About Master keying

[poor paperclip picker]

I have read some threads in the forum where people briefly talk about master keying. Also the place where I worked this past summer used it. I would just like to know the basics on how it works. Like are there certain pins used that allows that slight change in the keys? Do the pins have a little extra room to move to allow the different keys to work? I would just like to understand the concept of this and how the pins work in these locks.

Thanks.

[kg4boj]

the way it works is there are more pins added to the stack to allow more than one shear line to be present in the lock...

ie if we are only looking at two pin stacks, lets say one has the following bitting 11 and another lock has a 44.
obviously the same key wont work in both, but lets say we add # 3 master pins on top of the 11 bitted lock. The lock will work with a key cut to 11, 14,or 44 bitting. Now if you had a key cut to 11, it would work the first (11) but not the second (44) but you could have a key cut to (44) that would work both.

[poor paperclip picker]

ok that makes some sense now. so are there more than 2 pins in each hole?
____top pin
|| ___shear line
||----bottom pin
V

But in a master keyed

||___first master pin and shear line
||_____second master pin and shear line
||----bottom pin
V

I dont know if this is right but i am guessing. I think this was how a lock was setup when I took one apart this summer.

[elbarto]

from what I have read about master keying there can be more than just one master pin in the each pin stack but you diagram is correct.

Is there any info on this site that goes through the process of developing a small system for masterkeying. There seems to be alot of considerations you need to make for phantom keys and how many orders of keying you want in a system. There is some info on the net that explains the principle of master keying but I haven't come across anything yet that gives you a good idea of how to write up a system by hand.

[JK_the_CJer]

the way it works is there are more pins added to the stack to allow more than one shear line to be present in the lock...

ie if we are only looking at two pin stacks, lets say one has the following bitting 11 and another lock has a 44.
obviously the same key wont work in both, but lets say we add # 3 master pins on top of the 11 bitted lock. The lock will work with a key cut to 11, 14,or 44 bitting. Now if you had a key cut to 11, it would work the first (11) but not the second (44) but you could have a key cut to (44) that would work both.

A key cut to 41 will also operate the lock. I'm not in the mood to work out the math, but you can imagine how masterkeying (not including master rings) dramatically increases the number of keys that will open a lock. This also makes picking significantly easier in most cases (you get two chances per masterkeyed stack instead of one to hit that shear line!) Some master key systems have an additional vulnerability described by Matt Blaze in his paper "Rights-Amplification in Master Keyed Systems" (something like that anyway). If someone knows of a really good paper on masterkeying systems in general, I'd love a link. The specifics of TMK, GMK, cross-keying, maison keying, etc.. are still a very alien world to me.