The Research Of Chaotic Sequence-based Digital Image Encryption Algorithm In Space Domain

Digital image is the main carrier for people to obtain information in daily life.It has been widely used in various fields.At the same time,the security of image information has became an increasingly concerned issue.One of the most direct ways to protect image security is to encrypt digital images,but traditional data encryption systems are mainly used for encrypting text data and are not applicable to encrypt digital image with characteristics like large amount of data,high information redundancy and strong correlation.In recent years,researchers found that the characteristics of chaotic system such as initial value sensitivity,pseudo-randomness,boundedness and ergodicity are in line with the requirements of image encryption system.Therefore,there are a lot of obvious advantages in applying chaotic system to image encryption algorithm.Based on the basic theory of chaotic cryptography and image encryption,two image encryption algorithms are proposed in this paper.The main contents are as follows:1.An image block encryption algorithm based on double two-dimensional chaotic system is proposed.Firstly,the two-dimensional Henon map is used to scramble the image in rows and columns.Compare to point-by-point scrambling,the computation complexity is greatly reduced and the speed of the algorithm is improved.Then the image is divided into blocks and the two-demensional logistic chaotic system iteratively generates a pseudo-random sequence.Combined the sequence with blocked image and the lookup table which is produced by Henon map to generate a ciper stream.Finally,the diffusion is performed on the blocked image.In diffusion,the ciper stream,plaintext,and ciphertext interact with each other,which effectively improve the algorithm's ability to resist known-plaintext attacks and chosen-plaintext attacks.2.An image encryption algorithm based on hyperchaotic system and finite field theory is proposed.Firstly,by adding the state feedback controller,a hyperchaotic system is constructed based on the three-dimensional Lü chaotic system.The maximum Lyapunov exponent of the new system is bigger than many classical hyperchaotic systems,so it has a more significant chaotic behavior.Then,a sequence generator is designed based on this new hyperchaotic system.The generated sequences are tested in statistics and randomness.In the end,combined with the finite field theory,a plaintext-related image encryption algorithm is proposed,which can effectively solve the weak resistance ability to chosen-plaintext attack and chosen-cipertext attack in some high-dimensional chaotic image encryption algorithms.