[Feoj]

Not exactly as you describe, but very similar and still a good explanation of simple key exchange is [1]. However I believe (Its a long time since college for me...) Diffie Helman as mentioned elsewhere is a bit more complex [2].

[1] https://www.youtube.com/watch?v=U62S8SchxX4 [2] https://www.youtube.com/watch?v=pa4osob1XOk