Efficient Technique for Image Cryptography Using Sudoku Keys

This paper proposes a cryptographic technique on images based on the Sudoku solution. Sudoku is a number puzzle, which needs applying defined protocols and filling the empty boxes with numbers. Given a small size of numbers as input, solving the sudoku puzzle yields an expanded big size of numbers, which can be used as a key for the Encryption/Decryption of images. In this way, the given small size of numbers can be stored as the prime key, which means the key is compact. A prime key clue in the sudoku puzzle always leads to only one solution, which means the key is always stable. This feature is the background for the paper, where the Sudoku puzzle output can be innovatively introduced in image cryptography. Sudoku solution is expanded to any size image using a sequence of expansion techniques that involve filling of the number matrix, Linear X-Y rotational shifting, and reverse shifting based on a standard zig-zag pattern. The crypto key for an image dictates the details of positions, where the image pixels have to be shuffled. Shuffling is made at two levels, namely pixel and sub-pixel (RGB) levels for an image, with the latter having more effective Encryption. The brought-out technique falls under the Image scrambling method with partial diffusion. Performance metrics are impressive and are given by a Histogram deviation of 0.997, a Correlation coefficient of 10−2 and an NPCR of 99.98%. Hence, it is evident that the image cryptography with the sudoku kept in place is more efficient against Plaintext and Differential attacks.