Rainbow tables make password up to around 8 characters easy to crack, if
the
attacker has the time to pre-compute the tabes. Making rainbow tables
beyond
8 is long term planning, and somewhat disk intensive for script-kiddy
level
attacks.
It is instructive to look at this site:
http://www.loginrecovery.com/
I've used this website as an example in a class I gave, and I exchanged a
few e-mails with the owners of this site. They were very friendly and
explained that they used huge rainbow tables and that they could easily
crack passwords even longer than 14 characters.
I sent in a few test passwords of mine (very simple ones) and they were
all cracked in a minute. This was a sobering experience :-)
There may be more service providers like that, but this was the first one
I found. If you're in deep trouble, then paying 10 GBP for your forgotten
admin password is a good deal.
At our clients I try to defend the current Microsoft policy because IMHO
it's quite safe and reduces the load on the helpdesk:
Length: 8 chars or more
Complexity: enabled
Change: every 90-120 days
Lockout: after 50 (!) attempts - not 5 or 3 like we used to advise
The philosophy is that a lockout is only necessary if someone uses an
automated password guessing tool. The chance of guessing even a simple
password like "Banana01" (seen "in the wild") in 50 guesses is slight. And
having 50 tries once saved the day for me, after I changed my password
late at night and didn't know it anymore in the morning :-)
Greetings, Petr Kazil
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