[hashcash] Re: Hashcash vs. Time?
- From: Adam Back <adam@xxxxxxxxxxxxxxx>
- To: hashcash@xxxxxxxxxxxxx
- Date: Tue, 20 Apr 2004 16:57:24 -0400
Aside from challenge-response, another approach is to have an agreed
standardized stamp cost and change this over-time.
One convenient way to distribute this change over email that I
discussed is to include an extra header in email which authenticates
the update. Users send around the latest update in emails they send,
so that clients learn in a p2p fashion from other people, from new
clients (which would start with latest version) and so on.
I am supposing that one would change this value infrequently, say no
more frequently than 6months or 1 year, and that there would be in
addition a period of overlap. Eg. the previous periods stamp cost
should be accepted, but clients should generate the current stamp
cost.
Izzy Kindred also proposed distributing (domain specific costs, or
_user_ specific costs) via DNS.
Each approach has trade-offs:
challenge-response introduces unreliability in the form of
mail-filtering, double-bounce problems etc. where the postage required
message does not arrive;
DNS presumes that mail clients are online which is not ideal as email
is store and forward and at the time of stamp creation the MUA may not
be online; DNS is typically controlled by ISPs rather than users so
users would not without an additional protocol have ability to set per
user costs.
And standardized slowly updating overlapping periods via p2p runs the
risk that some MUAs may get out of sync. I thin k the risk of this is
minimized if updates are no more frequent than 6 months or 1 year, and
periods overlap; this would mean someone would have to receive no mail
(from any hashcash users or systems) for a period of 1 year (or 2
years) and to also have not updated their software in this time.
Adam
On Tue, Apr 13, 2004 at 11:46:46AM +0000, Scott Robinson wrote:
> How does hashcash stand up to Moore's law? How is this not a
> temporary solution?
> If I am missing something blindingly obvious, please CC me as I am
> not on this mailing list.
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