CN-113077373-B - Image encryption method based on chaotic mapping and bidirectional operation Feistel structure

Abstract

The invention provides an image encryption method based on a chaotic mapping and bidirectional operation Feistel structure, which is used for solving the problems that the conventional image encryption algorithm based on the chaotic mapping is insufficient in scrambling-diffusion and is separated from a plaintext in an encryption process, and is vulnerable to plaintext attack. The method comprises the steps of firstly generating a 256-bit hash value of a plaintext image by using an SHA-256 algorithm, calculating and correcting the hash value to obtain an initial value of a chaotic system, then updating the initial value by the iterative chaotic system, generating a pseudo-random sequence by the iterative chaotic system again, calculating and correcting the pseudo-random sequence to obtain a round key and a modulation matrix, secondly performing two-time bit scrambling, diffusion and pixel rearrangement operations on the image by using a bi-directional operation Feistel structure, and finally performing global scrambling and diffusion operations on the sequence by using the modulation matrix to generate a final ciphertext image. Experimental results and security analysis show that the encryption method provided by the invention enhances the sensitivity of algorithm plaintext, can effectively resist attack, and has good security.

Inventors

• TONG XIAOJUN
• LIU XILIN
• ZHANG MIAO
• WANG ZHU

Assignees

• 哈尔滨工业大学（威海）

Dates

Publication Date

20260512

Application Date

20210323

Claims (1)

1. 1. An image encryption method based on chaotic mapping and bidirectional operation Feistel structure is characterized by comprising the following steps: Firstly, generating 256bit hash value by using SHA-256 algorithm on plaintext image information, calculating and correcting the hash value to generate initial value of hyper-chaos Lorenz system , , And ; Different plaintext images will generate different 256bit hash values using the SHA-256 algorithm, the decimal representation of which is Dividing it into 4 groups, namely , , And The initial value of the hyper-chaos Lorenz system is calculated according to the following formula , , And After the initial value iteration hyper-chaos Lorenz system is used for 2000 times, values of x, y, z and w are generated and used as initial values after the system is updated; Second, continuing to iterate the chaotic system by using the updated initial value Generating 4 pseudo-random sequences , , And Generating 4 pseudo-random matrices X, Y, Z and W respectively by computing corrections to the 4 pseudo-random sequences, further computing corrections thereto, generating round keys , , And And has the size of The calculation and correction method of the 4 pseudo random matrixes X, Y, Z and W is as follows: Wherein the method comprises the steps of , , Indicating that the largest integer less than or equal to t is returned, Indicating the number n to t; Round key , , And (3) with The calculation correction method comprises the following steps: The method for calculating and correcting the modulation matrix Q is as follows: Third, the size is as follows Is spread out in the form of rows into a plain text image P Is defined by a vector R of one dimension, the vectors R are grouped in groups of 4 pixels, together, are divided into t= (R/4) groups, each group being , The last group is less than or equal to 4 pixels, different Feistel structures are built according to the number of the pixels in the group, and then bidirectional bit level scrambling, diffusion and pixel rearrangement operations are carried out on the image to generate a vector C; For 4 pixels in a group, namely The bidirectional operation Feistel structure bit level scrambling and diffusion formula is as follows: the pixel sequence in the group after rearrangement is ; For the last group there are 3 pixels, i.e The bidirectional operation Feistel structure bit level scrambling and diffusion formula is as follows: the pixel sequence in the group after rearrangement is ; For the last group there are 2 pixels, i.e The bidirectional operation Feistel structure bit level scrambling and diffusion formula is as follows: the pixel order in the group after rearrangement is ; For the last group there is 1 pixel, i.e Its value is rewritten as (255-J); Fourth, the vector C is pressed The method comprises the steps of (1) resetting an image information matrix C1, then expanding the image information matrix C1 into a one-dimensional vector C2 in a column mode, grouping the one-dimensional vector C2 in a mode that 4 pixels are in a group mode, wherein the last group is smaller than or equal to 4 pixels, and performing bit level scrambling, diffusion and pixel rearrangement operation on the vector C2 by using a third step to generate a one-dimensional vector C3; Fifthly, performing global scrambling and diffusion operation on the image information vector C3 by using a modulation matrix Q, and generating a final ciphertext image matrix C4; the global scrambling procedure method is as follows: spreading the modulation matrix Q in rows Is a sequence of (2) , According to the formula Calculating the sequence Will be The repeated elements in the set are reserved only in the first bit At the position of The values not appearing in (a) are added to the sequence from small to large At the end of (2), scrambling is performed according to the following formula: The global diffusion process method is as follows: reset C3 to The image information matrix of (2) is subjected to diffusion operation according to the following formula to generate a final ciphertext matrix C4; 。

