There are way more (real-world) versions than two, with quite a few arrangements that can cancel out some of the systematic error, both with and without inputs requiring a data connection, and with some augmented solutions passively broadcast as "one-way" data.
The funny thing is that the James Bond/ Tomorrow Never Dies plot device has turned out to be the most realistic, but doesn't actually require the theft of some encoding device, with various record and delay replay attacks.
Other underused plot device: lots is made out of over reliance on GPS and what would happen in the event of an attack on the system. But most ignores the fact that the US NAVSTAR GPS constellation is multipurpose, and is also a (confirmed) primary component of worldwide nuke detection, with some (afaik unconfirmed) claims of a missile launch detection capability, as well.
The funny thing is that the James Bond/ Tomorrow Never Dies plot device has turned out to be the most realistic, but doesn't actually require the theft of some encoding device, with various record and delay replay attacks.
Other underused plot device: lots is made out of over reliance on GPS and what would happen in the event of an attack on the system. But most ignores the fact that the US NAVSTAR GPS constellation is multipurpose, and is also a (confirmed) primary component of worldwide nuke detection, with some (afaik unconfirmed) claims of a missile launch detection capability, as well.