eric343 wrote:n2oah wrote:I believe one only opens the lock and one only closes the lock, kind of like Abloy shopkeeper's system.
The Yale Bicentric is a mastering system like the Corbin master ring. The top plug (mounted upside down) is usually the master. The upshot of the system is that you can have a totally separate keyway for the master key, allowing a much more complicated master key system and absolute protection against an adversary modifying a change key to make a master key.
Actually the Yale cylinder seen in this thread is nothing like a Corbin-Russwin Master Ring Cylinder... As far as what it is, for the purposes of this discussion it is two entirely independent and separate mortise cylinders arranged to fit within the space normally occupied by one...
The claim of being harder to modify a change key to make a master key doesn't apply, the cylinder technology we are talking about here contains two entirely separate master key systems in the separate plugs which have nothing to do with each other at all so there would be no way a change key in one system could become a master key or any other key in the other, even if both plugs shared the same keyway...
Each unique 6-pin plug can support 15,625 different change keys if there is no cross keying which would introduce key interchange...
It is too bad that these cylinders are not still made, they would be excellent for the application of college dorm room locks as the keys the resident students would have and use would not allow them any access to decode any of the master keys...
Now a Corbin-Russwin Master Ring Cylinder is an entirely different animal, the keys have to follow some rules since they are operating the same plug albeit with a ring around it for the second shear line... Master keys do not have to be associated to the change keys under them directly by sharing constant cuts -- Master Ring cylinder change keys are unassociated to their master keys...
Master Ring cylinders when properly keyed are also immune to decoding the master key by means of possessing a change key, as the change keys and master keys do not operate the same shear line and therefore you can not still turn the cylinder unless all the pin stacks are aligned at either the plug or ring shear lines, having some stacks lined up at one or the other doesn't allow the cylinder to operate...
~~ Evan