From: Adam Back <aba@dcs.ex.ac.uk>
Date: Sun, 14 Dec 1997 08:34:53 +0800
To: bill.stewart@pobox.com
Subject: supeona immune postage free list (Re: hashcash spam prevention & firewalls)
In-Reply-To: <3.0.3.32.19971213101329.007794a0@popd.ix.netcom.com>
Message-ID: <199712132340.XAA03750@server.eternity.org>
MIME-Version: 1.0
Content-Type: text/plain




Bill Stewart <bill.stewart@pobox.com> writes:
> It also creates a valuable soft-target traffic analysis database;
> unlike current sendmail logs, it'll probably stick around for an
> extended period of time, and be readily subpoenaed.

I think I figured out a solution to this nasty problem prompted by
Robert Costner's comments:

How about this alternative which achieves the same functionality and
removes the juicy supeona target:

Turn on hashash database for all mails.  That means hashcash gets put
in the database to prevent double spending.  (If we don't do this
spammers will club together and do one mega-spam reusing the same
hashcash they generated with their spam fest motivated CPU farm and
hit you with spam from many addresses, or all forged as from the same
address or whatever).

So now when you reply to a message, on it's way out via the mail hub,
mark the hashcash token as reusable.  This means that the sender can
cache sent hashcash tokens, and re-use them when after he gets a
reply.

Adam
-- 
Now officially an EAR violation...
Have *you* exported RSA today? --> http://www.dcs.ex.ac.uk/~aba/rsa/

print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<>
)]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"|dc`