From: paul@poboy.b17c.ingr.com (Paul Robichaux)
Date: Wed, 13 Oct 93 06:39:59 PDT
To: gg@well.sf.ca.us (George A. Gleason)
Subject: Re: Spread-spectrum net (vulnerability of)
In-Reply-To: <93Oct13.033350pdt.13932-3@well.sf.ca.us>
Message-ID: <199310131338.AA02798@poboy.b17c.ingr.com>
MIME-Version: 1.0
Content-Type: text/plain


> I'm not so sure... in cellular systems, cells must know where the handsets
> are located in order to send incoming calls.  Your transmitter has a
> physical location which could presumably be tracked in the normal manner,
> and I would expect the overall routing information in a net to be
> susceptible to traffic analysis in any case.  An individual who is using the
> system to communicate wouldn't be able to find the physical address of
> another user, but e.g. an intelligence agency which was looking at the
> entire network would.  Even assuming spread-spectrum and various link
> encryption techniques on top of whatever end-user encryption is supplied;
> with enough traffic and enough time, it should be possible to do TA.  

Cell systems have to know which cell you're in (visualize each cell as
a circle centered on the cell site) to know how to route a call _to_
you. I believe the MTSO (== cellular CO) will route the call directly
to the cell site for the cell you're in.

Of course, the cell will also know what cell you're in when you
originate a call. This knowledge is useful for traffic analysis, but
it's also required for the system to be able to route incoming and
outgoing calls.

An alternative is the ham packet radio-style addressing of
user@node@node..., where "user" represents the call sign of the
intended receiver and each node represents the call of a digipeater
between the sender and recipient. The hard part here is that you must
be able to dynamically generate a route between Alice and Bob if
either of them move from their last known location.

Of course, there's always store-and-forward. A spread-spectrum network
of small digipeaters, combined with crypto remailing and pool
software, would really be something. I'm not sure that it would work
well for spread-spectrum SLIP, though.

-Paul

-- 
Paul Robichaux, KD4JZG     | "Change the world for a better tomorrow. But
perobich@ingr.com          |  watch your ass today." - aaron@halcyon.com
Intergraph Federal Systems | Be a cryptography user- ask me how.