I have a space for computers secured with a simple deadbolt. Someone keeps comin

Question

I have a space for computers secured with a simple deadbolt. Someone keeps coming to pick the lock. While working there, I have scared them away three times.

There are cameras, but not in useful places or all exits and the building manager won't let me run wires for more. I contacted the police, but maybe it is a low priority for them.

With each subsequent visit, does a lock picker gain further progress in undermining the door's ability to keep out? Could they be doing something to the door each time that is getting them closer to being able to open the lock really quickly? Is there anything I can do to stop their ability to pick the lock?

Explanation / Answer

Yes, there's a classic attack that involves incremental access.

The attacker starts out with a blank key and a lighter (or candle, or similar). Before visiting the door, he uses the lighter to put a thin layer of soot on the top edge of the blank key.

The attacker approaches the door, puts the key in, jiggles the key a bit, grumbles something about how the office numbers changing, and leaves.

Then in private he examines the scratch pattern on the key. Where there's evidence that the pins were bound, he files the key down a bit. Every day he visits the door with his soot-prepared key, and every day he progressively files it down a bit more, using the scratch pattern in the soot as his guide.

Then, one day, he'll have filed the key to match all of the pins, and the door will open.

This attack has the advantage that it doesn't look like an attack. It just looks like a lost tenant who briefly visits the wrong door, and then leaves once he's realized his mistake. And when he's done, he'll have a working key.

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