Re: [Cfrg] draft-housley-ccm-mode-00.txt

David Wagner <daw@cs.berkeley.edu> Fri, 16 August 2002 17:10 UTC

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From: David Wagner <daw@cs.berkeley.edu>
Message-Id: <200208161707.g7GH7HO10814@mozart.cs.berkeley.edu>
Subject: Re: [Cfrg] draft-housley-ccm-mode-00.txt
To: Ge.Weijers@Sun.COM (=?ISO-8859-1?Q?G=E9?= Weijers)
Date: Fri, 16 Aug 2002 10:07:17 -0700 (PDT)
Cc: daw@mozart.cs.berkeley.edu (David Wagner), cfrg@ietf.org
In-Reply-To: <3D5D2D7A.1000508@sun.com> from "=?ISO-8859-1?Q?G=E9?= Weijers" at Aug 16, 2002 09:51:06 AM
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> An advantage I can see is the use of the same key for both 
> authentication and encryption. [...] Using the same key 
> halves the key storage requirements for an 802.11 base station.

It is easy to achieve the same thing with the standard generic
composition.  You pick a 128-bit key, and derive the encryption and
authentication keys separately using a PRF: Ke = F_K(0), Ka = F_K(1).
This is all very standard, and is done in IPSec and TLS, for instance.
So I don't see this as an advantage or an disadvantage.

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