The inside of a typical pin tumbler lock, animation shows how the pins are set to enable the cylinder to turn and release the latch/deadbolt:
You can also set pins on top of one another so that multiple keys can successfully turn the cylinder, using a "master" key and a "change" key. The idea is that several cylinders will be keyed to the "master" and each cylinder will also be keyed to its own unique "change" key.
- Cylinder Locks on Wikipedia
- Lockpicking slides and links by TOOOL (The Open Organisation of Lockpickers)
- In California, it is lawful to duplicate existent keys. Further, a "Locksmith" is defined as a person who engages "in the business of rekeying..." etc, "for any consideration or compensation whatsoever" ('consideration' meaning benefit of a contract i.e. not a gift).
(j) "Locksmith" means any person who, for any consideration or compensation whatsoever, engages, directly or indirectly and as a primary or secondary object, in the business of rekeying, installing, repairing, opening, modifying locks, or who originates keys for locks, including, but not limited to, electronic cloning of transponder keys and any other electronic programming of automotive keys and electronic operating devices, such as key fobs, door and ignition key devices, and successive electronic and other high-security key technology. A "locksmith" does not mean a person whose activities are limited to making a duplicate key from an existing key.
- In California, it is lawful to possess lock picks (i.e. circumvention tools) by statue, the state must prove criminal intent.
- Section 466-469 of the California Penal Code
California Penal Code - §s 466-469. Burglarious And Larcenous Instruments And Deadly Weapons. § 466. Every person having upon him or her in his or her possession a picklock, crow, keybit, crowbar, screwdriver, vise grip pliers, water-pump pliers, slide hammer, slim jim, tension bar, lock pick gun, tubular lock pick, floor-safe door puller, master key, ceramic or porcelain spark plug chips or pieces, or other instrument or tool with intent feloniously to break or enter into any building, railroad car, aircraft, or vessel, trailer coach, or vehicle …, , or who shall knowingly make or alter, or shall attempt to make or alter, any key or other instrument named above so that the same will fit or open the lock of a building, railroad car, aircraft, vessel, trailer coach, or vehicle …, without being requested to do so by some person having the right to open the same, or who shall make, alter, or repair any instrument or thing, knowing or having reason to believe that it is intended to be used in committing a misdemeanor or felony, is guilty of a misdemeanor. § 466.3. (a) Whoever possesses a key, tool, instrument, explosive, or device, or a drawing, print, or mold of a key, tool, instrument, explosive, or device, designed to open, break into, tamper with, or damage a coin-operated machine …, with intent to commit a theft from such machine, is punishable by imprisonment … or by fine ….