M-138-bar

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.

Oak-Island-bar

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.

Untersberg-2-bar

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.

Treasures-bar

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.

Scorpion-bar

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.

Catokwacopa-bar

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

DCT-Challenge

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.

Codex-Seraphianus-bar

The Codex Seraphinianus is an unusual book, a beautiful artwork, and an unsolved crypto mystery. It’s the Voynich Manuscript of the 20th century.

Petersen-Pseudonym-bar

This is the shortest cryptogram I have ever introduced on this blog: 46, 9, 4-57, 3, 5. Can a reader decipher it?

Red-Triangle-2-bar

A new internet mystery game, named “Red Triangle”, has surfaced. Meanwhile, six chapters with crypto puzzles and other challenges are known to exist. Is the Red Triangle the new Cicada 3301?