http://checkpasswd-pam.sourceforge.net/


checkpassword-pam is an implementation of checkpassword-compatible
authentication program.

Checkpassword is described in <URL:http://cr.yp.to/checkpwd.html>


checkpassword-pam was written from scratch.  There are several older
packages called checkpassword-pam, derived from DJB's checkpassword
code.   This checkpassword-pam is more modern and
administrator-friendly.


If you are using Linux-PAM, make sure it is more recent than 0.59.
Incompatibilities are in the PAM conversation function (number of
requests vs number of responses).  All modern Linux distribution use
PAM newer than that.