Hello. This is a demonstration of my little, simple wooden
combination lock model.
Like all single dial combination locks, it has a series of rotors
behind the dial.
The first of these rotors is coupled directly to the dial.
And there's a series of little tabs on the rotors.
So that if I turn the dial clockwise far enough
Eventually, the first rotor will catch the second rotor.
And if I keep turning that will eventually catch the third rotors.
So, if I've turned it clockwise by at least two turns
I'm guaranteed to have caught the third rotor with the tabs.
And, so by turning the first dial all the way onto
the first number of the combination I line up the
rear-most rotor with the bar. Which if all the notches are lined up
will drop into them and open the lock.
So, that's why you have to turn a combination
lock clockwise by at least two turns
before you dial in the first combination.
Now, if I were to keep turning clockwise
I'd eventually turn the back-most rotor past the notch here.
So, now by reversing and turning counter-clockwise by, at least, one turn
I have this tab catch the second rotor in the opposite direction.
And now, dialing into the second number of the combination
which is 21 that lines up the second rotor.
And now, reversing the direction again, I just have to dial in the third number
which is 11 and I have all three notches lined up.
And, I can just open the lock.
Now, interesting aspect of combination locks
is it's important to clear the combination after you're done using it.
This lock doesn't really have anything in there to do that automatically.
So, if I open this lock very slowly
You can see that the notches are still lined up and
I can just open it again.
There's various strategies for clearing this kind of combination.
On the Dudley lock, the combination is cleared by essentially releasing
the bar from the notches with a bit of a snap which gives them
a bit of a sideways kick. So, with this Dudley lock
which is currently open. When I close it, even if I close it very, very slowly.
You can see just the front dial get a bit of a kick.
And now the combination is cleared. And even if I set the
front dial to where it was.
The internal rotors have also been kicked a bit so
this lock can't be opened so this is very good on the Dudley lock.
It does really clear the combination.
Demonstrating how the Dudley lock does this
I just simply open the lock with a little bit of a snap.
And you can see the rotors have spun past where they were.
So, now the combination is effectively cleared.
So, whoever wants to get into this lock now,
actually needs to dial in the combination again.
The Master lock, on the other hand employs a less elegant strategy
of clearing the combination. So, let me open this Master lock
to demonstrate. So, we dial in the combination.
And we open it.
Now when I close this it doesn't actually
even rotate the rotors. So, if I don't do anything about it
you can still see the last number of the combination.
But it doesn't open again. So, you think, well, this is secure but
really its not. Because the numbers still in there.
So, if I just turn the dial to the right 10 and back to the left by 10
somehow it opens again. Without me actually knowing the combination.
So, if you encounter one of these Master locks.
And you'd like to get into it.
Just try turning the dial right by 10 and left by 10
and you might just be able to get into it.
I have to warn you. This doesn't work every time.
And it very rarely works more than once.
So, if I close this lock again. And try that trick again.
Most often, it won't work a second time.
There, so can't get into it anymore now. But
it's worth a try if you want to get into a Master lock.
It's an interesting little security vulnerability.
For more on my Wooden Combination Lock
Go to woodgears. ca/combolock