Security engineers see the world differently than other engineers. Instead of focusing on how systems work, they focus on how systems fail, how they can be made to fail, and how to prevent–or protect against–those failures. Most software vulnerabilities don’t ever appear in normal operations, only when an attacker deliberately exploits them. So security engineers need to think like attackers.People without the mindset sometimes think they can design security products, but they can’t. And you see the results all over society–in snake-oil cryptography, software, Internet protocols, voting machines, and fare card and other payment systems. Many of these systems had someone in charge of “security” on their teams, but it wasn’t someone who thought like an attacker.Â Â
There’s an interesting parallel between this statement and how most software quality is handled. Quality and Security are similar. In fact, I see security as a very specific subset of quality-mindedness. Certainly both require the same mindset to ensure – rather than thinking merely “how will this work”, a quality-focused person will also, or perhaps alternately think: “how might this be breakable”. From this simple change in thinking flows several important approaches
- Constraint-based thinking (as opposed to solution based thinking): allows an architect/developer to conceive of the set of possible solutions, rather than an enumeration of solutions. By looking at constraints, a developer implements the lean principle of deciding as late as possible, with as full information as possible.
- Test-First: As one thinks of how it might break, scenarios emerge that can form the basis of test cases. These cases form a sort of executable acceptance criteria
- Lateral Thinking: The constraint+test approach starts to get people into a very different mode, where vastly different kinds of solutions show up. The creative exercise of trying to break something provides insights that can change the whole approach of the system.
Â Schneier goes on to ponderÂ
This mindset is difficult to teach, and may be something you’re born with or not. But in order to train people possessing the mindset, they need to search for and find security vulnerabilities–again and again and again. And this is true regardless of the domain. Good cryptographers discover vulnerabilities in others’ algorithms and protocols. Good software security experts find vulnerabilities in others’ code. Good airport security designers figure out new ways to subvert airport security. And so on.Â Â
Â Here again – I think it’s possible to help people get a mind-set about quality, but some do seem to have a knack. It’s important to have some of these people on your teams, as they’ll disturb the waters and identify potential failure modes. These are going to be the ones who want to “mistake proof” (to borrow Toyota’s phrase) the system by writing more unit tests and other executable proofs of the system. But most importantly (and I can personally testify to this) it is critical that people just write more tests. It is a learned skill to start to think of “how might this fail” until it becomes a background mental thread, always popping up risk models.A related concept is Demmings’ “systems-thinking”, which, applied to software quality, causes one to start looking at whole ecosystems of error states. This is when fearless re-factoring starts to pay off, because the elimination of duplication allows one to catch classes of error in fewer and fewer locations, where they’re easier to fix. There are many and multifarious spin-off effects of this inverted questioning and the mindset it generates. Try it yourself. When you’re writing code, ask yourself how you might break it? What inputs, external state, etc. might cause it to fail, crash, or behave in odd ways. This starts to show you where you might have state leaking into the wild, or side-effects from excessively complex interactions in your code. So quality focus can start to improve not only the external perception of your product, but also its fitness to new requirements by making it more resilient and less brittle. Cleaner interactions and less duplication allow for much faster implementation of new features.I could go on, but I just wanted to convey this sense of “attitude” or “mindset,” over mere technique. Technique can help you get to a certain level, but you have to let it “click”, and the powerful questions can sometimes help.