Cross Keying Question

[0x69616e]

For starters, I'm a complete newbie at this. Be gentle.

My SO has two kids who occasionally swing by my place after school because it's easier for me to get home than for her to get home from time to time (I work two blocks from my house). I'd like to re-pin my front door (We both have Schlage 5 pin, SC1 keyways) so that her kids can use the key to their Mom's house to open my front door without changing any of the other locks in my house that are keyed alike.

If our locks are bitted like thisL

Code: Select all

21639
88437


I think I'd need to re-pin the two locks like this:

Code: Select all

21437
672x2 (Master Pin)


Could someone help me do the math on this?

Thanks;

[GWiens2001]

That is correct on the key pins and Master pins.

Also, just for your information, the proper term is master keying.

Keep up your good learning!

Gordon

[cledry]

You are correct. Fortunately the keys are more than 1 depth different in the corresponding positions.

[jimu57]

Looks good. Do you have pins? I have Schlage and master pins I could send you. Free of course. PM me if you need anything.

[demux]

Keep in mind that if you do it this way (master 4 chambers of a 5 chamber lock), you're not only allowing the two keys you intend to open that lock, but also every other key that has any combination of those cuts at any of the mastered positions. E.g.

28437
21437
88639
...

You're also making it much easier to pick the lock, as there are now two valid positions the pins can be set to in almost every chamber.

If you don't mind asking your SO's kid to carry one extra key, you might master the locks like so:

21639 <-- your key, aka the master
61639 <-- the new change key for this single lock

Doing it this way will only allow for the two keys you expect to be able to open the lock.

Not that your proposed way is necessarily wrong, just want you to be aware of the tradeoff in security for the added convenience.

[GWiens2001]

The master keying proposed by the OP would result in 16 possible keys that would operate the lock.

Since you want their key to work in your locks, you might consider just key your locks to match their key. If you have some locks you don't want their key to open, then that is a different story and would require master keying.

Gordon

[jimu57]

Put in an electronic push buttom combination lock.

[Tyler J. Thomas]

The master keying proposed by the OP would result in 16 possible keys that would operate the lock.

Don't take this personally but I really hate this "point" about master keying.

Accounting for MACS, "straight line" keys, and observing Schlage's key bitting specification, there is something in the order of 66,000 possible bittings for a 5 pin cylinder. 16 incidental master keys represent 0.0002424% of available combinations. And yeah, I understand "it's not the likelihood it's what's at stake" but I don't buy that. The data and examples don't support that people, nefarious or otherwise, going out and trying random keys on locks. Using the same circumstances you'd have a 1:4,125 chance of a random key, observing all other previously discussed "rules", working this lock; over your lifetime you'd have a better chance of being struck by lightning.

Keep in mind that a box of Schlage blanks usually come in quantities of 50 (Ilco sells them as high as 250). That's 81 boxes of key blanks you'd have to cut, in hopefully the right rhyme or reason, in order to go out and be statistically favored to unlock his locks.

[GWiens2001]

Happen to agree with you on that, Tyler. And no offense taken.

That is why my first comment made no mention of it. Just pointing it out since others had referred to the vulnerability. 16 is not that many, though picking is much easier. Not many lock-picking thieves, and hope it stays that way.

Gordon

[Tyler J. Thomas]

That is why my first comment made no mention of it. Just pointing it out since others had referred to the vulnerability. 16 is not that many, though picking is much easier. Not many lock-picking thieves, and hope it stays that way.

Gordon

Same here!