Notes on Picking Pin Tumbler Locks

Matt Blaze
University of Pennsylvania

7 November 2003 (revised 6 December 2003)



NOTE: These notes are intended primarily for students in my security seminar; a few of the references here are locally specific and may be confusing to others. Most of the content, however, is generic, and security researchers and practitioners, students of locksmithing, surreptitious entry specialists, and others with an interest in this subject may find it helpful, especially in conjunction with other resources. This page and all photos and other content here are protected under copyright, and unauthorized reproduction or use is prohibited. Contact me for permission.

Mechanical locks (and techniques for defeating them) are inherently interesting to many scientists, engineers, and others, and an understanding of the principles for evaluating and techniques for attacking locks, in addition to being useful in its own right, can provide subtle insight into security more generally. Pin-tumbler lock picking has long been among the common skills of the security community.

The first step toward learning to defeat locks is a thorough understanding of how they work, where their security comes from, and how their design and manufacture introduces potentially exploitable vulnerabilities. A detailed introduction to locks is well beyond the scope of this document; we assume here that you already understand, or have access to, the basic principles. This is intended only as a supplemental, practical guide.

In this document. we focus specifically on the conventional "pin tumbler" lock, which is the most common commercial and residential design used in the United States. Many of the principles can be applied to other keyed lock types, although sometimes the techniques and tools must be adapted. Some pin tumbler locks incorporate "high security" features, including secondary locking mechanisms and features intended specifically to frustrate picking. While some of these features can be defeated with conventional picking tools and are covered here, picking high security locks generally requires specialized tools and techniques (often designed for a specific brand or model of lock) and are beyond our scope here.

There has been quite a bit written, on the Internet and in print, about lock picking. While some of the literature of this subject is quite good, much of it is amateurish, apparently written to appeal to an "underground" audience and not especially rigorous or complete. Some of it is just factually wrong, or obviously based only on speculation.

Probably the best book I've found on picking locks is the Gerry Finch Manual of Lock Picking, which unfortunately appears to be out of print as of this writing. It is aimed at locksmith practitioners but has a cogent discussion of principles as well as technique. If you can find a copy for sale, get it. (Some of the approach in this document is influenced by that of the Finch book).

Another tutorial reference is The National Locksmith Guide to Picking and Impressioning by Robert Sieveking. It's aimed at working locksmiths, and has a broad discussion of picking techniques and principles, albeit with less depth than the Finch book.

An excellent (and currently available) reference is Marc W. Tobias' Locks, Safes and Security. The book is an encyclopedic guide to mechanical locks, how to evaluate them, and how to defeat them, aimed primarily at investigators, law enforcement and intelligence operatives. It's 1400 pages, costs about $200, and is available from amazon.com (that's the crypto.com associate link) or directly from its publisher at www.security.org. It is a worthwhile investment for anyone with a serious interest in the subject, and repays careful study.

For those unfortunate neo-anti-Luddites who refuse to acknowledge the value of anything not available on the Web, I suggest, at a minimum, reading the MIT Guide to Lockpicking, which, while not perfect, has the virtue of being free (and readily available online). See www.lysator.liu.se/mit-guide/mit-guide.html.

A word of warning however: some of the terminology in the MIT Guide is non-standard and can be a bit confusing. For example, the method it calls "scrubbing" is called "raking" by almost everyone else (it's not something I suggest you spend much time on, at least at first, by the way). The pick design it calls a "rake" is called a "hook" by the rest of the world (it's the kind of pick you'll be using most). But the MIT Guide does cover most of the basics and is a quick read.

What is Lock Picking?

"Lock picking" is usually defined as manipulating tumblers to operate a lock without the use of, or access to, a correct key. Although somewhat romanticized by popular media and culture, in reality the significance of lock picking is usually dwarfed by other, more practical threats. Other classes of attack, not discussed here but at least as worthy of study and scrutiny, include lock decoding, which is concerned with producing a working key based only on access to the external interface of the lock, lock bypass, which aims to unlatch the underlying locking mechanism without operating the lock at all, and forced entry, which, as the term suggests, involves the destructive application of force to the lock or its surroundings. And of course there is the surest and fastest method of all: the use of the correct key. Any physical security assessment should consider defenses against the full range of potential threats, not just vulnerability to lock picking.

From the attacker's perspective, too, lock picking is rarely the most efficient, most economical, fastest, or easiest method of entry. Picking locks requires skill, practice, and the use of rather unusual (and not widely available) tools. Few burglars can afford to risk exposure during the time required to pick even relatively easy locks, and unexplained possession of lock picking tools is often considered prima facia evidence of criminal intent. Criminals generally prefer either procuring a key or forced entry for speed, certainty, and stealth, notwithstanding whatever property damage or evidence is left behind. Surreptitious entry (e.g., for espionage or law enforcement surveillance) is likewise often best accomplished by obtaining a key or through the use of specialized decoding or bypass tools designed to quickly and quietly defeat the locks used by the target.

Lock picking is useful and worth studying for its generality and simplicity. The principles and skills of lock picking, once mastered, can be applied against the vast majority of commercial pin tumbler locks, and the basic tools, if somewhat unusual, are quite simple. Lock picking is a core skill of the locksmithing trade and is also of value to those evaluating, investigating, and studying security systems.

Picking depends on weaknesses in the implementation of locks -- small manufacturing imperfections -- rather than fundamental, abstract design flaws that would be present no matter how carefully made the locks might be. (Contrast this, for example, to the weaknesses in the keyspaces of master keyed systems, which are independent of the physical qualities of the locks themselves). However, because the precision with which locks can be manufactured is limited by physical processes, materials, economics, and usability considerations, exploitable weaknesses almost always exist in practice. (That said, better quality locks can be difficult and time consuming to pick.)

Picking Pin Tumbler Locks

The modern pin tumbler lock is quite simple, dating back to ancient Egypt but not commercially mass-produced until the middle of the 19th century. The basic design consists of a rotatable cylinder tube, called the plug, linked to the underlying locking mechanism. Around the circumference of the plug is a shell, which is fixed to the door or container. Rotation of the plug within the shell operates the locking mechanism. In the locked state the plug is prevented from rotating by a set of movable pin stacks, typically under spring pressure, that protrude from holes in the top of the opening in the shell into corresponding holes drilled into the top of the plug. Each pin stack is cut in one or more places perpendicular to its length. See Figure 1. (In practice, the cuts are produced by stacking pin segments of particular lengths, not by actually cutting the pins; hence the term "pin stack.")

