RSA Encryption is a really neat application of modulo (remainder) theory. This video goes through what (at least to me!) is a pretty intense little proof!
What I looked up after recording: RSA is for Ron Rivest, Adi Shamir, Leonard Adleman. They published the algorithm in 1977. Another guy, Clifford Cocks, who was an English mathematician working for British Intelligence had already discovered it back in 1973, but that wasn't declassified until 1997. So I was kinda right in what I remembered about the story.
