Security assessment on block-Cat-map based permutation applied to image encryption scheme

• The paper investigates the security of block-Cat-map based permutation.
• All the keystreams can be revealed by choosing eight images.
• Only the permutation can be cryptanalyzed by choosing seven special images.

Recently, an image encryption scheme is proposed using block-Cat-map based permutation and chaos based substitution. This paper investigates the security of the scheme. As for different images, the keys keep fixed, so the chaotic keystreams generated by they are also unchanged. Our target is to reveal these chaotic keystreams equivalent to the chaotic keys by using chosen plaintext attack. Security assessment shows that all the keystreams can be revealed by choosing eight images for the situation of only one round encryption. In addition, only the block-Cat-map based permutation can be cryptanalyzed by choosing seven special images.