What Is Lock Bumping & Should I Care?

Bumping, also referred to as "rapping" is not new. In fact, it's been around for at least half a century! When this method is used correctly it is extremely effective in over 90% cylinder type locks. As with any other lock picking technique it requires some time and patience to master. A bump key is a key in which all the cuts are at the maximum depth. Bump keys can be cut for standard pin tumbler type locks as well as "dimple" locks.

In the 1970s, locksmiths in Denmark shared a technique for knocking on a lock cylinder while applying slight pressure to the back of the lock plug. When the pins would jump inside of the cylinder, the plug would be able to slide out freely, thus enabling the locksmith to disassemble the lock quickly. The use of a bump key was not introduced until some time later and was first recognized as a potential security problem around 2002–2003 by Klaus Noch who brought it to the attention of the German media. After further examination of the procedure, a white paper was drafted in 2005 by Barry Wels & Rop Gonggrijp of The Open Organization of Lockpickers (TOOOL) detailing the method and its applicability.

A patent exists for a lock device following the same principle as the bump key from 1926–1928. The technique then attracted more popular attention in 2005 when a Dutch television show, Nova, broadcast a story about the method. After the method received further publicity from TOOOL presentations at security conference talks, members of TOOOL and a Dutch consumer group, Dutch Consumentenbond, analyzed the capability of the method on 70 different lock models and with trained and untrained users in a 2006 study.

At the same time, Marc Tobias, an American security expert, began to talk publicly in the United States about the technique and its potential security threats. In 2006, he released two further white papers regarding the technique and its potential legal ramifications.

High-quality locks may be more vulnerable to bumping unless they employ specific countermeasures. More precise manufacturing tolerances within the cylinder make bumping easier because the mechanical tolerances of the lock are smaller, which means there is less loss of force in other directions and pins move more freely and smoothly. Locks made of hardened steel are more vulnerable because they are less prone to damage during the bumping process that 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 not any safer from bumping. While the correct key blanks cannot be obtained legally without permission or registration with relevant locksmith associations, regular keys can be filed down to act as bump keys.

Locks that have trap pins that engage when a pin does not support them will jam a lock's cylinder. Another countermeasure is shallow drilling, in which one or more of the pin stacks is drilled slightly shallower than the others. If an attempt were made on a lock that has shallow drilled pin stacks, the bump key will be unable to bump the shallow drilled pins because they are too high for the bump key to engage. Many bump-resistant locks are available which can not be easily opened through the lock bumping method.

Of course you can also prevent such worries with an access solution such ISONAS' PoE PowerNet IP or SimonsVoss' Digital Locking & Access Control System.


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