Meshtastic: Quick review and some notes

LoRa, often seen as LoRa PHY, is a proprietary/patented radio communication technique and specifies the physical layer of the standard. A separate layer build on top of LoRa called LoRaWAN that adds support for higher level APIs is often used for IoT devices. Meshtastic uses only the LoRa PHY layer.

LoRa uses the ISM band, which doesn't require a license to operate on under specific conditions, so everyone can use this band and transmit to it, even encrypted messages.

LoRa has been reverse engineered and various GNU Radio implementations of it have been developed (receive only, transceiver). For more information on LoRa, I recommend watching this talk from Matt Knight.

This is the list of officially supported hardware. Some of them are development boards for which the Meshtastic project wrote a custom firmware for and converted them into Meshtastic devices. The rest are hardware projects build specifically targeting Meshtastic as a use case. More devices that are in development stages exist, but are not part of the above list as they're not "production ready".

Most devices aren't open source hardware. Published schematics in the form of PDFs (with no license files) exist for a few of the commercial devices. For the community designed devices, usually full CAD/schematic files are provided. However, since LoRa is patented, I believe a truly open device for now is impossible to get.

The most popular device, the TTGO T-Beam, is powered by an ESP32 for BLE and Wi-Fi, a SX1276 for LoRa, has a 0.96 inch OLED display, a NEO-6m GPS receiver, a SMA antenna connector, a 18650 cell for battery power and a USB port. The USB port can charge the battery, act as an API interface to communicate with the device and flash new firmware to the device.

There are three ways to interact with most boards, via BLE, via Wi-Fi or via the USB port. I tried all three and everything worked out of the box. The Android application is easy to use and pretty bare bones. It also has a debug log interface that makes it easy to troubleshoot issues in case any arise. The Python CLI app was also very intuitive to use, but I didn't get to use it much since BLE was easier to use.

The Meshtastic documentation has a page dedicated on their encryption scheme. I'm not a cryptography expert, but I've dabbled in cryptography a bit, so here's what my understanding of it is.

It uses a symmetric AES256 cipher, with the key being derived from the Channel name. This means, that all nodes in the mesh use the same key and a single node compromise will reveal the key. Since the same key is used throught the session, a leaked key can decrypt all past and future messages (i.e there's no Perfect Forward Secrecy). Encryption is hardware accelerated on ESP32 based boards.

For an off-the-grid emergency messenger this sounds fine to me, not everything needs to be perfect. I'm not sure if the baud rate of the mesh network allows for more advanced encryption schemes (assymetric ciphers) in the first place.

I want to perform more range tests, some especially long ones but with direct line of sight from the top of a mountain. I, also, would like to give different antennas a try, since all of the tests performed so far were with a small build-in omni-directional antenna.

Reticulum, a cryptography based networking protocol for local and wide area networks, has support for LoRa based devices. Specifically, it supports the same TTGO T-Beam device, so I would like to see how other projects behave on the same hardware. Reticulum has the advantage that it supports modern cryptography and allows combining of different networks adapters, i.e. a LoRa device with an Ethernet one.