From: eric@remailer.net (Eric Hughes)
Date: Sun, 5 Feb 95 20:32:42 PST
To: cypherpunks@toad.com
Subject: Re: "encrypt tcp connections" hacks
In-Reply-To: <9502060202.AA03281@snark.imsi.com>
Message-ID: <199502060431.UAA18798@largo.remailer.net>
MIME-Version: 1.0
Content-Type: text/plain


Perry advocates IPSP as an almost-panacea for Internet security.  I
disagree.  I'll quote only the most relevant bits:

   From: "Perry E. Metzger" <perry@imsi.com>

   > I don't just want one or two encrypted applications -- like
   > the Kerberos telnet and rcp -- but something to transparently provide
   > privacy for all TCP sockets -- like SMTP sockets between (re)mailers,
   > NNTP, X11, FTP, MUDs, etc.

   Well, in the long term, my hope is that people use IPSP for this. It
   will mean that the kernels on their machines simply deal with all this
   stuff and that userland applications get to ignore it 90% of the time.

   [...]

   However, I'd say that this isn't going to be a permanently deployed
   thing on the net -- that much we can be pretty sure of.

The basic problem with assuming IPSP as a universal encryption
solution is that it answers an incomplete threat model.  IPSP works
where you trust the endpoints but not the intermediates.  When you
don't trust the endpoints for silence, but do trust them for routing,
IPSP doesn't work.  Let me make this concrete:

TIA on netcom.

Suppose I'm running extruded netcom ports on winsock clients using TIA
to multiplex the serial line.  (Some of you may be doing this right
now.)  My Netscape connection is passing from my MS Windows machine
through netcom over the internet to my web server of the moment.  IPSP
doesn't provide end-to-end security in this case, because the endpoint
for the IP packet (netcom) doesn't coincide with the endpoint of the
actual connection (the home machine).  A maxim:

Trust boundaries are not the same as machine boundaries.

It's fallacious to argue simply that everyone's going to be _on_ the
Internet soon enough anyway, and that this problem will go away.
Absolutely not.  If anything, this kind of proxying for Internet
connectivity is going to be come _more_ common, and that as a result
of cypherpunk projects for realtime proxy services, such as web and
ftp proxies.

You don't want to trust the proxy in an anonymization service to do
your crypto for you, just like (if you're smart) you won't trust your
secrets to netcom even for processes, much less for filesystems.  And
you can't say that all proxies are going to be IP-to-IP proxies,
either.  Some of them are going to be proxying the whole protocol,
some will participate partially, some not at all.  What this does
indicate, however, is that the need for peer-to-peer encryption will
be necessary at _each_ level of abstraction, and pretty much forever.

It will be an interesting and practical exercise in trust modeling to
figure out how to pass one layers policy requirement for a secure
channel to a service offering at a lower layer.  The problems involved
here are going to be extremely difficult to make work for anything
approaching generality.

Eric