Thumbnail-preserving encryption by sum-preserving within blocks based on exponential chaotic map

With the dramatic increase in the number of images in recent years, more and more images are stored in the cloud space. Traditional image encryption only guarantees the confidentiality of the image without taking into account the availability of the image, which greatly weakens the convenience of cloud storage. Thumbnail-preserving encryption (TPE) is used to break this deadlock, which can take into account the availability and confidentiality of the image at the same time. However, the existing multi-pixel TPE scheme has poor temporal performance, and the 2-pixel TPE scheme requires multiple encryptions to ensure the confidentiality of the image. Due to the excellent properties of chaotic maps, in this paper, a 3-pixel thumbnail-preserving encryption algorithm based on exponential chaotic map is proposed by combining chaotic map with TPE scheme. The experimental results show that the proposed chaotic map has good chaotic properties, the TPE scheme has better temporal performance and higher security, which is somewhat competitiveness.