About 110 years ago, a Mariechen Schäfer living in Frankfurt, Germany received an encrypted postcard. Can a reader solve it?

In WW2, later US president John F. Kennedy and his crew disappeared after their torpedo boat had sunk. Can my readers help to make sense of an encrypted message that was sent a few days later?

In the 1950s, a US company published weekly newspaper advertisements that included crypto puzzles. Here are three of these.

Two months ago, US book author A.J. Jacobs showed me the encrypted journal of psychologist Abraham Maslow (1908-1970). My readers did a good job in analyzing this cryptogram. Now, A.J. asks for additional help.

In 1943, the British intecepted an encrypted radio message sent from an airplane. Can a reader decipher it?

British WW2 soldier and prisoner of war Donald Hill kept a steganographic diary. A 13-minute TV documentary available on YouTube tells this story.

In 1908, an ecrypted postcard signed with “Somebody” was sent to a sobriety organisation in Northern Ireland. Can a reader decipher it?

Blog reader Christoph Tenzer has sent me a nice crypto challenge, based on an enhanced Caesar cipher. Can a reader solve it?

A sword showcased in a Havana, Cuba museum bears an encrypted inscription. Can a reader decipher it?

The homophonic Polybius is a simple but hard to break manual cipher. Can a reader break a message I have encrypted in this scheme?