I heard about bump keys recently, and had a little time to play around this morning.  I read an article about them, and watched a youtube video, and away I went.  It took about 15 minutes to hand-file a key.  And then another 20 minutes to try the "pull-back" method, file the key a little more and switch to the "minimal-movement" method, spray a little WD-40 in the lock -- tada!  I was kind of surprised that it actually worked.

I tried again, and it took me maybe 10 minutes to open it.  You have to bang harder than you might expect.  The next time was maybe 2 minutes, and then 30 seconds.  I switched to the door handle (I had been working on the deadbolt -- there apparently is some risk of breaking the lock, and I figured if I can only choose one lock to have working, I would rather have the handle lock working) and I opened it in about 10 seconds. 


I am not going to run out and buy new locks, but it is interesting that you can do it.  I hadn't really realized how a pin-tumbler lock worked before.  There is actually a good bit of physics involved - so I guess that means we should teach it in our schools.



Homemade bump key

Heather didn't really believe that a key that looked like that could open our door. 

Posted by Jon Daley on December 13, 2006, 7:20 am | Read 17020 times
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Watch out for the Richard Feynman effect: He once showed the folks at the Oak Ridge labs, where they were doing research for the atomic bomb, how vulnerable their "top secret" safes were to anyone who knew a few simple tricks. The government's response? Declare Feynman to be the problem, not their own bad practices. (From Surely You're Joking, Mr. Feynman.)
Posted by SursumCorda on December 13, 2006, 8:23 am

Wow, and I can't even make the right key work often time. It was great to read the pdf article you linked to. I discovered I wasn't picturing how the pins worked correctly. Now I know.
Posted by Harp on December 13, 2006, 11:09 am

I was looking at this "problem" and from what I remember, locks with tighter tolerances, ie more expensive ones, are MORE prone to be opened in this way.
Posted by Mike Q on December 13, 2006, 10:19 pm

Yes, that is what the articles I saw have said.
Posted by jondaley on December 14, 2006, 7:41 am

@jondaley This is a BIG problem. It's particularly bad when sites like http://www.bumpkey.us actually sell these damn things to just about anyone that wants them!
Posted by Allen Seymore on December 19, 2006, 2:35 am

Someone pointed out the other day that this would be a great spare key to hide outside under a rock, etc. Rather than hide a "real" key, hide one of these. That way, even if someone found it, they still probably wouldn't know how to use it.

Allen: I have been thinking about various different ways of making a bump key proof lock. I guess there are different budgets, so it isn't possible to get a one-size fits all lock, and there are various tradeoffs in complexity, cost and security.
It seems like the best solutions involve multiple locks, which is then a pretty big pain, at least for me.
I probably should write some articles on the different locks I have been thinking about.
Posted by jondaley on December 19, 2006, 6:50 am
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