Secure Image Encryption Algorithm Based on Playfair using Multiple Secret Keys, Scan Pattern and Pix Transformation

Image encryption is a scheme designed to ensure that the image is securely shared between a sender and the intended receiver. Encryption encodes the image so that no adversary can interpret its content. In this paper, an image encryption scheme has been proposed based on the simple monoalphabetic polygraphic substitution cipher – Playfair. The intention is to achieve a completely scrambled encrypted image utilizing the benefits of Playfair's simplicity, security and high throughput. To achieve this, the algorithm additionally incorporates usage of several secure mechanisms which are XOR operation with a key, multiple secret key generation for encryption, scan patterns to select pixel value pairs for encryption and pixel value transformations. The algorithm uses the transformations used in the rounds of AES to generate multiple keys so that there is minimum correlation between the keys used for different blocks attributed to the properties of these transformations. The algorithm has been designed to give good results with all types of images; especially focusing on those with uniform background. The proposed cryptosystem is designed to offer security, simplicity and speed. Measures like histogram analysis and correlation coefficient show that the system is able to produce good encryption results. Also the decrypted image is similar in quality to the original image as shown by the PSNR and SSIM.