Medical Image Encryption with Fractional Discrete Cosine Transform, Arnold Transform and AES

In this paper, we propose a novel encryption algorithm for medical images. Our algorithm is based around ad-vanced encryption standard (AES), however, its simple algebraic structure and the encryption process of every block may become a major concern in security. This is because the block-wise nature of implementation can pass the features of the actual image to visible in the encrypted image. We addressed this issue by introducing two new encryption layers i.e., Fractional Discrete Cosine Transform (FrDCT) and Arnold Transform. unlike the block-wise AES, these two layers are applied image-wide. together this cascade provides excellent security and key sensitivity while preserving the quality of the medical images. The proposed method has been compared with contemporary methods in both quantitative and qualitative manner which further validated our ideas. Even slight change in keys <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\Delta\approx\pm 0.001)$</tex> causes a failure in decryption. This shows the robustness of the proposed algorithm.