With no key in the lock, all the pin stack cuts rest within the plug. When a key is inserted into the keyway slot at the front of the plug, the pin stacks are raised within the plug and shell. (Wards in the keyway restrict the keys that can be inserted.) The plug can rotate freely only if the key lifts every pin stack's cut to align at the border between the plug and shell. The plug/shell border is called the shear line. See Figure 2. The plug will be blocked from rotating if any pin stack is lifted either not far enough (with the cut still in the plug below the shear line) or too far (with the cut pushed above the shear line and into the shell); to rotate, all pin stacks must have a cut at the shear line. The height (or cut depth) of a key under each pin stack position is called its bitting; the bitting of a key is the "secret" needed to open a lock. A key that is bitted to the wrong depth in even one pin position will not operate the lock. Typical commercial and residential locks have five or six pin stacks (although four and seven aren't unheard of), with from four to ten distinct cut depths used on each.


Pin Tumbler Cylinder

Figure 1. A pin tumbler lock cylinder. Left: Cylinder face, the lock's "user interface." Note the keyway, which is cut into the plug, which in turn sits inside the shell. Right: Side view, with part of the shell and plug cut away to expose the six pin stacks. Note the border between the plug and shell, which forms the shear line, and the cuts in each pin stack resting within the plug.


Keyed Cylinder

Figure 2. Pin tumbler lock with a correct key inserted. Left: The correct key lifts the pin stacks to align the cuts at the shear line. Right: With all of the cuts at the shear line, the plug can rotate freely within the shell. Here the plug has been turned slightly toward the camera, so that the tops of the pins in the plug are visible.



In an ideal lock, all of the pin holes in the plug would be in perfect alignment with the corresponding holes in the shell, the centerline of the plug would be exactly parallel to that of the shell, and all of the pins would be exactly the same diameter. If you tried to rotate the plug of such a lock without a key in the keyway, the top pin segment of each pin stack would block the plug at exactly the same number of degrees of rotation; each pin stack would contribute equally to preventing the plug from turning. In practice, of course, locks aren't perfect: the pin holes in the plug are slightly out of alignment with respect to the shell and the pins and pin holes are each of a slightly different diameter. These imperfections are very small -- as little as .0001 inches in some cases -- but they are what allow us to manipulate ("pick") locks open without using the correct key.

Pin tumbler lock picking consists of raising the cuts on each pin stack to the shear line, one by one, until the plug turns freely. In particular note that because the pins are slightly out of alignment, as the plug is turned gently, only the pin stack that is most out of alignment actually prevents further rotation. The top pin of the most misaligned pin stack becomes "pinched" at the shear line between the plug and the shell. If this pin stack is slowly pushed up with torque applied to the plug, eventually its cut will reach the shear line and the plug will turn a bit more. The top pin of that pin stack will be trapped above the shear line, the bottom pin will fall freely, and now a new pin stack (the next most misaligned one) prevents further rotation.

The basic algorithm for picking locks is remarkably simple:

That's it -- now you know almost everything there is to know about lock picking. The rest is just technique -- locating and recognizing the state of each pin stack, manipulating the pins, applying torque to the plug. It's hard to learn these skills all at once on off-the-shelf commercial locks, but that's what many people who try to learn lock picking end up doing (before giving up in frustration). It's much easier to learn each skill in isolation, using locks specifically set up for the purpose. In the lab there is a collection of "training locks," mounted on boards, for practice. These locks are specially pinned to facilitate a more step-by-step approach.

The basic skills of pin tumbler lock picking include selecting the proper tools, manipulating pins through the keyway, applying torque, and recognizing the state of each pin.

Lock Picking Tools

Success in lock picking is mostly a matter of skill. Good tools are important, to be sure, but once a few basic tools are available the student of lock picking is usually better off investing in new locks on which to practice rather than in new picking tools.

Picking tools are designed to perform one of two basic functions: manipulating pins and turning the plug. Two tools -- one for each function -- are used simultaneously when picking a lock. Picks probe and lift the individual pin tumblers through the keyway, while torque tools control the degree and force of plug rotation. Both the pick and the torque tool also amplify and transmit feedback about the state of the lock back to their user. (Other names for the torque tool are turning tool, torque wrench, torsion wrench, and tension wrench. The term "tension" is mechanically inaccurate here, since the tool's function involves torque, not tension).

A wide variety of lock picking tools are commercially available from locksmithing supply vendors, often packaged in elaborate (and expensive) kits containing a baffling array of oddly shaped instruments of dubious utility. A few basic tools are sufficient to pick the majority of commonly used locks. Unfortunately, many of the commercially available lock pick kits consist mostly of useless gimmicks. Worse, they often omit the designs that are of the most practical value.

The proper pick and torque tool selection depend on the shape of the keyway, the features of the lock, the picking technique, and the individual preferences of the user. Examples of some of the better quality commercially available picking tools can be found at www.crypto.com/photos/misc/picks/.

Picks

Over the years, the locksmithing industry has settled on a number of "standard" pick designs. Unfortunately, these designs are less than ideal, and many of the "standard" picks are too large to fit and move comfortably in common lock keyways. Many experienced locksmiths and expert lock pickers prefer "home made" tools to the commercial selections, especially for picking unusual and high security locks.

The shape of the tip is the most obvious difference between picking tools, with hooks, half-diamond, ball, double ball, wave, sawtooth and other styles available. It is not clear what some of these picks are intended to actually do. For most of the picking methods discussed here, in which tumblers are manipulated one by one, a "hook"-style pick is generally used. A functional pick kit should contain several different size hooks to accommodate a range of different keyway shapes.

