TPE-DNA: Approximate thumbnail preserving encryption based on difference expansion and DNA encoding

As cloud storage technology evolves, a growing user base is uploading client-acquired images to the cloud. However, the storage of unencrypted images on these platforms raises concerns regarding unauthorized data mining and the potential for theft by malicious third parties. Thumbnail preservation encryption (TPE) has been introduced to address the balance between privacy and usability of images stored in the cloud. Existing approximate TPE methods, however, are prone to more information leakage from cipher images and often fail to achieve perfect reconstruction of the plain images. This paper introduces an enhanced approximate TPE strategy that integrates DNA encoding with differential expansion, ensuring that the information exposed by the cipher image is limited exclusively to the thumbnail of the plain image, without compromising additional details. The DNA encoding rules, along with its associated operations and decoding rules, are governed by a piecewise linear chaotic map, with the encryption key derived from the hash value of the plain image to bolster system security. The application of differential expansion facilitates reversible data hiding, enabling the decryption algorithm to accurately reconstruct the plain image without loss. Simulation outcomes confirm the efficacy and reliability of the proposed approximate TPE scheme.