Sounds silly...
Has anyone tried placing an older firmware and renaming it to the latest to trick the p3?
But i'm sure DJI is smarter this and uses checksums before unloadinge bin file.
I'm still on .19 and a not willing to try...
Yes, checksum is minimum required to check fw integrity. Without an help from Dji engineers, this is a very complex and time consuming reverse engineering task to do, and very dangerous too.