Along with the rapid development of network technology

digital images

as the main carriers of information expression

have been widely used in commercial

economic

aerospace

military

defense

and other fields. However

they entail the risk of information leakage in image storage and transmission. The security problem of image data must be solved effectively. Moreover

some image algorithms have poor self-adaptability and weak keys. This paper proposes an adaptive encryption algorithm of blocking diffusion based on the ChaCha20 hash operation (BDCH) to solve these issues. First

BDCH translates a plain image into a square image by filling the chaotic sequences that are generated using a piece wise linear chaotic map (PWLCM). Second

a 512-bit initial key and the sum of plain-image pixels are used as input tothe ChaCha2 hash operation to generatean initial 8×8 hash matrix. The matrix is then combined with a chaotic sequence through a PWLCM map

whose inputs consist ofthe average of the initial hash matrix

initial key

and normalized average of plainimage pixels to form an 8×8 hash key matrix. Third

permutation and diffusion are simultaneously implemented on the whole image using an Arnold map and PWLCM.The image is then segmented into an 8×8 array of non-overlapping blocks. In the end

the hash key matrix is used to diffuse the blocks with two rounds and to finish the encryption process. The BDCH algorithm can solve the issue of weak keys by co-producing a hash key matrix using the initial hash matrix and the PWLCM chaotic sequences

thereby increasing the key space. Plain-image information is also a part of the input keys of ChaCha20

Arnold map

and PWLCM chaotic map

thereby enhancing self-adaptability and plain text sensitivity. The simulation results and performance analysis on seven gray and color images show that the BDCH algorithm achieves a larger key space

higher sensitivity to both key and plainimages

and faster encryption speed. The BDCH algorithm

which combines simultaneous permutation

diffusion

and hash key matrix blocking nonlinear diffusion

can effectively resist various attacks and is suitable for all kinds of grayscale and color images.