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

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.