In 1877, US engineer Frank S. Baldwin received a patent for a cipher disk. Blog reader Matthias Brüstle has encrypted two plaintexts with this method. Can a reader break these?

In the Second World War, the Germans used a manual cipher, the “double box”. Here’s a double-box cryptogram for my readers to solve.

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

A team of computer scientists has improved the record for factorizing prime number products from 795 to 829 bit.

Last December, Jarl Van Eycke and Louie Helm solved a bigram-substitution ciphertext consisting of 750 letters – a new world record was reached. Now I have created a 600-letter bigram challenge. Can it be solved, too, or have we reached the end of the line?

Today I’m going to introduce an alternate reality game (ARG) created by US puzzle designer Zachary Epstein. It was launched only a few days ago.

Today I’m presenting a 24 letter message that has been encrypted with a Playfair cipher. Such a short Playfair cryptogram has never been solved before.

The 1980s rock band Arcadia published a few encrypted messages on their record covers and in a sheet music book. The solutions are not known to me.

The autokey cipher is a variant of the Vigenère cipher that was once considered unbreakable. With today’s means it can be deciphered. Can a reader solve the challenge I’m introducing today?