crypt PLAINTEXT,SALT
Encrypts a string exactly like the crypt(3) function in
the C library (assuming that you actually have a version
there that has not been extirpated as a potential
munition). This can prove useful for checking the
password file for lousy passwords, amongst other things.
Only the guys wearing white hats should do this.

Note that `crypt()' is intended to be a one-way
function, much like breaking eggs to make an omelette.
There is no (known) corresponding decrypt function. As a
result, this function isn't all that useful for
cryptography. (For that, see your nearby CPAN mirror.)

When verifying an existing encrypted string you should
use the encrypted text as the salt (like `crypt($plain,
$crypted) eq $crypted'). This allows your code to work
with the standard `crypt()' and with more exotic
implementations. When choosing a new salt create a
random two character string whose characters come from
the set `[/0-9A-Za-z]' (like `join '', ('.', '/', 0..9,
'A'..'Z', 'a'..'z')[rand 64, rand 64]').

Here's an example that makes sure that whoever runs this
program knows their own password:

$pwd = (getpwuid($< ))[1];

system "stty -echo";
print "Password: ";
chomp($word = <STDIN> );
print "\n";
system "stty echo";

if (crypt($word, $pwd) ne $pwd) {
die "Sorry...\n";
} else {
print "ok\n";
}

Of course, typing in your own password to whoever asks
you for it is unwise.