Ok, have been reading back through the specifications, to send more then 8 bytes, your after a multipacket PGN, the data layer specs would be 61184 for Proprietary A, or 65280-65535 for proprietary B, or 51712 in response to a request from your primary unit

All of these use pgn 60160 to send messages broken up into chunks of 7 bytes with the first byte acting as the sequence number, using this method you can send up to 1785 Bytes at a time with 1 PGN

The exact document your after is J1939.21 Data Link Layer, the 2014 version can usually be found for free online

Then for your actual data scheme, You encrypt the message using what ever fancy mode you want, unless your constrained for data rate, I would say deliberately include a CRC at the end of the encrypted message byte stream to know to discard and retry before you run the decryption, if you wanted to be a bit painful you might append another CRC to your message before you encrypt it, but I do have to agree if they have broken the encryption, a CRC will not slow them down much,

At a minimum it will probably give you some heads up that tampering is happening, which you might use to trigger some internal key regeneration to mess with whatever work they just succeeded at.

Encryption is all about making breaking into the device with a wire sniffer as painful as possible, if they can just rip the devices firmware your kind of spent either way

bump

hello

hello

@KyleeHolcomb hello?

Hi

so what i want to achieve

is that having two rpi's with canberries

I want to make an auth system

to prevent spoof and replay attacks

I had many ideas

but some of them seem uncomplete

the reason is that we have the ability to send 64bit of message

I thought a random num generator to prevent spoof and hash to prevent replay

hash its a bit tricky because we need to send 2 messages one follow the other and we cannot be sure that no-one wont send something the same time

I thought about doing multi layer encryption

use a rolling code encyption,

this way each message is encoded differenly, and also means if any messages are replayed, they are invalidated

or as a much simpler method, include a sequence number in your messages and keep track of what your up to, if the sequence number is the same or less, then discard