tworks. We will discuss the applicability on network-attached devices, which support multiple par- allel high-speed sessions over an insecure network such as the Internet or the WAN. Three fundamental types of network applications require security-related processing: Virtual private networks (VPNs). Electronic transactions. Wireless communications. VPN is a generic term that describes several unrelated technologies and approaches toward building and managing a communication network between computers. This is done in a way that the users of the VPN have the continuous impression of communicating with each other over a closed, private, and secure network that is inaccessible to unauthorized outsiders. The word impression is a key term here as a VPN is not deployed over physically private links; it is deployed over a public and insecure network instead. VPNs are created in two fundamental ways: By using network-induced methodologies and techniques such as the Multiprotocol Label Switching (MPLS) approach, where sets of labels are created for specific VPNs that the carrier sets up and manages for the customer. These labels are attached to all legitimate packets. On their way to a des- tination, these packets are switched and routed appropriately by the core network MPLS-enabled routers/switches in such a way that no physical access is given to packets originating from and des- tined to users who do not belong to a specific VPN. By applying cryptographic techniques, especially encryption and authentication, on the payload of packets. A security context is created that allows the generation of packets, which can still be routed by the core network like all regular packets (as their address headers are not encrypted and there- fore are comprehensible by the routers), but whose payload is encrypted in such a way that only the intended recipient can decipher and therefore recover the original payload content. The first technique among these two does not require cryptographic processing because the net- work infrastructure