How do we exchange a secret key in the clear? Spoiler: We don't - Dr Mike Pound shows us exactly what happens. Mathematics bit: https://www.youtube.com/watch?v=Yjrfm_oRO0w Computing Limit: https://www.youtube.com/watch?v=jv2H9fp9dT8 https://www.facebook.com/computerphile https://twitter.com/computer_phile This video was filmed and edited by Sean Riley. Computer Science at the University of Nottingham: https://bit.ly/nottscomputer Computerphile is a sister project to Brady Haran's Numberphile. More at http://www.bradyharan.com/