On Thu, Dec 02, 1999 at 06:08:46PM -0500, Steven M. Bellovin wrote:
> In message <[EMAIL PROTECTED]>, Declan McCullagh wri
> tes:
> > While much of it resonates as true, the timing -- just before crucial
> > oversight hearings and concerns about illegal NSA spying -- might be a
> > little coincidental:
> >   http://www.wired.com/news/politics/0,1283,32770,00.html
> > 
> > Last week's CNN article and televised report raised near-identical concerns
> > about newfound NSA eavesdropping ineffectiveness:
> >   http://www.cnn.com/US/9911/25/nsa.woes/
> These two articles state that "The worldwide move to digital, rather than
> analog, phones and other equipment is making eavesdropping more difficult.
> So are fax machines".  Can someone tell me why "digital" is harder for NSA?
> Fax should be easier than voice, since there is in-band caller information.
> (In the U.S., that information is legally required to be accurate.  I wonder
> if they've ever seen pages from "Cali Cartel, Inc.")

        I think this is a generic reference to digital wireless 
communications rather than digital signalling on undersea fiber trunks and
the like.

        Digital wireless communications, particularly CDMA, are quite a
bit more complex to intercept.  This is because of active power control
which keeps the signal levels from the handset very low and because the
signalling protocols are considerably more complicated and extensive 
than older analog cellphones, as is the signal processing required to
recover the modulation from the rf.   Even such relatively simple things
as use of vocoded voice forces the system to use echo cancellation
because the delay through a vocoder makes echoes annoying - this means
that the base station side of the transmission carries little or no
mobile signal, unlike analog cellphones where both sides of the
conversation can usually be intercepted on just the base to mobile

        And much of the worlds wireless phone plant is GSM, which is
almost always encrypted, which must add significantly to NSAs burden
intercepting it, even if they can break keys very quickly...

        Dave Emery N1PRE,  [EMAIL PROTECTED]  DIE Consulting, Weston, Mass. 
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88 C3 18

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