4.3.2. Creating User Passwords Within an Organization

If there are a significant number of users within an organization, the system administrators have two basic options available to force the use of good passwords. They can create passwords for the user, or they can let users create their own passwords, while verifying the passwords are of acceptable quality.
Creating the passwords for the users ensures that the passwords are good, but it becomes a daunting task as the organization grows. It also increases the risk of users writing their passwords down.
For these reasons, most system administrators prefer to have the users create their own passwords, but actively verify that the passwords are good and, in some cases, force users to change their passwords periodically through password aging.

4.3.2.1. Forcing Strong Passwords

To protect the network from intrusion it is a good idea for system administrators to verify that the passwords used within an organization are strong ones. When users are asked to create or change passwords, they can use the command line application passwd, which is Pluggable Authentication Manager (PAM) aware and therefore checks to see if the password is easy to crack or too short in length via the pam_cracklib.so PAM module. Since PAM is customizable, it is possible to add further password integrity checkers, such as pam_passwdqc (available from http://www.openwall.com/passwdqc/) or to write a new module. For a list of available PAM modules, refer to http://www.kernel.org/pub/linux/libs/pam/modules.html. For more information about PAM, refer to the chapter titled Pluggable Authentication Modules (PAM) in the Reference Guide.
It should be noted, however, that the check performed on passwords at the time of their creation does not discover bad passwords as effectively as running a password cracking program against the passwords within the organization.
There are many password cracking programs that run under Red Hat Enterprise Linux although none ship with the operating system. Below is a brief list of some of the more popular password cracking programs:

Note

None of these tools are supplied with Red Hat Enterprise Linux and are therefore not supported by Red Hat, Inc in any way.
  • John The Ripper — A fast and flexible password cracking program. It allows the use of multiple word lists and is capable of brute-force password cracking. It is available online at http://www.openwall.com/john/.
  • Crack — Perhaps the most well known password cracking software, Crack is also very fast, though not as easy to use as John The Ripper. It can be found online at http://www.crypticide.com/users/alecm/.
  • Slurpie — Slurpie is similar to John The Ripper and Crack, but it is designed to run on multiple computers simultaneously, creating a distributed password cracking attack. It can be found along with a number of other distributed attack security evaluation tools online at http://www.ussrback.com/distributed.htm.

Warning

Always get authorization in writing before attempting to crack passwords within an organization.