Solving Pre-1996 Master Locks

by d4ftv4dd3r

NOTE!!: If you have a patience/learning problem, jump down to "For the impatient" below. My apologies for this long and dry article.

Regarding picking Master locks in your article, :

http://www.totse.com/en/bad_ideas/locks_and_security/piklock.html

Masterlocks will not be able to be opened using the technique described with the hairpin, due to the way the the lock is constructed. They use 3 pretty heavy duty metal disks with slots in them to hold the locking mechanism in place, so unless the hairpin is strong enough to twist the metal of 2-3 disks, it won't open. However, there is a flaw to their construction.

It is possible to determine the 3rd number on any master lock built before 1996 or so to a very high degree of precision and short amount of time. First of all, a bit of theory. They way a master lock works, is when you turn the dial, you are directly turning the disk of the 3rd number of the combination. The 3rd disk in turn turns the second, and the second turns the first. That's why you have to fully rotate the dial 2 or 3 times in the clockwise direction before going to the first number, so as to make sure that the first disk is being turned. Each disk has a little nub that protrudes from it's face, the second disk having one on each face so it is able to touch both the first and third nubs. So when you turn the dial, you are turning the 3rd disk, then the nub of the 3rd disk collides with that of the second and turns the second, and then the nub on the second collides with the first and turns the first. By the way, each disk has a deep slot in it. When you enter the correct combination, in effect, you are aligning the 3 slots of the disks in the correct position. The locking mechanism can now rotate and slide into the slots of the disks, freeing the latch.

To prevent people from simply pulling on the latch and rotating the dial to feel where the slot is on the third disk, the kind people at Master installed a 4th dummy disk, with "random" notches in it. That is why when you pull on the latch of a master lock, you find that it only turns a few degrees, and then stops, with seemingly random stops every few degrees. However, with any lock built before 1996 or so (not sure of exact date), not all dummy slots are equal, and the third number is still very findable.

F O R T H E I M P A T I E N T

If you have a lock to experiment with, you will find that for every dummy slot, there is a matching dummy slot every interval of 10. For instance, if you pull on the latch and turn the dial and finds that it stops on the number "12", indeed you will find that it stops also at "22", "32" and "2". If you find another at "6", you will see that it stops also on 16, 26, and 36. So bloody what you say? Here is the deadly trick. Say for instance you find the dial stops on "3", and you jiggle the dial a little bit and find that the red arrow, with a modest amount of jiggling, can point to either side of the 3 tick. Now you test 13, and see that, jiggling it, it is the same, that the red arrow is directly centered on the 13 and you can manipulate it to point on either side of the tick. But, when you test 23, you find that the tick is to the left of the 23 tick, that with a good amount of jiggling, it is directly in the middle of 22 and 23 and can point to either.You have found the 3rd number. It is 23. To verify, you test 33, and find that it is like 13 and 3.

What may also happen is this: You find that 3, 13, and 33, instead of being directly pointed by the red arrow, are all off centered to the left a little bit, but 23 is pointed by the arrow straight on. Again, 23 is your 3rd number. It is the deviant one that is the 3rd. With newer master locks, the notches are all identical, as far as I can tell.

"Now what about the first and second numbers you bloody prick?", you say. "There's still a bajillion and a half possible combinations!!!!@!". Worry not. The people of Master were kind to the likes of us, and were lazy. Let me jump straight to it.

Let x represent the first number, y the second, and z the third, which is known. let the symbol "%" represent "modulus", which yields the remainder of a division. So for instance, 7 % 3 = 1, because the remainder of 7/3 is 1. Let this then, be known:

z % 4 = x % 4

z % 4 = (y % 4) + 2

In other words, if z is 15, than x may be 3, 7, 11, 15, 19, 23, 27, 31, etc. And y may be 1, 5, 9, 13, 17, 21, etc.

(Note: the above equation still holds true for post-1996 master locks. It's just that it's harder to find the 3rd number...)

Now, that narrowed down the combination by quite a bit. With this knowledge, anyone can open an old master lock within 20 minutes or so, with some concentration. But with proper technique, a masterlock may be broken in 7 minutes or less, depending on the combo.

Remember all that jazz about the rotating disks and all that useless information? Here's where it becomes useful. Here is a sample of how, if one forgets his masterlock combo, one would find it again.

FOR THE REEEALLLYYYY IMPATIENT

1. The 'user' finds that the third number is 17

2. The 'user' turns the dial clockwise several rotations, until he is moving all three disks. (you can actually feel when the second disk begins rotating, and the first)

3. The user continues turning clockwise and stops on the number 1, his first guess for the first number.

4. The user then begins turning the dial counter-clockwise slowly, until he feels the third disk (for he is directly turning the third disk) collide with the second disk. (Which should happen around 0 or 39, in this case)

5. The user rotates the second disk to the 3 position, his/her first guess for the second number.

6. The user then rotates the dial (and the third disk) to the predetermined 3rd number, 13.

7. The user pulls on the latch. Assuming it does not open, for that would prove to be boring, the user continues as such:

8. The user SLOWLY, rotates the dial counterclock wise until he/she feels the second dial, at the number 3 where he/she left it.

9. The user rotates counterclockwise from 3 to 7.

10. The user then rotates clockwise back to 13.

11. User pulls latch.

12. user rotates counterclockwise till the user hits the second dial at 7, and pushes it to 11.

13. user rotates clockwise back to 13.

14. user pulls latch.

As you now notice, we are saving lots, and lots of time by never touching the first disk, and moving the second disk in strategic amounts. (intervals of 4) After you have finished every combo for you first guess at the first number, rotate clockwise several times to reset the disks, and begin on your next guess for the first number, which is probably 5. This method is also very economical because absolutely no damage is done to the lock, and you can safely retrieve the working combo in the least amount of time.

If ever any of you have the time, try hacksawing one open. A vise is very helpful, but the metal armor of the lock is not too tough to get through. Just go in a big circle and hacksaw the face off. Use an old screwdriver to pry the dial off.

- d4ft