Images encryption using AES and variable permutations

TL;DR

This paper introduces a novel image encryption method combining AES with variable permutations, using pseudo-random constants derived from transcendental numbers, ensuring lossless encryption suitable for sensitive applications.

Contribution

It presents a new permutation-based encryption algorithm integrated with AES, utilizing transcendental numbers for pseudo-random permutation selection, and evaluates its effectiveness with multiple security metrics.

Findings

High entropy and low correlation in encrypted images

Effective resistance to sensitivity analysis

Maintains lossless encryption suitable for secure applications

Abstract

This work proposes a different procedure to encrypt images of 256 grey levels and colour, using the symmetric system Advanced Encryption Standard with a variable permutation in the first round, after the x-or operation. Variable permutation means using a different one for each input block of 128 bits. In this vein, an algorithm is constructed that defines a Bijective function between sets Nm = {n in N, 0 <= n < fac(m)} with n >= 2 and Pm = {pi, pi is a permutation of 0, 1, ..., m-1}. This algorithm calculates permutations on 128 positions with 127 known constants. The transcendental numbers are used to select the 127 constants in a pseudo-random way. The proposed encryption quality is evaluated by the following criteria: Correlation; horizontal, vertical and diagonal, Entropy and Discrete Fourier Transform. The latter uses the NIST standard 800-22. Also, a sensitivity analysis was performed in encrypted figures. Furthermore, an additional test is proposed which considers the distribution of 256 shades of the three colours; red, green and blue for colour images. On the other hand, it is important to mention that the images are encrypted without loss of information because many banking companies and some safety area countries do not allow the figures to go through a compression process with information loss. i.e., it is forbidden to use formats such as JPEG.