Lock bumping

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Lock bumping is a lock picking technique for opening a pin tumbler lock using a specially-crafted bump key. One bump key will work for all locks of the same type.

1 Bump key
2 Bumping
3 Explanation
4 Countermeasures
5 History
6 External links

[edit] Bump key

The bump key is made by filing down a key blank (or another key made for the targeted type of lock) to the lowest level in each groove. Slight elevations are left between the groves--if these are too steep, the key will not enter or leave the lock. The tip and shoulder of the key must also be filed down by approximately 1 millimeter. (The shoulder is that part of the key which touches the outer portion of the lock when the key is fully inserted.)

[edit] Bumping

The technique involves inserting the bump key into the lock and tapping the key one or more times with a mallet or similar device, while applying a slight turning force (torque) to the key. In some cases, a tap with a finger is all you need. After a little bit of practice, this will open the lock. The skill level required to bump a lock is minuscule compared to other lock picking techniques; bumping is a feasible method for compromising locks by just about anyone.

[edit] Explanation

Hitting the key forces it deeper into the lock, allowed by the removed shoulder and tip. The bottom internal pins are forced up because of the elevations that were left standing between the groves. Each bottom pin transmits this upward impulse to the pin sitting immediately on top of it. The top pins fly upwards, while the bottom pins remain down. (The same effect is seen when hitting a billiard ball that touches another: only the second ball will move.) As the top pins separate from the bottom pins, the cylinder can be turned and the lock opened.

[edit] Countermeasures

Ironically, more precise manufacturing tolerances within the cylinder make bumping easier as the pins move more freely and smoothly. Also, more expensive locks made of hardened steel are actually more vulnerable because they are less prone to damage during the bumping process which might cause a cheaper lock to jam.

Locks having security pins (spool or mushroom pins, etc.) --even when combined with a regular tumbler mechanism-- generally make bumping somewhat more difficult but not impossible.

Electronic locks, magnetic locks and locks using rotating disks are not vulnerable to this attack.

Because a bump key must have the same blank profile as the lock it is made to open, restricted or registered key profiles are much safer from bumping, as the correct keyblanks cannot legally be obtained without permission and/or registration with relevant locksmiths' associations.

[edit] History

Many believe that lock bumping originated in Denmark in the 1950s^{[citation needed]}, but this is far from clear, and possibly started independently in several places. A Dutch TV show explaining the technique was broadcast in April 2005 and found its way to internet video sites in 2006, popularizing the technique considerably.