On one hand, there are fairly well-established best practices regarding password policies.  Non-dictionary words, 8-15 characters, etc.  SANS has a great (if a little strict) password policy document here which is a great starting point for any security administrator.

On the other hand, users have a hard time remembering complicated passwords, especially ones that are frequently rotated.  A well-enforced password policy won’t let users choose their name, dictionary-based words, or any other ‘easy’ passwords, so the user is stuck with having to remember a complicated acrostic, or a random string of characters.  And what do users tend to do in this situation?  Write down the password.

So, what’s wrong with this practice?  Nothing!  It’s even been advocated by various security gurus for years.  But you need adequate physical controls around the password list.  That’s the rub – in a large IT organization,  how does one protect from users carrying around scraps of paper?  Adding a further layer of complication, what about the case of shared logins and passwords?  The problem can become overwhelming quickly.

In an IT environment where Role-Based Access Controls (RBAC) are implemented, I would be inclined to not explicitly discourage users from writing down their individual passwords – because we’re all pretty good at physically controlling pieces of paper (money, anyone?).  I may encourage the use of a tool such as Password Safe,  but there’s only so much that you can do to control the behavior of the users.

Where common usernames and passwords are shared between many people (a tragic case!), the problem of password management becomes much trickier.  I’ve seen systems with multiple versions of a common password list, with each user having their own copy.  I’ve seen password lists distributed betweeen a dozen users via unencrypted email.  I’ve seen printed sheets of passwords “hidden” underneath the keyboard of a common workstation.  I’ve seen post-it-notes on monitors.  All of these situations are terrible, but in reality, they’re also unavoidable.  The best an administrator control for is to provide adequate physical controls; limiting access to the password lists.  It would take a very highly-motivated attacker to get past a security guard, keycarded doors, and a staff that’s advised to pay attention to unrecognized people in the building – and your security response policy should take into account the situation of a password breach and have plans for rapidly shutting down access and rotating shared passwords.

In summary, there’s only so much that you can do to control the behavior of users, especially when asking them to remember complicated passwords.  I would advocate RBAC authenticating against a common directory server in all possible circumstances, so that a breached username and password can be compartmentalized, protecting against damage.  If that’s not possible, educating the users about controlling access to their passwords, and providing for adequate physical controls is about the best you can do.  And as always, having a response policy that takes into account the circumstances of a password breach is critical.  IT has evolved to the point where users are getting comfortable with the strictness of password policies, but as an administrator or security professional, it’s important to consider the vulnerabilities and to keep in mind the careful balance of usability and security.