A French magazine article reports on an encrypted diary written by a pedophile priest. The plaintext is not known to me. Can a reader break it?

In 2008 the magazine “The Canadian Philatelist” published an interesting article about encrypted postcards. Among other things, this article mentions a nice pigpen-enciphered postcard you can try to decipher.

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?

A few years ago, German late-night show host Stefan Raab presented a number puzzle in his show “TV total”. It involves cryptography and should be easy to solve for readers of this blog.

In 1875 a German crypto book author published a cryptogram and promised to pay 100 Silvermarks to the first one who solved it. It’s probably to late now to win this prize, but I’m sure some of my readers are still interested in breaking this cryptogram.

From 1833 to 1836 two lovers in England exchanged 35 love messages via encrypted newspaper advertisements. The key is known. Can my readers help me to decrypt these messages?

Olivia von Westernhagen, who works as a journalist for the German computer magazine c’t, has provided me an article she wrote, which is based on material she found on my blog. It’s a great read, but it’s available in German only.

Various codebreakers have solved thousands of original Enigma messages from World War II over the last few years. Here’s a message of this kind that is still unsolved. Can my readers help?

In 1921 an encrypted telegram was sent from the Portuguese embassy in Berlin to Lisbon. The plaintext is known, but the encryption method used isn’t. Can a reader help?

HistoCrypt 2019 will take place from June 23-26, 2019 in Mons, Belgium. Here’s the Call for Papers. Apart from scientific papers, non-academic presentations are invited.