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Re: CISCO PIX Vulnerability
From: Damir.Rajnovic () EUROCERT NET (Damir Rajnovic)
Date: Thu, 4 Jun 1998 07:54:00 +0100


Hi there,

At 19:25 -0700 3/6/98, David Wagner wrote:
In article <v03007801b19b0b9bd8f5 () [194 82 141 242]> you write:
CISCO PIX Private Link feature uses DES key that is only 48 bits in length.
[...]
Apparently, knowing what bits are fixed will not bring attacker
any additional 'gain' in breaking a DES. At least I was told that by
people from sci.crypt group.

Either the sci.crypt folks were confused, or I am.  With only 48
unknown bits in the DES key, you can break the encryption 2^8 = 256
times faster than you can break DES.  This is a serious weakness.

Probably I was unclear. What I want to say is that it does not matter
what bits inside key are known. It is the same if you know that first
8 bits are 0 or middle or end bits. In all cases you must put the same
effort to break encryption. In that sense there is no 'additional gain'
knowing WHAT bits are fixed it does matter only that some are fixed.

Cheers,

Gaus


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