Active X components. Since the proxy functionality includes analysis of the application layers, it must have separate programs for each application, such as SMTP (e-mail), HTTP (web applications), FTP, Real Audio and Telnet. Security With increasing voice over IP traffic there is a need to mix VoIP and ordinary IP data traffic. Since the data traffic should pass firewalls, there is a need for firewalls supporting the SIP protocol used for mixed traffic. 6.10 CONFIDENTIALITY: ENCRYPTION AND KEY MANAGEMENT 6.10.1 BASIC CRYPTOGRAPHY The first solution to protect IP packets is to simply encrypt the packet. This guarantees that no one can read the content. However, we must remember that encryption does not prevent modification of the packet. It means that it provides confidentiality but not integrity. For example, if a packet consists of just one bit of data: 0 or 1, then it is 0 or 1 in encrypted form and someone can change the bit. In this example, the modifier can be quite sure that he can change the message by changing the bit. In most cases this is not that trivial, but it is still possible to garble the message SO that the receiver does not notice. Another problem with plain encryption is that you cannot encrypt headers of the packet for communication reasons, however, the modifier can still often successfully attack by modifying headers. The two main purposes of cryptography are: to maintain the confidentiality of messages; and to guarantee the integrity of messages. Confidentiality is provided by encryption, whereas integrity can be provided by authen- tication codes or digital signatures. A fairly common standard for cryptography is called pretty good privacy (PGP). You are beautiful You are beautiful Key 1 Key 2 Public channel 17%g9+a# Message Encryption Decryption Message Ciphertext 17%g9+a# Eavesdropper Figure 6.19 The idea of confidentiality Understanding Changing Telecommunications - Building a Successful Telecom Business PGP was initially created by one person. It has become widespread because it is a f