Copyright © 2010 Jun He et al. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Wang and Yu proposed a block cipher scheme based on dynamic sequences generated
by multiple chaotic systems, which overcomes the problem of periodical degradation on
random sequences due to computational precision. Their scheme has a feature that a
plaintext is encrypted by a keystream created from several one-dimensional chaotic maps.
However, this feature results in some weaknesses of the encryption algorithm. We show
three kinds of attacks in this paper, through which one can recover the plaintext from
a given ciphertext without the secret key. We also present an improvement on their
scheme, which prevents the three attacks mentioned above. Security of the enhanced
cipher is presented and analyzed, which shows that our improved scheme is secure under
the current attacks.