cracklib

CrackLib is a library containing a C function (well, lots of functions
really, but you only need to use one of them) which may be used in a
"passwd"-like program.

The idea is simple: try to prevent users from choosing passwords that
could be guessed by "Crack" by filtering them out, at source.

CrackLib is an offshoot of the version 5 "Crack" software, and
contains a considerable number of ideas nicked from the new software.

NOTE THIS WELL: CrackLib is NOT a replacement "passwd" program.
CrackLib is a LIBRARY. CrackLib is what trendy marketdroid types would
probably call an "enabler".

The idea is that you wire it into your _own_ "passwd" program (if you
have source); alternatively, you wire it into something like "shadow"
from off of the net. You can use it in other things, too.