What Are Attack Trees?

Attack trees are a way of visually representing computer security threats in a branching model to determine which threats are most likely and how to effectively block threats. Security expert Bruce Schneier proposed the attack tree model, and it is widely used in a range of settings. Information technology staff members and security consultants can use this among many methods to find weak points in a system and develop a plan for addressing them.

In attack trees, security specialists detail all of the potential ways to attack a system. This method is used primarily in computer security, but it also can be applied to other topics, such as household security. In a household where something valuable is stored in the bedroom, for instance, an attack tree would explore different ways people could access that item, from breaking in through the bedroom window to establishing a friendship and taking advantage of the access provided at a dinner party to steal the object.

The goal of the attack, such as accessing confidential files or stealing money, is the root of the attack tree. Each branch represents a different method for accomplishing that goal, and the branches might leaf out in a number of directions, with various options for enacting those methods. To intercept email, for instance, someone could befriend a system administrator who has high-level passwords or hack into the system to grab a copy of emails as they pass through a given server.

With a graphical representation of possible system exploits, it is possible to assign values of difficulty to various items on the chart. Attack trees can help security professionals determine where the weak points lie, versus areas of high security that probably do not need additional measures. Costs also can be a consideration; a method might be very easy but so expensive that the cost creates a significant barrier, and thus it might be a lower priority than a more difficult but very cheap option. Attack trees can help security professionals set priorities when it comes to improving security and evolving to stay ahead of threats.

Creativity is critical in the creation of attack trees. Security professionals must "think outside the box" when it comes to exploring possible exploits that might be used to access a secure system. A lack of foresight could lead to missing an obvious issue, such as the possibility that someone could walk into an unlocked room and simply steal a server that contains the desired confidential data.