These kinds of techniques VPN

These kinds of techniques consider the entire 2D image data as a 1D textual bit-stream and then apply any conventional cipher that has been validated in modern cryptography such as DES (Data Encryption Standard) [22], IDEA (International Data Encryption Algorithm), [23] and AES (Advanced Encryption Standard) [24] to encrypt. Figure 1 shows the principle of the modern cryptography mechanism-based encryption algorithm.The major problems of the algorithms lie in the following two aspects. One is that the encryption speed may be too slow. The other is that they do not consider the information redundancy existing in the uncompressed images. A possible way to overcome these problems is the selective encryption, i.e., partly encrypting the given image. It is useful for realizing perceptual encryption. However, these encryption methods are not sufficiently secure against known/chosen-plaintext attacks