Image Encryption Based on 2D Coupled Map Lattices
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摘要:
为了平衡混沌系统的复杂性和效率之间的关系,将分段Logistic映射(piecewise Logistic map,PLM)引入到二维耦合映像格子(2D coupled map lattices,2DCML)模型中. 采用暂态转换以使模型的输出序列服从均匀分布,进而得到T2DCML模型,基于此模型提出了一类图像加密算法. 在加密算法中,利用模型输出的伪随机序列构造两个初等变换矩阵,对图像进行置乱操作;然后再从模型中提取状态值的比特构造整数序列,对置乱后的图像进行扩散操作;经过若干轮的置乱与扩散操作,产生最后的加密图像. 仿真实验及性能分析表明:该算法的相关系数的绝对平均值为0.001 3,信息熵为7.999 3,像素变化率(number of pixel change rate,NPCR)和统一平均变化强度(unified average change intensity,UACI)分别为99.63%和33.60%,能够有效满足图像在网络中安全传输的需求.
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关键词:
- 分段Logistic映射 /
- 二维耦合映像格子模型 /
- 混沌序列 /
- 图像加密
Abstract:Piecewise Logistic map (PLM) is introduced into 2D coupled map lattices (2DCML) model to face a tradeoff between complexity and efficiency of chaotic systems, and a transformation method based on transient status values is used to make the output sequence of the model obey a uniform distribution. Then, the T2DCML model is built. According to the T2DCML model, an image encryption algorithm is proposed, in which encryption algorithm, the pseudo-random sequence output by the model is used to construct two elementary transformation matrices and the image is scrambled by the matrices. Then, the bits of the state value are extracted from the model to construct an integer sequence and the scrambled image is diffused by the integer sequence. Finally, the encrypted image is produced by multi-rounds of confusion and diffusion. Simulation experiments and performance analysis show that the absolute average correlation coefficient of the algorithm is 0.001 3, the information entropy is 7.999 3, and the number of pixel change rate (NPCR) and the unified average change intensity (UACI) is 99.63% and 33.60%, respectively, revealing that the algorithm can effectively meet the needs of the safe transmission of images in the network.
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Key words:
- piecewise Logistic map /
- 2D coupled map lattices /
- chaotic sequences /
- image encryption
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表 1 NIST套件的测试结果
Table 1. Test results of NIST suites
测试指标 P 值 通过率 结果 Frequency 0.719 747 0.993 通过 BlockFrequency 0.996 335 0.988 通过 CumulativeSums* 0.817 162 0.995 通过 Runs 0.765 632 0.988 通过 LongestRun 0.071 620 0.987 通过 Rank 0.179 584 0.990 通过 FFT 0.492 436 0.992 通过 NonOverlappingTemplate* 0.496 164 0.990 通过 OverlappingTemplate 0.209 948 0.983 通过 Universal 0.755 819 0.989 通过 ApproximateEntropy 0.075 719 0.986 通过 RandomExcursions* 0.627 887 0.989 通过 RandomExcursionsVariant* 0.540 402 0.992 通过 Serial* 0.676 598 0.986 通过 LinearComplexity 0.096 000 0.997 通过 表 2 加密前后相邻像素间的相关系数
Table 2. Correlation coefficients between adjacent pixels
图像 水平方向 垂直方向 对角方向 Lena 明文 0.975 1 0.983 1 0.958 2 Lena 密文 0.001 2 0.000 6 0.001 6 Baboon 明文 0.888 0 0.746 8 0.716 0 Baboon 密文 0.001 1 0.000 4 0.003 3 Pepper 明文 0.977 4 0.975 8 0.962 7 Pepper 密文 0.000 8 0.002 6 0.001 2 White 明文 1.000 0 1.000 0 1.000 0 White 密文 −0.001 4 −0.000 1 0.002 9 Black 明文 1.000 0 1.000 0 1.000 0 Black 密文 0.003 0 −0.000 5 −0.002 2 表 3 加密前后图像的信息熵
Table 3. Information entropies of images
图像 明文信息熵 密文信息熵 Lena 7.445 5 7.999 3 Baboon 7.222 2 7.999 2 Pepper 7.364 4 7.999 3 White 0 7.999 3 Black 0 7.999 2 表 4 密文图像的差异
Table 4. Differences between ciphertext images
% 图像 测试 1 测试 2 测试 3 测试 4 Lena 99.592 99.614 99.598 99.602 Baboon 99.619 99.599 99.592 99.598 Pepper 99.621 99.622 99.615 99.619 White 99.623 99.618 99.613 99.617 Black 99.607 99.611 99.617 99.579 表 5 密文图像的NPCR和UACI
Table 5. NPCR and UACI of ciphertext images
% 图像 NPCR UACI Lena 99.59 33.44 Baboon 99.64 33.50 Pepper 99.60 33.50 White 99.59 33.53 Black 99.60 33.49 表 6 算法性能对比
Table 6. Comparison of algorithm performance
加密算法 相关系数 信息熵 NPCR/% UACI/% 水平 垂直 对角 绝对平均值 本文算法 −0.002 5 −0.000 2 0.001 1 0.001 3 7.999 3 99.63 33.60 文献[4] −0.022 3 −0.008 4 −0.008 6 0.013 1 7.997 4 99.61 33.46 文献[5] −0.038 1 −0.029 1 0.002 7 0.023 3 7.999 2 99.61 33.45 文献[6] 0.069 3 0.061 0 −0.024 2 0.051 5 7.999 1 99.57 33.41 文献[7] 0.001 4 0.003 8 0.001 1 0.002 1 7.999 3 99.59 文献[8] −0.023 0 0.001 9 −0.003 4 0.009 4 7.969 6 99.62 33.51 文献[9] −0.014 4 −0.003 4 0.010 7 0.009 5 7.997 0 99.60 32.91 文献[10] 0.016 3 −0.002 9 0.030 9 0.016 7 7.999 3 99.60 33.45 -
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