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 HowStuffWorks,
we'll look at the very real practice of lock picking,
exploring the fascinating technology of locks and keys in the
process.
Under Lock and Key Locksmiths define
lock-picking as the manipulation of a lock's components to
open a lock without a key. To understand lock-picking, then,
you first have to know how locks and keys work.
Locks come in all shapes and sizes, with many innovative
design variations. You can get a clear idea of the process of
lock picking by examining one simple, representative lock.
Most locks are based on fairly similar concepts.
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 Pin is Mightier than the Sword The most
common lock design is the cylinder lock. In the
cylinder lock, the key turns a cylinder, or plug, which
turns an attached cam (see illustration below). When the plug
is turned one way, the cam pulls in on the bolt and the door
can open. When the plug turns the other way, the cam releases
the bolt and the spring snaps it into place so the door cannot
open. In a deadbolt lock, there is no spring mechanism -- the
turning cylinder slides the bolt forward and backward. A
deadbolt is more secure than a spring-driven latch since it's
much harder to push the bolt in from the side of the door.
Inside a cylinder lock, there is a sort of puzzle, which
only the correct key can solve. The main variation in lock
designs is the nature of this puzzle. One of the most common
puzzles -- and one of the easiest to pick -- is the
pin-and-tumbler design.
The main components in the pin-and-tumbler design are a
series of small pins of varying length. The pins are
divided up into pairs. Each pair rests in a shaft running
through the central cylinder plug and into the housing around
the plug. Springs at the top of the shafts keep the pin pairs
in position in the plug. When no key is inserted, the bottom
pin in each pair is completely inside the plug, while the
upper pin is halfway in the plug and halfway in the housing.
The position of these upper pins keeps the plug from turning
-- the pins bind the plug to the housing.
Click on the buttons to see
what happens when you insert the wrong key in a lock (top) as
compared to the correct key (bottom).
When you insert a key, the series of notches in the key
push the pin pairs up to different levels. The incorrect key
will push the pins so that most of the top pins are still
partly in the plug and partly in the housing. The correct key
will push each pin pair up just enough so that the point where
the two pins come together lines up perfectly with the space
where the cylinder and the housing come together (this point
is called the shear line). To put it another way, the
key will push the pins up so that all of the upper pins are
inserted completely in the housing, while all of the lower
pins rest completely in the plug. Without any pins binding it
to the housing, the plug moves freely, and you can push the
bolt in and out.
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.
The Weakest Link In the last section, we saw
that the correct key will position the pins in a
pin-and-tumbler lock so that all of the lower pins rest in the
cylinder plug and all of the upper pins rest in the cylinder
housing. To pick this sort of lock, you simply move each pin
pair into the correct position, one by one.
There are two main elements involved in the picking
process:
Picks - Picks are long, thin pieces of metal that
curve up at the end (like a dentist's pick). They are used
to reach into the lock and push the pins up
Tension wrench - Tension wrenches come in all
shapes and sizes. Functionally, they aren't very complex.
The simplest sort of tension wrench is a thin flathead
screwdriver.
The first step in picking a lock is to insert the tension
wrench into the keyhole and turn it in the same direction that
you would turn the key. This turns the plug so that it is
slightly offset from the housing around it. As you can see in
the diagram below, this creates a slight ledge in the pin
shafts.
While applying pressure on the plug, you insert a pick into
the keyhole and begin lifting the pins. The object is to lift
each pin pair up to the level at which the top pin moves
completely into the housing, as if pushed by the correct key.
When you do this while applying pressure with the tension
wrench, you feel or hear a slight click when the pin falls
into position. This is the sound of the upper pin falling into
place on the ledge in the shaft. The ledge keeps the upper pin
wedged in the housing, so it won't fall back down into the
plug. In this way, you move each pin pair into the correct
position until all of the upper pins are pushed completely
into the housing and all of the lower pins rest inside the
plug. At this point, the plug rotates freely and you can open
the lock.
Another technique is raking. Raking is much less
precise than actually picking. To rake a lock, you insert a
pick with a wider tip all the way to the back of the plug.
Then you pull the rake out quickly so that it bounces all of
the pins up on its way out. As the rake exits, you turn the
plug with the tension wrench. As they're moving up and down,
some of the upper pins will happen to fall on the ledge
created by the turning plug. Often, locksmiths will start by
raking the pins, and then pick any remaining pins
individually.
Conceptually, the lock-picking process is quite simple, but
it is a very difficult skill to master. Locksmiths have to
learn exactly the right pressure to apply and what sounds to
listen for. They also must hone their sense of touch to the
point where they can feel the slight forces of the moving pins
and plug. Additionally, they must learn to visualize all the
pieces inside the lock. Successful lock picking depends on
complete familiarity with the lock's design.
Lock Varieties In the last section, we
looked at pin-and-tumbler cylinder locks. You'll find this
sort of lock everywhere, from houses to padlocks. They are so
popular because they are relatively inexpensive but offer fair
security. For a typical pin-and-tumbler lock with five pins,
there are about a million different pin configurations. When
you consider the number of lock companies and lock designs,
the chances of a criminal having the same key as you is fairly
remote.
A pin-and-tumbler cylinder
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.
Re-Keying a Lock One cool thing about
pin-and-tumbler locks is that you can re-configure them to fit
an existing key (provided that the key is for the same lock
design). The advantages of this are obvious: You can add new
locks to your home or business without attaching a bunch of
new keys to your key ring.
To make a new key for an existing lock, you cut a series of
notches in the key so that it raises each of the upper pins
just above the shear line. Essentially, you cut a pattern in
the metal that matches the pattern of the pins in the lock. To
change a lock so that it fits an existing key, you simply work
in the opposite direction: You change the pattern of the pins
in the lock so that it matches the pattern of notches in the
key. If the lock is designed with a universal keying
system, any locksmith can re-key the lock in no time. You
can also get locks re-keyed at most hardware stores.
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.
Master
Keys
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.
The Picker Code Lock picking is an essential
skill for locksmiths because it lets them get past a lock
without destroying it. When you lock yourself out of your
house or lose your key, a locksmith can let you back in very
easily.
Lock-picking skills are not particularly common among
burglars, mainly because there are so many other, simpler ways
of breaking into a house (throwing a brick through a back
window, for example). For the most part, only intruders who
need to cover their tracks, such as spies and detectives, will
bother to pick a lock.
Somewhere between the locksmith and the burglar is the
recreational lock-picker, sometimes called a hacker.
Like expert computer hackers, their code is to pick locks for
the fun of it. Of course, breaking into any private property,
no matter the intent, is illegal and unethical. If a person
picks a lock that belongs to someone else, chances are the
person will be arrested and face serious breaking-and-entering
charges.
Simply understanding the principles of lock picking may
change your whole attitude toward locks and keys. Lock picking
clearly demonstrates that normal locks are not infallible
devices. They provide a level of security that can be breached
with minimal effort. Most locks serve only to keep honest
people honest and to discourage criminals. With the right
tools, a determined intruder can break into almost anything.
For more information on lock picking and the technology of
locks and keys, check out the links on the next page.
