From: Tom Weinstein <tomw@netscape.com>
Date: Wed, 25 Jun 1997 14:05:06 +0800
To: Adam Back <aba@dcs.ex.ac.uk>
Subject: Re: Wiener paper (was Re: Comparing Cryptographic Key Sizes)
In-Reply-To: <199706241754.SAA00563@server.test.net>
Message-ID: <33B0B3AE.A9CDA6E4@netscape.com>
MIME-Version: 1.0
Content-Type: text/plain



Adam Back wrote:
> 
> Re comments that I should re-read the paper, here is what Wiener's
> paper says about estimated costs of a specialized DES key breaker:
> 
>  $100,000 for a machine to break DES in an average of  35 hrs
>  $1 mil   for a machine to break DES in an average of 3.5 hrs
>  $10 mil  for a machine to break DES in an average of  21 mins
> 
> It was as Peter says published in 1993.
> 
> Wiener also budgets for $500,000 in design costs (wages, parts, fab
> etc).
> 
> Another interesting part of the design is that it is based on a
> pipelined chip, clocked at 50Mhz which can try 50 Million keys/sec.
> 
> 35 hours sounds a reasonable amount of time to break a Swift banking
> transfer key protecting trillions of dollars of funds.

One thing that I haven't heard anybody mention yet is that if time is
important, you can break keys in an arbitrarily short period of time,
if there's a continuous sequence of transactions.  Assume it takes 35
hrs to crack a key (with 50% probability), This means that you have a
1.4% chance to crack it in one hour.  If you give up after an hour and
pick a new transaction to crack, you have a 50% chance of cracking at
least one transaction after 48 hours, and they will all have been
cracked in less than an hour.

-- 
What is appropriate for the master is not appropriate| Tom Weinstein
for the novice.  You must understand Tao before      | tomw@netscape.com
transcending structure.  -- The Tao of Programming   |