Spies used to meet in the park to exchange code words, now things have moved on - Robert Miles explains the principle of Public/Private Key Cryptography note1: Yes, it should have been 'Obi Wan' not 'Obi One' :) note2: The string of 'garbage' text in the two examples should have been different to illustrate more clearly that there are two different systems in use. This video was filmed and edited by Sean Riley. Computer Science at the University of Nottingham: Computerphile is a sister project to Brady Haran's Numberphile. See the full list of Brady's video projects at: