Sitting at RSA Europe, listening to Bruce 'BT' Schneier's keynote. Even though the picture implies handwaving, there was really none: it was Mr. Schneier's usual good stuff - nothing new though, but it was nice to see the man in real life.
In the beginning of his keynote, Schneier discussed whether safety is part of security or vice versa, and (being a security guy) decided that security is a superset of the two. This gives me a rare excuse to blog what I've been lately thinking about the difference between the two, and quality. I try to be brief.
Anyone who has stumbled upon quality engineering knows a bunch of varying definitions for quality. Usually, the definition goes along the lines that if a product fulfills its defined specifications, it is of high quality. (Hence, even a crappy product can have high quality if it was specified to be crap. There are other definitions such as those defining quality as the lack of negative externalities, but I am not using them here, although I like thinking in externalities.)
Then, if you have a look at various papers trying to define security, it is often defined as a system that fulfills its specifications in a hostile environment and under attack - or failing that, fails gracefully. So, security builds on the definition of quality and extends that with a notion of robustness.
What I believe is the key finding here is that safety is also often defined through a system that fulfills its specifications while misused in any foreseeable way - or again, fails gracefully. (What is important here is to note that safety engineering looks at purposeful, if not outright malicious, misuse, not only accidental misuse - which was the reason why Schneier classified safety as a subset of security.)
Therefore, both security and safety are special cases of quality. What's the difference? In most cases, security engineering tries to protect assets that have a (relatively) easily defined financial value, such as data confidentiality or system accessability. Safety, on the other hand, aims to protect wetware, which (even though many economists try) is very hard to place a dollar value on.
There are some crossovers, though. Obviously for example fire damage to physical assets (which is addressed by safety engineering) is easily transferred into megabucks, but what is interesting that security engineering also has areas such as privacy that may affect the flesh-and-blood target in ways that cannot easily be given a financial valuation.
Anyway, this is where I currently am with my thoughts on the relation of security and safety. I'll get back to this when I have thought more of it.