Efficient image encryption algorithm based on ECC and dynamic S-box

Image encryption is widely used to convert digital images into an unreadable form when data is transferred through open networks and the internet. However, traditional cryptosystems have small encryption key sizes and are unsuitable for real-time implementation because image pixels have high redundancy and large data capacity. We have designed an image cryptosystem to tackle the issues related to the smaller key size and plaintext attacks. There are three phases of our proposed image cryptosystem. A pseudo-random number generator is used in the first phase to diffuse the pixels of the plain image. A substitution box generator is designed in the second phase to generate substitution boxes with high nonlinearity. The last phase provides an image encryption technique to encrypt grayscale images. The proposed scheme encrypts images with an entropy value close to the optimal value, which increases security. The encryption algorithm requires 0.556 s to encrypt a $256\times 256$ grayscale image. Further, extensive experiments show that the cryptosystem is highly sensitive to the input keys.