On 1/19/2006 3:41 PM, Sulaiman, Wilmar wrote:
Dear all,
I noticed that "best practice" for Minimum password length policy is
either 6 or 8 characters. I guess SANS institute considered a weak
password if it is less than 8 characters.
I would like to know where they derived the number (6 and 8 characters).
Is there any documentation to backup it up why the best practice for
minimum password length is set to 6?
Well, the amount of time it takes to brute force a password goes up
exponentially with every additional digit.
Suppose we are using alphanumeric passwords, which would give us a
possible 36 characters for each digit of the password. (Alphanumeric is
what is often touted to normal users in security lectures in my experience.)
Let us also suppose that we can attempt 1000 passwords a second (a
number which has no basis in fact, but is nice and round).
Thus:
possible number of passwords = possible number of characters ^ number of
characters in password.
and:
time to crack = number of passwords / number of attempts per second
361 = 36/1000 = 0.036 seconds (which is faster than you can blink)
362 = 1296/1000 = 1.296 seconds
363 = 46656/1000 = 46.656 seconds
364 = 1679616/1000 = 1679.616 seconds (27 minutes)
365 = 60466176/1000 = 60466.176 seconds (16 hours)
366 = 2176782336/1000 = 2176782.336 seconds (25 days)
So as you can see, the amount of time really spikes up by adding the
number of digits in your password.
Mind you, password crackers today are many times faster than the example
I did above. So, using a real numbers, security advisories have decided
that at 8 characters, it will take someone quite some time to crack the
password. (And I just don't recommend 6 characters, too trivial in
today's day and age.)
--
Neil.
http://voidfx.net
"Lord, grant me the strength to accept the things I cannot change, the
courage to try to change the things I can, and the wisdom to hide the
bodies of the people I had to kill because they pissed me off."
--Anonymous
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