Other differences between picks, aside from the shape of the tip, are the material, finish, width and thickness of the tang shaft, and the shape and material of the handle. Much of this is simply a matter of individual preference, but certain choices here can also have an impact on performance. The pick must be strong enough to resist bending or breaking while lifting pins, yet the shaft must be small and thin enough to maneuver freely around the keyway without disturbing other pins. Spring steel or stainless steel, between .020 and .035 inches thick, are typical materials. Many manufacturers outfit their picks with elaborate and supposedly "ergonomic" handles, but these often hinder performance as much as they might enhance it. (Bulky handles tend to dampen the transmission of feedback from the lock, and the "handle" part of the pick isn't actually where most of your grip should be in any case.)

Torque tools

The selection of the torque tool is just as important as that of the pick, but, again, commercial pick kits often fail to include a sufficient range of sizes and designs to allow good control and feel across the range of common locks. The traditional torque tool is made from stiff, flat spring steel, bent at a 90 degree angle to provide a small blade that fits in the keyway and a long handle to which torque is applied.

In general, the torque tool should be as thick as possible while still fitting in the keyway, and of a width sufficient to provide good control but without interfering with the picking tool's access to the pins. If the torque tool is too thin, it will tend to be "springy" and will absorb much of the fine movement and control needed to successfully pick better quality locks. Avoid so-called "feather-touch" and spring-loaded torque tools altogether. The tool should amplify, not dampen, the rotation of the plug.

Longer handles are as a rule better in torque tools; the farther from the plug the torque can be applied, the easier it is to detect and control fine movement. There is a tradeoff, of course, since a longer handle may be difficult to maneuver around obstacles.

Torque tools may be oriented vertically (with the handle in line with the keyway) or horizontally (with the handle perpendicular to the keyway); different people have different preferences. Vertical orientation requires a 90 degree twist in the blade. Most commercial torque tools are designed for horizontal orientation.

Another style of torque tool has two "prongs" that fit in the top and bottom of the keyway, with a cutout between them for the pick. This style of tool is especially useful for holding open automotive locks that have spring-loaded dust covers. The tool must have a good fit to be effective, however. Falle-Safe Security makes a set of vertically-oriented two-prong torque tools designed to fit snugly in a range of different pin tumbler keyways. They allow very precise control over torque, especially when employing advanced picking techniques that involve a slight reversing of the rotation of the keyway.

Your tools

Note: The author does not stock, sell, or distribute lock tools; if you're not a student in my seminar, please don't ask -- I can't help you. A variety of picking tools are available through most locksmith supply distributors.

The basic recommended pick set for this course includes four picks and four torque tools. The picks are made by Peterson International (a locksmithing tool vendor in upstate New York with manufacturing facilities in South Africa). Their web site, with descriptions of the tools, is at www.peterson-international.com. Three of the picks are of a "hook" design. They include a standard hook (called the "Hook" in Peterson's catalog), a larger hook (the "Gem"), and a deep curve (the "Reach"). The fourth pick is a "rake" of a long sawtooth design (the "Ripple"). The picks are available with blue plastic handles. black rubber handles, or red foam handles. I made the torque tools out of Peterson's .025 inch spring steel of different widths. Two of the tools orient the handle perpendicular to the keyway and two orient the handle vertically.

The three hook picks in this kit are sufficient to manipulate the vast majority of pin tumbler locks found in the US. Most of the esoteric pick designs in the huge, overpriced sets you see on the web and from locksmith suppliers are useless, and eventually end up being discarded in favor of the basic hooks.

That said, the Peterson hook picks are a bit too large to fit comfortably in more tightly warded keyways, especially those found on higher-security locks. (Locks in Europe also often have tighter keyways than typical US locks.) The "advanced" pick set for this course includes the Peterson picks plus the LAB model LPT015 kit, which contains a collection of six smaller picks (they're double-ended, giving total of 12 different picking tips), three double-ended standard torque tools in various sizes, and a "fork" two-prong torque tool (for automotive locks). LAB is a lock pin and locksmith tool manufacturer. Their web site is at www.lab-lockpins.com. The LAB picks can comfortably maneuver around even very tight keyways, and are among my personal favorites.

While the LAB picks are quite nice, their small size makes them rather delicate and easy to bend or break, especially as you're learning how much lifting force and torque are involved. The Peterson picks are more sturdy, at the expense of being bulkier (but they still fit easily in many of the keyways you'll be picking). For most locks, especially as you're starting out, a workable compromise is often the smaller Peterson hook.

Tutorial Exercises

If you're not in my seminar, the references to the lock boards in the lab don't apply, of course; you will need to configure your own training locks to follow these exercises. However, your efforts un-pinning and re-pinning locks will be time well spent -- you will progress much faster than you would if you tried to start out picking fully pinned cylinders. You will need a small set of cylinders in various keyways, a board or vice to hold them in while you practice, and a small re-pinning kit (extra pins and springs and a "follower" tool). There is a more detailed discussion of configuring training locks at the end of this document.

The following is a series of self-paced exercises to help you master the basic techniques of pin tumbler lock picking. In the lab you'll find a collection of small (12 inch by 18 inch) lock boards, each containing six specially pinned locks with a given keyway. The keyways include Arrow ("AR1"), Ilco-Schlage-multiplex ("SX"), Schlage-C ("SC"), and Yale-8 ("Y1"). While there are literally thousands of different keyways in commercial use in the United States and thousands more abroad, these four give a fairly representative sample of the different kinds of wardings (and pin manipulation problems) you are likely to encounter in common (non-high-security) locks.

Each board is labeled with its keyway, and each lock cylinder on a board is labeled with the number of installed pin stacks (from one to six) and the keying code for its pinning. The locks are drilled for up to six pins. The six character keying code gives the pinning from the front of the lock to the back, with a "-" for a missing pin stack and a digit for a pin that is installed. Small digits represent short bottom pins (that must be pushed up more to reach the shear line); large digits represent longer bottom pins (that need only be pushed up a bit). The boards should be held vertically (e.g., in a vice or against a wall on a table) when used, simulating a typical door. Do not hold them in your lap. (And whatever you do, please don't remove them from the lab without checking with me first!)

