[6920] in bugtraq
Re: CISCO PIX Vulnerability
daemon@ATHENA.MIT.EDU (Damir Rajnovic)
Mon Jun 8 18:11:12 1998
Date: Fri, 5 Jun 1998 10:36:53 +0100
Reply-To: Damir Rajnovic <Damir.Rajnovic@EUROCERT.NET>
From: Damir Rajnovic <Damir.Rajnovic@EUROCERT.NET>
X-To: Mat Butler <mbutler@insight.com>
To: BUGTRAQ@NETSPACE.ORG
In-Reply-To: <Pine.LNX.3.96.980604100956.1210B-100000@core9.insight.com>
Hi there,
At 10:19 -0700 4/6/98, Mat Butler wrote:
>On Thu, 4 Jun 1998, Damir Rajnovic wrote:
>
>> Hi there,
>>
>> At 19:25 -0700 3/6/98, David Wagner wrote:
>> >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.
>
>If you know the bits in the key that are fixed, you create a program to
>generate all possible combinations with those bits fixed. (If nothing
>else, you create a list of every possible combination of the number of
>bits that aren't fixed, then insert the bits that are fixed before using
>the strings as keys.)
>
>It -does- matter if you know what bits are fixed. We're talking the -key-
>here. Not the output of the encryption.
Yes, but what I was trying to say is that if you know that first 8 bits
are fixed you can break encryption in X time units, so it will take again
X time units to break it if last 8 bits are fixed or any other 8 bits.
It will always take X time units no matter what 8 bits are known. There
is no, allegedly, 8 'preferred' bits that will allow you to break it in
less than X time units.
Cheers,
Gaus
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