Abstract: To enhance the security of digital images in transmission and solve the problems of strong correlation between image pixels and large amount of data, an image encryption algorithm based on fractional 2D- TFCDM mapping and improved Hilbert curve scrambling is proposed. Firstly, pseudo-random sequences are generated by fractional 2D-TFCDM mapping. Secondly, the plaintext image is partitioned and the subblock image is scrambled by the improved Hilbert curve. To fully weaken the correlation of the image and further improve the scrambling degree of the image, M×N Arnold transforms are performed on the image, and the parameters of each Arnold transform are changed. Finally, the XOR operation is combined with the average pixel value of the plaintext image for diffusion to obtain the final encrypted image. Three gray-scale images of 256×256 size are tested. The results show that the correlation between the pixels of the encrypted image is weak, and the encrypted image has good encryption effect, good statistical characteristics and strong anti-jamming ability, it can resist all kinds of common attacks effectively, and has good practical value in image encryption. 

Key words: image encryption, fractional 2D-TFCDM mapping, improved Hilbert curve, block scrambling, Arnold transform