[1815] in linux-security and linux-alert archive
[linux-security] Re: "Flavors of Security Through Obscurity"
daemon@ATHENA.MIT.EDU (lists@notatla.demon.co.uk)
Thu Jun 4 18:41:52 1998
Date: Thu, 4 Jun 1998 01:22:16 +0100
From: lists@notatla.demon.co.uk
To: ak@muc.de, linux-security@redhat.com
Resent-From: linux-security@redhat.com
Reply-To: linux-security@redhat.com
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From: Andi Kleen <ak@muc.de>
> There are already lots of these ciphers. Examples are the Russian GOST or
> Bruce Schneier's Blowfish cipher where the SBOXes can be changed and kept
> secret. Most publicly available Blowfish and GOST implemenations use fixed,
> known sboxes AFAIK (hexadecimal Pi in case of Blowfish, some standard set
> for GOST), but the ciphers were really designed to work with variable SBoxes.
>
> [mod: As I'm told, not just any S-boxes will do. You get a
> cryptographically weak cypher if you don't choose your S-boxes just
> right. Nobody knows how the DES people got it right, but they DID.
> Using PI might give you a good source of pseudorandom numbers, but
> it is unlikely to provide good S-Boxes. -- REW]
Excuse me being a little behind with my mail...
Blowfish relies on S-boxes derived from the key in a complicated
and slow way. Some of the initial setup uses PI. What separates
these pseudo-random boxes from the designed ones of DES is that these
are very large (and are used partially in series in each round). 1970's
hardware constrained DES to small S-boxes which would be weak if random.
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