Between Silk and Cyanide

Between Silk and Cyanide: A Codemaker's War 1941-1945 is a book by former Special Operations Executive (SOE) cryptographer Leo Marks, describing his work during the Second World War. It was published in 1998 by HarperCollins.

The title is derived from an incident related in the book, when Marks was asked why agents in occupied Europe should have their cryptographic material printed on silk (which was in very short supply). He summed his reply up by saying that it was "between silk and cyanide", meaning that it was a choice between the agent's surviving by making reliable coded radio transmissions with the help of the printed silk, and having to take a suicide pill.^[1] Unlike paper, which would be given away by rustling, silk would not be detected by a casual search if it was concealed in the lining of clothing.

While many of the incidents described in the book are humorous, a major theme is Marks' inability to convince his superiors that apparent mistakes made in radio transmissions from agents infiltrated into the Nazi-occupied Netherlands were prearranged duress codes. SOE management, unwilling to face the possibility that their Dutch network was compromised, insisted that the errors were attributable to poor operation by the recently trained Morse code operators and continued to parachute in new agents to sites prearranged with the compromised network, leading to their immediate capture and later execution by the Nazis.^[2]

Marks' interest in cryptography dated from reading Poe's The Gold-Bug as a child. His father Benjamin was a partner in the book shop, Marks & Co at 84 Charing Cross Road. As a boy, Leo had begun his code-breaking with that used by his father, in noting the prices in his second-hand books.

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