How Lock Picking Works Click here to print this article.
Keys are one of the most basic and essential machines we use every day.
Most people carry five to 10 keys with them whenever they go out. On your key ring you might have several keys for the house, one or two more for the car and a few for the office or a friend's house. Your key ring is a clear demonstration of just how ubiquitous lock technology is: You probably interact with locks dozens of times every week.
The main reason we use locks everywhere is that they provide us with a sense of security. But in movies and on television, spies, detectives and burglars can open a lock very easily, sometimes using only a couple of paper clips. This is a sobering thought, to say the least: Is it really possible for someone to open a lock so easily?
In this edition of stuff.dewsoftoverseas.com, we'll look at the very real practice of lock picking, exploring the fascinating technology of locks and keys in the process.
A standard deadbolt lock. When you turn the key, the bolt slides into a notch on the door frame.
Think about the normal dead-bolt lock you might find on a front door. In this sort of lock, a movable bolt or latch is embedded in the door so it can be extended out the side. This bolt is lined up with a notch in the frame. When you turn the lock, the bolt extends into the notch in the frame, so the door can't move. When you retract the bolt, the door moves freely.
The lock's only job is to make it simple for someone with a key to move the bolt but difficult for someone without a key to move it. In the next section, we'll see how this works in a basic cylinder lock.
A cylinder deadbolt lock, in the open position (top) and the locked position (bottom)
The pins in a pin-and-tumbler lock when no key is inserted (top) and when the correct key is inserted (bottom). When the correct key is inserted, all of the pins are pushed up to the same level, flush with the shear line.
This simple puzzle design is very effective. Since the pins are hidden inside the lock, it's fairly difficult for most people to move the plug without the correct key. But, with a lot of practice, it is possible to solve the puzzle by other means. In the next section, we'll see how a locksmith goes about picking this sort of lock.
Another common type of cylinder lock is the wafer-tumbler lock. These work the same basic way as pin-and-tumblers, but they have thin wafer-shaped tumblers rather than pins. You pick the wafers exactly the same way you pick pins -- in fact, it is a little bit easier to pick wafer-tumbler locks because the keyhole is wider.
Some designs use single wafers rather than wafer pairs. These wafers are spring loaded so that they extend out of the cylinder, binding with the lock housing. The wafers have a hole in the center that the key will fit through. The correct key pulls the wafers down just enough so that they are all retracted into the plug. The incorrect key will either pull the wafers down only part of the way or will pull them down too far, causing them to extend out the other side of the plug.
A wafer-tumbler cylinder lock
Double-wafer locks have wafer tumblers on both ends of the plug. To pick these locks, you work the wafers on both sides as you apply pressure with the tension wrench. Wafer locks are found in most filing cabinets, lockers and cars, as well as in many padlock designs.
Tubular locks offer superior protection to pin-tumbler locks and wafer-tumbler locks, but they are also more expensive. Instead of one row of pins, tubular locks have pins positioned all the way around the circumference of the cylinder plug. This makes them much harder to pick. Conventional lock-picking techniques usually don't work on this type of lock.
Some pin-tumbler locks have modified pins that make picking more difficult. In the most common variation, the upper pins have a mushroom-shaped head. This odd shape causes the plug to shift early, before you have actually pushed the top pin all the way up. This makes it more difficult to put the pins in position. It also makes it very hard to get an accurate feel for what's going on inside the lock.
Tools of the Trade
Experienced lock-pickers can make do with a few paper clips and a basic screwdriver, but the job is a lot easier when they have the proper tools. A basic lock-picking kit contains a tension wrench and several different picks. The picks differ mainly in the shape of their heads. Different heads are suited for particular sorts of locks and particular picking techniques.
Some lock-pickers will also use an electric pick gun. A pick gun basically consists of one or more vibrating, pick-shaped pieces of metal. You insert these long pieces of metal into the lock, just as you would insert a pick. As the metal pieces vibrate, they push the pins up. This works something like raking a lock. You turn the gun as the picks vibrate, so you catch some of the pins at the shear line. Sometimes these devices will open the lock in a matter of seconds, and sometimes they won't work at all. Most recreational lock-pickers avoid these devices because they take the puzzle-solving element out of the process.
The shafts of a pin-and-tumbler lock contain several springs and tiny pins.
In this basic six-pin lock set, you can see how this re-keying works. When you open up the shafts in the cylinder and empty them out, you have six springs and 12 tiny pins. All of the upper pins are exactly the same size. The remaining six pins (the lower pins) will be of various lengths to match up with the notches on the key.
The right combination of pins lines up perfectly with the notches in the key.
The process of re-keying a lock is very simple. The locksmith removes all of the pins from the cylinder. Then, drawing from a collection of replacement pins of various sizes, the locksmith selects new lower pins that fit perfectly between the notches of the key and the shear line. This way, when you insert the new key, the lower pins will push all the upper pins just above the shear line, allowing the cylinder to turn freely. (This process may vary depending on the particular design of the lock).
It doesn't matter how long the upper pins are (since they all rest above the shear line when the key is inserted), so the locksmith simply re-inserts the six original upper pins that came with the lock. And that's all there is to re-keying. The entire process takes only a few minutes.
Some locks are designed to work with two different keys. The change key will open only that specific lock, while the master key will open that lock and several others in a group. In these locks, a few of the pin pairs are separated by a third pin called a master wafer or spacer.
When three pins are combined in a shaft, there are two ways to position the pins so they open the lock. The change key might raise the pins so that the shear line is just above the top of the master wafer, while the master key would raise the pins so the shear line is at the bottom of the master wafer. In both cases, there is a gap at the shear line and the key is able to turn.
In this lock design, the lowest pin would be the same length in each lock in the group, but the master wafer would vary in length. This lets one person, say a building manager, access many different locks, while each individual key-holder can open only his or her own lock.