It is very important when you do the exercises that you not move on to the next until you have completely and comfortably mastered the exercise you're working on. That means being able to reliably pick the lock, both clockwise and counterclockwise, and being confident that you know how you opened it. A good rule of thumb is to be able to complete an exercise at least ten times clockwise and then another ten times counterclockwise before considering it complete and moving on. It can become very tempting to "cheat" a bit here and move ahead the moment you get a difficult lock open the first time, but that will only make the rest of the course that much harder.

You should be relaxed, comfortable and able to concentrate when you do these exercises. Lock picking involves fine movement and control, and if you're in a hurry, uncomfortable, frustrated, or distracted you will not make progress. Take frequent breaks, and don't try to complete the whole course in one day. Everything will still be there tomorrow.

Exercise 1: Selecting Tools and Manipulating Pins

Find the board with the six "Arrow AR1" keyway locks. This keyway is common in commercial and residential locks in the US, and is close in shape and size to a number of other common keyways, including that used by Kwikset, a very popular (and easily defeated) line of US residential locks. The keyway is relatively open and easy to move a pick through, making it a good starting point.

Using the five or six pin lock, find a pick that lets you locate and lift each pin across its full range of motion without disturbing adjacent pins too much. (Make sure the lock is in the locked stated when you do this; if it's already been picked, rotate the plug until you hear the pins snap back into place.) Lift each of the pins from front to back. Try all your different picks. You'll probably end up deciding that the small Peterson hook works best, but experiment with all the picks.

Work your pick into the keyway and feel the pins. First count them, making sure you find all five (or six). (One way to do this is by lifting all the pins to their full height with an upside-down pick and then slowly withdrawing it, listening for the sounds of the pins dropping.) Now lift each pin individually and note what the spring pressure feels like (you can pivot the pick off the front of one of the horizontal wards in the keyway as you do this). The pins toward the back may feel a bit different from the pins in the front. Take your time with this. You should be able to confidently find each pin and push it all the way up, without jamming the pick against anything or moving other pins. Lifting pins is one of the basic actions of lock picking, and it's worth taking the time now to become good at it.

It is important to develop a "mental image" of the internal state of the lock, the locations of the pins and your pick, etc, as you manipulate the pins. Intuitively visualizing the inside of a lock takes a bit of practice, but will pay off as you start picking locks in earnest.

Hold your pick as you would a pencil when you work the pins. (A common mistake is to hold the pick as if it were a shovel.) Your index and middle fingers should be touching the edge of the pick close to where it enters the keyway. The pick handle should not be making contact with the palm of your hand. See Figures 3 and 4.

Once you're comfortable with the AR1 keyway, move on to the "Ilco SX" keyway locks and repeat the exercise. This keyway is a bit more "open" (it's intended to allow several different key profiles to fit in it), and so requires the use of a larger pick than the Arrow AR1 keyway does. You'll probably find the large hook or deep curve pick works well here.

When you feel confident visualizing and using picks to maneuver around the pins in the AR1 and SX keyways, you're ready to start actually opening locks.


Holding a Pick

Figure 3. Holding a pick. Note that the pick should be held mostly by the shaft of the tang, not the "handle." This allows better control and feedback. A very tight grip is not required, nor is great force used. This pick is a LAB double-ended "hook/rake" (held for use with the hook end).




Manipulating Pins

Figure 4. Manipulating pins. Find the ward directly under the pins and pivot the shaft of the pick at the font of the keyway. Move your fingers close to the keyway as you do this. This pick is a Peterson "Hook" with a plastic handle.



Exercise 2: Applying Torque

Go back to the "Arrow AR1" keyway lock board and find the one pin lock.

Try each of your torque tools in the lock. Insert the tip of the tool in the keyway, allowing enough room for your pick to enter and manipulate the pins. The handle of the torque tool serves as a lever to turn the plug. It is usually possible to insert the torque tool at either the top or bottom part of the keyway. I usually find that the very top of the plug, directly in front of the pins, to be a good place to apply torque, but you have to be careful that the tool doesn't touch the front-most pin. See Figure 5.

With the tool in the keyway, apply torque and try to turn the plug. It won't turn, of course, because the cut of the (single) pin stack is still below the shear line and its top pin is preventing the plug from rotating. Now, while continuing to apply torque, insert your pick and find and slowly lift the pin stack. You'll notice that it resists more than it did in the previous exercise because its top pin is pinched between the plug and the shell at the shear line by the torque you're applying. In lock picking terminology, we say that the pin statck is binding.

As you lift the pin stack with torque applied, eventually its cut will reach the shear line, allowing the plug to turn; the top pin will then be completely trapped in the shell, while the bottom pin stays in the plug, no longer held down by spring pressure. (The numbers on the front of the practice locks indicate the keying codes, from the front-most pin stack to the rear-most. Smaller numbers correspond to shorter bottom pins, which must be raised higher to reach the shear line.)

Reset the lock by returning the plug to the vertical locked position and try again but with torque applied in the other direction. You have to be prepared to pick locks in either direction. Some locks will open both clockwise and counterclockwise, but many will only open when turned a particular way, depending on the configuration of the underlying locking mechanism. (If you pick a lock in the wrong direction you will have to either reset the lock and start over or use a "plug spinner" tool to rotate the plug back fast enough that the pins do not reset as they pass the 12 o'clock position.) As a general rule, locks mounted on the left side of a door open clockwise, while locks on the right side of a door open counterclockwise. There are exceptions, however. Take note of the direction the keys turn on doors you use to help develop an inituition about which direction to apply torque.

Continue with the one pin lock, trying to apply less and less torque each time. Learn to apply the minimum amount of torque needed to turn the plug. Spend more time on this exercise than you think you need to; most people never learn to properly apply the light touch needed to pick better quality locks.


Applying Torque

Figure 5. Applying torque. Several positions are possible; here a vertically-oriented torque tool is used at the top of the keyway. You must be careful to avoid touching the front-most pin with the blade of the tool, but this position has the advantage of allowing maximum room to maneuver the pick.



Exercise 3: Picking Two Pins

For this exercise, you'll be using the two pin AR1 lock.

Apply some torque to the plug and feel the two pin stacks with your pick. One of them should feel springy, just as it did with no torque applied. The other should give you a bit of resistance. If both feel springy, you're not applying enough torque (which is unlikely). If both resist, you're applying too much (the more likely mistake).

