Three years ago, I published my initial work to understand and reverse engineer my car, specifically the headunit of my 2021 Honda Civic. 1

The initial response was incredibly encouraging. I’m writing to give a project update.

Keys to the Kingdom

The biggest progress has been made while mapping out the update process.

Honda supports updating the headunit via USB. There are a number of Honda-specific checks, but ultimately the USB drive contains a signed AOSP update file that gets staged and applied via Android recovery. The good news? They left the publicly-known AOSP test key in res/keys *, and, even though they modified the recovery binary, the verify_file signature logic matches stock AOSP.

So as long as you can properly format a USB drive and sign it with the publicly-known AOSP test key, you can install whatever you want to the headunit, without conventional root access (no need for su with setuid ).…