Security Requirements

Security in computer systems consists broadly of the following:

• Establishing a base of things that we trust, which constitute little or no risk those things that we do not have to worry about

• Taking precautions that protect us from either malicious or accidental acts

• A combination of these things

For example, on a personal computer at home, members of the family are allowed to use the computer they can run software, open or modify documents, and may be allowed to change the configuration by modifying settings or installing new software. If there are children in the family, a set of restrictions may be applied to safeguard the system, the information, or the children themselves: they are given a set of programs they can run, they may not be allowed to install new software, or they may need to be supervised while surfing the Internet. If the computer is connected to the Internet, it is likely that the system is safeguarded by additional constraints, such as preventing external users from accessing the system at all through the use of a firewall.

In this example, as in many other scenarios, there are two significant components that work together to build secure systems identity and availability. Being able to identify a user permits us to define what that user is allowed to do. We can make information or system resources available to users in a way that does not compromise security. Typically, this is performed by authorizing trusted identities to use system resources.

In networked systems, where the participants are often unknown to or separated from one another, authenticity and integrity make up a large part of the equation for a secure system. Authenticity proves the identity and origin of something, whereas integrity provides the assurance that it has not been altered.

In both cases, the issue of confidentiality is almost always important. Confidentiality ensures that information or resources are only revealed to approved parties.

Finally, as users or systems interact with one another, it often becomes necessary for them to prove that an act occurred or a commitment was made. Nonrepudiation is the property of a system that enables it to do this.

Modern computing systems include mechanisms to meet these needs. However, because the Internet is a system of independent, interconnected systems, for the most part security has been localized to the systems themselves or the intranets they are connected to. As they begin to work in a peer-to-peer fashion, the systems will have to work together to provide scaled-up secure services between themselves.