Image encryption by redirection and cyclical shift

In this thesis, we present a novel method for encrypting and decrypting large amounts of data such as 2-D images, both gray-scale and color, without the loss of information, and using private keys of varying lengths. The proposed method is based on the concept of the tensor representation of an image and splitting the two-dimensional (2-D) discrete Fourier transform (DFT) by one-dimensional (1-D) DFTs of signals from the tensor representation, or transform. The pixels in the original image can be re-organized, or redirected, in such a way that these 1-D splitting-signals can be easily calculated by each row (or column) of the image. This redirection, followed by a cyclical shift of the image, causes the image to become distorted. Repeating several iterations of redirecting, followed by a cyclical shift, makes for an encrypted image that is uncorrelated. The decryption algorithm uses the encrypted data, and processes them in inverse order, with an identical number of iterations. The encryption method is very efficient, as it has a cpu-working time of approximately 0.0156s for encrypting a gray-scale image of size 256×256, and 0.6250s for an image of size 512×512. Simulation results of the purposed method are presented to show the performance for the image encryption method.