Threat Modeling

CHAPTER 4Attack Trees

As Bruce Schneier wrote in his introduction to the subject, “Attack trees provide a formal, methodical way of describing the security of systems, based on varying attacks. Basically, you represent attacks against a system in a tree structure, with the goal as the root node and different ways of achieving that goal as leaf nodes” (Schneier, 1999).

In this chapter you'll learn about the attack tree building block as an alternative to STRIDE. You can use attack trees as a way to find threats, as a way to organize threats found with other building blocks, or both. You'll start with how to use an attack tree that's provided to you, and from there learn various ways you can create trees. You'll also examine several example and real attack trees and see how they fit into finding threats. The chapter closes with some additional perspective on attack trees.

Working with Attack Trees

Attack trees work well as a building block for threat enumeration in the four-step framework. They have been presented as a full approach to threat modeling (Salter, 1998), but the threat modeling community has learned a lot since then.

There are three ways you can use attack trees to enumerate threats: You can use an attack tree someone else created to help you find threats. You can create a tree to help you think through threats for a project you're working on. Or you can create trees with the intent that others will use them. Creating new trees for general use is challenging, even ...