In 1890, a year after her wedding, a Bavarian princess received two encrypted postcards. Can a reader decipher them?

In Canberra, Australia, there is a set of eight steel pillars bearing encrypted inscriptions. So far, they have not received much attention in the codebreaking community. Some of the cryptograms are still unsolved.

In 1897, an unknown person published an encrypted advertisement in the Daily Telegraph. The only two words left in the clear are JIM LOCKET. Can a reader break this cryptogram?

British author Lady Gwendolen Gascoyne-Cecil encrypted a passage in her diary. This cryptogram has never been solved.

Over two decades ago, a series of strange messages were spread in the Usenet. Their origin and purpose are still a mystery.

Scottish poet Thomas Urquhart (1611-1660) left behind two unsolved cryptograms. Along with many others, they are listed on a website maintained by Eugen Antal.

In 1931, a woman from Bonn, Germany, received an encrypted postcard from Switzerland. Can a reader break this cryptogram?

The “Playfair for Three” is a manual cipher that works similar as the Playfair, but is based on trigraphs instead of digraphs. Can you solve a challenge cryptogram that has been made with this method? 

Substituting letter pairs (also known as bigrams or digraphs) is an encryption method invented in the 16th century. Can you break a new challenge I have made?

In March, I blogged about a TV documentary about the Kryptos sculture produced by CNN. It has now aired and is available on Youtube.