Reversible data hiding in encrypted image based on key-controlled balanced Huffman coding

To achieve privacy protection and effective management in cloud computing, and solve the problem of existing reversible data hiding in encrypted image (RDH-EI) algorithms being unable to resist existing various attacks, an RDH-EI algorithm based on key-controlled balanced Huffman coding (KBHC) is proposed. The novelty lies in KBHC and variable-length bit scrambling. KBHC possesses non-preset, balanced, and key-controlled characteristics, providing the proposed algorithm with high capacity and enhanced security. The non-preset allows coding tables to be adaptively generated based on prediction error maps, resulting in shorter encoded streams for higher embedding capacity. The balanced characteristic is achieved by adjusting the subtrees, so that the balance rate in the encoded stream is 0.014, and can also reach 0.065 for particularly smooth images, achieving uniform distribution of the encoded stream, thereby improving the ability to resist statistical analysis attacks. The random key controls the leaf nodes scrambling in the Huffman tree, which realizes the variability of the encoded stream and avoids the potential security risks caused by timestamp reconstruction, laying the foundation to achieve differential attack security. Variable-length bit scrambling determines the pseudo-random extension length and scrambling sequence by both the encryption key and coding table information, effectively resists brute force attacks and ensures up to 100 % difference rate between scrambling sequences generated in each run. Experimental results demonstrate that compared to several RDH-EI methods, the proposed algorithm achieves higher embedding capacity and security under acceptable complexity. The average embedding rate of three databases reaches 3.897 bpp, and the proposed algorithm effectively resists statistical analysis attacks, COA, KPA, and differential attack.