High-efficiency and visual-usability image encryption based on thumbnail preserving and chaotic system

Privacy concerns may be caused after uploading images into image hosting platforms. For traditional image encryption, images with rich content and meaning are transformed into noise-like encrypted images without any visual information, which can protect privacy from infringement but at the expense of visual usability. Recently, thumbnail-preserving encryption (TPE) was proposed to balance privacy and usability by preserving the thumbnail unchanged after encrypting. On the other hand, a large number of pseudo-random functions with high computational complexity are utilized in the existing TPE schemes, which makes the encryption and decryption time too long. Motivated by this, we deeply analyze the characteristics of TPE and propose a scheme to organically combine TPE with chaotic systems, which reduces the encryption and decryption time exponentially besides ensuring security. The experiments show that the time cost is reduced dozens of times as well as relatively stable compared with the existing schemes. Meanwhile, encrypted images have high visual quality and can resist some commonly used attacks including differential attack and face detection and the balance between privacy and visual usability is achieved.