The resistant pin stack is the called the binding pin. It's binding because it's the one most out of alignment in the direction you're turning, and so its top pin is being pinched (gently) between the plug and the shell.

While continuing to apply torque, slowly push the binding pin up. Eventually, you'll reach a point where the plug will turn ever so slightly and the pin will not go up any farther. You may hear a faint "click." This is because you've pushed the cut (between the bottom and the top pin) up to exactly the shear line. Now the top pin is above the shear line and the bottom pin is below it. If you release pressure with your pick while still applying torque, the bottom pin will drop freely, and will not have any spring pressure if you try to push it back up. When the plug turned slightly, it trapped the top pin above the shear line, preventing it from re-entering the plug. Now the plug is being prevented from moving by the next most misaligned pin (which, in this case, is the other pin, since there are only two).

Now (as long as you continue to apply torque) the other pin should be binding. Push it up slowly as you did before. When you reach the shear line, the plug will turn. Congratulations, you've picked the (two pin) lock.

It's possible that the plug will turn as soon as you set the first pin; if this happens, it's because you inadvertently lifted the other pin with the shaft of your pick while you were working on the first one. While this might have gotten the lock open, you just as easily might have pushed the cut past the shear line entirely, preventing the lock from opening altogether. Learn to pick this lock one pin at a time.

Practice picking the two pin lock until you can do it easily and naturally. Your goal is to learn to do this with the absolute minimum amount of torque needed to bind the most misaligned pin enough to distinguish it from the other one. Develop a light touch. In particular, you should feel when you set a pin as much in the torque tool as you do in the pick.

Now apply torque in the other direction. Chances are the two pins will be reversed -- the formerly springy one will give resistance and the formerly stuck one will be springy. (Why?)

Keep practicing with the two pin lock, trying to lighten your touch as you do, and making sure you consistently can pick the pins one at a time.

Exercise 4: Recognizing Pin States

For this exercise, you'll be continuing with the two pin AR1 lock.

A pin stack in a lock being picked might be in any of four states:

Only one pin stack should be in a binding state at any given time, of course. It's important to be able to distinguish among these four states. Much of lock picking skill depends on testing pins stacks for the purpose of finding which to push up next and assuring that no pins are overset. For this exercise, you'll use your torque tool and pick on the two pin lock to put the pins in each of these states to learn what they feel like with your pick. These skills become very important when picking better quality locks, so take your time here.

First, apply light torque (as you practiced in the previous exercises) to the two pin cylinder and gently feel each pin. One of the pins should be unset/binding ("squishy") while the other should be unset/not-binding ("springy"). Find the binding pin and the non-binding pin. Now release torque and try again, but this time lift the pins as little as you can when you test them, while still distinguishing between the two states. Repeat this exercise until you can reliably distinguish between a binding and a non-binding pin with very little lifting. (Excessively lifting a pin while testing it increases the risk of oversetting it or disturbing adjacent pins.)

Now re-apply torque and set the first binding pin. Once you do this, one of the pins will be in the unset/binding state while the other (the one you set) will be in the set/not-binding state . Again, repeat the exercise with the aim of learning to distinguish between these states with as little lifting as possible.

Finally, lift the pin that sets first very high before you apply torque. This will overset the pin. Learn what a pin in that state feels like. It becomes distinguishable from an unset/binding pin stack when you try to set it; while it binds, it does not set, no matter how much further it is lifted.

Exercise 5: Three Pins

Continue with the AR1 lock board.

Once you've mastered the two pin lock and can distinguish reliably among pin states, you should have little trouble with a three pin lock.

You should already be able to distinguish between an unset pin that isn't binding, an already set pin, and a pin that is binding. Observe that after you set the first pin, your three pin cylinder has one pin in each of three different states: set/not-binding, unset/not-binding, and unset/binding. Practice distinguishing between the pin states and then finish picking the cylinder. Remember to practice this several times, in both directions.

If you inadvertently push a pin up too far or are applying so much torque that more than one pin is binding, you may have an overset pin instead. If this happens, you won't get the lock open until you release torque and start over. An important skill when picking is to recognize when this has happened so you don't waste time before you start over.

Spend a lot of time playing with the three pin lock so that you can recognize the pin states easily and naturally. Note that these locks have been deliberately pinned with a short pin behind a long one. You'll need to be careful not to disturb the long pin when you push the short pin up.

Exercise 6: Four Pins and Up

Again, continue with the AR1 locks.

When you're comfortable picking the three pin lock (in both directions) move on to a fourth pin, and when you've mastered that, a fifth and then a sixth. As you work with locks more populated with pins, it becomes increasingly critical to avoid accidently disturbing the pins adjacent to the one you're working on. If you're having trouble, you may be pushing adjacent pins up past the shear line as you pick a pin, causing them to be overset even before they start to bind.

Eventually, you'll be able to comfortably pick the locks with five and six pins installed. As you progress, you should know the state of the lock at all times: which pins are set, which aren't, which one is binding. You should always know which pin you're working on at any given time. Once you've picked a cylinder, you should know in exactly what order the pins pick.

Note that while many locks pick predominantly back to front or front to back, there are exceptions, and you may find that the binding pin stack "jumps around" from the back to the front to the middle and so on. Get in the habit of making a systematic "inventory" of the states of the pin stacks after you set each new pin. Do not assume that the next pin will be adjacent to the one you just set.

While a fairly wide range of torque will sometimes pick these locks, try find the lightest torque that works. Better quality locks are less forgiving of too much torque.

Exercise 7: Different Keyways

Once you've mastered the AR1 keyway locks, repeat exercises 2 through 6 with the "Ilco SX" keyway locks. This keyway is more "open" than the Arrow, and there aren't really any "platforms" on which to pivot your pick. The Peterson "Reach" deep curve pick works well for this keyway, pivoting from the bottom of the keyway at the front.

When you've mastered the SX locks, try the "Schlage SC" keyway locks. These locks add a new challenge: maneuvering the pick. Again, try to find and lift all the pins with the different hook picks without applying any torque. You may need to turn the pick a bit to fully lift the pins. It will take a bit of practice to find just the right technique. Become comfortable with this before you try picking this lock with torque or you could bend or break your picks. You may find one of the smaller LAB hook picks to be easier here than the larger Peterson picks, although you can usually still pick this keyway with the small Peterson hook.

