The main idea of the image VPN

The main idea of the image transform domain-based image encryption is that the digital image is operated in the transform domain. Then the pretreated information is encrypted by using other techniques especially chaos. The pretreatment techniques include fractional Fourier transform (FRT) [25-30], discrete wavelet transform (DWT) [31,32], and so on. The encryption method in which the digital image is firstly operated in the transform domain is more effective than the one in which the digital image is only encrypted in the spatial domain. This is because it is necessary to consider the particularity and the redundancy of the image data, the reliability of encrypting the mass data, and the influence of other operations such as loss compression, format conversion, and so on. The image transform domain-based encryption algorithm considers the above problems adequately and owns higher applicability. However, this method owns only computational security. It is possible that this algorithm can be broken by using the computers owning great and striking computational power.