(Sorry Andy, I was ease dropping =] )

As tough as Masterlocks are, they are just mechanical gadgets. You can reverse engineer an old Masterlock to reveal its combination. I wish I had a lock with me… if you have one try it out yourself!

Steps to reveal the combination of an old Masterlock:

1) blah blah blah… (steps needed to find the last digit of the combination that doesn't use number thoery) …and that's the last number **x** of the combination

2) Perform **x modulus 4**. We know there are infinitely many integers that are equivalent to x modulus 4, however the range of numbers on the Masterlock dial is from 0-39, therefore there exists 10 digits that are equivalent to x modulus 4. These are all the possiblities for the **second number** of our combination. Let's place them in a set of all possible second number **y**.

3) Perform **y modulus 4** to acquire all possiblilities for the **first number** and catalog them in a set of all possible first number **z**. We also know that there exists 10 possible integers from 0-39 that are equivalent to y modulus 4.

4) This leaves 10 * 10 * 1 = **100 possibilities left**, and that my friends is a lot fewer than 40 * 40 * 40 = 64,000 combinations that exist.

5) Try those 100 combinations, making sure you cross off ones you've already tried.

Notes:

I want to know why we have to use modulus 4? But first I'd rather try the method out!

Sources:

http://www.whatsmypass.com/?p=399

http://everything2.com/index.pl?node_id=1304470