Years ago, Otto Leiberich, the former president of the West German cipher authority, told me about a little known encryption system developed by his team. Can you break a challenge cryptogram I have created with this system?

The encrypted inscription on the Kryptos sculpture located in front of the CIA building in Langley, Virginia, is the world’s most famous crypto puzzle. In March, a Kryptos gathering organized by Elonka Dunin will take place.

In the early 19th century, an unknown person sent an encrypted postcard from Munich to Berlin. It is not hard to decipher.

Louis XIV of France, also known as the Sun King, is one of the most important figures in European history. An encrypted letter he wrote in 1693 has never been deciphered.

In 2017 I blogged about a Pigpen ciphertext that had been discovered in the London suburb of Croydon. This cryptogram is still unsolved.

In 1905 and 1906 a man named Harry sent a series of encrypted postcards to a friend named Charlie. Can a reader decipher these messages?

A French magazine article reports on an encrypted diary written by a pedophile priest. The plaintext is not known to me. Can a reader break it?

In 1875 a German crypto book author published a cryptogram and promised to pay 100 Silvermarks to the first one who solved it. It’s probably to late now to win this prize, but I’m sure some of my readers are still interested in breaking this cryptogram.

Various codebreakers have solved thousands of original Enigma messages from World War II over the last few years. Here’s a message of this kind that is still unsolved. Can my readers help?

In 1921 an encrypted telegram was sent from the Portuguese embassy in Berlin to Lisbon. The plaintext is known, but the encryption method used isn’t. Can a reader help?