Image Encryption Algorithm Improvement And Performance Analysis

Arnold transform algorithm is simple and have a good algebraic structure and rigorous mathematical theory.image scrambling effect is good, easy to decrypt. Arnold transform can change encryption keys by controlling the number of transform,and be widely used in the field of digital image encryption.But the key space is too small, are susceptible to brute-force attack.Arnold transformation does not meet Kerckhoffs criteria, and cryptographic algorithm and the key can not be effectively separated.In this paper, we propose four improved algorithms based on Arnold transform.The algorithms expands the scope of application of Arnold transform,and in this paper,we compare the advantages and disadvantages between the algorithms.The innovation of this paper include the following aspects:1. I Propose Partition-based Arnold transform algorithm (algorithm 2), by finding a random image pixel, the image is divided into four square, and Arnold transform with different iterations, then combined into encrypted image.In this way,the algorithm extends the Arnold transform key space to achieve the separation of the algorithm and key,and meet the criteria Kerckhoffs.The algorithm enhanced the ability of anti-brute-force attack, through the experiments prove that the algorithm 2 achieved good encryption effect.2. In this paper,Partition-based Arnold transform algorithm is applied to transform the color image(algorithm 3),through the RGB image is decomposed into R, G, B,and used algorithm 2 to obtained better encryption effect.3.This paper proposed rectangular image scrambling method (algorithm 4),the rectangular image is divided into several square images by algorithm 4 to Arnold-transform. Algorithm 4 is used to solve the problem that arnold transform algorithm can not deal with rectangular images. algorithm 4 also enhance the security of the algorithm.4.Proposed bitplane-based Arnold transform algorithm (algorithm 5). First,the algorithm extracted 8 bit-planes from gray-scale image.Transform every plane in a different key K (A, S, L1, L2, L3, L4) by partition-based Arnold transform.This 8 bit-planes to be combined in sequence with the original image completely different scrambling image.