In recent years, a number of image encryption schemes based on DNA coding and nonlinear dynamics have been proposed. Generally, these DNA-based schemes first encode plaintext images into DNA sequences and then encrypt them with pseudorandom elements produced by chaotic systems or other nonlinear dynamics. Although ciphertexts can pass some security tests, many image encryption schemes are being shown to have intrinsic flaws and that they cannot guarantee a high level of security. In this paper, we cryptanalyze a family of image encryption schemes for which the encryption kernel is DNA coding or its variant. The complex DNA operation can be simplified as a substitution box (S-box). The whole cryptosystem's security level is thus significantly decreased and is vulnerable to the chosen-plaintext attack. Applications of this concept to break five ciphers are theoretically presented and experimentally verified. In addition, some suggestions for resisting similar attacks are also given in this paper.

Recently, an image encryption scheme based on a 2D hyperchaotic map is proposed. It adopts the permutation–diffusion architecture and consists of three steps, which are permutation, forward diffusion, and backward diffusion. In this paper, we break this cipher with both the chosen-plaintext attack (CPA) and the chosen-ciphertext attack (CCA). According to our analysis, we found the two complex diffusion processes could be simplified into two simple diffusions and a modular addition operation. Based on this, the equivalent key can be obtained with CPA and CCA. Detailed theoretical derivations and the results of experiments confirmed the feasibility of our attack methods. When the image size was $256\times 256$, the running time of the attacks was less than 2 hours on a laptop with a 2.59 GHz Intel Core i7 and 16 GB DDR3 memory. Other sizes of images were also tested, and some rules were found. In addition, the probability of other attacks has also been discussed, and some suggestions for improvements are given. The source codes are publicly available and can be found online.

Permutation is a commonly used operation in image encryption schemes. Many schemes adopt a separate row and column permutation to increase the encryption efficiency while ignoring the security. This paper proposes an efficient known-plaintext attack (KPA) for row-column-based permutation. A special ID method based on the Pearson correlation coefficient is proposed to label each column or row. Only one pair of known plaintext-ciphertext images is enough to determine the permutation rules completely. With this attack method for permutation, a classic permutation-then-XOR image encryption scheme is broken with only two known plaintext-ciphertext image pairs. A numerical example of the proposed attack is provided to show the process intuitively and clearly. In addition, the cryptanalyses of two related image ciphers are introduced. Detailed theoretical derivations and extensive experiments confirmed the feasibility and efficiency of the proposed attacks. The related MATLAB codes are publicly available and can be found online.