A Secure Medical Image Scrambling Using Argon2i, AES-CTR with Feedback-Based Diffusion

Abstract

The modern healthcare systems consider the secure transmission and storage of medical images as vital because of the sensitivity of patient data and the strict privacy regulations. This paper presents a secure and reversible RGB medical image scrambling and encryption scheme that aims to defend diagnostic images from unauthorized access, while, guaranteeing the integrity of the data. A 512- bit master key is generated through the memory-hard Argon2i algorithm which makes the system extremely resistant to brute-force and dictionary attacks. Domain-separated subkeys are generated using master key via AES in counter (CTR) mode.  These subkeys are utilized at confusion and diffusion stages of the encryption and decryption process. The image confusion is performed with the use of a Fisher-Yates permutation which is controlled by cryptographically secure keystreams thereby disrupting spatial pixel relationships. The diffusion is done at both single colour channel and total colour channel levels utilizing a feedback-based mechanism that combines XOR operation, modular addition, and bit-level permutation. Both confusion and diffusion process ensures a strong avalanche effect across the entire image. Performance analysis shows that the proposed method provides an effective balance between security and computational efficiency, making it suitable for secure storage and transmission of medical images in telemedicine and healthcare information systems.