Real-world communications over the Internet are becoming more and more widespread. In particular, commercial transactions, which deserve a high level of security, often take place over our beloved--though insecure --packet network. Furthermore, VPNs (virtual private networks, i.e., private networks deployed over a public packet infrastructure) are definitely emerging as the solution of choice for the interconnection of distant offices belonging to the same company.

Unfortunately, IP packets carry our precious data in a clear form that is easily intercepted by malicious users. Doing this on a common Linux-based PC is actually quite easy, provided that one has access to the network segment over which the desired packets are traveling.

Several different solutions exist that allow us to cope with this problem, each operating at a different level of abstraction. In this article, we will discuss the differences between and purposes of application-level security, socket-level security and network-level security.

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