Between Silk and Cyanide: A Codemaker's Story 1941-1945
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(British & Australian editions, original cover, 1998.)
Background image is a "Worked Out Key" (WOK) printed on silk; photograph shows FANY radio operators receiving morse code transmissions from secret agents.
Between Silk and Cyanide is the title of a book by former SOE cryptographer Leo Marks, describing his work during the Second World War. The title is derived from an incident related in the book, when he is asked why spies in occupied Europe should have their cryptographic material written on silk (which was in very short supply). Marks said that he replied that it was "between silk and cyanide," meaning that it was a choice between a spy surviving, and having to take a suicide pill.
At the age of 8, Leo Marks discovered the great game of code-making and -breaking in his father's London bookshop (located at 84 Charing Cross Road), thanks to a first edition of Poe's The Gold-Bug. At 23, as World War II was being played out in earnest, he hoped to use his cryptographic talent for the British war effort. However, as Marks's witty memoir Between Silk and Cyanide relates, he failed to get into British Intelligence's premier cryptographic department at Bletchley Park.
While everyone else who took the assessment test appears to head off to Bletchley ("the promised land"), Marks is instead sent to what his Sergeant describes as "some potty outfit in Baker Street, an open house for misfits." This outfit was the Special Operations Executive (SOE), which was instructed, in Winston Churchill's stirring phrase, to "Set Europe Ablaze." Marks's duties included monitoring code security so that secret agents sent into occupied Europe could report back as safely as possible.
When Marks arrived at SOE, the common wisdom was that it was easiest and sufficiently secure for men and women in the field to use poem codes to encrypt their intelligence reports before transmitting them to Britain in Morse code via portable radio sets.
Unfortunately, since the Germans had equal access to the classics of literature poem codes were not very secure; over time, and especially if an agent used the same words of his poem repeatedly, Sicherheitsdienst cryptographers could work out the poem being used and then easily break any subsequent encryption sent by that agent. "Reference books," as Marks remarked, "are jackboots when used by cryptographers".
While unable to immediately change official SOE encryption policy, to make poem codes more secure Marks insisted that agents should write their own poems or use his original works instead, several of which are cheerily obscene ("Is de Gaulle's prick / Twelve inches thick," etc). While the use of original poetry as an encryption key was more secure than using poems published in books, Marks soon felt that original doggerel was just as dangerous, since even slight misspellings could render encrypted messages indecipherable and risk agents' lives by their being asked to re-transmit a corrected copy.
His first solution was the development of "WOKs" (Worked-Out Keys), preferably printed on silk so that they could be easily concealed within clothing and be undetectable if the agent was frisked. An operative would use one key, send the message, and immediately cut off and burn the strip of code alphabet which had been used. This would ensure no code alphabet would be used twice, making decryption of each transmission more difficult for the enemy. Due to the heavy demand for silk to make parachutes, Marks had to persist in his efforts to obtain a supply. While occasionally landing him in comic terrain, his project was deadly serious: he impressed the importance of screen-printed silk for his WOKs on a disbelieving officer who asked what the difference was between printing the codes on silk instead of on paper by replying "it's the difference between silk and cyanide". Codes written on paper could be found more easily and would confirm that a searched SOE agent was in fact a spy, leading to their arrest, torture and execution by the Gestapo. For such eventualities agents were issued with a suicide pill made of potassium cyanide, although some did not choose to exercise that option or were unable to if the pill was found and confiscated.
In one of the book's great anecdotes, Marks visits Colonel Wills - perhaps a model for Ian Fleming's character Q - in order to sort out the best ways to print his code keys. Before solving this minor problem (invisible ink), Wills showed Marks several new projects - one of which involved an exotic array of dung from different animals, courtesy of the London Zoo. This gadgetmaster planned to model life-sized reproductions of the droppings of various species from around the world and pack them with explosives, personalised for all parts of Europe, Africa, and Asia. "Once trodden on or driven over (hopefully by the enemy) the whole lot would go off with a series of explosions even more violent than the ones which had produced it," Marks quipped.
Another project of Marks', named by him "Operation Gift-Horse", was a deception scheme aimed to disguise the more secure WOK code traffic as poem code traffic, so that German cryptographers would think "Gift-Horsed" messages were easier to break than they actually were. This was done by adding false duplicate indicator groups to WOK-keys, to give the appearance that an agent had repeated the use of certain words of their code poem. The aim of Gift Horse was to waste the enemy's time, and was deployed prior to D-Day, when code traffic increased dramatically. He also promoted the use of one-time pads by SOE agents, with mixed success.
Despite many amusing and irreverent observations, the author never loses sight of the importance of his vocation, and Between Silk and Cyanide is as poignant as it is engaging. Marks evokes pathos with the story of his own personal loss (encapsulated in his poem The Life That I Have), and shares with the reader his despair and frustration as he records agents blown - lost to the enemy both by misfortune or by folly. Readers will find it hard to forget Marks's personal recollections of famous SOE agents such as Violette Szabo, Noor Inayat Khan, and the "White Rabbit", Flight Lieutenant F. F. E. Yeo-Thomas.
- Leo Marks, Between Silk And Cyanide (HarperCollins, 1998). ISBN 0-002-55944-7. (British edition)
- Leo Marks, Between Silk And Cyanide: A Codemaker's Story 1941-1945 (HarperCollins, 1998). ISBN 0-684-86780-X.
- Leo Marks, Between Silk And Cyanide: A Codemaker's War 1941-1945 (HarperCollins, 1998). ISBN 0-00-653063-X
