Password history anyone?

[Brian Jones <jonesy@CS.Princeton.EDU>]

Hi,

I'm looking for thoughts on how to implement a password history scheme.  The
idea is that you can store the last 'n' passwords a user has used, and
whenever they change their password, whatever the app is that is being used
to change it does a compare against these 'used' passwords, and if there's a
match, it returns an error.  Presumably, this would be a multi-valued
attribute that you could tag onto your 'People' entries.

I'm contemplating putting something together manually for this (schema and
supporting app), but I wanted to see if anyone has already done some of the
work or has some horror stories or success stories or other info I might
learn from. 

Thanks 
brian.