Last December, Jarl Van Eycke and Louie Helm solved a bigram-substitution ciphertext consisting of 750 letters – a new world record was reached. Now I have created a 600-letter bigram challenge. Can it be solved, too, or have we reached the end of the line?

Today I visited the USS Pampanito, a museum u-boat at Fisherman’s Wharf in San Francisco. I was especially interested in the encryption machine that is allegedly on display on this ship. My trip ended up as a disappointment.

Crypto collector Ralph Simpson owns a small cipher device that consists of two metal disks. The origin and the purpose of this unusual tool are unknown. Suggestions from readers are welcome.

Five years ago I asked my readers for information about seven little-known cryptograms created by criminals. Meanwhile, I’m a little wiser, but I still would like to know more about some of these encrypted messages.

Blog reader Mario Gerlach has provided me a picture of an encrypted graffiti he saw in Nördlingen, Germany. Can a reader solve this cryptogram?

Earlier this week I gave an interview (in German) about Crypto AG and the RUBICON affair. It is now available online.

According to recent press reports, the CIA and the BND secretly acquired Swiss crypto machine manufacturer Crypto AG and sold backdoored encryption technology.

An encrypted diary recently posted on Reddit looks easy to solve, but so far nobody has broken it.

On Reddit I found two messages allegedly left behind by people who committed suicide.

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