Re: Password policy

["Mclaughlin, Kevin L (mclaugkl)" <mclaugkl () UCMAIL UC EDU>]

Hi:

I guess I will chime in on why passwords should have an expiration
time/date.  

 

Brute force attacks take time --> given enough time any password can be
broken and discovered --> by forcing a change periodically you make any
targeted brute force attacker start over.   How long does it take?  The
chart below gives an idea:

 

 

If you only use words from a dictionary or a purely numeric password, a
hacker only has to try a limited list of possibilities. A hacking
program can try the full set in under one minute. If you use the full
set of characters and the techniques above, you force a hacker to
continue trying every possible combination to find yours.  

If we assume that the password is 8 characters long, this table shows
how many times a hacker may have to before guessing your password.  Most
password crackers have rules that can try millions of word variants per
second, so the more algorithmically complex your password, the better.

 

Character sets used in password 

Calculation 

Possible Combinations 

Dictionary words (in english): 
(It is debatable but lets generously say ~600,000 words) 

--

600,000

Numbers only 

10^8

100,000,000

Lowercase Alpha set only 

26^8

208,827,064,576

Full Alpha set

52^8

53,459,728,531,456

Full Alpha + Number set

62^8

218,340,105,584,896

Full set of allowed printable characters set:  

(10+26+26+19)^8

645,753,531,245,761

 

 

-Kevin

 

Kevin L. McLaughlin

CISSP, PMP, ITIL Master Certified

Director, Information Security

University of Cincinnati

513-556-9177 (w)

513-703-3211 (m)

mclaugkl () ucmail uc edu

 

 

  

 

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________________________________

From: Geoff Nathan [mailto:geoffnathan () WAYNE EDU] 
Sent: Wednesday, November 01, 2006 3:10 PM
To: SECURITY () LISTSERV EDUCAUSE EDU
Subject: Re: [SECURITY] Password policy

 

Kellogg, Brian D. wrote: 

A couple questions:

 

1.      Do most enforce password expirations?  I came from a large
corporation and they enforced a 90 day password expiration policy.  It
seemed to have the effect of making passwords less secure as most would
write them down in obvious places.

Something that nobody so far has touched is exactly what function an
expiration policy fulfills.  Remembering nine passwords is not merely
'inconvenient', it's cognitively challenging for normal people (those
who have difficulty memorizing arbitrary information).  So, if a
password is sufficiently complex to discourage brute force attacks
(unless you're the NSA, of course..), what is accomplished by making
people change it?  If it is compromised, it doesn't matter that it'll be
changed in, say, four days or four months.  I know lots of places have
frequent change rules, but then lots of places require 1 qt. zip lock
bags (and will confiscate your liquids if you use a gallon bag).  We
have some choice here (unless the state requires it), so maybe we can be
a little rational in our security policies.



1.       
2.      Do most enforce a strong password policy?

As soon as we get the technology under control to do so we will.



1.       
2.      Any other recommendations/insights along this line would be
helpful.

 

 

 

Thanks,

 

Brian






-- 
Geoffrey S. Nathan <geoffnathan () wayne edu>
<mailto:geoffnathan () wayne edu> 
 
Faculty Liaison, Computing and Information Technology,<p>
and Associate Professor of English, Linguistics Program<p>
Phone Numbers (313) 577-1259 or (313) 577-8621<p>
Wayne State University<p>
Detroit, MI, 48202