Thing a Week 2: Cracking Combination Locks

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Single-dial combination locks are a common appearance in safes and places such as locker rooms and school hallways where tons of locks need to be used in many different places. These combination locks unlock by spinning a dial clockwise to the first number, reversing the direction to the second number, and rotating clockwise again for the third and final number (assuming the padlock only has three-number combinations, which this guide will cover). On the inside, the dial you turn moves three disks (called cams) that align each notch so that the lock’s latch can fit through them and open the lock.

Now, when you look at the average combination lock, it may quite possibly have 40 or 60 numbers on the dial. For the purpose of this article, we’ll assume we have a lock with 40 different digits on the dial. Most of the cheaper locks also have a little bit of “wiggle” room, that allows people to open the lock as long as they are within a digit or two of the true digit. For the sake of math, we’ll assume we’re dealing with a super awesome lock that requires the exact number to be entered.

Alright, math. We have one lock with three digits to enter in the combination, and each digit ranges from 0 to 39, for a total of 64,000 possible combinations (40 * 40 * 40 = 64000) to work with. Assuming you’ve got crazy fingers and you can enter a combination in ten seconds, you’d spend over a week of 24/7 spinning if you tried to brute force every possible combination.

Well, that’s without a sneaky trick. What if I told you that with a little practice, some trial and error, and a tad of information, you could cut down the possible combinations to merely one hundred.

What’s that, you say? That’s still too many numbers? Well, then obviously what’s locked inside isn’t that important to you. Or–you know–maybe you should look into shimmies if your lock isn’t that expensive. In any case, just following these simple steps will reduce the number of possible combinations by 99.84%.

  1. Pull upwards on the latch to apply tension to the inner workings of the lock. When you have a firm hold, apply a fair amount of pressure to the dial and turn it counter-clockwise until you feel the click of the hinge locking.
  2. When you hear the click, write down the number you’ve landed on. Continue to do this until you have twelve numbers.
  3. Seven of these twelve numbers will have landed between two digits on the dial. Cross those seven out, and you’re left with five numbers.
  4. Four of the remaining five digits should end in the same digit. Cross those four out and you’re left with a winner: it’s one of your numbers.

That’s the easy part. For the second part — the part that takes the majority of your time — you’ll need these four sets of magic numbers:

0, 4, 8, 12, 16, 20, 24, 28, 32, 36
0, 6, 10, 14, 18, 22, 26, 30, 34, 38
0, 4, 8, 12, 16, 20, 24, 28, 32, 36

———-

1, 5, 9, 13, 17, 21, 25, 29, 33, 37
1, 7, 11, 15, 19, 23, 27, 31, 35, 39
1, 5, 9, 13, 17, 21, 25, 29, 33, 37

———-

2, 6, 10, 14, 18, 22, 26, 30, 34, 38
2, 8, 12, 16, 20, 24, 28, 32, 36, 0
2, 6, 10, 14, 18, 22, 26, 30, 34, 38

———-

3, 7, 11, 15, 19, 23, 27, 31, 35, 39
3, 9, 13, 17, 21, 25, 29, 33, 37, 1
3, 7, 11, 15, 19, 23, 27, 31, 35, 39

Alrighty, now that those jolly sets are out of the way, let’s get started. What you want to do first is find which set of numbers the number you found earlier first appears in. In our example, we’ll assume you found the number 4 earlier.

  1. Find your number in the third row.
  2. Try the first digit in the first row, then the first digit in the second row, then your magic digit from earlier. (In this case, you would try the combination 0-0-4).
  3. If it doesn’t work, move over one column in the first row and try the second digit in the first row, then the first digit in the second row, then your magic number. (So now you would try the combination 4-0-4).
  4. Keep moving over in the first row until you reach the last number. After that last number, you’ll move over one digit in the second row and reset your first row back to the first digit and start over. (So you would try the combination 0-6-4, and then the next combinations would be 4-6-4, then 8-6-4, and so on.)

That’s really all there is to it. This method cuts the possible combinations down to a maximum of 100. You have to also remember that it’s unlikely you’ll try EVERY possible combination, and that a lot of combination locks are lenient on “close” numbers, which means you’ll actually try far less numbers than 100 most of the time.

When the lock finally pops open, you’ll feel a huge rush of adrenaline and pride. Try not to smile too wide!

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