Sunday, 8 March 2020

ESP32 impersonates a Particle Xenon

With the announcement that Particle will no longer manufacture the Xenon development board and drop their OpenThread based mesh networking solution. We decided to see if we could impersonate an existing claimed Xenon(s) (ie one that is already registered on the cloud) on alternative hardware. Hence the idea of 'bring your own device' to connect to the cloud.

After reviewing the device-os source code for a few months it turned out to get a proof of concept working I need a implemented at minimum the following:

1. Port across the dtls protocol layer as it turns out the Gen 3 devices create a secure UDP socket connection over dtls.
2. Extract the devices private key and the cloud public key (no certificates are stored). Particles implementation of the dtls handshake purely relies on Raw Public Key support (RFC7250).
3. Implement a COAP layer as the 'Spark protocol' is built on top of this.

The above was implemented as set of library functions using the ESP32-IDF and I reused the ESP32 (LILYGO TTGO) from the previous post which fortunately hosts a OLED 128x64 display. In the video we demonstrate :

1. Connects to a wifi access point.
2. Retrieves time from a SNTP server.
3. Connects to the Particle Cloud via a dtsl handshake.
4. Sends a number of 'Spark protocol' messages to let the cloud know the Xenon is alive.
5. Awaits commands from the Cloud, including ping and signal operations. When receiving the signal command the screen scrolls the text from left to right.

I liked to thank for sponsoring the hardware and development time for this article.