Last year, press reports said that the Devil’s Letter, a notable Italian cryptogram, was solved. It was a good example of how fake news are born.

In the last decade of the 19th century, an unknown person sent three encrypted messages from a place named Bristol. Can a reader decipher these messages?

My readers are pretty good at solving encrypted postcards. However, the two specimens I am going to introduce today look pretty hard to decipher, as the messages are pretty short.

The M-138 is a low-tech cipher device from the first half of the 20th century. Though being quite simple, the M-138 is hard to break.

Among the most popular stories in cryptology are those about a hidden treasure, the location of which is described in an encrypted text. Here are three more stories of this kind.

According to a legend, an encrypted message was found in a cave of the Untersberg, a mountain in the Northern Alps. The cleartext is not known.

Among the most popular stories in cryptology are those about a hidden treasure, the location of which is described in an encrypted text. Here are three stories of this kind.

In 1991, an unknown person sent a number of letters to the presenter of the TV show “America’s Most Wanted”. The anonymous writer claimed to have committed 23 crimes. Some of the letters were encrypted in a similar style as the Zodiac Killer messages.

Two encrypted newspaper advertisements from 1875 puzzle cryptologists. Is the first ad the key to the second?

In 2013 George Lasry broke a ciphertext many had considered unbreakable. In the wake of this success, a few crypto experts created a similar challenge with an even higher level of difficulty. Is this one unbreakable? So far, nobody has solved it.