full-disclosure - guidelines for good password policy and maintenance / user centric identity with single passwords (or a small number at most over time)

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Message-ID: <200603270557.k2R5vaBw019752@turing-police.cc.vt.edu>
Date: Mon Mar 27 06:57:58 2006
From: Valdis.Kletnieks at vt.edu (Valdis.Kletnieks@...edu)
Subject: guidelines for good password policy and
	maintenance / user centric identity with single passwords (or a
	small number at most over time) 

On Sun, 26 Mar 2006 20:12:04 +0200, Anders B Jansson said:
> 128 bit entropy in a password requires a long randomized passphrase.

Do you really need a full 128 bits of entropy?  Certainly 64 bits or
so isn't sufficient - but re-evaluate what you *really* need from the
password - 80, 96, or 112 bits may suffice...

> Avoiding accented chars (which is good unless you want to be locked out)
> You'll end up with just under 6 1/2 bits per char.

And that's assuming you pick a totally random series from the 96 or so
printable characters.  On the other hand,  common english text manages a
whole whopping 2 1/2 bits per character. 

> And a password/passphrase meeting all requirements above and being at least
> 20 chars long isn't very usable.

On the other hand, "My unckle Fred's purple iguane has a wart on its eyelid."
is 57 characters long and gets you at least fairly close to 128 bits of
entropy.  More if you randomly insert a special character or three.

(As an aside, note that wr17ing 1t in '1337 sty1e doesn't add much entropy -
only about 1 bit of entropy (since all you need to do is record "was it an
o or a 0", or "1 or l" or '3 or e' and so on.  Random injection of special
characters, such as 'igu#ana' adds more entropy....
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