针对图像分层树集划分编码的安全性问题,提出一种将小波变换和SHA-1(security hash algorithm-1)相结合的图像加密算法(DSCE)。首先将图像小波变换后的系数分为低频和高频两部分,然后将低频系数、初始密钥及图像像素和,通过SHA-1置乱加密SPIHT编码高频系数;将部分加密高频系数和初始密钥,通过SHA-1置乱加密Huffman编码低频系数,在压缩过程中实现低频和高频部分相互加密。仿真结果表明,DSCE算法密钥空间大,对密钥和明文敏感,同时有效提高图像存储和传输效率。

For the security of the set partition in hierarchical trees compression, an algorithm of joint image compression and encryption with discrete wavelet transform and secure Hash algorithm-1 (named as DSCE) is proposed in this paper. First, the wavelet transform coefficients of the plain image are divided into a high-frequency and a low-frequency part. Then, the low-frequency coefficients, the initial keys, and the sum of total pixels are the input data of the SHA-1 to output the 160-bit hash value. The 160-bit hash value is used to produce a sub-key and to perturb the initial keys. The high-frequency coefficients are permuted by a sub-key produced with the 160-bit hash value. The initial keys perturbed with 160-bit hash value are used to partially encrypt the high-frequency coefficients encoded with the SPIHT code. Third, the partial encrypted high-frequency coefficients and the initial keys are input to the SHA-1 to output another 160-bit hash value. The hash value is used to produce a sub-key to permute the low-frequency coefficients, and it is also used to perturb the initial keys to encrypt the low-frequency coefficients encoded with Huffman code. This new DSCE algorithm can implement the mutual encryption between low-frequency and high-frequency in the process of compression. The simulation results show that our algorithm not only has a large key space, but also is highly sensitive to both the key and plain-image. Moreover, it can increase the efficiency of image storage and transmission.