The wonderful "ArtOfTheProblem" YouTube channel has a great 10-minute video highlighting the encryption methods used during World War II, specifically focusing on the Enigma machine. While going through why the encryption is so difficult, the video then reveals two mistakes that German operators and the machine's designer made, allowing the Allies to crack the codes created by the device.
Any student of security and/or cryptography will enjoy this look at our past:
Keith Shaw rounds up the best in geek video in his ITworld.tv blog. Follow Keith on Twitter at @shawkeith. For the latest IT news, analysis and how-tos, follow ITworld on Twitter, Facebook, and Google+.