A New Thumbnail Preserving Encryption Scheme

Cloud services can store a large number of images, but cannot protect the security of user privacy. The traditional image encryption scheme improves the privacy security, but reduces the visibility of the image, which makes the image invisible in the cloud service. To maintain both cloud storage security and visual usability, Tajik et al. proposed a thumbnail preserving encryption (TPE) scheme so that the encrypted image is presented as a low-resolution version of the plaintext image. However, this scheme only scrambles and replaces pixels, and has low security. Aiming at the problem of low security of this method, this paper proposes a new thumbnail preserving encryption scheme (New-TPE). The plaintext image information is used as part of the key to construct the correlation between the encryption process and the plaintext image; The optimal random value is selected from multiple random values and is added to the pixel value replacement process, which increases the degree of variation of pixel values before and after the replacement and reduces the correlation between adjacent pixels; The simulated annealing idea is introduced to select the optimal scrambling sequence within the range; A displacement function scrambling method is proposed to reduce the correlation between adjacent pixels. The experimental results show that the proposed scheme has higher security and a better balance between image privacy and security.