Actually Lana’s old coworkers would get more bang for their buck by picking up the stray voice conversations of people on the way to lunch in Nicosia.
The only nearly unbreakable encryption is one in which the keys are used by each distant communicating end and the keys are personally exchanged on a periodic basis. A system in which the key itself is useless if intercepted.
(Not many people know that Henry the VIII killed Mary Queen of Scott, after her messages were intercepted. They were nailed to the bottom of an empty water barrel. She forgot the basic law of sending messages - make sure the information in the message is useless if found. She had no way of encrypting the message and could not maintain any kind of key exchange while held in the Tower of London.)
As for us today, then is it up to your curious enemies as to what form does the key come in paper, plastic, or metal. So Igor, Ivan, and Misha want to jump me on the way from the plane, ship, or car, they will have to know what they are looking for and who they are looking for.
Inside the key there is a complex algorithm that only works in a specialized device that is connected to the data network. This kind of key-exchange is very difficult to break because you do not know what number to start with and you have no idea how long the number is.
The Enigma only had three to six wheels of 26 characters – which gave you a little over 30 million letter combinations. Just 56 bit Encryption has over 100,000,000,000,000,000 key combinations and it was invented in the mid-70s. Commercially we are up to 1,024 bit these days, so who knows how high the key number is now?
The term Echelon - or the collection of Open Source data from electronic emissions exists, well it exists in many countries.