|Applying the Method to
the Master Models 2002 and 2010 "High Security" Combination
These "high security" padlocks open as follows: the user dials the combination in the same way as for other Master single dial padlocks, but, after dialing the last number, the user turns the knob left until it stops, then pulls on the shackle to open the lock.
These locks do not have "sticking places" to help locate the last number. Locating the last number narrows down the number of combinations to try. However, even though we must try more combinations, we find these locks easier to open than the "standard security" Master combination locks, because the shackle does not have to be pulled each time to determine if the correct combination has been dialed.
We bought and tested two locks and the combinations followed the pattern found on other Master locks.* The pattern is as follows: If we know the last number, the possible first numbers are the last number and the numbers spaced four apart on the lock dial, starting at the last number. The possible second numbers are half way between, on the lock dial, the possible first numbers. (Furthermore, for each first number tried, only 8 of the 10 possible second numbers may be used with that first number.)
On the locks where we could locate the last number, we narrowed the possible first numbers down to 10 out of the 40 numbers on the lock dial. On these "high security" locks, we could do the same thing by locating the last number, but we can't locate the last number. So, we start out with 40 possible first numbers, the 40 numbers on the dial. However, the lock allows for sloppy dialing. If we try the 20 even first numbers, the lock will probably open, even if we are off by 1 on both the first and second number. Both of our locks opened using even numbers, although the manufacturer's combinations only had odd numbers. So, our method starts out by trying the even numbers as first numbers. If we haven't opened the lock after trying all the even numbers, we will go back and try the odd numbers as first numbers. So, here is the method:
Let's start by trying 0 as our first number. Two turns right, and continue, stopping precisely on 0. Now, one turn left, and continue 2 marks past our first number, so we stop precisely at 2.
A) Now, right almost a full turn to 4 marks before reaching the number we just dialed from the left. (On the first pass, that number was 2, so we stop at 6.)
B) Left exactly a full turn, stopping at the number we just finished dialing from the right.
Repeat A and B until you reach 6 marks before your first number when turning the dial left in step B. (When trying 0 as your first number, stop when you return to 34 turning left in step B.)
While turning left in step B, if the dial refuses to turn any further, then the lock is ready to open! Don't pull the shackle just yet. Make a note of your first number, and the number last dialed in step A is your second number (not the number dialed in step B.) Let the dial dial come back to the right. Move the dial back and forth by lightly turning the dial to the spots where the dial becomes harder to turn. The last number is in the range of movement. Make a note of the number. Now, turn left until the dial stops, then pull the shackle to verify that the lock opens.
If the lock opens and your last number was even, you now have the correct combination. If your last number was odd, both your first and second numbers are off by one, and your lock opened because it allows for sloppy dialing. Your lock should open more reliably with the correct combination, found as follows. Starting your last number, turn the dial 4 marks at a time until you are one mark away from the first number you tried. You are now at the correct first number. Now, move the dial 2 marks in either direction, then move the dial 4 marks at a time until you are 1 mark away from the second number you dialed. You are now at your second number.
Most likely, your lock hasn't opened so far. Try 2 as your first number, as follows. Two turns right, then stop at 2, then one turn left and continue 2 marks further to 4. Then, steps A) and B). (The first stop in step A is at 8.)
Continue with the other even numbers until you have tried the last one, 38. If the lock hasn't opened, go back and try the odd numbers the same way.
There are 20 even numbers on the dial. We took between 90 and 120 seconds to try each first number, so it would take us 30-40 minutes to try all of them, but we are sure that we could improve our speed. Since a champion Rubik's cube solver could solve the cube 10 times faster than we could, we expect that the best padlock solver could open the lock in four minutes or less. A machine like the Locracker should be even faster and simpler, since the 2 solenoids are not used, just the stepper motor and lock holder on the left in the picture. (However, if the dial is turned too fast when turning left, it may not catch and stop.)
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Simplified dialing procedure for use when the combination is known, and description of a design change which would effectively thwart this method.
* We realize that two locks is too small for a valid statistical sample. However, we find that Master has used this pattern on so many of its locks that we are inclined to believe that these models follow the same pattern, even though we have only checked two locks.