[hashcash] Re: response to "proof of work proves not to work"?

  • From: "John Honan" <jhonan@xxxxxxxxx>
  • To: hashcash@xxxxxxxxxxxxx
  • Date: Mon, 17 Jul 2006 20:18:20 +0100

On 7/17/06, Eric S. Johansson <esj@xxxxxxxxxx> wrote:

Adam Megacz wrote:

> Did you publish your analysis?  Even informally?  If you have a
> well-written rebuttal paper that's as detailed as theirs I will
> certainly point people to it.

I looked around and couldn't find the draft but it shouldn't be hard to
spin another one.  As I said in my other post, the basic argument is
that they used the wrong metric of cost.  Yes, if you purchase a piece
of hardware, and generate an infinite number of stamps, the average cost
per stamp will drop with respect to time.  Or, the first stamp is the
most expensive in all the rest come for free.

I've also done some calculations on spammer profitability and breakeven. I
used this approach;

If it takes x seconds for a spammer to stamp and send an email, then if x is
large enough it should be possible to impact the spammers profitability
enough to deter them from sending spam in the first place.

When we work out what the spammers breakeven point is, we can then derive
how long it should take to calculate a Hashcash stamp to make them
unprofitable. There are only a certain number of seconds in a day, which
means the spammer is limited in the maximum amount of stamped email they can
send per CPU per day.

You're right in that we have to make some assumptions about spam response
rates, profit-per-response and cost of running one CPU, but this is the
basic approach I took. Based on my calculations, I figured the optimum stamp
size to put a spammer out of business is 59 seconds - or about a 30-bit
stamp size on a fast processor; which brings up the issue of cpu

I'd really like to take a look at your approach to the calculations whenever
you post them.


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