Re: Current Best Practice regarding Password Change policy

["Doty, Timothy T." <tdoty () MST EDU>]

First, I want to emphasize that I agree with a lot of what you say, but there are two points I would like to respond in 
counter to.

You start with “I want a balanced security policy that protects my organization and does not itself become the greater 
threat” (well put). Interestingly, a charge levied by critics of periodic password changes is that it *does* weaken 
overall security. Your discussion never mentions this possibility as being evaluated, but instead appears to use the 
argument that “while it does not address a particular security concern, but it does address another.”

That is well and good (and I think it is important to not get stuck on requiring complete solutions or endlessly 
debating the incremental gain/loss of particular methods), but the argument-by-analogy doesn’t work when the things 
being discussed are not analogous. You compare a password to a physical key used to access a house with live in guests. 
There are two critical differences: 1) the key is physical, passwords are not and 2) the key (encoding) is shared, 
(most) passwords are not/should not be.

Physical: a key is a token. A user doesn’t care about the encoding it represents, they present the token and are 
granted access. One way to improve the security of a lock is to increase the number of “bits” used to open it. It makes 
the key a little longer, but it is still just a key. A user *does* care about a password – they have to remember it. 
The “encoding” becomes very significant and if you increase the security by extending the number of characters it 
(generically) becomes harder to remember. Another difference is that a key, being physical, becomes clear at some point 
that it is lost. A password is “lost” when the user forgets it, but it can be exposed/compromised/what have you without 
any clear way to tell that someone else has knowledge of it and can use it to gain unauthorized access.

Shared: I’m not aware of people with shared living arrangements* who preventively have their lock re-keyed every month, 
six months, year or in fact on any periodic basis. Locks are typically changed when a person leaves or a key is lost 
(if then)**. Shared passwords are generally not a good idea, but they happen for a variety of reasons. When a person 
with knowledge of the shared password leaves the shared password should be changed. But in the typical case where the 
password is not shared the use-case of change-with-personnel is not relevant.

I’m not meaning to argue for or against periodic password changes. For many institutions they are a fact due to 
external requirements so the question is moot for them anyway. But I think it is very risky to use an analogy, for 
illustration or argument, when the points of comparison are so dissimilar as physical objects and matters of knowledge 
are.

* a security facility might very well have such a requirement, for example, to cover the case of a key being copied, 
but that does not follow the “live in guest” analogy presented, nor does it follow the typical case where passwords are 
not supposed to be shared.

** and if there were frequent thefts my experience is that instead of mandating periodic lock changes 
additional/different measures would be put in place, such as evicting guests/firing employees, installing cameras or 
silent, monitored alarms (particularly after losses with no break in).

Tim Doty

 

 

From: The EDUCAUSE Security Constituent Group Listserv [mailto:SECURITY () LISTSERV EDUCAUSE EDU] On Behalf Of Dexter 
Caldwell
Sent: Friday, September 24, 2010 2:31 PM
To: SECURITY () LISTSERV EDUCAUSE EDU
Subject: Re: [SECURITY] Current Best Practice regarding Password Change policy

 

I have to agree.  On this issue, I view password aging as simply a part of a set of tools for managing passwords.  
Because of the changes in password threats over the years- one thing seems clear.  If we as an industry fail to  to use 
any of our very few defense methods, the attackers will soon figure it out and eventually it will become a point of 
weakness if for no other reason that it becomes an easier entry point as other methods are shored up against attack.

 

With respect to auditors, we all need auditors to help drive security initiatives to some degree and add weight or 
perspective to our recommendations, however, I try to to keep in mind, I are not here to argue brute force statistical 
differences in password quality or the mathematical superiority of one adjustment or another.  I am here to provide a 
means of real world protection to the organization.  Any exposure potentially puts at risk everyone in an entire system 
and at worst everyone in the entire organization not to mention the enterprise (non-person related) business data that 
the system may hold.   In that sense, once I'm within compliance (legal, auditor, or what have you)- then it doesn't 
matter what the auditors say.  What matters to me is how can I best protect the assets I'm focused on.

 

My logic is really quite simple.  I want a balanced security policy that protects my organization and does not itself 
become the greater threat.  Imho, password changes help do that in one major way.  They reduce the time of exposure.  
They do not or may not prevent the risk of exposure.  Nevertheless, there are other tools for that.  The other thing 
password changes provide is that they can be a tool that is one of your best and most basic security awareness 
initiative altogether in that they get people thinking about security and their access if only once a year, once every 
6 months, once a month- whatever works for you.  When managed properly password changes I think increase your 
protection and help influence awareness.

