Doesn't take any fancy encryption. We have had simple, utterly unbeatable cryptography since ancient times: the one time pad. It's just a nightmare for key distribution. We use one-way encryption in environments where we have to publish keys--for example, websites. You need to be able to look at the key for this website (note the https on the URL) in order to talk to it, but you aren't able to pretend to be the website with that info.)It varies by platform....Is there a good on-line description of EXACTLY how nukes are armed and launched?
I've always thought that thePermissive action link (PAL) was active on most nuclear warheads making it impossible to detonate unless a special hard-to-get code was provided. (With one-way encryption so that even knowledge of the warhead's code wouldn't allow arming.)
Bombs have no such issue. Just pick a truly random number for the key for the bomb. The important part is the important control electronics are inside the explosives--in order to do any sort of physical attack on the security system you must have already taken actions which render the bomb permanently unserviceable and at that point the code becomes meaningless. You also count the number of times a code is received and at a certain number you trigger the electronic destruct. (Fries the electronics package, same effect that the bomb has to be remanufactured.)