[hashcash] Re: hashcash v1 questions

  • From: Adam Back <adam@xxxxxxxxxxxxxxx>
  • To: hashcash@xxxxxxxxxxxxx
  • Date: Tue, 1 Jun 2004 03:39:51 -0400

On Tue, Jun 01, 2004 at 03:00:47AM -0400, Hubert Chan wrote:
> >>>>> "Justin" == Justin  <justin-hashcash@xxxxxxxx> writes:
> Justin> Can't the counter be abused by starting it at an arbitrary
> Justin> value?  If it's used for filtering, inflating the counter gives
> Justin> the sender an advantage.
> I think that the counter is only meaningful to the recipient as
> "interesting statistics", and isn't supposed to have any practical
> purpose on the receiving end.  But I guess Adam would know more about
> that.

Correct.  We need something that can work through lots of values.  A
counter is a simple way to do that.  The receipient can't rely on the
sender counting in order.  We've seen this already with Jonathan
re-using the counter as a padding mechanism to start with a large
counter that is just before SHA1 boundary.

And all the recipient cares is that the msg hashes to desired number
of leading 0 bits.


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