Cryptanalysis and enhancement of image encryption scheme based on word-oriented feed back shift register

Abstract

In the recent past, an image encryption scheme has been proposed by Deb et al., based on the Logistic map, Arnold transformation, and word-oriented feedback shift register (wfsr). In this scheme, first the plain image is randomized and scrambled with the help of a Logistic map and Arnold transformation. Then, the pixels of an intermediate image are bit-wise XORed with output of the wfsr to obtain the cipher image. It is claimed that the scheme is secure against brute force and other existing cryptanalytical attacks. However, it is demonstrated that the scheme is not secure against chosen plaintext attack (CPA). In our study, first, the output sequence of wfsr, corresponding to the fixed key, is obtained by choosing one plain and cipher image pair. Subsequently, the composition of Logistic map and Arnold transformation is inverted with the help of four randomly chosen plain and cipher image pairs. After that, the plain image is retrieved from the cipher image in real-time with the help of recovered wfsr sequence and inverse of composite function. Mathematical proof and experimental validation is given. Based on this analysis, the reason for applicability of CPA is discussed. Finally, the original scheme is modified in such a way that it resists CPA and also maintains the qualities of the original scheme.