Modifying an older Corbin for pick resistance

[FarmerFreak]

I got my hands on an old an very uncommon lock cylinder. It is an odd sized mortise cylinder, with a master key sleeve in it!!

I took a picture of it next to a standard Sargent mortise cylinder for size reference.


Because of the way I assemble this lock I decided not to go through the hassle of taking it apart to take pictures. (I didn't want to pry the cap off the top again )

This is how the lock is normally, 6 pin chambers with two shear lines. Kind of like Best IC, ...without the interchangeable part.


The temptation to make this lock extremely difficult to pick overwhelmed me. So the first thing I did was add a pin on the side to "loosely" lock the inner core and the master sleeve together. This made it so you had to pick the outer sleeve to get the lock to turn.

At this point it was very easy to pick the inner core, which will turn about 4-5 degrees and stop. And then if you didn't know better you would think that you made it to the spooled pins, halfway there, except all the pins are actually set to the bottom shear line!! Such a nasty little deceptive trick.

To make matters worse, or better (pending on how you look at it), I added a side bar to the outer sleeve. This sidebar has nothing directly related to the key. It serves one purpose. To prevent the outer sleeve from binding without first applying even more tension to the inner core, which can't turn. Unlike a Best core there aren't any holes in the bottom to try and grab on to. But in retrospect I probably should have added the sidebar to the inner core and loosely lock the outer sleeve to the housing.



If I only wanted to deter single pin picking this would likely be enough. But ...well...yeah.

I modified two chambers so they couldn't be pick gunned/key bumped. I also made sure that every chamber can be picked and set at 3 different depths, only one of which is correct.

[musicninja17]

Very nice! Sounds extremely secure to me.... is it still pickable at all now?

[LocksmithArmy]

What kind of tools do you use to make all these adjustments... You musht have a whole machine shop for tiny parts in your garage or somthing...

you should to a tour of your workstation for us

[FarmerFreak]

Very nice! Sounds extremely secure to me.... is it still pickable at all now?

I can pick it, but I believe that is only because I know exactly what the cuts are. For that reason it can obviously be picked, without knowing the cuts is a different story. I'm hoping (crosses fingers) that I can make it to Defcon next summer (I've never been). If I go I'm bringing this with me.

What kind of tools do you use to make all these adjustments... You musht have a whole machine shop for tiny parts in your garage or somthing...

You'd be surprised what you can do with very basic tools. To modify this lock I used: a vice, a small flat file (to cut in the grooves for the sidebar), a Dewalt drill and bits, a tap (I think it was a 6x32) to get some false gates for the 4th and 6th pins. Small wire cutters and tweezers.

Other materials are from a Corbin pin kit. Two Assa driver pins (4th and 6th spaces), two Medeco #6 master wafers (with a hole drilled through them, residing above the Assa driver pins) two older GM wafer springs (going through the Medeco pins), two Medeco springs cut a little bit shorter with the wire cutters. Two Schlage sidebar springs and a key blank to make the sidebar.

And of course some small screw drivers for the cam screws. Small hammer and punch to put the cap back on.

[LocksmithArmy]

quite creative, using other locks to make your lock...

nice work. I cant wait to get home and start playin with stuff like this

thanks for sharing

[FarmerFreak]

I was searching through some patents on google. Apparently the basic concept of what I was trying to do here has already been patented. The only real difference is that I used a couple of anti-bump pins!!

Other than that, they show a ball bearing instead of a sidebar. That would have the same affect though.

http://www.google.com/patents?id=54gYAA ... q=&f=false

However I haven't seen a lock like this on the market.

[FarmerFreak]

I have come up with a possible upgrade to this lock. I'm not planning on actually doing this right now. Partly because I have lent the lock to some people to play with. And partly because I like the way this lock acts right now. That said, if I did make this upgrade it would be a hugely awesome upgrade....I may actually do this upgrade at later time....

A big part of this upgrade is based off of the ideas in this thread. viewtopic.php?f=25&t=47065 Thank you inverseentropy for the Commit then authenticate idea.


The pin on the right still prevents the two cylinders from moving without each other. But now it is simply allowed to turn 10-20 degrees before even trying to turn the outer core. I imagine that this pin should be placed somewhere near the center of the lock (between pin spaces 3 and 4).


The second change would be to add a couple of pins like this to the side. These pins will completely lock the outer core from turning until the center core has turned and lifted these pins to the sheer line. Thus allowing the outer core to turn. This should prevent someone from being able to get any feeling from the outer sheer line (the important one). I imagine using four of these pins two in the first half of the lock and two and the second half of the lock.

The sidebar obviously helps to prevent any feel from the outer core. But locking the outer core completely, until the inner core has turned, is so much more fun.


Finally there would be a change in how the lock was keyed. For the sake of simplicity I have keyed the inner core identically for every chamber. All of the chambers will be allowed to turn on the same 3 depths. I could go 4 depths, but then I would be using smaller master pins, I personally don't want to do that.

