For secure transmission of digital images, existing cryptographic algorithms transform coherent visual information into a noise-like appearance prompting an adversary of the presence of a possible cipher. This paper proposes an algorithm that produces a visually coherent and meaningful cipher image. The proposed algorithm consists of a permutation-substitution subroutine to obtain a partial cipher. The Arnold-3D map does the permutation, and a delayed logistic map performs the substitution in this subroutine. The hiding of this partial cipher is done in the reference image using an integer wavelet transform. The pixels of the partial cipher are embedded in the four sub-bands of the decomposed reference image as 4 to 1-pixel encoding using Cantor-like pairing function. In addition to the lossless encryption scheme, the integer nature of all the sub-bands in the wavelet decomposition and the invertible pairing function facilitates the perfect reconstruction of the reference image. One of the significant novelty of this work lies in the subtle use of simple pairing functions, which prohibits the unnecessary increase in the size of the cipher, thereby reducing the storage and transmission costs.

为了安全地传输数字图像，现有的密码算法将相干的视觉信息转换为类似噪声的外观，从而提示可能存在密码的对手。本文提出了一种算法，该算法可产生视觉上连贯且有意义的密码图像。所提出的算法由置换置换子例程组成，以获取部分密码。Arnold-3D映射进行置换，而延迟logistic映射在此子例程中执行替换。使用整数小波变换在参考图像中隐藏此部分密码。部分密码的像素被嵌入到分解后的参考图像的四个子带中，作为使用Cantor类配对函数的4到1像素编码。除了无损加密方案之外，小波分解中所有子带的整数性质和可逆配对功能有利于参考图像的完美重建。这项工作的一大新颖之处在于巧妙地使用了简单的配对功能，从而避免了密码大小的不必要增加，从而降低了存储和传输成本。