Schlage SC is a very common keyway. You may well have one of these locks on your house.

Finally, for a real challenge, try the Yale "Y1" keyway locks. The Y1 keyway is one of the toughest you are likely to encounter in real lock installations in the US. Note how the wards extend across the front of the pins; this is called a "paracentric" design in locksmithing parlance. To pick this keyway, you'll need a small hook pick and a bit of twisting as you lift. You'll probably want to use one of the smaller LAB picks, although the small Peterson hook will sometimes do with care and practice. You may want to use one of the smaller torque tools as well, or put your torque tool in the bottom part of the keyway instead of the (curvy) top.

With practice, even this keyway will eventually seem easy to maneuver.

Exercise 8: Using Rake Picks

So far, we've been picking locks "a pin at a time," with a single pin stack set at the shear line in the sequence dictated by whatever misalignments are present in the cylinder. Raking, in contrast, is a class of picking techniques in which several pin stack may be set at the shear line simultaneously. While pin-at-a-time picking is usually the most reliable way to open a given lock (and the skills used essential for mastery of other techniques), raking can sometimes open a lock more quickly. Often raking is used to best effect in conjunction with pin-at-a-time picking.

There are many different styles of raking, some of which entail the use of special rake picks specifically designed for a particular technique. You do not need to master them all, and it is certainly not necessary to accumulate a large collection of different rakes. However, it is worth experimenting with different rakes and raking techniques to find one or two that work well for you.

The most comprehensive treatment of raking techniques I've found is in the Finch Manual of Lock Picking, although other authors have different perspectives on the subject. What follows is a brief summary of several of the most popular techniques. Note that excessive raking with any of these techniques will tend to overset pins, so be prepared to release torque and start over from time to time.

Sawtooth

Sawtooth rakes, such as the Peterson "Ripple" and the Falle-Safe rakes, have 5 or more very acute peaks along the length of the pick's edge. When inserted quickly in and out of the keyway and rubbed along the bottoms of the pins, they tend to make each pin stack "jump" rapidly. As the peaks hit the pin stacks, energy is transferred from the bottom pins to the top pins, much like the action of the cue ball in billiards. When the energy transfers, the top pin moves up while the bottom pin slows down, and a gap is created between the two pins. If the shear line is within this gap as torque is applied, it may set. The multiple peaks allow several, or even all, pin stacks to set simultaneously. (This, by the way, is the same principle used by mechanical "pick guns" and by "bump keys").

Apply very light torque while energetically moving the sawtooth rake in and out of the keyway. Do not push up hard against the pins; use just enough pressure to cause the pin stacks to jump.

Rubbing

Many inexpensive locks are grossly misaligned, making them quite forgiving of chaotic picking technique. Rubbing exploits this by simulating several passes of pin-at-a-time picking in a few "strokes" across the pin stacks.

While applying light to moderate torque, push and pull a gently rounded rake pick from front to back and back to front along the pin stacks. Vary the amount of lifting between strokes but do not force the pins, lest you overset them. Alternatively, you can use the rounded edge of an inverted hook pick instead of a special rake pick.

Jiggle Key Raking

Very "wavy" rake picks can simulate various key profiles, and can be surprisingly successful at opening poorly-made locks.

Apply light torque while pivoting a long, wavy rake inside the lock, inserting and removing it slightly as you go. If not successful, invert the pick and try again with the inverted profile.

Reverse Picking

While pins are usually set by raising the cut from the plug to the shear line, they can also be picked by first oversetting the cut to within the shell and then lowering it to the shear line. This technique requires a great deal of practice to master, but has the surprising property of sometimes being more effective against better made locks.

Using an inverted pick, raise all the pin stacks to their maximum height. Now apply heavy torque, with the aim of pinching all the bottom pins at the shear line. Gradually ease up on the torque, allowing pins to drop one at a time. An oscillating motion with the torque is often helpful here. Note that although heavy torque is required, this technique also demands high sensitivity and control.

Exercise 9: "Final Exam"

The large board has locks with eight different keyways, representing many of the most common keyway designs used in the US. There are locks with two, five, and six pins in each keyway, but the keying codes aren't labeled on them.

If you can pick all (or at least most) of the locks on this board, you are well prepared against the typical locks installed in residential and commercial buildings in the US. (In some areas, especially urban centers, higher security locks are more common, but that remains the exception rather than the rule).

Exercise 10: ("Extra Credit") Security Pins

Some lock manufacturers and locksmiths install special "security pins" intended to resist lock picking. The most common security pins are the "spool" and "mushroom" top pin designs, which are thinner in their mid-section. These pins falsely set before they reach the shear line. See Figure 6.

Spool and Mushroom Pins

Picking locks with spool and mushroom pins takes practice, both to recognize them and to effectively neutralize them when they are encountered. The first sign of spool and mushroom pins is that the lock will appear to be picked, but will only turn a few degrees. See Figure 6 for an example of a spool pin.

To determine which pin stacks have these pins, gently push up each "set" pin. The pin stacks with regular pins will feel just as you'd expect, with a hard stop when the bottom pin hits the shear line. Pin stacks with partially set spool and mushrooms, on the other hand, will feel a bit different. There will be a slight "backward" pressure on the torque tool. To neutralize a partially set spool or mushroom pin, reduce torque and push the pin up, allowing the plug to rotate backward a bit as you do. (It is often helpful to do this with "rocking" motion between the pick and the torque tool, gradually increasing the degree to which the plug is allowed to rotate backward). When the pin stack truly sets at the shear line, it will feel like an ordinary set pin. Note that other pins may unset at this point, and may have to be picked again.

An alternative technique, which I have not seen mentioned in the literature, is to first determine which pin stacks have security pins and which have regular pins (by picking normally and noting which stacks are false set). Now release torque and start over, taking care to pick all the pin stacks with spool/mushroom pins while leaving at least one regular pin stack unset (this will require a light touch and good sensitivity). When the final (non-security) pin is set, the lock should open.


