Meshtastic (LoRa) RF protocol reverse engineered from RF to Bytestream for GnuRadio

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Author: infosec.exchange via jwconway

I just finished building this Gnuradio flow over the weekend. This GnuRadio flow enables any SDR to receive incoming Meshtastic/LoRa radio data and convert/extract the data to a bytestream.

Meshtastic is a off-grid low-bandwidth high resiliency radio communication system. It uses inexpensive radios to facilitate a mesh communication system.

https://meshtastic.org

Normally, you need a Semtech LoRa chip to transmit and receive. My project was instead to make a full stack to emulate or replace a Semtech chip by using an SDR (software defined radio).

I’ve been able to create, with thanks to https://github.com/tapparelj/gr-lora_sdr , to create the full Gnuradio frontend to receive Meshtastic/LoRa data and decode them to the bytestream.

Why is this important?

There are 7 default presets in Meshtastic. However all members of the same group have to use the same preset. With this flow, your receiver SDR can listen to all 7 presets at the same time.

In some jurisdictions, where we have more bandwidth (EU is locked to a single channel), a wider band SDR like a HackRF can listen to larger chunks of the band, and catch Meshtastic comms on other frequencies.

Once I get a Transmit stack created, we’ll be able to try Meshtastic on other frequencies outside the 900MHz ISM band. For us amateur radio operators, this can mean running LoRa on 6M or 10M bands. This means, that instead of Line-of-sight with 900MHz, we can go hundreds or thousands of miles with very little power used.

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Meshtastic (LoRa) RF protocol reverse engineered from RF to Bytestream for GnuRadio