For the first time in over ten years, the FBI has published a challenge cipher. Can you solve it?

Konstantin Hamidullin from Latvia has solved my Playfair challenge from November 2019. With only 26 letters, this is the shortest Playfair cryptogram ever broken.

A children’s book from the 1980s contains numerous encrypted and hidden messages. Can a reader solve four of these?

After the First World War, Italian engineer Luigi Nicoletti invented a transposition cipher tool. Can you break a ciphertext I created with this device?

Two online games for crypto enthusiasts have been launched – one in Germany, one in Poland.

In a well-known codebreaking book from the 1930s, a Playfair-encrypted message with a (probably fictive) background story is provided. Can a reader break this cipher?

20 years ago, Jim Gillogly, a great codebreaker and reader of this blog, created three crypto challenges – a Playfair, a Double Playfair, and a Double Column Transposition. Can you solve them?

Here’s a nice crypto challenge I found in a paper about the Fourth International Students’ Olympiad in Cryptography. Can you solve it?

The Playfair cipher is an encryption method from the 19th century. Some say that a Playfair-encrypted message of 50 or less letters is still secure today, if the method is used properly. Let’s put this claim to the test.

Crypto puzzle games in the advent time have a long tradition. Here are two nice ones of this year’s season.