Security Patterns in Practice: Designing Secure Architectures Using Software Patterns

CHAPTER 2

Patterns and Security Patterns

Each problem that I solved became a rule which served afterwards to solve other problems.

René Descartes, Discourse on Method

2.1 What is a Security Pattern?

A security pattern describes a solution to the problem of controlling (stopping or mitigating) a set of specific threats through some security mechanism, defined in a given context [Sch06b]. This solution needs to resolve a set of forces, and can be expressed using UML class, sequence, state and activity diagrams. A set of consequences indicate how well the forces were satisfied; in particular, how well the attacks were handled. A security pattern is not directly related to a vulnerability, but is directly related to a threat. The specific threat may be the result of one or more vulnerabilities, but the pattern is not intended to repair the vulnerability, but to stop or mitigate the threat.

Figure 2.1 shows a generic diagram illustrating the effect of the use of security patterns as deployed in a specific architecture. The sequence diagrams on the left of the figure indicate possible attacks (threats) to a context defined by a deployment diagram. For example, a context may include distributed systems, distributed systems using web services, or operating systems. Typical objects in the deployment diagram (O1, O2, O3) are instantiated from classes in the application class diagram (Classes A, B and C respectively for this example). SP₁ denotes the security pattern solution that is able ...