xssfox:
In part one I left you with a cliff hanger regarding page calls. And I particularly like this little note:
This shouldn’t be hard
Like it’s a radio from 1993. Easy right?
That was nearly 7 months ago.
Page calls are text messages sent between radios. Essentially SMS for radios. Or I guess WhatsApp(?) messages for radios. The protocol is very similar to the selcall protocol, just with the message spliced in…. however…..
Codan decided that page calls should be locked down. My assumption here is that the 93xx series of radios were the first by Codan to be advanced enough to allow paging and to keep a market edge they wanted to make it harder for competitors to provide interoperability (pretty sad imho). So page calls include two extra bytes that are validated before receiving.
The rest of the post details the process taken to reverse engineer the generation of these two bytes, including the development of not one, but two 8051 emulators.