In 1901 an unknown person sent an encrypted postcard from Iserlohn, Germany, to nearby Arnsberg. Can a reader decipher it?


At the HistoCrypt in Uppsala, Craig Bauer gave a talk about famous cryptograms. Among other things, he defended his solution of the second Zodiac Killer cryptogram, which was heavily criticized by the readers of this blog.


Two encrypted newspaper advertisements from 1875 are still unsoved. Is the first one the key to the second?


A dog tag introduced by a Reddit reader bears an inscription that looks like encrypted text. Can a reader solve this cryptogram?


A Donald Duck comic story, which was recently republished in a German Disney magazine, contains an encrypted message. The solution, if it exists, appears to be unknown. Can a reader break this cryptogram?


Here’s a great challenge for my readers: Robert Bunch (1820-1881), a British spy in the US Civil War, left behind a number of encrypted messages that have never been deciphered. Can you solve this mystery?


Only little is publicly known about the encryption systems used by the German terrorist organisation, RAF. A recent TV documentary that shows a number of encrypted RAF messages along with a key provides at least some basic information.


A postcard from 1903 is encrypted in a dancing men code, like it is described in a famous Sherlock Holmes story. Can a reader decipher it?


A fifth encrypted bottle post has been found in the river Alster in Hamburg. Still, nobody seems to have a clue what these strange messages mean.


Here’s a postcard written in English that contains two kinds of encryption. Can a reader decipher this two-part cryptogram?