, which has attracted
much attention from the chaotic cryptography community: some of its
modifications and also attacks have been reported in recent years. In [Phys.
Lett. A 307 (2003) 22], we suggested a method to enhance the security of
Baptista-type cryptosystem, which can successfully resist all proposed attacks.
However, the enhanced Baptista-type cryptosystem has a nontrivial defect, which
produces errors in the decrypted data with a generally small but nonzero
probability, and the consequent error propagation exists. In this Letter, we
analyze this defect and discuss how to rectify it. In addition, we point out
some newly-found problems existing in all Baptista-type cryptosystems and
consequently propose corresponding countermeasures.
