Does anyone know of private key encryption that would be suitable for use
in a PIC uC for encrypting small byte stream messages?

It doesn't have to withstand detailed cryptanalysis, but the harder to
break, the better.  I had initially thought of just having a rotating 16
bit key that is xored with each byte.  This seems like it might be pretty
easy to crack though.  I really have no experience with this sort of thing.

We're not transmitting credit card numbers or anything, we just want to
obscure our underlying protocol for marketing purposes.

Any pointers?

Erik Reikes
Software Engineer
Xsilogy, Inc.

ereikes@xsilogy.com
ph : (858) 535-5113
fax : (858) 535-5163
cell : (858) 663-1206