It's a common theme. In The Hunt for Red October, the Russian captain (who holds one missile key) murders the political officer (who holds the other missile key) and publicly holds both keys for himself.

Just prior to that, they use their keys to jointly open a safe containing the file with their orders (analog to decryption?). Maybe that's what the name is alluding to.

I immediately thought of Crimson Tide (Denzel Washington & Gene Hackman), but War Games is definitely a memorable one. "Turn your key, sir!"