As some of you know, I’ve always been pretty critical of quantitative risk frameworks for information security, especially the Annualized Loss Expectancy (ALE) model taught in most of the infosec books. It isn’t that I think quantitative is bad, or that qualitative is always materially better, but I’m not a fan of funny math.
Let’s take ALE. The key to the model is that your annual predicted losses are the losses from a single event, times the annual rate of occurrence. This works well for some areas, such as shrinkage and laptop losses, but is worthless for most of information security. Why? Because we don’t have any way to measure the value of information assets.
Oh, sure, there are plenty of models out there that fake their way through this, but I’ve never seen one that is consistent, accurate, and measurable. The closest we get is Lindstrom’s Razor, which states that the value of an asset is at least as great as the cost of the defenses you place around it. (I consider that an implied or assumed value, which may bear no correlation to the real value).
I’m really only asking for one thing out of a valuation/loss model:
The losses predicted by a risk model before an incident should equal, within a reasonable tolerance, those experienced after an incident.
In other words, if you state that X asset has $Y value, when you experience a breach or incident involving X, you should experience $Y + (response costs) losses. I added, “within a reasonable tolerance” since I don’t think we need complete accuracy, but we should at least be in the ballpark. You’ll notice this also means we need a framework, process, and metrics to accurately measure losses after an incident.
If someone comes into my home and steals my TV, I know how much it costs to replace it. If they take a work of art, maybe there’s an insurance value or similar investment/replacement cost (likely based on what I paid for it). If they steal all my family photos? Priceless – since they are impossible to replace and I can’t put a dollar sign on their personal value. What if they come in and make a copy of my TV, but don’t steal it? Er… Umm… Ugh.
I don’t think this is an unreasonable position, but I have yet to see a risk framework with a value/loss model that meets this basic requirement for information assets.