Secure communication is everywhere: when using your online bank account, sending an email, or sharing a secret over your favorite chat service. But how does this work? How do you secure your messages? And what happens when quantum computers can break this communication security?
Suppose you are Eve. How would you try to find out what the contents of the 4-bit message in this video was? How would your answer change if the message was 400 bits? Why do you think encryption with a private key is considered secure?
If you are interested in an expert and rigorous mathematical insight on the subject, take a look at the book "A Mathematical Theory of Communication" by Shannon, C.E. (Bell System Technical Journal, July 1948). One relevant chapter can be found here.