Listening to P25 “Fed” Radio with a $20 RTL-SDR Dongle

A guy takes the feed from an RTL-SDR $20 software defined radio and
pipes the output to an open source digital decoder package. All of a sudden all the gaping vulnerabilities we saw in Matt Blaze’s “Why (Special Agent) Johnny Still Can’t Encrypt”* are accessible to anyone.

I will note that, as far as I know, listening to unencrypted public safety radio in all its flavors is still legal.

And, key point here, because it works on commodity hardware & open source software, one can do this as just one person. (Which we all ultimately are.) Being free from dependency on large companies and the like may seem less important for day to day things, but in security it’s critical.

* http://www.crypto.com/blog/p25/

http://dangerousprototypes.com/2012/06/06/decoding-p25-with-sdr-dsd-and-rtlsdr/

“This is another illustration of the amazing utility of the RTL-SDR and SDR# software. Here proct0r links the output from SDR# to a program known as DSD. DSD is an open source command line program originally coded in C by anonymous for Linux for the purpose of decoding digital protocols via a PC soundcard. The program accepts audio taken from the discriminator output from a scanner or amateur radio receiver fed to the soundcard input. DSD is then run (using the appropriate arguments, depending on the mode and parameters involved) with the resulting demodulated speech directed to the soundcard output jack. Additionally, various protocol decodes (P25 among them) provide a running display of certain packet data in the terminal window.”