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1996-12-31 - Hardening lists against spam attacks

Header Data

From: Bill Frantz <frantz@netcom.com>
To: cypherpunks@toad.com
Message Hash: 834118d0685fa708dd1a993b0c00423b9a35e142b32f673cb29145c8da41f5d2
Message ID: <v03007803aeee6643cfe0@[206.217.121.121]>
Reply To: N/A
UTC Datetime: 1996-12-31 07:01:00 UTC
Raw Date: Mon, 30 Dec 1996 23:01:00 -0800 (PST)

Raw message

From: Bill Frantz <frantz@netcom.com>
Date: Mon, 30 Dec 1996 23:01:00 -0800 (PST)
To: cypherpunks@toad.com
Subject: Hardening lists against spam attacks
Message-ID: <v03007803aeee6643cfe0@[206.217.121.121]>
MIME-Version: 1.0
Content-Type: text/plain


The Christmas attack against this list shows the need to develop lists
which are resistant to attacks.  If cyberspace is to become the town square
of the next century, we need to be able to discourage brown shirts attacks
on political gatherings.  If lists are to be a major part of the political
life of the community, then they must be resistant to attacks from
knowledgeable, well financed attackers, not just the shits who were the
most recent perps.

There are several principles which should be observed:

(1) Since attacks are based on sending to the list, receiving the list
should remain substantially unchanged.

(2) Spam attacks should be throttled at the source, so they do not act as a
denial of service attack on the list server.

Here is a sketch of a protocol which attempts to achieve these goals:

(1) All messages sent to the list must be encrypted with the list's public
key.  This requirement is primarily to protect the posting token (see
below).  However, it alone will probably reduce the problem.  Certainly it
will eliminate the effectiveness of the "subscribe the list to some other
list" attacks.

(2) In order to post to the list, the poster must have a valid posting
token.  These tokens are available, in limited number, anonymously.  Tokens
remain valid unless canceled for abuse.  However, if too many posts are
received with a given token, TCP performance on sockets using that token
may become arbitrarily slow (or the circuit may be dropped).

(3) In order to limit the number of posting tokens, the list server will
only issue a few per day.  The lucky few who get them, everyone who asks
under normal circumstances, may be determined by an algorithm designed to
limit token collection by future attackers.  (This area is where this
proposal needs work!)


-------------------------------------------------------------------------
Bill Frantz       | Client in California, POP3 | Periwinkle -- Consulting
(408)356-8506     | in Pittsburgh, Packets in  | 16345 Englewood Ave.
frantz@netcom.com | Pakistan. - me             | Los Gatos, CA 95032, USA

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