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xkcd #2869: Puzzles
(imgs.xkcd.com)
Alt text:
Why couldn't the amulet have been hidden by Aunt Alice, who understands modern key exchange algorithms?
The clues were a series of riddles that had 13, 1, 8, and 5 somewhere in their text. Try letters of the alphabet, you wind up with MAHE. What if 1 and 8 was 18? 13, 18, 5 is MRE. "Mister E." "Mystery!" "And what's another word for mystery?" "Enigma!" Mister E. Nygma. Edward Nygma."
Which manages to be extremely basic yet such a stretch at the same time.