Research On Color Image Encryption Algorithm Based On Frequency Domain

With the widespread use of digital products such as smart phones,digital cameras,and tablet PCs,the collection and transmission of digital image information has reached an unprecedented depth and breadth.The information security of digital images in the storage and transmission process has aroused people's concern,and has become an important research topic in the field of information security.Security protection of image information not only involves national security,such as satellite reconnaissance images,military drawings;it also involves the protection of general civil fields such as personal privacy images,medical images.Therefore,research on the security protection of digital image information has important academic significance and practical application value.Image encryption is one of the main methods to protect the security of image information.Most traditional cryptographic algorithms have high security and efficiency when dealing with text data.However,due to the large amount of data information,the strong correlation between neighboring pixels,and the high redundancy of digital images,traditional cryptographic algorithms have been overly effective.Low and weak security issues.Chaos theory is a theory for the study of nonlinear dynamic systems.Chaotic systems have excellent characteristics such as extreme sensitivity to initial conditions and parameters,fast decaying autocorrelation,mixture,pseudo-randomness,and long-term unpredictability.The system is particularly suitable for designing image encryption algorithms.Because of its higher efficiency and security than other types of encryption algorithms,image encryption algorithms based on frequency domain are applied in the field of image encryption.Based on the above analysis,by using chaotic systems,discrete wavelet transform and discrete cosine transform technology,this paper designs two color image encryption algorithms,and gives numerical simulation results and performance analysis of encryption algorithms.The main work and research results of this paper are as follows:1?Combine SCAN method and two-dimensional discrete wavelet transform technology,a new color image encryption algorithm is proposed.First,the color plaintext image is decomposed into red,green,and blue primary color components,each component is divided into several non-overlapping sub-blocks,and each sub-block is further divided.Then,using LSS and 2D-LASM chaotic systems to generate random sequences,some of the random sequences are used as scanning paths of the SCAN method for image scrambling operations and diffusion operations.Secondly,the image is transformed from the spatial domain to the frequency domain by two-dimensional discrete wavelet transform to obtain four sub-band matrices.The sub-band matrix is scrambled according to the above-mentioned chaotic sequence.Finally,a discrete wavelet inverse transform is performed on the image to obtain the final cipher-text image.The experimental analysis shows that this scheme has low pixel correlation,and strong key sensitivity and fast running time.2?A color image encryption scheme combining discrete wavelet transform and discrete cosine transform is designed.Firstly,the original color image is divided into three primary color components,which are subjected to discrete cosine transform(DCT)transform respectively to obtain DC sequence and AC sequence,and the sequence is updated to obtain disturbed sequences,and the image is scrambled;Next,the two-dimensional decimal scrambling matrix is converted into a three-dimensional binary matrix,and the resulting scrambling matrix is subjected to a two-dimensional discrete wavelet transform(DWT)to obtain four sub-bands.The sub-bands are scrambled by the scrambling sequence and perform Two-dimensional inverse discrete wavelet transform(DWT)obtains the intermediate binary matrix,then performs an XOR operation on the above binary matrix to obtain a three-dimensional binary matrix,converts it into a two-dimensional decimal matrix,and performs a discrete cosine transform on it to obtain a DC sequence.Second,use the DC sequence to construct the initial value of the SHA-256 hash function,and use the returned 256-bit hexadecimal hash value as the initial value of the chaotic map.Finally,use a single-wheel diffusion operation to change the image pixel value to obtain the cipher image.Experimental simulation results show that this algorithm is a lossless color image encryption scheme that can resist various attacks.