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Scanning Electron Microscope Analysis of Pin Tumblers

December 20th, 2009 | Posted by revdisk in Information Security

Naturally, everyone knows picking locks makes some sort of marks on the pins. Steel is harder than brass, ergo it’s pretty likely to scrape away brass material. I got interested and looked around a bit. I saw a couple decent photos taken with a high MP camera and cropped, but nothing truly showing close up shots. So, I decided to toss a couple pins under an scanning electron microscope. I didn’t happen to have one in my kitchen, so I went to the logical folks. Nanotech physics geeks, of course.

I went to the local Target and picked up three Master branded doorknobs. I liked the brand, as they seemed decent quality but not overly expensive. One was left pristine, one was picked, and one was bumped. I bagged all three cylinders and mailed them off along with a couple bags of candy. If you ever want to get geeks to do something, bribe them with sugar and/or caffeine. In this case, I decided to entertain myself by sending them Smarties and Nerds. I was gonna include a bag of Dum-Dums for the nano geeks to give to the chemistry department, but decided that wouldn’t be nice.

Anyways, onto the photos:

I chopped down the photos a bit to save on bandwidth. Download and zoom to view properly. If anyone really wants the larger files, let me know. They’re not substantially different than if you just zoomed in on the provided. All pins were imaged, and numbered from front to back. Pin 1 being closest to the keyway, Pin 5 being furthest in.

Pristine Cylinder, Pin 5, Photo C

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I noticed deep, long scratches even on the unused cylinder. Likely they tested a key at the factory. They were on all pins in all cylinders tested. Often one long scratch, and several smaller ones at different angles.

Pristine Cylinder, Pin 5, Photo D

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Different shot of the same pin. You can notice some surface deformation from manufacturing.

Pristine Cylinder, Pin 2

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You may notice black specks in various photos. This is primarily dust, but occasionally specks of brass or other contaminates. This is a 100 micron shot of one example of a piece of dust.

Picked Cylinder, Pin 1, Photo B

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And now we get to the interesting part. You can fairly clearly see evidence of picking. It does not look even remotely like the key marks. They are significantly less uniform in both length and angle, as keys generally do not have that much play when entering or leaving a lock. The most telling factor (if you look closely) is that they damage the edges of the pin. While key marks do leave scrapes on the pins, they do not mutilate the edges of the pins anywhere near to the same level as picking.

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Here is a close up shot of the edge of Picked Cylinder, Pin 1. The edge mutilation is quite visible.

Picked Cylinder, Pin 1, Photo C

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Another shot of Pin 1.

Bump Cylinder, Pin 2, Photo B

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The evidence of bumping is slightly harder to see at first glance. Bumping appears to leave deeper key marks. Occassionally these key marks are punctuated, like dashes. Regular key marks are long, smooth scrapes.

Bump Cylinder, Pin 2, Photo C

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Another shot of the same pin. Note the punctuated key marks.

Bump Cylinder, Pin 3, Photo C

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Bumping also plays hell on the edges of a pin. Very deep key marks.

Bump Cylinder, Pin 5, Photo D

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Nice clear photo of both punctuated key marks and deep key marks on the edge of the pins.

Pristine Cylinder, Pin 3, Photo C

50 micron shot of a key mark. Key marks are approximately 25 microns wide.

Pristine Cylinder, Pin 3, Photo N

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Another 50 micron shot of a key mark.

Picked Cylinder, Pin 3, Photo A

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Clear shots of pick marks at the edge of a pin

Picked Cylinder, Pin 3, Photo C

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Closer shot of pick marks

All images courtesy of Jeff Doughty and the Nano-Development Lab at Portland State University.

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