[PATCH] Add support for XKCD-style wordlist passwords

[Matthieu Weber]

On Tue, 30 Oct 2018 at 08:01PM +0100, Kjetil Torgrim Homme wrote:
> Den 30. okt. 2018 12:10, skreiv Matthieu Weber:
> > On Tue, 30 Oct 2018 at 10:33AM +0100, Kjetil Torgrim Homme wrote:
> >> yes, but sometimes you need to enter this password by hand.  I use horse
> >> battery passwords when I might need to enter the password on a mobile
> >> phone or on a console in a chilly data centre in the middle of the
> >> night.  both of these will often have problems with strange characters
> >> or keyboard layouts (is "&" on Shift 6 or Shift 7?  since there is often
> >> no echo, there is no way to be sure!)
> > 
> > So you want passwords that are easy to type: generate passwords that are
> > made entirely of lowercase letters, all you need is 40% more characters
> > to have the same entropy as a password made of alphanumerics+symbols
> > i.e., 11 characters instead of 8. They will be easy enough to type even
> > on exotic keyboards, and can be generated using only tools that pass
> > uses already. All you need is to add to “pass generate” an option to
> > reduce $CHARACTER_SET to [:lower:].
> 
> it is not easy to type wahseepienoofac on a mobile phone, IMHO.  but
> adding periods (not hyphens!  the key moves around) will help - not for
> entropy, but to make it easier to read and track how far I've gotten:
> 
>   wah.see.pie.noo.fac

What about whitespace instead of periods? The period may be located on
an awkward key on some keyboard layout, but (I hope) the spacebar is
universal.

> (I just realised I am lucky that I never have qwertz or azerty in my
> environment...  that would reduce the number of available letters to 21,
> ertuiop/sdfghjkl/xcvbnm, by my count.  digits, comma and period brings
> the total to 33.)

If you consider that you cannot trust the letters printed on the
keyboard's keys to know how to type a given character, then you are
totally screwed if someone is using dvorak, colemak, bépo, neo, das… you
won't be able to have a single usable character for your passphrases :(

> >> average length of 13 characters.  this doesn't really help entropy,
> >> though.  489533 distinct words give 18.9 bits of entropy each, so the
> >> above pass phrases (of four words) have 75 bits, or 5.74e+22.  still not
> >> a huge amount, but the attacker would have to know that this is the
> >> method I use to make pass phrases to successfully reduce his search space.
> > 
> > You can get 75 bits of entropy with 16 lowercase letters or 14
> > mixed-case letters. That is surely easier to type than your example.
> 
> it really depends on your keyboard and brain :-)

True. But then again, if you trust the way the password is hashed on the
remote system, you can allow for a much shorter password, as the hashing
algorithm will slow down an attacker to the equivalent of a dozen bits
of entropy.

Matthieu
-- 
 (~._.~)            Matthieu Weber - mweber at free.fr              (~._.~)
  ( ? )                http://weber.fi.eu.org/                    ( ? ) 
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