Abus spool pin

Figure 6. Abus "spool" top pin. The name comes from the resemblance to an empty spool of thread. The thin midsection falsely sets.



Serrated pins

Serrated pins can be very difficult to neutralize. See Figure 7 for an example of a serrated pin. The serrated section tends to false set and jam as long as torque is applied. (Some cylinders also serrate the pin chamber itself, exacerbating the difficulty of picking).

If only serrated top pins are used, reverse picking may be successful. If serrated bottom pins are used as well (as they are in, e.g., certain American brand padlocks), snap guns, bump keys, or sawtooth raking are likely the only picking techniques that will succeed, especially for the novice. However, because they jam when false set, locks with serrated pins tend to impression very well (impressioning is a decoding technique that produces a working key based on marks left on a progressively cut key blank).


LAB serrated pin

Figure 7. LAB Serrated top pin. The serrated section falsely sets and jams as long as torque is applied.



Other Kinds of Locks

While the pin tumbler cylinder is by far the most popular door locking mechanism in the United States, it is not the only kind of keyed lock in common use. Other lock types include "European profile" cylinders, master keyed locks, master ring and SFIC cylinders, tubular pin tumbler locks, dimple-key pin tumbler locks, pin tumbler locks with secondary locking mechanisms, wafer tumbler locks, disk tumbler locks, lever tumbler locks, combination locks, and electronic locks. While many of the principles of pin tumbler lock picking apply or can be adapted to other mechanical lock designs, a complete discussion of these locks and techniques for defeating them is beyond the scope of this document. (Tobias' Locks, Safes and Security is a good reference for this purpose.)

"European Profile" Cylinders

A common door lock mechanism in Europe uses a standardized "European profile" lock module. These are typically pin tumbler locks, but their orientation is "upside down" with respect to the convention for locks installed in the United States. The pins are at the bottom of the keyway rather than the top.

High security locks are more routinely installed in Europe than they are in the United States. This may be a consequence of more stringent European insurance standards for physical security.

Master-Keyed Pin Tumbler Locks

Most pin tumbler cylinders can be "master keyed" to allow more than one key bitting to operate it. The usual scheme for master keying involves using more than one cut in some or all pin stacks (this is accomplished by adding additional pin segments). (This method of master keying introduces fundamental vulnerabilities; see my paper on the subject at www.crypto.com/papers/mk.pdf.)

Master keying does not introduce any significant complications for lock picking. In fact, master keyed pin stacks are easier to pick than those that are single-keyed; there are two chances to lift a cut to the shear line. (If a picked master keyed cylinder is rotated 180 degrees, there is some risk of a very thin pin segment becoming trapped at the top of the keyway, but this is rarely an issue in practice).

Master-Ring and SFIC Cylinders

Ordinary pin tumbler locks have a single shear line (the boundary between the plug and the shell). Master ring and small-format interchangeable core (SFIC) locks, however, have two shear lines, formed by a concentric plug-within-a-plug. The two shear lines are keyed independently by a "double height" pin stack, with one set of cuts keyed to each. Master ring cylinders (which are no longer in common commercial production but were once marketed by Corbin) use this mechanism to provide independently-keyed master keying. SFIC cylinders (such as those made by Best), used in large institutional lock systems, employ a similar mechanism to provide two kinds of keys: regular keys that operate the lock and control keys that unlock and remove the cylinder core itself. See www.crypto.com/photos/misc/sfic/.

Master ring and SFIC locks can be very difficult to pick. Because there are two independent shear lines, there is no way to control, or even tell, at which shear line a given pin stack sets. If just one pin sets at the "other" shear line, the lock will not open even though all the pin stacks are picked. In a lock with six pin stacks with a uniform chance of a pin setting at either shear line, the probability of a picked lock actually opening is only 1/64. Picking techniques for these locks involve the use of special torque tools designed to put torque on only one of the two concentric plugs. Snap guns are occasionally successful as well.

Tubular Pin Tumbler Locks

Tubular cylinders typically have four to eight pin tumblers arranged in a circular pattern around the circumference of the plug. The design is based on the late 18th century British Bramah lock (still in production and use today). The basic principles of operation are essentially the same as those of the standard pin tumbler lock, except that the tumblers are exposed at the front of the cylinder and a round ("tubular") key is used.

Tubular locks suffer from the same manufacturing imperfections as other locks and so can be picked with essentially the same techniques. However, the design of the cylinder requires the use of special tools to manipulate the pins and apply torque. A popular style of tool for these locks decodes them via impressioning techniques.

These locks are no more or less inherently secure than standard pin tumbler locks, although the external exposure of their pins makes picking them (and designing sophisticated picking tools for them) somewhat simpler. However, some tubular cylinders (e.g. the Ace-II lock and the tubular models of American-brand padlocks) are made to very tight tolerances and use mushroom, spool, and serrated security pins.

Dimple-Key Pin Tumbler Locks

A few pin tumbler lock products orient the key horizontally in the keyway and use a flat key bitted with variable-depth holes ("dimples") rather than the cuts used for the familiar "sawtooth" key. These locks can be picked according to the same principles as used for ordinary pin tumbler locks, but, again, different tools are used to accommodate the different shape of the keyway.

Many dimple key locks also incorporate secondary high security locking mechanisms. For example, Mul-T-Lock cylinders use special "telescoping" pins that contain two independently keyed tumblers.

Secondary Locking Mechanisms

High-security locks often incorporate one or more secondary locking mechanisms beyond that provided by the conventional pin tumblers.

Many of these mechanisms involve the use of a "sidebar" that must retract before the plug can rotate. A variety of schemes are used to key the sidebar. For example, Medeco locks use special wedge-shaped bottom pins that are rotated into one of several possible positions by the key cuts (which can be cut at different angles). Each pins has a groove cut in its side at the position corresponding to its correct rotation. The sidebar must engage these grooves in order to retract and allow plug rotation. Schlage Primus locks also use a sidebar. The Primus sidebar is keyed by additional side tumblers that engage a secondary bitting cut into the side of the key.

In addition to making picking more difficult, secondary locking mechanisms are sometimes also intended to make it more difficult to reproduce unauthorized copies of keys. Making keys for these locks often requires the use of special equipment and unusual, proprietary key blanks.

