A Novel Image Encryption Scheme Based on Different Block Sizes for Grayscale and Color Images.

In this paper, two image encryption schemes are proposed for grayscale andcolor images. The two encryption schemes are based on dividing each image intoblocks of different sizes. In the first scheme, the two dimension ($2$D) inputimage is divided into various blocks of size $N \times N$. Each block istransformed into a one dimensional ($1$D) array by using the Zigzag pattern.Then, the exclusive or (XOR) logical operation is used to encrypt each blockwith the analogous secret key. In the second scheme, after the transformationprocess, the first block of each image is encrypted by the corresponding secretkey. Then, before the next block is encrypted, it is XORed with the firstencrypted block to become the next input to the encrypting routine and so on.This feedback mechanism depends on the cipher block chaining (CBC) mode ofoperation which considers the heart of some ciphers because it is highlynonlinear. In the case of color images, the color component is separated intoblocks with the same size and different secret keys. The used secret keysequences are generated from elliptic curves (EC) over a \textit{binary} finitefield $\mathbb{F}_{2^{m}}$. Finally, the experimental results are carried outand security analysis of the ciphered images are demonstrated that the twoproposed schemes had a better performance in terms of security, sensitivity androbustness.