From: Kent Crispin <kent@songbird.com>
Date: Sat, 9 Aug 1997 08:05:26 +0800
To: cypherpunks@cyberpass.net
Subject: Re: some hashcash advocacy
In-Reply-To: <97Aug8.131019edt.32257@brickwall.ceddec.com>
Message-ID: <19970808165350.55775@bywater.songbird.com>
MIME-Version: 1.0
Content-Type: text/plain



On Fri, Aug 08, 1997 at 10:45:29PM +0100, Adam Back wrote:
[...]
> I wasn't talking about remailers above, but about end users.  Hashcash
> allows the recipient to filter out email that hasn't got postage.

Ie, hashcash is a fancy techie oriented self-labelling technique.  :-)

I didn't read the code, but it seems that the double spending
protection is just local to the recipient (ie, there isn't a trusted
central clearinghouse that checks against double spending on a global
basis).  Thus, a spammer could calculate postage for a message, then
send 100000 copies.  Hashcash would guarantee that each user only got
one copy, but there are easier ways to do that.  [If the checking was
done at an ISP level, of course, only one message would get through. 
But that requires widespread deployment at the ISP level, not the
individual user level, and checking at the ISP level requires
that the ISP keep a database of users mail preferences.]

But without a central clearinghouse hashcash seems useless to me as a 
means of combating spam.  And of course, a central clearinghouse 
brings up a whole raft of other issues concerning trust and so on...

[...]

> You could auto-add anyone you ever manually replied to to the
> no-postage list even.

I would rather pursue a "tit-for-tat" strategy for email, but
unfortunately tit-for-tat requires stable identities... 

-- 
Kent Crispin				"No reason to get excited",
kent@songbird.com			the thief he kindly spoke...
PGP fingerprint:   B1 8B 72 ED 55 21 5E 44  61 F4 58 0F 72 10 65 55
http://songbird.com/kent/pgp_key.html