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Crypto puzzle games in the advent time have a long tradition. Here are two nice ones of this year’s season.

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The Reddit discussion group /r/codes is a forum for cryptographic questions of all kinds. Occasionally, interesting unsolved cryptograms can be found there.

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The fifth episode of HISTORY’s Zodiac Killer documentary revealed an alleged solution of the infamous Z340 cryptogram. Does it make sense?

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Four episodes of the Zodiac Killer documentary on HISTORY have aired now. The fourth one ended with Craig Bauer saying that he has broken Z340. Will episode 5 tell us the solution?

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In 2013 the German intelligence service BND published four challenge ciphers. To my knowlege, the solutions have never been published.

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In 1935 US president Franklin D. Roosevelt received an encrypted letter from an anonymous person. The solution of the main part is not known.

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Alexander Hamilton, one of the Founding Fathers of the United States, has become especially popular since a musical was written about him. Hamilton left behind a 26×26 turning grille.

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In the novel Mathias Sandorf by Jules Verne the use of a Turning Grille is described. Does a reader know other encrypted messages of this kind?

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In 1873 George Furlong, official at the soccer club Luton Town FC, sent an encrypted letter to his sister. Can a reader break this encryption?

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A postcard from 1906 is written in a combination of Morse code, numbers, and letters. Can a reader solve this unusal cryptogram?