Cryptanalysis of an Asymmetric Image Cryptosystem Based on Synchronized Unified Chaotic System and CNN

Cheng et al. proposed an asymmetric image encryption scheme which is based on adaptively synchronised chaotic cellular neural network and unified chaotic systems in [Communication in Nonlinear Science and Numerical Simulation 18(10) 2825-2837 2013]. The cryptosystem was asymmetric in nature and the synchronization error converged quickly to zero. Numerical simulations for performance evaluation included synchronization effectiveness, cryptosystem robustness and statistical analyses like key space, key sensitivity and NPCR/UACI analyses, all with effective results. But, this paper demonstrates the cryptanalysis of Cheng et al. cryptosystem by exploiting inherent deficiencies of encryption algorithm like low robustness and poor plain-image sensitivity. It is done by mounting the proposed cryptographic CPA or KPA attack which leads to successful retrieval of original plaintext image. The simulated cryptanalysis shows that Cheng et al. cryptosystem is not suitable for practical utility in image security applications.