in reply to
Re^2: Authentication with /etc/shadow
in thread Authentication with /etc/shadow
In my programming life, I've seen at least 2 orders of magnitude more problems caused by people manually mucking about with things that have nice defined API's for fanciful reasons, than problems caused by something being too slow for doing so.
If it's a problem, find out that it's a problem first, then fix it. And in this case, you'll eat the crypto overhead either way, so what do you think you'll save?