I think they are quite deliberately pointing out that dealers can communicate with their users in private, outside of law enforcement spying on them [Use case A1].
For encrypting the data as it's sent between gotennas we're using 1024 bit RSA. Not sure what level of detail you'd like.. but here are a few things to get you started!
RSA itself: http://bit.ly/1kDlTgP Cryptographic Services: http://bit.ly/1teLhPb More on CDSA (see above articles first): http://bit.ly/Ug2CLt
Much of our approach is fairly standard!