[Cryptography] improved identification of non-targets

[Jerry Leichter]

This is overkill.  All state armies (pretty) follow the long-agreed-upon laws of war.  Among these laws is the requirement that combatants wear their official uniforms.  Anyone engaging in combat not wearing uniform is classified as a spy and can be shot on sight.  A civilian airliner is "not in uniform" and should be treated the same way.

You'd have to get a lawyer familiar with all the complex details of the laws of war to say exactly how *existing* law applies, but a law in the same spirit could be based on a simple standard for broadcasting "I'm a civilian plane and not a legitimate military target" and should not be hard to agree to.  Anyone shooting down such a plane, or a combatant broadcasting such a signal, would be committing a war crime.

Perfect?  Hardly.  But state actors would generally obey the rules.  Non-state actors are not addressed by the laws of war and might not - but then again they might equally well shoot at a plane regardless of all the correct crypto codes that it broadcasts.  So you're left with the rather small case of non-state actors flying a plane that claims to be innocent but is not.  Of course, whatever system you might have had in place, the planes that were flown into buildings on 9/11 *were* legitimate civilian airliners, and would have been broadcasting legitimate codes.

If you think back at the real shoot-downs that were false positives - and non-shoot-downs that were false negatives (i.e., apparently legitimate planes that were used for attacks) - you'll see that the false positives were much more frequent.  In fact, I can't off-hand think of *any* false negatives:  9/11 doesn't qualify since I know of no evidence that anyone spotted the planes (even the one headed for the Pentagon), selected it as a target, but then decided to leave it alone it because it was a civilian airliner.

Yes, civilian planes could use some more protection - they aren't shot down all *that* often, but it's still way more often than it should be.  Almost all of the problem could be addressed fairly quickly and effectively by diplomacy and treaties - which a crypto solution would need *anyway*.
                                                        -- Jerry