We are manufacturing a sensor which transmits in 8 byte packets. This sensor will be used by several different receivers, some of which have very little spare RAM available (< 3 kb). On some of the receivers we will provide the software, in other cases, we will be providing the code to the manufacturer under NDA.
It is a commercial application and the sensor could be copied relatively easily. To create a small obstacle for copycat designs, we would like to add some encryption or obfuscation to the packets.
A few details on the radio packet:
- 8 byte packet
- tx several times a second
- the sensor measures analog conditions which can be altered by someone looking to 'crack' the encryption. Part of the packet will be this data. Sometimes the sensor will repeatedly send a null signal.
I thought of using Blowfish, but it is more RAM than I would like to allocate, and it is probably overkill in terms of encryption. Is there a lower RAM alternative of Blowfish?
I know that replacement ciphers are relatively easy to crack, but as I am only looking to slow someone down it may be suitable? Can someone point me towards a mehtod which is RAM efficient and requires some work to crack?