Lossless Thumbnail Preservation Encryption Based on Reversible Information Hiding

With the proliferation of multi-camera smartphones, image generation has proliferated and cloud storage services have become the primary tool for storing and sharing photos. However, this also poses privacy and security risks. Traditional image encryption techniques, while protecting privacy, also lead to loss of image availability in the cloud. To balance security and availability, TPE (Thumbnail Preserving Encryption) is proposed. However, the decryption effect of the existing schemes is generally unsatisfactory, and many existing schemes are unable to achieve perfect restoration in practical applications. Meanwhile, a few fully reversible schemes are limited by the proposed algorithms, which makes it difficult to be extended to a wider range of applications. To solve this contradiction, this paper proposes a TPE scheme based on reversible information hiding. Specifically, the scheme preserves the DC coefficients of the image during the encryption process and encrypts the AC coefficients to enhance the security of the image, thus obtaining the intermediate encrypted image. Then, the intermediate encrypted image is pre-decrypted, and the subtle error between the original image and the intermediate encrypted image is used as the compensation information. In order to achieve lossless decryption, we introduce the reversible information hiding technique to embed the compensation information into the intermediate image, and we finally obtain the encrypted image. This is also applicable to other high-quality TPE schemes and can provide ideas for their optimization direction. The experimental results show that this scheme not only achieves lossless decryption but also outperforms other TPE schemes in terms of visual effect, while the file extension size is kept at a low level. The research in this paper provides new ideas for balancing image privacy protection and usability, which has important theoretical and practical significance.