[ableal]

It's funny that no one is checking serial numbers. Nowadays it would not be too hard to look up in a database if the number was issued, is in use elsewhere, or belongs to a destroyed note.

Privacy, cost and protocol issues left as an exercise.

[kordless]

> in use elsewhere

Nope. No way to do that reliably with a piece of paper.

[mschuster91]

Why not make the serial numbers also a EC digital signature?!

[jbermudes]

Wouldn't it still be susceptible to replay attacks?

[wmf]

Paper-based PUFs, anyone?