It's not just individual code-cracking that can be used to defeat such a system. What would prevent people from taking an actual 767, gutting the center of it, and putting a bomb-bay there instead?
Doesn't each nations branch of the civil aviation authority operate with the co-operation and support of its legitimate government? I did mention a continuous cycle of valid codes. Of course there will always be edge cases. I didn't propose to address those.
How does one uniquely identify a military aircraft universally?
You can't, but you can uniquely identify a legitimate civilian aircraft.
I didn't "poo poo" idea, I just pointed out realistically that What one man can make, another can find a way around.
Respectfully Mr. Fugitive that is untrue. There are systems which cannot be reversed engineered. You already use these you're probably just unaware of them. Regarding work-arounds you only need to make it impractical enough that other approaches become considerably more viable. Look at international trade for example.
On top of that, who's to say the guy that comes up with "the idea" doesn't just turn around and sell it to the enemy anyway.
Aren't there already methods to secure important things?
I know what kind of world we live in, do you?
I have my subjective model of the world just like you do. Perhaps ours differ in that I would never be put off creating solutions that don't exist yet by people who are convinced they would never work.