If something is sold with phrases like “like …” or “compatible to …” or “drop in replacement for …” and in the same time it is much cheaper, then you should think twice if it is worth the money. In some cases I had to learn it the hard way.

Most time, the wireless communication between embedded devices like the Arduino happens in plain text. While block ciphers like AES are too bulky in terms of speed, payload and object code size, stream ciphers like RC4 do not offer a high level of security through the lack of diffusion. In this post I will describe a new method to use a modified stream cipher that offers diffusion and also works with no overhead on small payloads, that are common in such devices.