  This paper studies the security of a chaotic cryptosystem based on the Chua
circuit and implemented with State Controlled Cellular Neural Networks. It is
shown that the plaintext can be retrieved by ciphertext band-pass filtering
after an imperfect decoding with wrong receiver parameters. It is also shown
that the key space of the system can be notably reduced easing a brute force
attack. The system parameters were determined with high precision through the
analysis of the decoding error produced by the mismatch between receiver and
transmitter parameters.
