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?

Cryptocurrency platform Phemex has published a picture puzzle with a 2.1 bitcoin price for whoever provides the solution.

Jarl Van Eycke and Louie Helm recently solved a bigram substitution ciphertext consisting of 1000 letters – the shortest one ever broken. Now I have created a 750-letter challenge of the same kind.

Today I’m presenting a 26 letter message that has been encrypted with a Playfair cipher. To my knowledge, such a short Playfair cryptogram has never been solved before.

At the NSA Symposium on Cryptologic History, I gave a presentation about brute-force attacks. After a subsequent discussion with Whitfield Diffie, I realized that we need a new DES challenge. Here it is.

The straddle checkerboard was an important part of many Cold War ciphers. Can a reader decipher three ciphertexts I created with this encryption method?

The American Cryptogram Association (ACA) recently celebrated its 90th anniversary. One of the birthday presents was a cake bearing an encrypted inscription. Can you decipher it?

Singer and rapper Ghostemane has published a crypto challenge in a US music magazine. Can a reader solve it?

A recent book mentions a cipher used by a German spy during the Second World War. Can you break a message I encrypted with this method?