An Enhanced ElGamal Cryptosystem for Image Encryption and Decryption

ElGamal cryptosystem is one of the well-known public-key algorithms for its ability to generate different ciphertexts for the same plaintext on successive runs. However, this algorithm results in a ciphertext occupying a larger memory space than its plaintext due to its encryption nature. As a result, it is pretty infeasible to use data that require their encrypted form to have the same size, such as image data. To overcome this issue, we propose an enhanced ElGamal cryptosystem that can be used for any given digital data message, including image, text, and video. The proposed approach mainly tests image data, consisting of three stages: key pair generation, image encryption, and image decryption. First, we generate as many random bytes as required for encrypting or decrypting images using the sender or receiver's public key information. Then, we use an XOR operation between each pixel in the image and each randomly generated byte to obtain the encrypted or decrypted image. Experimental results revealed that the proposed approach gives excellent results in various evaluation metrics tested on four different color images.