Comparison of several wavelet coefficient confusion methods applied in multimedia encryption

Wavelet transform is widely used in image and video encoding. And some multimedia encryption methods have been proposed during the past decade. The methods based on wavelet coefficient confusion are often used in wavelet encoding. This paper proposes a coefficient confusion method based on quad-tree structure. The method, together with the other two confusion methods, is analyzed by comparing their key space, effect on compression ratio and bit rate control. And some means are proposed to strengthen the security of the encryption system. The analysis and experiment results show that the confusion method based on quad-tree confusion is of low-cost and is easy to realize bit rate control, so it is suitable for image or video encryption in network transform with real-time requirement, especially in mobile multimedia network.