From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Fri, 11 Feb 94 21:10:40 PST
To: rubin@citi.umich.edu
Subject: Re: Nx2 DES Found Weak
Message-ID: <9402120503.AA27541@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


	
> How is this different from a birthday attack ?

In Nx2 DES, you have   A -k1-> B -k2-> C .
In a birthday attack, you try values of k1' and k2' until you get k1', k2' s.t.
	E(A,k1') = B' = D(C,k2')
but that's only true for that particular plaintext set A,C.  
If you have B' = the same value of B that the original k1,k2 produced, you win,
but there may be many other values of B' besides the one for k1'=k1, k2'=k2.