Wafer Tumbler Locks

Many inexpensive locks, especially low-security "cam" locks such as those used to secure furniture and cabinets, do not use pin stacks for their tumblers. Instead, they use flat "wafers," typically extending across the full height of the plug. Each wafer has a large rectangular cutout through its middle and through which the key passes; the precise height of the cutout keys the wafer to different bittings. If the wafer is set too low by the key, it blocks rotation by extending out through the bottom of the plug, while if it is set too high, it extends out the top. A correctly keyed wafer is flush with the plug on the top and the bottom and allows rotation.

In general, wafer lock picking employs the same techniques and tools as those used for pin tumbler locks. Most wafer locks are made to very loose tolerances and have relatively open keyways, however, and are very easy to pick. However, note that because the tumblers are a single piece, sawtooth raking, snap guns, and bump keys are not effective against them. These locks are often quite susceptible to rubbing and jiggle-key raking.

Some wafter lock cylinders (especially certain Chicago-brand locks) are double bitted, with some wafers making contact with the key at the top of the keyway and others at the bottom. These locks must be picked at both the top and the bottom, sometimes alternating between them. Special double-sided jiggle-rake picks are commercially available for such locks.

Most automotive locks use wafer tumblers. Here, however, tighter tolerances and, in some cases, high-security secondary mechanisms, are more common.

Disk Tumbler Locks

Some high security locks, such as those manufactured by Abloy and Abus, use round disk tumblers that are rotated into position by a specially designed key bitted with angled cuts corresponding to each tumbler. These locks are unusual in not requiring springs on the individual tumblers and are therefore especially well suited to outdoor use under extreme conditions. In the United States, disk tumbler cylinders are used primarily for padlocks situated in harsh environments, especially by public utilities and railroads. They require special picking tools to manipulate the tumblers and apply torque.

Lever Tumbler Locks

The commercial lever lock mechanism dates back to the early 19th century Chubb lock (and, indeed, to well before). It remains in wide use in certain applications, especially safe deposit locks, safes, small cabinet locks, and mailbox locks. In many countries, especially the U.K. and India, they are commonly used for door locks and padlocks as well. Their security ranges from being quite rudimentary to being among the most formidable locks in commercial use.

Lever locks employ a set of "lever" tumblers raised to a specific height by the key bitting. Each lever has a cutout, called a gate, through which part of the locking bolt, called the fence or the stump, must travel. Picking these locks involves putting torque on the locking bolt and raising the gates to the correct height. As with pin tumbler locks, because the levers, gates, and fence are slightly out of alignment, it is usually possible to raise and pick the levers one at time.

Picking lever locks generally requires different tools from those used for pin tumbler locks, and high security lever locks often require specialized purpose-made tools.

Combination Locks

Not all locks use a physical key. Combination locks require the user to "dial in" a secret combination, analogous to a password. Mechanical combination locks are common on inexpensive padlocks, safe locks, and to control access to high security vaults. The typical combination lock design involves a set of (usually three or four) disk tumblers around a spindle connected to the external dial. Each disk has a notch cut in its edge. The lock mechanism can open when the notches on the disks are lined up at a particular rotation. The disks are connected in sequence via interlocking cams such that one rotation of the dial engages the first disk, two rotations engage the second, and so on.

Although combination lock manipulation exploits some of the same kinds of imperfections as pin tumbler lock picking, the principles and techniques are quite different and are well beyond the scope of this document.

Electronic Locks

Inexpensive and low-power embedded micro-controllers are increasingly serving as the foundation of modern security and access control systems. Electronic locks, of course, do not have mechanical tumblers and are so not vulnerable to many of the physical manipulations exploited in tradtional lock picking. However, that is not to suggest that electronic locks are inherently more secure than their mechanical counterparts. The underlying locking mechanism is still mechanical and may be subject to mechanical bypass. The electronic control mechanism may be vulnerable to new attacks, e.g., through the introduction of RF or power faults or via "Tempest" monitoring. And, of course, electronic locks have at their root software whose size and complexity grows as they become more sophisticated (and as they are networked into centralized control systems). There is no reason to believe that the software used in electronc lock systems is any less subject to bugs, vulnerabilities and protocol failures than the typical (buggy) software used in other applications of similar complexity. Indeed, security system software may well be considerably worse, since it is often purpose-written and may be subject to only limited scrutiny and testing.

Now What?

Picking locks very much involves "psychomotor" skill. Understanding the theory of lock picking is only a small part of being able to successfully pick locks. The only way to become proficient is to practice. The training locks in the lab are a good start, but you will probably learn more quickly if you have access to your own personal practice locks as well.

Obtain a collection of suitable lock cylinders. Ilco replacement cylinders are inexpensive and a good compromise between quality and pick-ability for practice (that's what the training locks here are) and are available in a many different commonly-used keyways. They cost between five and eight dollars each from various distributors, depending on the exact configuration. "Mortise" cylinders can be held in a small vice for practice and "Rim-type" cylinders can be mounted easily to a wooden board (which must be between one and two inches thick). Drill a 1-3/8 inch hole and use the mounting hardware supplied with the cylinder. You will also need a small re-pinning kit (available from locksmith suppliers as well as many home improvement and hardware stores) so you can easily add, remove, and re-arrange pins. (When you add or remove pins, you must add or remove the entire pin stack, including the bottom pin, top pin, and spring). See any text on locksmithing, or http://www.gregmiller.net/locks/disassemble.html, for basic descriptions of lock pinning.

It is always best to practice with your lock mounted to a door or wood platform, as they are here, or at least fixed in a vice. When you hold a cylinder in your hand you get different feedback from the pins than you do on a real door.

More than anything else success in picking depends on experience and practice with a range of locks. Over time, accumulate a varied collection of practice locks, and study different lock designs whenever you get the opportunity. (For example, see some of the photos of various locks on my web site.)



All images and text Copyright © 2003 by Matt Blaze. All rights reserved. You may not copy, modify or use these images or text, in whole or in part, for any commercial or non-commercial purpose without permission.

Home page is at http://www.crypto.com/ .