If there’s one problem in cloud computing you have to revisit regularly, it’s security. Security concerns, real or imagined, must be squarely addressed in order to convince an organization to use cloud computing. One highly useful technique for analyzing security issues and designing defenses is threat modeling, a security analysis technique long used at Microsoft. Threat modeling is useful in any software context, but is particularly valuable in cloud computing due to the widespread preoccupation with security. It’s also useful because technical and non-technical people alike can follow the diagrams easily. At some level this modeling is useful for general cloud scenarios, but as you start to get specific you will need to have your cloud platform in view, which in my case is Windows Azure.
To illustrate how threat modeling works in a cloud computing context, let’s address a specific threat. A common concern is that the use of shared resources in the cloud might compromise the security of your data by allowing it to fall into the wrong hands—what we call Data Isolation Failure. A data isolation failure is one of the primary risks organizations considering cloud computing worry about.
To create our threat model, we’ll start with the end result we’re trying to avoid: data in the wrong hands.
Next we need to think about what can lead to this end result that we don’t want. How could data of yours in the cloud end up in the wrong hands? It seems this could happen deliberately or by accident. We can draw two nodes, one for deliberate compromise and one for accidental compromise; we number the nodes so that we can reference them in discussions. Either one of these conditions is sufficient to cause data to be in the wrong hands, so this is an OR condition. We’ll see later on how to show an AND condition.