[RC5] DES coming...

Bruce Ford b.ford at qut.edu.au
Mon Nov 30 12:30:27 EST 1998


> Yes, it's less than two months to DES-II 3!
> And thanks to EFF the rules are like this:
> "The 'previous winner's' time that will be used for this next 
>  contest is 56 hours so the prizes are $10,000 for a break within 
>  14 hours, $5000 for a break within 28 hours and $1,000 for a break 
>  within 42 hours. After that - nothing."
> (http://www.rsa.com/rsalabs/des2/html/continued.html)
> 
> Right, we are pretty much faster than in July, but can we do it in as few
> hours as 42 or even 14 ??

Well EFF did us a bit of a disservice by only searching 25% of the 
keyspace to find the DES-II-2 key.

By 13 January 1999 we should be able to do approximately 200 Gkeys/s.  If 
we could put all of that online immediately our chances are:

14 hours: 14.0%
28 hours: 28.0%
42 hours: 42.0%

However, our ramp up for DES-II-2 fitted closely to 
rate=max_possible*(1-exp(-t/36.94)) where t is in hours.

This would give d.n chances of:

14 hours: 2.3%
28 hours: 8.4%
42 hours: 16.9%

The EFF pages give 92 Gkeys/s as their stated keyrate giving:

14 hours: 6.4%
28 hours 12.9%
42 hours: 19.3%

So even if we combine with EFF, the chance of finding the key in 42 hours 
is less than 100% and is probably closer to 36% than 61%.  

This assumes EFF have not upgraded their hardware.


Bruce Ford

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