One of the three depths corresponds to the correct depth for the outer core. I figure that a few anti-bump pins should still be placed somewhere randomly in the lock, regardless of what the actual depth is for that space. This would be to deter someone from turning the lock to the authenticating position (all cuts set at the deepest possible depth), and then trying to rap (or use a powerful pick gun!?) the cylinder in the hopes of bumping them past the outer sheer line.

To use this lock. There would be one minor trick to remember to get the key back out. To line up the two sheer lines. You simply need to turn the lock until you feel the sidebar click back into position, at that point you can turn the key back to the neutral position to be able to pull the key out.
(I love the ability to have a fully working 3d model in my head,...some say I'm crazy.)

[FarmerFreak]

Another thought. It would be cooler if this could be done on a seven pin lock. A six pin lock only leaves 729 possibilities when only using 3 depths. A seven pin lock would have 2187!

Of course there isn't any reason that I couldn't use different depths in each chamber, but I would still like to have a total of 3 depths in each chamber. And once these depths are figured out. Someone would only have to go through 729 try keys, or 2187 if it was a seven pin lock. Sometimes a little over-kill is a good thing.

[inverseentropy]

Ah, very good. Unlike my idea, this one can actually be easily built! I don't think it is too much of a problem to only have 729 possible combinations, because if someone was to run through all of them one by one with a pick they would be there forever. If the size of the bottommost pin for each chamber is varied then even though each lock only has 729 combos the set of combos will vary from lock to lock and that many tryout keys would need to be cut for every single lock. Of course, 7 pin will still always be better than 6 pin.

[inverseentropy]

There is a situation in which this lock could be picked. Suppose that one of the pin stacks happens to be the first stack to bind for the inner shear line but the last to bind for the outer shear line. Lift it by half a notch and apply tension. The bottom pin serves to transfer torque from the inner cylinder to the outer and since that stack is the last to bind on the outer shear line the outer cylinder can be picked. When it comes to the last pin stack (which was the one originally lifted by half a notch), just push it up and hope that it goes to the proper position. If not, repeat the process but starting with the first stack raised by one and a half times the size of the bottom pins, then two and a half, etc. Eventually by this process you will end up with the pins all being in the right position for the outer cylinder. The inner cylinder will be free to move independently at this point and there will be no torque on the outer cylinder, but hopefully it will have moved enough to hold the pins in position. Then just turn the inner cylinder until it contacts the outer and it should open. There are of course a lot of ifs here and this might not be workable unless there is a stack that binds first for the inner shear line and last for the outer shear line. Spool pins probably also foil this technique.

[FarmerFreak]

Suppose that one of the pin stacks happens to be the first stack to bind for the inner shear line but the last to bind for the outer shear line. Lift it by half a notch and apply tension.

This may be a possibility. Unless I do make this lock I don't think we will know for sure.

The counter measure is the pins on the right that lock the outer core from turning. Remember that I want to use four of those pins. If they are set up with roughly the same tolerances as the rest of the lock. Then they would also likely be part of the bind order. That should prevent the decoding of more than a few cuts. (I hope)

You would also have to make sure that you don't get fooled by the anti-bump pins. They have a weaker spring tension at the deeper depths. At about half way up they pick up the second driver pin and spring. This may affect how you are proposing to attack the lock, unless you knew about it. Simply so you don't decode them all as the middle depth. Something tells me you are smarter than that. And this wouldn't have fazed you.

[inverseentropy]

OK, I was looking at the first picture and forgot about the second one that has the spring pin on the right hand side. This attack would indeed be foiled if those bind before the outer shear line. I think just using slightly larger holes on the top of the cylinder would make that happen.

[FarmerFreak]

I think just using slightly larger holes on the top of the cylinder would make that happen.

Good call.

I like it.

The picture doesn't depict this too well. Just so everyone is clear. At the point where the larger diameter chambers get smaller, it should be beveled so the driver pins don't get caught and hang up.

[ElAbogado]

Another thought. It would be cooler if this could be done on a seven pin lock. A six pin lock only leaves 729 possibilities when only using 3 depths. A seven pin lock would have 2187!

Of course there isn't any reason that I couldn't use different depths in each chamber, but I would still like to have a total of 3 depths in each chamber. And once these depths are figured out. Someone would only have to go through 729 try keys, or 2187 if it was a seven pin lock. Sometimes a little over-kill is a good thing.

Cut and pin it to a non-standard depths and you have essentially zero try out keys to attack this lock with.
I am a fan of non standard depths for high security applications.

[Evan]

FarmerFreak:

That seems cool and all but you have defeated the purpose for which the cylinder was designed...

By locking the inner plug to the outer master ring all you have is ONE shear-line now with all the things you have added to it...

I hope you have modified the cam interface on the back of the cylinder, like they are covered on a Medeco high security cylinder for obvious reasons...

Have you also added drill protection to the keyway area of the cylinder ???

~~ Evan