Cryptanalysis of a discrete chaotic cryptosystem using external key

In recent years, a growing number of cryptosystems based on chaos have been proposed, many of them fundamentally flawed by a lack of robustness and security. In this Letter, we explain how to break a very recent block cipher algorithm based on the logistic map. This cryptosystem uses a 128-bit external key to derive the initial condition and number of iterations, but in a weak way allowing for attack. As a consequence, the complete 128-bit external key can be obtained in a few steps. Using some weaknesses in the system parameter generation another attack can be used to recover the complete key. (C) 2003 Elsevier B.V. All rights reserved.