Description

Image encryption method based on chaotic mapping and bidirectional operation Feistel structure Technical Field The invention belongs to the technical field of digital image encryption, and particularly relates to an image encryption method based on chaotic mapping and a bidirectional operation Feistel structure. Background Along with the rapid development of information technologies such as the Internet, multimedia becomes a main way for information transmission, and images serving as carriers of information have the characteristics of vivid images and large information quantity and become an indispensable part of communication and communication in daily life of people. In real life, it is important to protect the image data security, and the image encryption technology is a method for effectively protecting and transmitting the digital image information. Because the image has the characteristics of large data volume, high redundancy, strong pixel correlation and the like, the traditional encryption algorithm is not applicable any more. The chaotic system has the characteristics of initial value sensitivity, pseudo-randomness, non-periodicity and the like which are matched with the characteristics required by cryptography And (5) combining. At present, the chaotic encryption technology is widely applied in the field of information security, in particular in the field of image encryption. The Feistel structure is a block cipher structure proposed by a secret code reader Horst Feistel, is a symmetrical cipher algorithm which can be rapidly realized, and has great development potential in the technical fields of information encryption, hiding, authentication and the like. Disclosure of Invention Aiming at the problems that the prior partial image encryption method has insufficient scrambling-diffusion and large time consumption, and the encryption process is separated from the plaintext and is easy to attack by the plaintext, the invention adopts the hyper-chaos Lorenz system to combine and construct a Feistel structure to carry out bidirectional bit-level scrambling, diffusion and pixel rearrangement on the plaintext image and then carry out global scrambling and diffusion operation, thereby realizing the aim of encrypting the transmitted image. The invention relates to two main modules, the first is bit level scrambling, diffusion and pixel rearrangement of an image Feistel structure, and the second is global scrambling and diffusion of an image. 1. Bit-level scrambling, diffusion and pixel rearrangement of image Feistel structures 1.1 Round key and modulation matrix generation Generating 256bit hash value by using SHA-256 algorithm on plaintext image information, calculating initial value of chaotic system,,And。 The invention adopts a hyperchaotic Lorenz system, which is a well-known four-dimensional chaotic system with complex dynamic behaviors, and the equation is as follows: Wherein, the ,,AndA, b, c and r are control parameters of the system, which are state variables of the system, where a=10, b=8/3, c=28,When the system is in a hyperchaotic state. Different plaintext images will generate different 256bit hash values using the SHA-256 algorithm, the decimal representation of which isDividing it into 4 groups, namely,,AndThe initial value of the hyper-chaos Lorenz system is calculated according to the following formula,,AndGiven the system parameter values, i.e., a=10, b=8/3, c=28, r= -1, after iterating the hyper-chaotic Lorenz system 2000 times with the initial values, values of x, y, z and w are generated as initial values after system update; continuing to iterate the chaotic system by using the updated initial value Generating 4 pseudo-random sequences,,AndGenerating 4 pseudo-random matrices X, Y, Z and W respectively by computing corrections to the 4 pseudo-random sequences, further computing corrections thereto, generating round keys ,,AndAnd has the size ofIs a modulation matrix Q of (a); 4. The calculation correction method of the pseudo-random matrixes X, Y, Z and W is as follows: Wherein the method comprises the steps of ,,Indicating that the largest integer less than or equal to t is returned,Indicating that the number n is complementary to t. Round key,,And (3) withThe calculation correction method comprises the following steps: The method for calculating and correcting the modulation matrix Q is as follows: 1.2 Constructing a Feistel structure, and performing row bit level scrambling, diffusion and pixel rearrangement operations on an image Will be of the size ofIs spread out in the form of rows into a plain text image PIs defined by a vector R of one dimension, the vectors R are grouped in groups of 4 pixels, together, are divided into t= (R/4) groups, each group being,The last group is less than or equal to 4 pixels, different Feistel structures are built according to the number of the pixels in the group, and then bidirectional bit level scrambling, diffusion and pixel rearrangement o