methods of image information hiding VPN

With the popularization of computer and Internet, the information is commonly transmitted via the Internet. However, the important information in transmission is easily intercepted by unknown persons or hackers on the Internet. Therefore, the problem of information security becomes more and more important. Information hiding [1] is usually used to protect the important information from disclosing when it is transmitting over an insecure channel. Image encryption [2-5] is one of the most important methods of image information hiding. By using image encryption algorithms, the sender encrypts the plaintext into the ciphertext. Only the authorized receiver could decrypt the ciphertext with the secret key(s) to obtain the plaintext. The image encryption methods mainly include three types, namely, pixel scrambling, pixel replacement, and combination between them. Pixel scrambling transform is very simple and easy to achieve, but the security is lower. Since the positions of the pixels are only altered and the pixel gray values are not altered, they can't resist statistical attacks effectively. Pixel replacement is that the gray values are altered by some operations such as XOR operation, but this type cannot resist plain attacks effectively. The third type is the combination of the above two types. The encryption techniques mainly include compression methodology, modern  cryptography mechanism,  chaos techniques, DNA techniques, and so on. In this paper, we summarize the main encryption algorithms and classify them based on the means.