Toward a Secret Sky

This is the second part of a series of ESP-IDF tutorials that I will complete as I learn stuff. Read part 1. One of the best things about Arduino is the ability to just block for a period with: delay(1000); // hang on a second, buddy It’s also one of the worst things. As soon as you need to do a few things at the same time, you will end up using better systems, like calling millis() or using the elapsedMillis library. Anyway, the IDF has you covered. You can delay, but amazingly it appears that once you multi-task (which you will with Free RTOS), the delay doesn’t block the other tasks from running. My Notes: Read the docs, now or later https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/freertos.html Delay doesn’t have to block like Arduino. Delay some milliseconds like this: vTaskDelay(pdMS_TO_TICKS(10)); Since vTaskDelay accepts ticks, the pdMS_TO_TICKS macro will convert for you. Help yourself out by adding your own macros if you are lazy. I am lazy. #...

I'll soon return to the basic tutorials on the ESP-IDF. This tutorial is a one-off on a topic I find interesting. "How can I validate that data from an embedded device came from that device?" This sounds like a job for public key cryptography. I'm no crypto engineer by any means, but I can certainly use libraries. The ESP IDF ships with mbedtls , which is a surprisingly comprehensive suite of crypto. The library is owned by some people called ARM mbed, so I am guessing you can run it on any ARM. Here's the scheme: Create a public/private key pair (RSA in this example) on the embedded device and store it in memory. In our case in the SPIFFS file system. Send the public key to the server Hash and sign every data packet you will send the server with the private key. Embed the signature as a header in the HTTP request Validate the signature on the server when receiving data The remainder of this post will show you how to do those things. The code is kind of intense i...