[fanagra32]

> Make the math use bigger numbers.

Also, add redundancy so that if something is read out wrong then there is guaranteed to be no match. Error-correcting codes have been around for centuries (well, almost). Simplest way to do this is to add a fourth digit which acts as a checksum. Nobody needs to know this, but it will make the legal combinations very few in the space of total combinations, so if something is read out wrong you'll notice right away.