 

If I had  5 live-in guests in my house each of which had their own different key to my home, and I knew that regardless 
of my preaching, that occasionsly someone would distribute an unauthorized key, or lose their key,  or that the house 
gets broken into with no signs of forced entry, then  I might feel that changing locks and distributing new keys 
occasionaly was not a bad thing.  It might not increase lock strength, but that's not the point.  The point is if I've 
been compromised and I know that my whole house was violated, it helps me have greater assurance that when my house was 
entered that 1 the exposed key no longer works and two, if they copied other keys lying around compromised other locks, 
I know that it won't be that way forever.  In other words, for my situation, they add a significant layer of protection 
to my home to be worth the some effort.   But that effort itself is a configurable variable to some degree.  I might 
not change the locks every thirty days (high effort) unless I had a breakin or attempted breakin events happening with 
a frequency that warranted that change.  A good balance might be every 6 months (lower cost, lower impact, etc.)  If I 
had a thousand locks and a higher frequency of attack or exposure, I might see fit to put more effort into changing 
locks because of the greater cost and likelihood of the risk of exposure.  At least then I have a policy that 1) 
provides reasonable security without throwing away tools.  2) Have a policy I can defend in the event we have have a 
serious costly security event and every know-it-all security pundit in the world begins to question every thing we do 
with phrases like 'gross negligence' and "Well everyone knows..." and "best practices indicate...30 days,but this 
organization had NO CHANGE POLICY WHATSOEVER?!"   All this to say in my opinion we spend too much time debating things 
and trying to prove things that are not worth proving.  It's just common sense that at the very least password changes 
reduce an exposed password, therefore it seems to me to be a good tool for controlling that particular variable of 
security threats and that is what I use it for.   Therefore it's irrelevant whether or how much it impacts entropy.  
The real problem is that passwords are and outdated form of security in the first place, but there are not many fully 
developed alternatives that globally provide the same ease of use, ability to work with all of our applications (and 
users),  at similarly reasonable cost of management as usernames and passwords.

 

The EDUCAUSE Security Constituent Group Listserv <SECURITY () LISTSERV EDUCAUSE EDU> writes:

I agreed with this line of thinking in 199[78], before watching intruders hand-code password-recording trojaned 
versions of sshd and ssh on rooted UNIX systems during the course of an investigation.  The code did a nice job of 
host/client/account/password capture and loggin, which was *way* more efficient than the ad-hoc telnet/pop/ftp packet 
sniffers of the day.  

 

In the current environment of rampant keyloggers and man-in-the-browser crimeware, I'm completely over the line of 
thinking that the best way to get credentials is to attack a server's store of them.  I think the bad guys have pretty 
much moved on, as well.

 

Grudgingly, I come to agreement with the Standard Audit Advice, though not for the reasons it was written in the first 
place.

 

I see it as a hygienic measure; way to reap compromised credentials *eventually*, rather than letting them go on 
indefinitely, somewhat sooner rather than later for some classes of accountholders.  Given how easy it is to steal 
credentials client-side, you may actually force a change before it gets used (due to the size of the pile of booty), 
though I certainly wouldn't depend on that.  

 

I don't know whether that puts me on the white or black side of the issue.  :-)

 

  -jml

 

> > > Roger Safian <r-safian () NORTHWESTERN EDU> 2010-09-24 09:31 >>>

I'd suggest that password aging should be based on the risk that somebody

could obtain, and crack, the password hashes.  It's not a 

black and white issue, regardless of what the Auditors, Spaf, or I say about

it.

 

-----Original Message-----

From: The EDUCAUSE Security Constituent Group Listserv

[mailto:SECURITY () LISTSERV EDUCAUSE EDU] On Behalf Of Valdis Kletnieks

Sent: Friday, September 24, 2010 7:53 AM

To: SECURITY () LISTSERV EDUCAUSE EDU 

Subject: Re: [SECURITY] Current Best Practice regarding Password Change

policy

 

On Fri, 24 Sep 2010 08:28:02 EDT, Barbara Deschapelles said:

 

> We currently require all, Students, Faculty and Staff, to change 

> passwords every 90 days and we are enforcing unique passwords (no 

> repeats). This is a relatively new requirement here and we are getting 

> a lot of push back on the change.  I'd like to get a feel for what 

> people accept as current best practice for password change intervals 

> and other related policies, and also, if it is different than the best 

> practice what people are actually doing (if you wish to share that :-)

 

There's "what everybody is doing because auditors insist" and "what actually

makes sense in today's computing environment".  Make sure to read what Gene

Spafford wrote about it:

 

http://www.cerias.purdue.edu/site/blog/post/password-change-myths/ 

http://www.cerias.purdue.edu/site/blog/post/passwords-and-myth/ 

 

(Anybody want to publicly admit they were able to sell the auditors on what

Spaf said, and managed to eliminate mandatory changes?)

Attachment: smime.p7s
Description: