Thumbnail-preserving Encryption Based On Improved Logistic Map

Plaintext images and images encrypted using traditional encryption schemes in cloud storage represent the extremes of usability and privacy.Obviously,neither of these schemes is what we expected.Recently,thumbnail-preserving encryption(TPE)has been proposed to balance the usability and privacy of images in the cloud.An ideal TPE scheme should have the characteristics of lossless decryption,identical thumbnails,low time complexity and the ability to resist certain attacks.However,none of the existing schemes can satisfy all the requirements simultaneously.Motivated by this idea,we propose a new TPE scheme based on an improved logistic map,which takes advantage of the good dynamics of the chaotic system and withstands the experimental evaluations in terms of privacy and usability.In addition,we also designed an image encryption algorithm with reflexivity based on XOR operation.This algorithm can make multiple pixels in the plaintext image correspond to one pixel in the ciphertext image,that is,there is a many-to-one relationship,which effectively improves the security.The main research contents and results are as follows:1.A parameter perturbation and linear feedback model based on delay variable is proposed and applied to Logistic map.The improved Logistic map is better than the original Logistic map in Lyapunov exponent,Approximate entropy and Permutation entropy,and has better dynamic characteristics.2.Two pixels are randomly indexed by the chaotic sequence generated by the improved Logistic map,and the digits of the pixel values expressed in decimal are exchanged according to the exchange rules to achieve TPE.In the exchange rules of the scheme,the exchange success rate is about 80.11%.3.A TPE scheme combining binary bits of swapping pixel values with "rank-then-encrypt" is proposed.In this scheme,the improved Logistic map is used to index pixels and randomly change pixel values,which is an ideal TPE scheme.4.By analyzing the reflexivity of XOR operation and combining the transformation of image pixel value,an image encryption algorithm with many-to-one relation between plaintext pixel and ciphertext pixel is realized.