Ultimately, computer system security may be reduced to the physical security of the components of the computing system. This introduction focuses on the security of systems which use Internet technology. Such systems themselves are often distributed over a geographic area and are accessed by users which are potentially at any geographic location.
How the Internet works is a very large subject and many resources are available for study [Come 95,Come 96,Come 97,Come 98]. A brief description of how the Internet works is given to provide a context for the following sections.
An internet is a collection of interconnected networks. The interesting part of internet technology lies in the methods used to connect the individual networks in an internet. The simplest method of interconnection of two networks is to have a single machine which contains a network interface on each network. Such a machine can function as an information router, forwarding data from one network to another.
It is customary to subdivide files into reasonably small sized blocks, called packets, so that the transmission of a large file from one network station to another does not unfairly monopolize the bandwidth (transmission capacity) of the network media (cable).