Increased security does not provide comfort to paranoid people. Security with some very basic protections that we are naive to believe,that we do not need. During this time when the Internet provides essential communication between tens of millions of people and is being increasingly used as a tool for commerce, security becomes a tremendously important issue to deal with. There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting passwords. One essential aspect for secure communications is that of cryptography. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. The main theme of any successful cryptographic protocol lies on the encryption and decryption process. Now when we say this, the key used for the mentioned processes comes into picture. Это и многое другое вы найдете в книге Secure communication in p2p networks (Mohammed azharuddin Adhoni)