I can see some interesting discussions about what it means to be random, and what sorts of characteristics we might want from a 'random' activity in different situations.

Yes, always a worthwhile thread. Also fun would be to take some clubhouse crypto texts and crack them. Although permuting the 26 uppercase letters yields 403,291,461,126,605,635,584,000,000 possible arrangements (looks impressive), if we know the plaintext is in English, then we can always apply some valuable clues, e.g. letter frequency, in descending order, tends towards ETAOINSHRDLU, plus we have commonly occuring letter combos, like ET EA OU. And if the encrypted text isn't chunked (e.g. into 5-letter strings), to obscure word lengths, then we have a lot more to go on: frequent 3-letter words like AND THE would suggest substitutions. Indeed, finding the most common letter (say V) and then finding 3-letter words ending in V would give a good hypothesis for the T and H substitutions. I'd be in favor of leaving all these clues intact (e.g. not even chunking at first) and allowing students to successfully crack a few clubhouse messages. Then you could go to a next level of difficulty (e.g. add chunking). As per usual, the cryptographer and cracker share the same mind, as do computer security folks and hackers (in the popular media sense of hacker). Kirby