In the computer biz, that's a variation on a hashing function ;-)
For myself, I write my PINs on my credit and debit cards in binary with a bit shift and padded on the ends with my own binary bit sequence. Told a couple of CS PHDs that they could have everything in the account if they could figure it out in the number of tries allowed before the card locked itself out. Mathematically it was highly improbable. It keeps me fresh in converting binary to numbers. And no, I don't tell them if it is in octal or hex! Had to get the PINs reset after they took their tries and missed ;-)
Sounds like you know how to have fun, but... lol it would really suck to have your cards locked! :)