In article <BA3BF0FA.2A037%zenadsl6186@zen.co.uk>, Peter Fairbrother <zenadsl6186@zen.co.uk> wrote:
Get the "pull" from a "party popper" and wrap it in a dollar bill. Record the serial number of the bill (some crypto here maybe). Make it impossible to open the closet without setting the "pull" off, ie no trapdoor.
Fairly good tamper-evidence, and the token is hard (and very illegal!) to forge.
Most of the security features of a dollar bill are not directed toward the serial number; they are designed to prevent changing the denomination, or to increase the cost of creating a real-looking bill from scratch. Changing the serial number is likely to be fairly straightforward. For this to be secure, you would have to keep the serial number a secret; and in that case, the paper could be any piece of paper with a secret written on it.
Depends on your threat model, of course.
But of course. -- Shields.