Image Encryption Techniques Based On Chaotic Maps And Its Implementation On STM32

Cloud computing is a model for enabling ubiquitous,convenient,on-demand network access to a shared pool of configurable computing resource(e.g.,network,servers,storage,applications)that can be rapidly provisioned and released with minimal management effort or service provider interaction.Attracted by these appealing features,both individuals and enterprises are actively outsourcing their data to the cloud.But,outsourcing sensitive information to remote servers will involve privacy concerns,such as,images in multimedia information.The main approach of preserving privacy data is to encrypt it before outsourcing.Usually,the AES and DES algorithms are used to encrypt the image files to be uploaded.However,in order to ensure the security of these methods,the encryption process is usually controlled by the secret keys in a very complex way,which is difficult to implement a fast encryption process for multimedia information with a large amount of data.Moreover,these traditional encryption methods are challenged by statistical analysis techniques in the background of large data where statistical attacks are becoming more and more easy to succeed.Because chaotic systems have some excellent properties,such as pseudo-randomness,sensitivity to initial condition,non-linear dynamics and unpredictable manners,more and more researches have used them to improve the security of the encrypted images.Starting from chaotic maps,this article proposes some new encryption schemes for digital images,and our main contributions are as follows.(1)Image encryption scheme based on multiple discrete chaotic maps.An image encryption algorithm is designed by combining Logistic and Henon map effectively.First,the random sequence which is generated by Logistic map is sorted as an ascending order,and the transformation functions of pixel's indexes can be obtained in this process.Then,the original image pixels are scrambled according to these functions.And then,the encrypted image pixel matrix can be obtained by multiplying the scrambled pixel matrix and another chaotic matrix which is constructed by using Henon map.Finally,the decryption algorithm is designed and its performances are analyzed.In order to further improve the security of the encryption algorithm and realize real-time image encryption,dynatomic modular curve is used to optimize the algorithm.(2)Image encryption scheme based on chaotic map and dynatomic modular curve.An image encryption algorithm is designed by combining Logistic map and projective transformation effectively.First,the definition of dynatomic modular curve and its periodic points are introduced,and a property of the dynatomic modular curve is proved,that is,the conditions for generating rational curve from dynatomic modular curve.Second,the relationship between the Logistic map and the dynatomic modular curve is discussed.Finally,the encryption algorithm which is composed of permutation of pixels and substitution is given.In order to eliminate sufficiently the relation between adjacent pixels in the encrypted image,pixel values of the original image are sorted as index function,which derives from Logistic map and dynatomic modular curve.And the XOR operation is performed between the scrambled pixel sequence and another projective transformation sequence.Experiments and non-parametric hypothesis tests demonstrate that the proposed algorithm is secure to resist different types of attacks and it can be applied to real-time encryption.This algorithm can effectively improve the randomness of chaotic mapping sequences used for scrambling and substitution operations,and resist different types of statistical attacks.In this algorithm,the dynatomic modular curve is applied to encrypt the image for the first time.It can not only improve the calculation accuracy by adding infinite points and infinite lines,but also expand the range of chaotic data.In addition,from the point of view of arithmetic dynamics,the chaotic behavior of Logistic mapping is also examined in this article.The Chi-square and K-S test are used to test the distribution of the pixels and the correlation coefficients of adjacent pixels in the encrypted image,separately.They are helpful to verify the security of encryption algorithm from the perspective of statistical analysis.The security of encryption algorithm is closely related to the dynamic behavior of chaotic system.A simple time-delay system may have much more complex dynamicbehavior than discrete chaotic system and continuous chaotic system.So it can improve the security of encryption algorithm on the basis of guaranteeing the operation efficiency.Therefore,a fast and secure image encryption scheme can be designed based on the time-delay chaotic system.(3)Image encryption scheme based on the delay chaotic maps and improved random number generator.A multi-rounds image encryption algorithm is proposed by combining a class of time-delay chaotic maps with improved Gauss error function and digital discarding technique effectively.The algorithm is mainly composed of two modules,one is the random number generation module,and the other is the pixel encryption module.First,the chaotic sequence derived from a first-order time-delay differential equation is mapped to another sequence by using the improved Gauss error function,and then the data is truncated and recombined to obtain the random numbers.After scrambling the pixels of the original image by using the generated random numbers,the first round encrypted pixels can be obtained by performing XOR operation between the scrambled pixel sequence and another sequence which derived from the improved random number generator.And then,the encrypted image and the generator are used for the next round encryption after selecting an encrypted pixel value of the previous round.Simulation experiments demonstrate that the proposed algorithm can not only improve the randomness of time-delay chaotic map sequences,but also effectively resist brute force attacks,differential attacks,entropy attacks and statistical attacks.In addition,the cryptosystem has high key sensitivity and large key space.Infinite-dimensional time-delay systems are used to generate data sources,it makes prediction more difficult.In addition,by adding adjusting parameters to the Gauss error function,the uniformity of the generated sequence is enhanced.After analyzing the influence of parameters on the convergence speed of the algorithm and data uniformity,a multi-round image encryption algorithm is proposed,which improves the computational complexity and security to a certain extent.The simulation results show that the algorithm can not only effectively resist various attacks,but also has high key sensitivity and large key space.(4)It has an important application value to implement the proposed algorithms on embedded hardware under the background of the rapid development of intelligent technology.Therefore,the implementation methods of image encryption algorithms on STM32 are discussed by the way of developing projects.First,the role of STM32 in implementing algorithms is introduced.And then,the implementation methods aredesigned from the aspects of development environment and flowchart,hardware construction,software design,specific implementation steps,implementation results and improved schemes.Finally,the prototypes are developed and the encrypted(decrypted)image with size of 320×240ps is successfully displayed on LCD and personal computer.Finally,the research work is summarized,the problems that need to be optimized and solved in the next step are pointed out,and the future work to be done is prospected.