New Worlds: Locks . . . and How to Pick Them

(This post is part of my Patreon-supported New Worlds series.)

Anybody who’s played a rogue in Dungeons & Dragons is familiar with “thieves’ tools” as an essential item of equipment, with which one can pick locks and disarm traps. But what are these tools? And in a pre-industrial society, what do the locks that are being picked look like? (Traps are outside the scope of this essay, and honestly outside the scope of my knowledge, though now I’m thinking maybe I should read up on them for a future piece.)

For just about as long as we’ve had stores of valuable items, we’ve wanted to keep them safe. As in, we’ve found the remains of a lock in an ancient Assyrian site. I don’t know how old the evidence for lockpicking is, but it’s safe to assume the practice goes back at least as far, because criminals are like cats: if you try to keep them out of something, they’ll immediately try to get in.

If you want truly detailed specifics on different kinds of locks you can find abundant information online, but here’s a quick rundown. The warded lock (or ward lock) is the kind that produced the stereotypical old-fashioned iron key that even now is often used as a symbol for security. In that design, the slots cut into the key permit its blade to slide past obstacles or wards within the lock and rise high enough to lift the latch or trigger the mechanism that does. In the pin tumbler locks on many of our doors today (primitive forms of which go back to Egypt), springs push a series of pin pairs downward, preventing the plug or center bit of the lock from turning; when you insert the key, the notches push the pins up so that the break-point between each pair lines up with the edge of the plug and permits it to turn. A wafer tumbler lock is similar, except that the obstacles to the plug turning are each a single piece, rather than separate pairs like the pins, and a tubular lock has horizontal pins instead, which are pushed backward when you insert the key. A lever tumbler lock has flat plates that are cut in a fashion which prevents the bolt from sliding back; here the key lifts those plates out of the way, freeing the path of the bolt. And of course modern technology has given us all kinds of magnetic locks and electronic locks and other things not commonly seen in history or a D&D campaign.

But all of these locks come with vulnerabilities. You’ve probably heard the phrase “skeleton key;” that’s specific to warded locks. In that design, you don’t actually need the whole blade of the key; you only need the bit that activates the mechanism. Skeleton keys are therefore stripped-down versions of common key designs (hence “skeleton,” I presume), and you can get past many warded locks by trying different basic designs until you find the one that will turn. Therefore, rogue’s kit likely includes several types of skeleton key.

With pin tumbler locks, on the other hand, TV and movies would have you believe all you need is a hairpin. That’s not quite accurate: you need two hairpins. These locks are defeated by lifting each pin individually to the correct level where the plug can turn — but since they’re spring-loaded, you need a way to keep them in place while you go to work on the next pin. You achieve this with a torsion wrench, a second tool you slide into the bottom of the keyway and press on just hard enough to create a tiny “lip” between the plug and the body of the lock above. This lip catches the top half of each pin pair and keeps it from falling back down after you’ve lifted it high enough. There are many different kinds of picks for manipulating the pins, but which one you use often comes down to personal preference or technique. (Hairpins are suboptimal.)

Those are the most common types, followed perhaps by the lever tumbler lock — I haven’t been able to find out how old that one is, as the only history I can find for it involves an improvement (or was it the original version?) being invented in the eighteenth century. That improvement illustrates an important point, which is that, like weapons and armor, locks and lockpicking techniques have been in an arms race since Day One. For the first few thousand years of their existence, pin tumbler locks were easily defeated because there was only one pin in each position . . . so if you just lifted them all as far as you could, then the door would open. It wasn’t until the early nineteenth century that someone invented the double-acting version, where the second pin in the stack meant you had to lift each segment to a precise height. Similarly, a lever lock may include things like false gates to make you think you’ve got the lever in the right position, or a “curtain” that makes it harder to engage the cam while also picking the levers.

So modern locks and lockpicking involve a dizzying array of mechanisms designed to thwart picking, and in some cases to leave clear evidence if a lock has been picked. At the same time, YouTube offers a dizzying array of videos showing how locks can be defeated in five seconds with a rake pick mounted on a pumpkin-carving saw or a folded-up condom wrapper. (That second one is faintly NSFW due to the nature of the device the lock is on . . .) Even locks touted by their manufacturers as being extremely secure are often easily defeated by someone with the right tools. One site I looked at said that the most important element these days in making a lock unpickable is obscurity: if its security features are unfamiliar, then the attacker won’t know how to approach it.

Which raises some fun possibilities in speculative fiction. In fantasy you can often lean on magic as being the wild card that prevents someone from getting in, but I want to read the science fiction story where the thieves show up armed with the latest in high-tech electronic toys . . . only to be defeated by the strange, archaic device known as a double-acting pin tumbler lock.

Of course, at that point the intruder may just break down the door instead. Which is why next week we’ll be talking about physical security more generally.

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New Worlds: Locks . . . and How to Pick Them — 7 Comments

  1. Ross Anderson’s _Security Engineering_ has a whole chapter on physical locks and their problems, including the “if they’re determined and they have time and don’t care about alerting people, they’ll just take the door off its hinges” issue. Or break the windows, etc.

    • I’ve got that book on my wish list, yeah. And a lot of it does come down to the question of subtlety — which is why physical security is not just about barriers but also surveillance and alarms, so that you have the tradeoff of “I can get past the barrier, but if I do it this way, someone is going to notice and come after me.”

  2. One of my favorite moments in the movie Ever After is when DaVinci frees Danielle from the locked cellar by removing the door hinges. I love moments when intelligence is demonstrated by the ability to see the world differently from how we’ve been trained to see it (see also, the Doctor Who episode where Mickey is looking for a weapon, and K-9 reminds him “We are in a car.”)

    • There are so many security vulnerabilities that boil down to “we never thought about what would happen if someone did X.” Yesterday I watched a forty-five minute talk given by a guy who’s a “physical pen tester,” i.e. someone whose job is to see if he can physically penetrate what’s supposed to be a secure building or area in a building. One of the first things he says is that people assume he spends a lot of time picking locks, when in fact it’s much easier to bypass the locks entirely — by taking doors off their hinges, jimmying a badly-installed latch, or convincing people they should let him in.

  3. Pingback: New Worlds: Locks . . . and How to Pick Them - Swan Tower

  4. You neglected H’wood’s other favorite — the handcuff lock! Which points out that some locks are not for securing valuables, but for securing people.

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