DCT域内的数字图像加密算法

Digital Image Encryption Algorithm in DCT Domain

提出了一种能与JPEG标准兼容的、适用范围更广的DCT域内的数字图像加密算法。由于JPEG标准对DC系数采用差分编码而对AC系数采用游程长度编码,算法将明文图像分成若干8×8子块,并在分块DCT后对各子块的AC系数和DC系数分别实施不同策略的加密变换。算法在DC系数加密过程中引入分段思想,在AC系数加密过程中引入质量因子,在保证加密质量的同时,既保持了各分段DC系数的"相邻"性又保持了分块直方图不变,不仅能有效控制加密过程图像大小增长,对统计攻击、穷举攻击、裁剪等攻击也有较强的鲁棒性。

An algorithm in JPEG standard and has DCT domain of digital images a more extensive application is proposed, which is compatible with scope. In JPEG standard, the DC coefficients are coded in differential encoding, while the AC coefficients are coded in RLC （Run Length Coding）, they are different. So the proposed algorithm divides the cover image into blocks, run DCT for each block, and then takes different strategies in the encrypting algorithms for AC and DC coefficients. In the encryption process, the proposed algorithm introduces segmentation thought for the DC ：coefficients, and introduces quality factor for the AC coefficients. Aiming at the encryption quality, the proposed algorithm keeps the similarity in every DC coefficients segment and the histogram of the DCT coefficients. Compared to other algorithms, the prdposed algorithm can keep the size of the cover image during the encryption process efficiently and has an ideal robustness against statistical, enumerating or clipping attacks.