From: Stu@nemesis.wimsey.com (Stuart Smith)
Date: Mon, 4 Jul 94 04:37:35 PDT
To: cypherpunks@toad.com
Subject: Re: Password Difficulties
In-Reply-To: <199407020841.AA23083@world.std.com>
Message-ID: <2e16ea88.nemesis@nemesis.wimsey.com>
MIME-Version: 1.0
Content-Type: text/plain


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In article <199407020841.AA23083@world.std.com> you write:
>Back to a rephrasing of my original question: should programs like PGP
>super-duper encrypt the private key (and remove those hints poeple
>have mentioned recently) as a way of slowing down brute-force attacks?

In general, multiple encryption does not signifigantly increase
security.  Just for starters, we don't know if IDEA is a group..
If it is, you can encrypt all you want and you won't get one
extra bit of security.  Trying to analyse just *one*
cryptosystem or algorithm for security holes and information
leaks is hard enough - trying to analyse the interaction between
several layers of said algorithm or even between different
algorithms seems harder and lacking in promise.  Of course you
could view this as defence of multiple-encryption: "if there
*is* some weird interaction that reveals my key when you xor the
secret-key file with any Nick Danger script, no one will ever
discover it because it will be too hard"  but this strikes me as
the security through obscurity myth.

You can't get something for nothing.  With a 12 bit pass phrase,
you have 12 bits of security - I don't see any known way to
increase this without increasing the pass phrase length.

I haven't looked into this alot, but I wonder how the approach
used with many unix passwd utilities would fare?  For instance,
checking password/phrase crackability if you will - comparing
against a dictionary, measuring entropy or just plain not
accepting pass phrases shorter than x.  Also, many passwd utils
will generate "pronouncable" random text.  Perhaps with several
short words generated thusly would get you the entropy you need.

Thoughts?

- --
 Baba baby mama shaggy papa baba bro baba rock a shaggy baba sister
shag saggy hey doc baba baby shaggy hey baba can you dig it baba baba
        E7 E3 90 7E 16 2E F3 45   *   28 24 2E C6 03 02 37 5C 
   Stuart Smith                           <stu@nemesis.wimsey.com>

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