A simple but effective message encryption could be http://en.wikipedia.org/wiki/XTEA it is lightweight and should be fast enough.
@Pinnchus started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
A simple but effective message encryption could be http://en.wikipedia.org/wiki/XTEA it is lightweight and should be fast enough.