[jdietrich]

If you have a blank key and access to the lock, you can quite quickly produce a working key with only a hand file. Keys can also be readily decoded duplicated based on a photograph of the key.

These aren't plausible attack vectors for domestic burglars (they'll just break a window), but they are meaningful threats in high-security environments. A duplicate key confounds a lot of the countermeasures used to prevent and detect unauthorised entry.

https://www.youtube.com/watch?v=jciQpGdAVtc

https://www.youtube.com/watch?v=AayXf5aRFTI

[jstanley]

I tried to do this once, but despite some (small amount of) hand filing experience at the time, I was not able to produce a working key before getting bored and giving up. I even had an existing worn key to try and copy.

I reckon I could do it now (but for that matter I also reckoned I could do it then).

I would not back the average person's chances. It's harder than it looks.

[SamBam]

If you're using this technique to 3D print a key to match a specific keyway, you probably already aren't the average person.