Security Mechanisms in Network Protocols

This paper describes few, popular security mechanisms used by network protocols. Many of protocols were designed with assumption that there are no intruders, that every device in the network should trust to other devices and users. Such assumption was true many years ago. The network situation has been changed for last ten years and we should realize that some properties of existing protocols may be abused. Basic level of trust is necessary, but if this level is too high, standard protocols may be abused. This paper is also an attempt to create some basic rules and requirements which should be met by secure network protocols.