If you read 128 bits of data from /dev/urandom, and then map the result to a space of 2128 possible passwords, then it doesn't actually matter what the possible

If you read 128 bits of data from /dev/urandom, and then map the result to a space of 2128 possible passwords, then it doesn't actually matter what the possible passwords are, as long as it's a one-to-one mapping.