Can someone explain this statement to me?

[SIG]

Hello,

I was reading an article about master keys and there's a statement that doesn't make sense to me. Could someone please clarify?

http://www.crypto.com/papers/mk.pdf

"If every pin is mastered according to a standard TPP scheme, disassembly of a single lock will reveal 2^p potential master keys, where p is the number of pin stacks."

Makes sense.

"If the change key to a disassembled lock is available, the cuts corresponding to its bitting can be eliminated from each pin stack, making the correct bitting of the true master unambiguously clear from a single sample."

This is the part that I don't understand. Say you disassemble the lock and measure the pins, determining that the potential keys that fit the lock have some combination of 55555 and 44444 cuts (55545, 44454, etc.). One combination of this, of course, has to be the master configuration. What I don't understand is how the change key would cut 2^p combinations down to one. If the change key is 55544, obviously, that can't be the master key as well. But why can't the master configuration still be 55545, 44454, or any combination in between?

Sorry if the answer is really obvious!

Thanks!

[Evan]

The answer is obvious...

You are using the Blaze paper as a "hack" without understanding the concept of masterkeying or any of the terminology... You should know that he basically publicly disclosed a known reverse engineering technique that dates back to 1958 called the Dayton Method...

First with TPP (Total Position Progression) generated master key systems the top master key and change keys NEVER share any of the same cuts in the same positions ever...

So if you take apart a lock and find it filled with #4 bottom pins and #1 master pins, and you have a known change key of 55544 in hand the "proper" top master key can only be 44455 according to the rules for designing the system...

The other "functional" combinations which are permutations of 55555 and 44444 which would operate the lock are not actual keys in the master keying system and are referred to as "ghost keys" or "phantom keys" that some people often mistakenly attempt to use as an additional level of keying without realizing that severe key interchange can occur if you do not eliminate many valid change key bittings that will never be able to be used from the system at its implementation...

~~ Evan

[SIG]

You are using the Blaze paper as a "hack" without understanding the concept of masterkeying or any of the terminology... You should know that he basically publicly disclosed a known reverse engineering technique that dates back to 1958 called the Dayton Method...

First with TPP (Total Position Progression) generated master key systems the top master key and change keys NEVER share any of the same cuts in the same positions ever...

I thought I understood the terminology; I thought TPP stood for something else. Isn't the Dayton method the main focus of the paper?

Thanks for clarifying!

[cledry]

Evan explained it very well. Nothing to add, other than it made perfect sense when I read it. It is something we use every day in locksmithing.