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Fritz Menzer was one of the brightest German cryptologists of the Second World War. A number of important points in his biography are still unclear. Can my readers solve these mysteries?

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A Reddit user has posted a postcard from Sweden written in 1910. Can a reader decipher it?

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An advertisement poster that is currently shown in London underground trains contains an encrypted message. It is not very hard to solve.

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In World War II German secret agents used a little known cipher device named Schlüsselrad (Cipher Wheel). An old document blog reader Ralph Erskine made me aware of contains the first photographs I have ever seen of this device, as well as some additional information.

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“Chief Security Officer”, my 24th book, has just been published. Contrary to my other publications, this one is a cartoon book. It tells funny, yet true stories about IT security.

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According to a Reddit post, a needlework made in the 1980s contains a hidden message. The details are not known any more. Can you find this message?

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From 1884-1887 a series of 25 encrypted newspaper advertisements was published in the “Daily Telegraph”. The key is known. Can you help me to decrypt these messages?

Arithmetic-Book-Cryptogram-3-bar

Four years ago I blogged about an encrypted (?) text a blog reader had found in an old school book. It is still unsolved. Meanwhile I have better scans and some additional information.

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On Wikimedia, photographs of a number of lesser-known encryption devices from Switzerland are available. Can a reader tell me more about them?