What is the history of authenticating nuclear launch codes? Were hashes used for verification? How would a nuclear launch base be able to verify that the code is correct, and how were new codes transmitted (networks? radios?) to the bases? Has anyone ever 'hacked' the nuclear code authentication mechanism? Did nuclear devices stop working if the incorrect code was entered? Other than personnell related security measures, what sort of technical measures existed? How secure were the actual codes?
The details have of course changed with time and technology. For many years the final launch code deep inside the ICBM missle sites was "00000000" 20 years Launch Code. The logic was that it was a very difficult assignment for constantly rotating crew in the bunkers and they needed something they could remember.
It has been standard policy in the U.S. to always maintain a human in the loop, multiple humans actually, to preclude any possibility of an automated launch.
There are a number of relatively current descriptions of the details: