The enigma machine is over 80 years old now. That was just the last machine before modern computing. There were all sorts of other machines and techniques for cryptography long before the modern era. The first forms of encryption are over 3500 years old.
well of course they existed. But I can't think of an example of a pre-internet era where forms of encryption of a grade high enough to stop law enforcement, and probably all/most government can read them, was easy and accessible enough that your average highschooler would without thinking about it encrypt a grocery list he's sending to his mom.
So easy a child could use it... or the current secretary of war (with some minor mistakes of adding in reporters into rooms etc...).