From: jdd@aiki.demon.co.uk (Jim Dixon)
Date: Sat, 6 Aug 94 10:19:38 PDT
To: cypherpunks@toad.com
Subject: Re: Remailer ideas
Message-ID: <4071@aiki.demon.co.uk>
MIME-Version: 1.0
Content-Type: text/plain


In message <9408051709.AA14763@ah.com> Eric Hughes writes:
> Jim Dixon analogizes between the Internet and remailer networks.  The
> analogy has some merit, but yet breaks down badly with the very first
> point:
> 
>       *	all packets should be acknowledged
> 
> This is not the way the Internet works.

There are some problems with vocabulary here and some conceptual
problems.  The objective is a system which is highly reliable and
resistant to traffic analysis.	If you have three messages in, one 10
bytes long, one 1000 bytes long, and one 1,000,000 bytes long, and you
send them out to three different destinations, it does not take
genius to see which is which, no matter what order they are dispatched
in.  But if you send them out as packets, each say 4096 bytes long,
with all packets acknowledged, and the routing of the packets is random,
and noise has been introduced ... traffic analysis is very difficult.

TCP/IP is designed to work in an environment which is unreliable but
also unhostile.  The sliding window algorithm and acknowledgement at
the message level is suitable for that environment.  TCP/IP has been
optimized for speed.

[stuff omitted]

> Further, in email, there's currently no notion of a connection.

The internal functioning of RemailerNet is not the same as the
functioning of the email system.  All RemailerNet communications are
reliable.  Packets are acknowledged and the acknowledgement includes
a hash of the packet contents, so that the packet cannot be tampered
with.  Acknowledgements will in general take different routes from
packets.

>       *	users should communicate with trusted gateways
> 
> This point is only half true, because the analogy only subsumes one
> kind of trust.  For remailers there is both trust in delivery and
> trust in silence, the destruction of the message and information about
> it.

'Trust in silence' is a good term.  This can be enhanced in a number
of ways.  If you are corresponding with someone you know, you encrypt
your messages.	If you are corresponding with a stranger, you encrypt
your message with the public key of a far gateway; then post it to
the far gateway through a near gateway.  The near gateway knows who
is sending, but cannot read the message and does not know the
destination.  The far gateway decrypts the message before delivering
it, so it knows the message and the destination, but not the sender.
If you are sufficiently paranoid, you put your message inside
yet another envelope, mailing it through the near gateway to a
far gateway, which posts it on to another gateway, which finally
posts it to its destination.

Remailer gateways should be spread very wide geographically if the
network is to be secure.  If you are very concerned about anonymity,
bounce a message through gateways in, say, the USA, Finland, Russia,
and Ireland.  If your concerns are about your employer, say, the
probability of his getting at four different gateways in four
different jurisdictions simultaneously is vanishingly small.  If
your concerns are about governmental authorities, they are not
that much higher.

--
Jim Dixon