基于超混沌映射的医学图像小波域加密算法
Encryption Method of Medical Image Based on Wavelet Transform and Hyper-Chaotic Mapping

针对当前医学图像加密算法在抗攻击能力和加密效率上的不足，提出了一种新颖的基于小波变换和超混沌映射的医学图像加密算法．首先，分析了LeGall 5/3整数小波变换的特点，提出利用去相关性强度指标确定小波变换分解级数，充分降低像素间相关性；然后，设计新的二维超混沌系统产生快速伪随机序列，提高混沌密码的安全性和产生效率；最后，对选取的医学图像小波低频系数进行两轮扩散加密，增加密文对明文的敏感性和降低迭代次数．实验结果表明，算法具有高安全性和良好的加密效率，与现有方法相比，密文像素相关性降低20%,以上，加密所需时间约为原方法的0.01倍．算法适用于大容量医学图像的实时加密和解密．
Aiming at the shortages of medical image encryption algorithm in the anti-attack ability and running efficiency，a novel medical image encryption algorithm based on wavelet transform and hyper-chaotic mapping was pro-posed．Firstly，the characteristics of integer wavelet transform of LeGall 5/3 were analyzed and a decorrelation magnitude index was proposed to determine the decomposition level number of wavelet transform．In this way，the correlation a mong image’s pixels was weakened．Then，a new two-dimensional hyper-chaotic mapping was de-signed to generate pseudo random sequences rapidly，and the security and efficiency of chaotic cipher were im-proved．Finally，the low frequency coefficients of the medical image were encrypted by two rounds of diffusion encryption，so the sensitivity between the encrypted text and plain text was enhanced and the number of iteration was reduced．The experimental results show that the proposed algorithm has a high level of security and encryption efficiency．In addition，compared with the previous similar methods，the presented method reduces the pixels’ rela-tionship of encrypted images by 20%，and shortens the encryption time by 100 times．The proposed algorithm can be applied to real time encryption and decryption of large volume medical image