Masterkey puzzle

[peterwn]

Given the following seven change keys, what is the masterkey bitting?
269766
241140
843326
687366
241588
221562
041348

[Evan]

If it is a standard TPP keying system the top master key can only be:

405904

If it is a RC keying system then the "3-in-6" top master key would be:

241366

269766 3-in-6 X---XX
241140 3-in-6 XXX---
843326 3-in-6 -X-X-X
687366 3-in-6 ---XXX
241588 3-in-6 XXX---
221562 3-in-6 X-X-X-
041348 3-in-6 -XXX--

~~ Evan

[ARF-GEF]

Great answer Evan! Thank you:)
Can you detail how you got to the TPP answer? What is TPP?

[Evan]

TPP (Total Position Progression) is a process used to obtain key bittings in a master key system wherein bittings of change keys differ from those of the top master key in all bitting positions... It is one of the two methods for split pin master keying...

RC (Rotating Constant) is a process used to obtain key bittings in a master key system wherein one or more cut(s) in a key of any level which remain constant throughout all levels and are identical to the top master key cuts in their corresponding positions. The positions where the top master key cuts are held constant may be moved, always in a logical sequence...

So pretty much all split pin keying systems other than dimple or magnetic bitted keys which use positional master keying will be either TPP or RC...

To come up with the answer for the TPP master key all you have to do is look at the list of the change keys knowing that the possible bitting depths in any chamber are either Even ( 0, 2, 4, 6, 8 ) or Odd ( 1, 3, 5, 7, 9 ) and look for the bittings which are never used in a given position in the list of change keys...

The answer for the RC master key requires more experience with master keying to figure out, but in general, the master key bitting in any position is usually the bitting which appears most frequently in that position on the bitting list... Then you have to be able to figure out how many cuts from the TMK are constant in the system -- that number never changes within a keying system, so each key in a 3-in-6 system will have 3 bittings from the TMK on a 6-pin key rotated around through the various patterns available...

~~ Evan

[ARF-GEF]

Thanks, great info

[peterwn]

Congratulations, Evan
I was looking for a RC answer, as the TPP answer, while having the characteristics of a top masterkey was a MACS of 9 which is unlikely in practice.

Years ago, someone complained to me that they could not get a key cut for their garage. He showed me the key and if was from a British Yale multiplex system. I suggested the best thing to do was to swap it for a conventional cylinder I could give him. I dismantled the cylinder and found three spacers and thought it looked like 'variations on a theme' system. They had a MACS of 4, like their ordinary Yale 8 cylinders. My puzzle is based on that lock but with a different MK bitting. The key was stamped 4xxx with 160 below which looked like a system number and key number (which it was). Soon after I discovered that the (then) Education Board bulk ordered masterkeyed locks for its schools so its maintenance officers could access buildings during school vacations and would issue the appropriate number of locks to builders to fit to new schools. They must have issued one lock too many to a builder who then fitted it to a garage he built without realizing that the future owner could have difficulty obtaining keys. While Yale required UK users to order extra keys from their Willenhall factory, they did supply blanks to foreign locksmith wholesalers on condition that those getting keys cut provide written authority with locksmiths / keycutters requiring a written authority on school letterhead being sufficient. These locks were a nuisance because of the 'red tape' of getting keys made, that they were not GMK'd for the larger schools, and while each sub-batch used the same profile, three or more profiles would be prevalent in each locality then a new one would appear causing a delay while blanks were ordered.

Finally some petty criminal got wind of the existence of a masterkey and broke into the Board offices and stole one, then raided schools of their valuable equipment. The Board went out of existence with a change of school administration and presumably most of these locks would have been replaced by now.