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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. The pins toward the back may feel a bit different from the pins in the front. 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. 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. See Figure 5. With the tool in the keyway, apply torque and try to turn the plug. Figure 2. Pin tumbler lock with a correct key inserted. 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. Note the border between the plug and shell, which forms the shear line, and the cuts in each pin stack resting within the plug. Around the circumference of the plug is a shell, which is fixed to the door or container. 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.

The top pin of the most misaligned pin stack becomes "pinched" at the shear line between the plug and the shell. The basic algorithm for picking locks is remarkably simple: - Apply a small amount of torque to the plug. The rest is just technique -- locating and recognizing the state of each pin stack, manipulating the pins, applying torque to the plug. 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. Left: The correct key lifts the pin stacks to align the cuts at the shear line. 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. Reset the lock by returning the plug to the vertical locked position and try again but with torque applied in the other direction.

There will be a slight "backward" pressure on the torque tool. Both the pick and the torque tool also amplify and transmit feedback about the state of the lock back to their user. Now apply torque in the other direction. The gong is a compelling sound, which might be said to be a unitive principle, and all these other sounds you now hear might be said to represent multiplicity. Of course, in this short space I’m showing you things that might normally go on for a considerably longer time. 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. Success in lock picking is mostly a matter of skill. 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. In the lab there is a collection of "training locks," mounted on boards, what is billiards for practice.

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. It's much easier to learn each skill in isolation, using locks specifically set up for the purpose. 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. Here the plug has been turned slightly toward the camera, so that the tops of the pins in the plug are visible. 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). 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.