US engineer Jon Paul has rebuilt the quantizer of the legendary voice encryption machine SIGSALY.

A US magazine has published a letter containing a hidden message written by a prison inmate. The message is given, but the method used has not been published. Can a reader solve this mystery?

Five weeks ago, I blogged about an encrypted diary kept by a French pedophile priest. Tony Gaffney has now broken the cipher. I hope, my readers can help to decrypt the two diary pages that are publicly available.

A few days ago, Queen Elizabeth II unveiled a new plaque that contains a hidden message. Can you break this code?

In 1931, codebreaker and book author Herbert Yardley published an encrypted message without providing the plaintext. Can a reader decipher it?

In 1918, during the last months of the First World War, a woman living in Southern Germany received two encrypted postcards from her lover. Can a reader find out what he wrote?

HistoCrypt 2019 (June 23-26 in Mons, Belgium) will feature a number of world-renowned invited speakers. If you want to speak at this event, too, submit a paper until March 22.

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?

Blog reader Matthias Axinger has drawn my attention to an encrypted message that played a role in the TV series “Operation Mozart”. Can you solve a cryptogram that was created with the same method?

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.