  In recent years many chaotic cryptosystems based on Baptista's seminal work
have been proposed. We analyze the security of two of the newest and most
interesting ones, which use a dynamically updated look-up table and also work
as stream ciphers. We provide different attack techniques to recover the
keystream used by the algorithms. The knowledge of this keystream provides the
attacker with the same information as the key and thus the security is broken.
We also show that the dependence on the plaintext, and not on the key, of the
look-up table updating mechanism facilitates cryptanalysis.
