Begin forwarded message:
From: Brad Templeton <btm@xxxxxxxxxxxxxx>
Date: August 10, 2005 4:06:15 PM EDT
To: David Farber <dave@xxxxxxxxxx>
Cc: tom_gray_grc@xxxxxxxxx
Subject: Re: [IP] more on VoIP CALEA -- the NSF does
work for guess
who ? djf
Dave, you can add this note to my prior note if you
wish to
forward it or either.
On Wed, Aug 10, 2005 at 06:14:07AM -0400, David
Farber wrote:
There is no great difficulty in arranging for the
interception of Internet-only voice calls,
contrary to
what has been written in earlier messages in this
thread.
....
It would seem to be very simple for providers such
as
SKPE and Vonage to intercept Internet-only voice
calls. The intereception could be done at the
packet
forwarder. In most cases the packet forwarder is
required. Even in cases where it is not required,
the
client software could be set up to accept a
management
instruction amd silently send all packets thorugh
a
forwarder without infromting the user.
Tom Gray
Skype, as far as we know (they don't reveal the
details) encrypts
end to end. The external PC which is recruited to
forward
packets for people behind NAT does not, as far as I
know, have
the ability to decode the voice. If it does, that
would be a
surprisingly poor encryption design, and a provider
like Skype
could change it.
Skype is standalone software. It queries Skype's
master servers
for information on where to do directory lookups and
find external
servers, but otherwise Skype's servers do not appear
to participate
in the calls, and thus, without modification of the
downloaded
software, could not interfere with or even be aware
of calls, short
of suborning the entire list of "volunteer"
forwarding computers
provided to the client.
And as I noted before, rerouting IP to IP calls adds
considerable
problems. I am building a VoIP phone service which
connects two
people by ringing both their phones. However, it
does not, as most
such services do, bridge the calls in a central
point. Both endpoints
send their audio to one another directly. A central
wiretap is
not workable on such a call. The system could tell
both endpoints
to talk to a bridge, which would be detectable and
increase latency.
One could easily provide software to watch for this
and turn on an
indicator on the phone saying, "Your line is
tapped!" In some ways,
criminals might find it more useful to have a phone
where they can
tell if it's tapped to provide disinformation,
rather than just
avoiding taps altogether as you would with Skype.
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