I hadn't heard of Udacity or Coursera before reading this thread today, so naturally I spent the last 6 hours browsing through the content. Both offer short interactive quizzes during the lecture, and I ran across this one in the Udacity Cryptography course.
Ah, I miss the good old days of the LAVA Lounge. Where have they gone?
Let's liven it up a little!
http://youtu.be/9bZkp7q19f0
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