A combination lock is a lock that requires the entering of a specific sequence of symbols to dislodge and open. Though the symbols are typically numerical, letters and other types of symbols may also be used to formulate a sequence. Depending on whether the lock is single-dial, multiple-dial or electronic; discs or keypads may be used to enter sequences. Combination locks are generally thought to be secure, but each type of combination lock has security flaws.
Combination locks can be found on almost anything that requires protected access. Usually, they can be seen on safes, bicycles, lockers and briefcases. The most common types of combination locks are single-dial and multiple-dial.
Multiple-dial locks are often used on bicycles and briefcases. The mechanism for these locks consist of a toothed pin and many notched, rotating discs. Multiple-dial locks are considered to be less secure than other types of combination locks. A combination lock like this is relatively easy to compromise due to its mechanical irregularities.
Single-dial locks are usually used in conjunction with padlocks and safes. Structurally, they consist of indented, parallel discs corresponding to a specific symbol and rotation sequence. Typically, the rotation follows a clockwise-counterclockwise-clockwise pattern. When the proper symbol sequence and rotational patterns are entered, the discs' indentions line up and open the lock.
Though a single-dial combination lock is often considered to be a secure locking mechanism, its structure is not foolproof. A combination lock can be tampered with and broken using the proper tools and strategy. In addition, a potential tamperer may only need a vague idea of the true combination to gain access, since certain combination locks may register slight variations in a combination sequence as correct. Numbers within a combination may also be mathematically related to each other.
Technological advances have made the electronic combination lock a reality. Combination locks of this nature can incorporate a keypad into their mechanism and require that a user manually enter a key code for access, as through a door. While these locks may appear to be especially secure, they present their own mechanism-specific problems. For example, tamperers may be able to gain access simply by examining the keypads for wear-and-tear on specific numbers and then determine the access code. Since these locks often require that a set code be shared, distribution of the code may increase the risk that those with unauthorized entry can gain access.