Two important events took place in the London area yesterday: the royal wedding and the “History of Cryptography and Codes” conference (including a presentation given by me). Hundreds of thousands of people came to see these two spectacles.


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


18-year-old chemistry student Paul Rubin was found dead with a cyanide poisoning in 1953. In his possession police found an encrypted message. This cryptogram has never been deciphered.


LC4 is a cipher that can be computed by hand. According to its creator, it is both secure and easy to use. Is LC4 better than other low-tech ciphers I have introduced on this blog?


Here’s another crypto postcard. As the encrypted part of the message has only 17 letters, it is probably hard to decipher.


Encrypted gravestones are rare, and they have a morbid charm. Here is one located in a town between Liverpool and Manchester. Can you decipher its encrypted inscription?


The Würzburg Residence is one of the most famous castles in Germany. A painting inside shows an encrypted inscription. The solution of this cryptogram is not known to me.


In 1909, an unmarried woman in Newcastle, Australia, received an encrypted postcard. Can a reader decipher it?


The second encrypted message from the Zodiac Killer is one of the world’s most famous unsolved cryptograms. According to computational linguist Tom Juzek, it will never be solved because no solution exists.


Murder victim Ricky McCormick left behind two encrypted notes. Both the crime and the cryptograms are unsolved to date.