During the development of this system it became soon obvious that security would be a paramount aspect of the system. For that reason we looked at adding transport layer security (TLS) encryption. This would use the integrated axTLS encryption library in the Sming framework together with AES certificates (host and client) to provide both verification that the host (servers) and clients (nodes) are who they say they are, but also provide a secure encrypted link.
In Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, we already looked at the handling of these client certificates and setting up of an encrypted MQTT connection. One detail which is not obvious from that were the troubles which we encountered while setting up this certificate system. As mentioned in Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, the ESP8266 does not have enough memory to allocate the default TLS handshake buffers and requires the use of the SSL fragment size extension on the side of...
