[RC5] Israeli Scientist Reports Discovery of Advance in Code Breaking

Ian Clelland iclelland at centralindustrial.com
Mon May 10 11:01:10 EDT 1999

-----Original Message-----
From: Jeff Woods <jdwoods at bga.com>
To: rc5 at lists.distributed.net <rc5 at lists.distributed.net>
Date: May 7, 1999 23:50
Subject: Re: [RC5] Israeli Scientist Reports Discovery of Advance in Code

>At 5/6/99 03:13 PM , Sanford Olson wrote:
>>Israeli Scientist Reports Discovery of Advance in Code Breaking
>>An Israeli computer scientist is expected to shake up the world of
>>cryptography this week when he introduces a design for a device that could
>>quickly unscramble computer-generated codes that until now have been
>>considered secure enough for financial and government communications. In a

[snip] :)

>I don't know if the rest of the article makes it clear, but Dr. (I presume
>got a PhD. ;) Adi Shamir just happens to be the "S" in RSA.  He's not just
>schmuck with a hare-brained idea.  Of course, it's remotely possible that
>might be a hare-brained idea, but at least he's no schmuck.  :)

Dr. Shamir's idea, essentially, is to build an optical computer (a
deceptively simple-looking device, in fact,) which is capable of performing
100,000+ divisions, logarithms, and additions in a single clock cycle. This
computation forms the backbone for the fastest-known algorithms used for
factoring large numbers. In his presentation, Shamir claimed that with
current manufacturing techniques, he could build such a device with a clock
period of 100 picoseconds (10 GHz clock speed,) which would mean that a
single device would be several orders of magnitude faster than the largest
(even distributed) factoring efforts which exist today.

Factoring very large numbers is probably the most direct way to "crack" many
public-key cryptosystems, like RSA. Private-key, or symmetric cryptosystems,
like RC5, don't depend on these kind of large numbers for their secrecy.
RC5-64 uses a smaller (64-bit) key which is generated randomly, the idea
being that if someone doesn't know the key, there is (hopefully) no way they
can find it, except by guessing, which is exactly what distributed.net has
been doing for some 564 days.

The success or failure of this machine, then, will in no way affect the
security of RC5 (or any other symmetric algorithm) -- with one very
important note: as was mentioned in a previous thread, the way that you give
your super-secret RC5 key to another person is to use a public-key algorithm
to encrypt it. If someone can break your public key, there's no reason to
search for the RC5 key, like distributed.net does -- it will be out in the
open for them to read, along with all the rest of your secrets.

Ian Clelland
Central Industrial Wire
Data Security Solutions - http://www.centralindustrial.com
mailto:iclelland at centralindustrial.com

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