[RC5] Moore's Law is irrelevant to d.net.

Ilmari Karonen iltzu at sci.fi
Tue Dec 14 22:51:02 EST 1999


[Some comments regarding an ongoing discussion, but not addressed to
anyone in particular. A summary is in the Subject: line.]


The "wait for better hardware" argument does not apply to d.net, since
the hardware we use is already there and gets upgraded effectively 
independently of what we use it for. (But if you're thinking about
upgrading to get a better RC5 keyrate, waiting for better hardware could
be a good idea. For that matter, waiting for a better reason could also be
a good idea..)

In fact, Moore's law has no effect on project ordering either. As I
have posted before, the expected profit rate of a challenge like RC5, DES
or CSC is (prize * keyrate / remaining keys).[1] To maximize expected
total profit at any point in the future, the most profitable challenge at
any moment should get priority.[2]

The keyrate term in the formula, however, is only needed to account for
the differences in the difficulty of cracking a single key, and could
equally well be measured as "keys per CPU time". The profit rate will then
be in "dollars per CPU time", and the ratio of CPU time to real time is
irrelevant, QED.


[1] By including any non-monetary benefits in the generic term "prize", we
can extend this formula to projects like OGR, as long as some agreement
can be achieved about the relative values of different projects.

[2] If there is a low-profit challenge with a deadline or a competing
effort, the problem gets a bit more complex, though. Essentially,
participation in such a challenge would reduce our expected profit rate,
while not participating would mean giving up the profit from that
challenge.

To make the correct decision here, we'd have to make some predictions
about the future - specifically about what the average profit rate will be
in the long run. Any projects with a lower expected profit rate than that
should be dropped, while those with a higher rate should be scheduled
before the deadline.

-- 
Ilmari Karonen - http://www.sci.fi/~iltzu/
"I've never had the nerve to phone up a stranger and say 'Excuse me, but did
you throw a dead bat at Ozzy?'"                       -- Nathan Tenny in AFU

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