At the time of their initial conception, most common network protocols, such as the Transmission Control Protocol (TCP) and the Internet Protocol (IP), were not developed with security concerns in mind. When DARPA launched the first steps towards the packet-switched network that gave birth to the modern Internet, engineering efforts were targeted towards the challenges of guaranteeing reliable communication of information packets across multiple stations from the source to its final destination. The reasons for this are not difficult to identify: the deployed devices were under the control of a few selected institutions, networking and computing technology was not readily available to potential attackers, electronic commerce was a distant goal, and the existing trust among the few users of the primitive network was sufficient to allow all attention to be focused on getting a fully functional computer network up and running.

A few decades later, with the exponential growth in number of users, devices, and connections, issues such as network access, authentication, integrity, and confidentiality became paramount for ensuring that the Internet and, more recently, broadband wireless networks could offer services that are secure and ultimately trusted by users of all ages and professions. By then, however, the layered architecture, in which the fundamental problems of transmission, medium access, routing, reliability, and congestion control are dealt with separately at different layers, was already ingrained in the available network devices and operating systems.