[Feature request] one-off PIN code instead master password

[popovn]

I want to use it on "alien" PC I fear keyloggers and aids. I propose to show the number and wait for answer is the correct PIN-code. Mathematical formula to calculate the Pin-code from the displayed number and know it'll just be me.

For example number=11, the formula = number*5-3, and waiting for response 52. After the incorrect PIN, the service should be unavailable for 10 min.