Lost User Account Passwords

[David Gavin]

On Wed, February 2, 2005 12:32, Tim Alberts said:
> I'm running apache on a FC3 linux box.  I'm trying to make user password
> control more available.  I know the passwd command to change user
> passwords.  My question is, if a user enters a password and they forget
> it, how can they get the password back out of the system without just
> re-entering a new one?
>
> Specifically, I'm using Linux-PAM with shadow passwords.  I don't want
> to give users root access.  I'm really trying to create a cgi/bash
> script that a user can enter their email address and it will email them
> there password.  Seems like a simple thing to do, but I haven't seen a
> command to retreive a current user password from Linux-PAM/shadow
> passwords.  I could use a MySQL database to keep track of this stuff,
> but I prefer to use the security that Linux already provides.  Plus,
> then I've got plain text passwords in a database or even if I encrypted
> them in the database, I have the passwords in two places and then
> there's the risk of them getting out of sink (however small a risk).
>
<SNIP>

 You can't recover the passwords from the passwd/shadow files. It's a
one-way encryption scheme - you supply a password at login and the system
encrypts it and compares the results with what is in the passwd/shadow
file. It it matches, you're in. Brute force password crackers just keep
trying strings from a dictionary hoping for a match. I've worked in
UNIX/Linux for ~ 20 years and never heard of anyone actually decrypting a
password string.
 You could set up a front-end that saves the pw in a db and then changes
it, but if a user bypasses it (using the passwd command) you'd no longer
have their current password in the db.....

Dave Gavin