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There is a specific pattern for each lock and key made in the world. A specific key can only open a specific lock which has the same pattern in which the key can fit.

This thread here suggests that there are millions of locks with the same key.

Yes, there are millions of locks with the same key. Think of it this way... Master lock has 8 depths and four pins for most of their locks.

8x8x8x8 = 4,096 possible key permutations, including keys that exceed MACS (Maximum Adjacent Cut Specifications). The actual number is lower than that. Yet Master Lock makes many thousands (hundreds of thousands?) of locks a year.

Kwikset has six depths and five pins for their normal home deadbolt lock.

6x6x6x6x6=7,776 permutations, again including those that exceed MACS. They must sell a million of those locks a year.

Many other commenters in the same thread make consistent claims.

Is it possible that somewhere in the world, two locks can randomly be of the same pattern - i.e. One key can open two different random locks?

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    Anecdotally, since you asked "ever", yes they do. Once, when I was changing my two front doors' deadbolts, I naturally picked up two of the same brand of door knob from next to each other on the shelf. About a week after I'd installed them and distributed keys to my family, it hit me that they just happened to have exactly the same key. – rhrgrt Sep 29 '15 at 16:20
  • Another Anecdote: The door key of a friend odfmain fitted the lock on my high-schools Elevator - he never took the stairs. – sum1stolemyname Sep 29 '15 at 20:15
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One key almost certainly can open someone else's lock in 'n' number of possibilities because even with the best locks, there are a finite number of combinations to which the lock maker sets the levers or pins. Therefore, eventually there will be duplicates of the pattern of locks. Padlocks typically having fewer than 1,000 effective combinations and cylinders having fewer than 20,000 combinations for lockers do not rank in value as very high security locks which is demonstrated by unlocking here and here.

Per Kwikset rekeying 2004 manual, for a Kwikset lock, there are 5 pins with 6 possible depths. That's 6 to the power of 5 or 7736 possibilities. One can also add two common key profiles (KW1 or Axxess #66) to this combination. Thus, most keys for the Kwikset lock will have about a 1 in 15,552 chance of matching a given lock. However, there are also some other less common profiles, and a small minority also uses 4 pins. If someone happens to have one of those locks with less common profiles and number of less pins, the key will be much less likely to match a random lock. Kwikset smartkey locks have been claimed to be vulnerable to hacking demonstrated by researchers here.

Per BSI, in terms of key security, EN 1303 grade 6, a UK standard for the grading of the security of cylinders in locks requires a minimum of six pins and at least 100,000 effective different combinations (that is combinations that are actually inside the range of combinations that are being produced) for their highest security rating of Grade 6. EN 1303 Grade 4 is achieved with five moveable pins and, at minimum, 15,000 effective combinations, but fewer than 30,000 combinations.

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    Please cite some sources. – gerrit Sep 29 '15 at 9:45
  • @Gerrit-sources cited – pericles316 Sep 29 '15 at 10:56

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