Cryptanalysis for Chaotic Image Encryption Schemes

This paper presents cryptanalysis methods for a class of chaos-based image encryption schemes with a permutation-diffusion architecture. Assuming that the permutation and diffusion session keys remain unchanged across all encryption and decryption rounds, the proposed chosen-plaintext and Chosen-Ciphertext Attacks (CCAs) exploit two properties of the diffusion equation. Under the Chosen-Plaintext Attack (CPA), the permutation key and the equivalent diffusion key are recovered for schemes with at most two encryption rounds. Under the CCA, the equivalent diffusion key is recovered for any number of decryption rounds, assuming that the permutation key has been recovered using Solak’s method. The proposed attacks are described step by step. Illustrative simulations demonstrate the key recovery process and the effectiveness of the proposed attacks and quantify the computational cost of the main recovery steps in diffusion-key recovery.