[shardling]

The private function divides the unknown square by another number you provide. It's possible that how long this division takes depends on just what the secret number is -- keeping track of this and carefully feeding it input might reveal the number. That's a timing attack. (This is something you really have to consider when designing cryptographic functions and other such hardcore stuff.)

I suspect that doing something with the random seed is more what the author had in mind, though.