I’m happy to announce that my new book, Post-Quanten-Kryptografie (“Post-Quantum Cryptography”), has just been published.

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At the HistoCrypt 2026, I came across an encrypted document, which was exhibited by French radio history expert Didier Clarençon. This document was reportedly found on eBay in 2009 together with a spy radio suitcase, as it was used by the British Special Operations Executive (SOE).

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A few days ago, M. E. Sprengelmeyer, a well-known American journalist, contacted me asking for help. Sprengelmeyer has had a distinguished career in journalism, as his Wikipedia page documents. While going through some old papers, he came across an encrypted message that he has been unable to decipher.

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At HistoCrypt 2026 in Amiens, French collector Edmond Kern presented his remarkable collection of historical cryptographic material. Besides a number of cipher devices, the collection includes many encrypted postcards. I am very grateful to Edmond for allowing me to feature these fascinating items on my blog. Today I am starting with the first postcard, and I expect several more will follow.

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The HistoCrypt 2026 conference in Amiens, France was a fantastic event. Despite the heat – we experienced some of the hottest days ever recorded in Central Europe – the conference atmosphere remained inspiring.

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The inscription on the Kryptos sculpture outside CIA headquarters in Langley, Virginia, is widely regarded as the most important cryptographic mystery of the past several decades.

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Of the many unsolved ciphers I have encountered over the years, this is one of the strangest.

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Among the many unsolved historical ciphers, one mystery that I find particularly intriguing is the Ohio Cryptogram. More than a century after its publication, this encrypted message remains unsolved.

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On this website, you will find a wide range of information about the history of cryptography, codebreaking, and related topics.

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