Reversible Data Hiding in Encrypted Medical Images Based on Huffman Tree Coding and Count-Encryption

Reversible data hiding in encrypted images (RDHEI) has been recognized as an effective method for overcoming management difficulties within picture archiving and communication system (PACS). However, most existing RDHEI algorithms still encounter notable challenges when applied to the PACS, specifically in terms of their key management, embedding capacity, and security. This paper introduces a novel framework and corresponding algorithm for reversible data hiding in encrypted medical images (RDHEMI) to bridge this gap. The framework employs a unique key for each patient and maintains consistency in the key linked to patient images regardless of changes in doctor, thereby addressing key management challenges. In the proposed algorithm, Huffman tree coding (HTC) integrates Huffman coding with innovative leaf-to-leaf coding, achieving a better compression performance for medical images than move-to-front (MTF) cache and Huffman coding, as medical images contain more smooth areas. Count-encryption (CE) produces encryption keys according to the frequency of encryption occurrences for an image and ensures a peak signal-tonoise ratio under 8 dB for multiple encryptions with the same key, enhancing the algorithm's resistance to attacks. The experimental results demonstrate that the proposed algorithm achieves high security to counter various attacks and outperforms existing algorithms in terms of the time complexity and embedding capacity, with an improvement of 0.21 bpp.