[Scan-DC] Metro: DC Fire and EMS radio encryption blamed for failure in de - DC News FOX 5 DC WTTG

[Jeff Krauss]

 From what I know of Distributed Antenna Systems like those used in 
the Metro tunnels, they do not touch the encrypted digital voice in 
the baseband data stream.

A DAS consists of one or more indoor transceivers with antennas that 
are connected (often by fiber) to an outdoor transceiver and antenna.

The handheld Fire Department radio transmits on the assigned 
frequency, that transmission is received by the indoor antenna in the 
tunnel, demodulated by the indoor receiver to a baseband data stream, 
and upconverted by the fiber transmitter to a light frequency for 
transmission over fiber to an outdoor transmitter and antenna.

The fiber receiver converts the light back to baseband data which is 
then sent to an outdoor transmitter that modulates the data stream on 
the same assigned frequency and transmits it to the Fire Department 
base station.

The process simply repeats the encrypted voice data stream without 
any need to decrypt it.

It's conceivable that a poorly-engineered DAS could have filters that 
introduce enough distortion so that data errors are introduced into 
the encrypted voice data stream.  Enough errors might affect 
decryption, but would probably have also affected rendering of 
unencrypted digital voice before the Fire Department started 
encrypting, and so would have been corrected then.

Jeff




At 12:16 AM 1/23/2015, Dewey3 wrote:
>I would respectfully disagree.  Antennas must be connected to "something"
>to work.  Just running "leaky" coax through the tunnels will not do
>anything if that coax is not connected to something to assist with/boost
>the received signal.  That something, if not encryption capable, is not
>going to carry/repeat an encrypted signal.  The only place where this would
>be a non-factor is with direct/simplex transmissions.  I know there were
>reports that the direct channels were not working (insert rhetorical why),
>but outside of those direct channels, encryption could have very much
>played a role.
>
>Dewey
>On Jan 22, 2015 11:04 PM, "Jeff Krauss" <jeff at krauss.ws> wrote:
>
> > Everyone should read Dave Statter's commentary and Dallas Lipp's comment
> > on Dave Statter's page.
> > http://www.statter911.com/2015/01/22/attention-members-
> > congress-reporters-metro-not-talk-dc-fire-radios-dcfd-
> > doesnt-talk-metros-radios/
> > Encryption may have created a problem for the public safety radio base
> > station located at the Metro ops communications center (OCC) in Landover,
> > but probably not for the distributed antenna system within Metro tunnels.
> > Encryption (although we hate it) probably had no impact on the incident.
> > Sorry.
> >
> >
> > At 10:46 PM 1/22/2015, Alan Henney wrote:
> >
> >  Metro: DC Fire and EMS radio encryption blamed for failure in de - DC
> >> News FOX 5 DC WTTG
> >>
> >> http://tinyurl.com/muoxjjk
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