A key code is a series of alphanumeric characters used by locksmiths to create a key. There are two kinds of key codes: blind codes and bitting

Bitting

A bitting is the part of the key that actually engages the tumblers to activate the lock. Bittings are often represented as a code which instructs how a key is to be cut by a locksmith. The bitting is usually a series of integers that is usually translated from a key code chart or from a...

 codes.

Blind codes

These are codes that require a chart or computer program to translate the blind code to a bitting code, which is used to create the actual key. Most key codes are blind codes, and publication of code books or software are restricted to licensed locksmiths in most jurisdictions for security reasons. Some locksmiths also create their own blind coding systems for identifying key systems they installed, or for customer identification and authorization in high security systems. Example: 23N7 (General Motors) or X2100 (Nissan) are examples of blind codes used for automotive ignition keys.

Many computer and manually generated master keying charts also utilize blind codes for identifying individual change keys and masters within the system.

Bitting code

The translated blind code which the locksmith actually uses to cut each cut on a blank key. Example: padlock blind code W123 translates to bitting code 25313, to which the locksmith would cut the key with his code machine by setting it to 25313.

Experienced locksmiths might be able to figure out a bitting code from looking at a picture of a key. This happened to Diebold voting machines in 2007 after they posted a picture of their master key online, people were able to make their own key to match it and open the machines. http://spiralbound.net/2007/01/25/diebold-voting-machine-key-copied-from-photo http://www.freedom-to-tinker.com/?p=1113