Cryptanalyzing a chaos-based image encryption algorithm using alternate structure

Recently, a chaos-based image encryption algorithm with an alternate structure (IEAS) was proposed. This paper applies the differential cryptanalysis on the IEAS and finds that some of its properties favor the differential attack which can recover an equivalent secret key with only a few number of chosen plain-images. Detailed procedures for cryptanalyzing IEAS with a lower round number are presented. Both theoretical analysis and experimental results are provided to show the vulnerability of IEAS against differential attack. In addition, some other security defects of IEAS, including insensitivity with respect to changes of plain-images and insufficient size of the key space, are also pointed out and verified.