E. Alvarez et al. presented a new chaotic encryption approach recently. But
soon G. Alvarez et al. broke it with four cryptanalytic methods and found
some other weaknesses. In this Letter we point out why the original scheme
is so vulnerable to the proposed four attacks. The chief reasons are two es
sential defects existing in the original scheme. Based on such a fact, we p
resent an improved encryption scheme to obtain higher security. The cryptog
raphic properties of the improved scheme are studied theoretically and expe
rimentally in detail. (C) 2001 Elsevier Science B.V. All rights reserved.