Cryptanalysis and improvement of medical image encryption using high-speed scrambling and pixel adaptive diffusion

A medical image encryption algorithm using high-speed scrambling and pixel adaptive diffusion was recently proposed by Hua et al. The algorithm mainly consists of random data insertion, high-speed scrambling, and pixel adaptive diffusion. Before performing the scrambling-diffusion process, external random pixels are inserted into the surrounding plain image. Then, high-speed scrambling and pixel adaptive diffusion are respectively used to randomly shuffle adjacent pixels and spread them throughout the cipher image. The authors claim that this scheme can achieve both high efficiency and strong robustness. However, under bad randomness, we have found that the cipher image can be completely recovered by using a chosen plain image attack. To increase resistance against such attacks, we propose an improved encryption scheme that performs nonlinear operations on permuted images using an enhanced version of the original algorithm. Experimental results and security analysis show that our improved encryption algorithm can not only resist chosen plain image attacks but also maintain the merits of the original algorithm. (C) 2019 Elsevier B.V. All rights reserved.