(Hmm, it's time for my bi-yearly DST rant. Here goes.)

One of the many lame excuses given for daylight savings time is that it cuts down on crime, since more crime occurs after dark. This might be true of violent crime, since fewer people will be out after dark, but what about other crimes? It's interesting to think about ways that criminals could exploit possible confusion, broken data-keeping, etc around the discontinuity caused by daylight saving time changes.

Q: Where were you on the night of October 30th 2005 between 1 and 2 am?
A: Well, I was at this bar with my friends that whole hour, I have an alibi.

Ok, that's a bit easy to catch (although there's a real life story of a similar trick being used to avoid manslaughter charges), but what about more subtle cheats? All-night workers last night could pretty easily cheat their employer out of an hour's pay, for 2 am to 3 am. Conversely, if they're not careful, their employer might cheat them next fall. The only people I've ever heard discuss this are all-night radio jockies, but those guys love to hear themselves talk enough that an extra hour to do it in is not a problem to them. I'll bet that a fry cook would rather get some extra sleep.

But this is still small, er, potatoes. For really nice exploits you have to take advantage of explicit failures of technology. One such failure is in the way Windows manages daylight savings changes. Unlike Unix, which elegantly flips between two time zones, such as EST and EDT, but still keeps counting each second from Jan 1st 1970, Windows actually changes the clock.

Despite a brainwashed nation that has been taught that moving the hands back or forward is the right thing to do, in the world of computers, it's bloody stupid. A google for "daylight savings windows bug" turns up a million or so hits caused by this behavior, describing problems like this:

Windows reports erroneous file modification times, which change according to daylight savings.

And this:

When Windows NT automatically adjusts for daylight savings time, the times on files on Windows NT file system (NTFS) partitions and the events in the event logs are retroactively shifted by one hour, even though the files and event records were created before the daylight savings time change.

Now, I think there's all kinds of potential for criminal fun in file modification timestamps being wrong, and log files having innaccurate times. Throw in the odd backup that fails to run due to being scheduled to run at a time that never exists, and the time slip begins to seem like an ideal time for shady activities. (And a very poor time to be in a hospital hooked up to windows-controlled life-support equipment. Double-dose of morphine, anyone?)

True story: A year ago I was at a fancy hotel, which was burgalarised. This hotel had electronic locks on the doors, which logged when the doors were opened, and by whom. The techies whose possessions were stolen were able to use this information, plus what they knew about when the theft must to have occurred, to narrow down the suspects to one or two hotel employees who opened the door at the right time. If those logs went to a machine running windows and the theft occurred during England's change to DST, it's quite possible the logs would have been useless.

It's not too far from this kind of scenario to something suitable as an entry in Schneier's movie-plot terrorist threats contest. Although it's worth noting that the airline industry deals with timezone changes all the time, so if they have any sense, the DST change is not an exceptional event for them. One of the interesting things about plane travel to me is the way a plane in flight between timezones is a space in which no defined time zone exists. But I digress..

I suspect that the real source of fetile bugs related to DST is in the interstices between operating systems where programs have to deal with the peculuarities of multiple OSes to behave correctly. Such as this unison/linux/windows bug. Put different systems together and they fail in myriad ways, and there's room in the cracks for criminal activity.

Thing is, I don't have a very good criminal mind, at all, so if any of the slightly weak approaches I've detailed above is feasable, it seems to me there must be some terrific scams, techniques, etc, that people who are good at thinking that way, and have the right motivation can use.