Category: Security

Receiving, Decoding and Decrypting GSM Signals with the RTL-SDR

A while back we did a small write up on receiving and analyzing cellular GSM signals with the RTL-SDR. Now blogger Domi has taken it further and has done an excellent big write up on his blog showing how to receive, decode, and also decrypt your own cell phone GSM signals with the RTL-SDR.

Domi’s big write up is split into four posts. It starts with an introduction to GSM, then focuses on setting up the environment and required software, then uncovering the TMSI (step to be released later), and then finally shows how to actually receive and decrypt your cell phone data such as voice and SMS messages.

GSM Decoding with Airprobe and Wireshark and RTL-SDR
GSM Decoding with Wireshark

Exploring Unintended Radio Emissions with the RTL-SDR – Talk now available on YouTube

A few weeks back we posted about some slides from the Defcon conference by information security researcher Melissa Elliot which detailed how she used an RTL-SDR to explore the world of unintended radio emissions.

The talk to go with the slides is now available on YouTube

DEF CON 21 - Melissa Elliott - Noise Floor Exploring Unintentional Radio Emissions

Potential Major Security Flaw on HP Laptop Discovered with RTL-SDR

Over on Reddit, user cronek discovered by using his RTL-SDR that the microphone on his HP EliteBook 8460p laptop computer was continuously and unintentionally transmitting the audio from the built in microphone at 24 MHz in FM modulation. He found that the only requirement needed for the microphone to transmit was that the laptop needed to be turned on – even muting the microphone did nothing to stop the transmission.

Click here to read the original post.

I accidentally stumbled upon a signal in the 24MHz range, appearing to be 4 carriers. I tuned to it and heard silence, then someone came into my office and started talking and I could hear them speak. The signal appeared to be coming from my other laptop (not the one running the SDR) and was pretty weak (my antenna, the crappy one that comes with the dongle, stuck to a metal stapler was right next to the HP laptop).

This is of potential concern as as the US Military is apparently transitioning to this particular laptop. However, this may be an isolated incident, as in the thread cronek explains that other laptops he tested did not display this behavior.

HP Laptop Microphone Leak at 24 MHz