🚀 go-pugleaf

In article <BuLCyD.DKG@cs.dal.ca> gauthier@ug.cs.dal.ca (Paul Gauthier) writes:
>In <7982@public.BTR.COM> grady@btr.BTR.COM (Grady Ward  grady@btr.com) writes:
>
>>For pronounceable passwords,
>> [...]
>
>Not relating specifically to this subject, but along the lines of passwords
>and security...
>
>Many system (almost all) provide a facility for the user's password to expire
>after a certain amount of time and then require a new password. What is
>the 'official' rationale concerning this practice?
>
>I assume the main brunt of the argument states that this somehow makes it
>harder for an attacker to guess a password.
>

Actually it does nothing to make it harder for an attacker to get the password.
It reduces the cost to you (value to the attacker) of a guess.
If I do get the password, it limits the amount of time I have to make an
attack.

The attacker may want to delay the attack until a time of his
choosing.  (We got the password into your air defense computer (which
strangely enough has a dial-in line) today, but we're not going to
launch the actual attack until December 7).

If someone really wants your password, then sooner or later they will tap
your line, or put a video camera in your ceiling.  It will be more expensive
for them if they have to maintain the wiretap or keep putting new batteries
in the video camera.

Finally, it may be that the system used to encrypt your password is of
'moderate' strength.  If it takes the bad guy an average of one month to
guess your password, and you change it every two weeks, then the bad guy
won't be able to log in as you most of the time.

Historically, people have placed unwarranted faith in the strength of their
cryptosystems.  Since we know this is a bad thing, we now like to place
unwarranted faith in the value of frequent key changes.
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