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A lock is a mechanical or electronic fastening device that is released by a physical object (such as a key, a key card, a fingerprint, an RFID card, a security token, a coin, etc.) providing secret information (such as swapping numbers or letters or passwords), or by a combination of these or can only be opened from one side like a door chain.

A key is a device used to actuate a lock (such as to lock or unlock it). A typical key is a small piece of metal made up of two parts: the drill bit or blade, which slides into the keyway of the lock and distinguishes between the different keys, and the bow, which remains protruding so that the torque can be applied by the user. In its simplest implementation, a key operates a lock or set of locks that are keyed alike, a lock/key system where each similar key lock requires the same unique key. The key acts as a security token for access to the locked area; only people with the correct key can open and access the lock. In more complex mechanical lock/key systems, two different keys, one of which is known as the master key, are used to open the lock. Common metals include brass, plated brass, nickel silver and steel.

The first known lock and key device was discovered in the ruins of Nineveh, the capital of ancient Assyria. Locks like this were then developed to become the Egyptian wooden pin lock, which consisted of a lock, door fixture or attachment and a key. When the key was inserted, the pins inside the fixture were removed from the holes drilled in the bolt, which allowed it to move. When the key was removed, the pins fell halfway into the bolt, preventing movement.

The protected lock has also been present since antiquity and remains the most recognizable lock and key design in the Western world. The first all-metal locks appeared between the 870s and 900s, and are attributed to English artisans. It is also said that the key was invented by Theodorus of Samos in the 6th century BC.

“The Romans invented the metal locks and keys and the security system provided by the services.”

Affluent Romans often kept their valuables in closed and secure boxes within their households, and carried the keys like rings on their fingers. The practice had two advantages: it kept the key handy at all times, while signaling that the wearer was wealthy and important enough to have money and jewelry that were worth securing.

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