## [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
```

```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
'egalitarianism'....```

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

John.