From: doug@netcom5.netcom.com (Doug Merritt)
Date: Fri, 3 Sep 93 21:17:15 PDT
To: cypherpunks@toad.com
Subject: Re: Remailer Reliability
Message-ID: <9309040413.AA23647@netcom5.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


sameer@netcom.com (Sameer Parekh)
>install-script I can add this little feature. Which newsgroup? Should
>someone create an alt.remail? How exactly would it be implemented? I'm
>thinking that simply the user would do:
> [...]
>	And the remailer would post to alt.remail:

There are two problems here. One is that the remailer exposes itself
and defeats traffic analysis avoidance.

The other is a standard transaction processing sort of problem; the
posting to alt.remail might fail even though all else worked.

Although I've dealt with transaction processing problems, it's a tricky
area, and I don't have a good text on the subject. Any recommendations?

b44729@achilles.ctd.anl.gov (Samuel Pigg) said:
>By breaking a message into pieces and sending them via different paths
>to the same destination ("path forking"), this can only make traffic
>analysis easier, because all the pieces lead to the same destination,
>and you can follow any of them to get to the anonymous recipient.

Depends on how it's done. As stated this analysis implies that traffic
analysis is *always* possible, since after all, the message must somehow
make it to its destination. In other words, I disagree.

Traffic analysers will have access to only some limited subset of
information. If a certain kind of blind remailing with multiple pathways
is practiced, then traffic analysis can be statistically defeated. The
bad guys might sometimes know that X sent a message somewhere.
Other times they might know Y received a message. Only improbably
(under ideal implementation circumstances) would powerful bad guys own
so many machines & networks that they would be able to deduce both
sender and recipient, and even then, if traffic were heavy (as it will
be in some years), it would be a statistical rather than certain deduction.

(This of course raises the (no doubt old-hat) problem that no single
remailer can be trusted, since it might be in the hands of the NSA or
KGB or something. In fact, since the NSA is famous for doing their job
well, this list must have NSA watchers, no question, even without paranoia,
and if I were them I'd be experimenting with remailers even now, to keep
up with trends. We'll never know how many remailers are trustworthy,
so we'll have to use statistical schemes to make compromise unlikely.)

This is all standard parallel remailing stuff. Add to this the possibility
that the different remailing paths may contain message fragments rather
than full messages, and it doesn't really change the security relative to
full message parallel remailing...unless it's done badly.

Badly would mean that some remailer is the one that finally recombines
fragments prior to final delivery. Better is if the recipient's host does the
recombination (and I worry about *that*, too).

This needs to be done in conjunction with other standard cypherpunk fare,
of course. The major design problem I've had is not with security, it's
with fault tolerance. Statistical fault tolerance is available, but I
prefer leaving that kind to the underlying base systems and networks,
and trying to find a top level algorithm that is 100% guaranteed to either
work or report failure, so long as the host systems/networks don't fail
undetectably. A handshake ACK of receipt would help, except that it might
not get back even if the original reached its destination.

Which is why I'm starting to think I need to research transaction
processing more thoroughly; some years back I'd heard that a centralized
server was still state of the art for 100% fail-safe/soft operation. Is this
still the case? If so, then we'll have to fall back on probabilistic
fault-tolerance, to avoid issues of central authority compromise.

>follow them all), as only one will arrive there and the rest would die
>after a number of remailer hops.

This is actually less safe than an approach which requires multiple
pieces to arrive via multiple paths. Bad luck might leave your one
path completely in the hands of bad guys (posing as cypherpunks, let's
say).

>I really think that non-deterministic "smart messages" are the way to
>go here.

This I agree with; but the way that is done is critical.

>A simple command language for the remailers would allow
>the header construction software already being worked on by
>ebrandt@jarthur.Claremont.EDU (CRM) and others to use tricks
>like this to defend against attacks. 

Cool. More info?

>	The defense complexity would be a function of the users'
>header construction software and needs. People who need "minimal"
>anonymity would have simpler anonymous address blocks, as compared to
>those who require "serious" anonymity, and the remailers themselves
>would have a lighter load (not having to implement very serious
>security for *all* messages-- just those that need it).

Strongly agree.

BTW I consider this emphasis on batch mail to be short sighted. I'm
designing for interactive cyberspace. I have a complete algorithm in
mind, except I think it still needs some more OLTP wisdom added in.

People have been telling me for a long while that I should hook up
with cypherpunks; seeing traffic over the last week since I joined
shows me why I heard that from so many sources. Tip of the hat to y'all;
this is a much juicier forum than I had guessed.

I only hope I can continue weathering the storm of heavy traffic, on
top of other email lists. :-)
	Doug