||This article's lead section may not adequately summarize key points of its contents. (December 2012)|
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (June 2012)|
Leo Marks in 2000, at the opening of the Violette Szabo Museum, Wormelow Tump
|Born||Leopold Samuel Marks
24 September 1920
|Died||15 January 2001
|Occupation||Cryptographer, screenwriter and playwright|
|Known for||Peeping Tom (screenplay)|
|Spouse(s)||Elena Gaussen (m. 1966–2000)|
Early life 
The son of an antiquarian bookseller in London, he was introduced to cryptography when his father showed him Edgar Allan Poe's story, "The Gold-Bug". From this early interest, he demonstrated his skill at codebreaking at an early age by deciphering his father's secret price codes that he wrote inside the covers of books. His father, Benjamin Marks, was joint owner of the Marks & Co bookshop at 84 Charing Cross Road, which achieved fame with the 1970 book of that title by New York writer Helene Hanff and the later plays and movie.
Work in cryptography 
In January 1942 I was escorted to the war by my parents in case I couldn't find it or met with an accident on the way.
Role at Bedford 
His original and unorthodox mode of thought led to his being the only one of his class judged not good enough to be sent to Bletchley Park; instead, he was sent to a rival organisation of the intelligence services, the recently formed Special Operations Executive (SOE). When his abilities became evident, he was referred to by Bletchley Park as "the one that got away".
Marks briefed many Allied agents sent into occupied Europe, including Noor Inayat Khan, the Grouse/Swallow team of four Norwegian Telemark saboteurs and his own close friend, the legendary White Rabbit, 'Tommy' Yeo-Thomas. An empathetic and imaginative personality (as well as a self-professed coward), Marks acted on the rarely expressed premise that agents in occupied territories deserved every support those enjoying safety and freedom could provide. In an interview with Channel Four included in the DVD of the film Peeping Tom, Marks quoted General Eisenhower as saying that his group's work shortened the war by three months, saving countless lives.
Developments of cryptographic practice 
Although in charge only of agent codes, the young Marks frequently walked into bureaucratic lion's dens in order to save lives in the field. One of his first challenges (resisted by the establishment) was to phase out double transposition ciphers using keys based on preselected poems. These poem ciphers had the limited advantage of being easy to memorise, but significant disadvantages, including limited cryptographic security, substantial minimum message sizes (short ones were easy to crack), and the fact that the method's complexity caused encoding errors.
Cryptographic security was enhanced by Marks's innovations, especially "worked-out keys". He was credited with inventing the letter one-time pad, but while he did independently discover the method, he later found it already in use at Bletchley.
Preference for original code poems 
While attempting to relegate poem codes to emergency use, he enhanced their security by promoting the use of original poems in preference to widely known ones, forcing a cracker to work it out the hard way for each message instead of guessing an agent's entire set of keys after breaking the key to a single message (or possibly just part of the key.) Marks wrote many poems later used by agents, the most famous being one he gave to the agent Violette Szabo, The Life That I Have, which gained popularity when it was used in the 1958 film about her, Carve Her Name With Pride. According to his book, Marks wrote the poem in Christmas 1943 about a girlfriend, Ruth, who had recently died in an air crash in Canada; supposedly the god-daughter of the head of SOE, Sir Charles Jocelyn Hambro.
The life that I have
Is all that I have
And the life that I have
The love that I have
Of the life that I have
Is yours and yours and yours.
A sleep I shall have
A rest I shall have
Yet death will be but a pause.
For the peace of my years
In the long green grass
Will be yours and yours and yours.
Gestapo activities and “Indecipherables” 
Gestapo signal tracers endangered clandestine radio operators, and their life expectancy averaged about six weeks. Therefore, short and less frequent transmissions from the codemaster were of value. The pressure could cause agents to make mistakes encoding messages, and the practice was for the home station to tell them to recode it (usually a safe activity) and retransmit it (dangerous, and increasingly so the longer it took). In response to this problem, Marks established, staffed and trained a group based at Grendon Underwood, Buckinghamshire to cryptanalyse garbled messages ("indecipherables") so they could be dealt with in England without forcing the agent to risk retransmitting from the field. Other innovations of his simplified encoding in the field, which reduced errors and made shorter messages possible, both of which reduced transmission time.
“Das Englandspiel” in the Netherlands 
The Germans generally did not execute captured radio operators out of hand. The goal was to turn and use them, or to extract enough information to imitate them. For the safety of entire underground "circuits", it was important to determine if an operator was genuine and still free, but means of independently checking were primitive. Marks became convinced (but unable to prove) that the situation in the Netherlands was out of SOE's control and that they were being toyed with by the Germans (who among themselves actually did call it a game—Das Englandspiel). He was repeatedly told (for political reasons) to keep his mouth shut while as many as 50 agents were delivered to the Gestapo. The other side of this story was published in 1953 by Marks' German opposite number in the Netherlands, Hermann Giskes, in London Calling North Pole.
Reporting to Brigadier Gubbins 
In his book (pp. 222–3), Marks describes the memorandum he wrote detailing his conviction that messages from the Netherlands were being sent by Germans or by agents who had been turned. His argument was that, despite harrowing circumstances, "not a single Dutch agent has been so overwrought that he's made a mistake in his coding...." Marks had to face Brigadier (later Sir) Colin Gubbins:
Described by Tommy [Marks' closest friend] as 'a real Highland toughie, bloody brilliant, should be the next CD', he was short enough to make me feel average, with a moustache which was as clipped as his delivery and eyes which didn't mirror his soul or any other such trivia. The general's eyes reflected the crossed swords on his shoulders, warning all comers not to cross them with him. It was a shock to realize they were focused on me.
Gubbins grills Marks. In particular he wants to know who has seen this report, who typed it (Marks did):
There was a warning gleam in those forbidding eyes. 'What did you tell Colonel Tiltman about the Dutch situation?'
'Nothing, sir, I was instructed not to discuss the country sections.'There was silence as Celt met Jew on the frontier of instinct. We then went our separate ways.
'And you always obey your instructions?'
'No, sir. But in this instance I did.'
After SOE 
He went on to write marginally successful plays and films, including The Girl Who Couldn't Quite! (1947), Cloudburst (1951), The Best Damn Lie (1957), Guns at Batasi (co-writer) (1964), Sebastian (1968) and Twisted Nerve (1968).
Marks also wrote the script for Michael Powell's Peeping Tom (1960), the story of a serial killer who films his victims while stabbing them. Marks provided the voice of Satan in Martin Scorsese's The Last Temptation of Christ (1988).
In 1998, Marks published a book about his work in SOE — Between Silk and Cyanide: A Codemaker's Story 1941-1945. The book was reportedly written in the early 1980s, but didn't receive the UK Government's approval for publication until 1998. Three of the poems published in the book were scrambled into the song "Dead Agents" by John Cale and performed at a series of multimedia concerts in London in April 1999
He married the portrait painter Elena Gaussen in 1966, a marriage that lasted until shortly before his death at home, from cancer, in January 2001.
- A Very British Psycho (1997), dir. Chris Rodley; included on the Criterion Collection DVD of Peeping Tom
- "The Long Life of a Poem", H2G2 Forum, 17 November 2012 http://h2g2.com/dna/h2g2/alabaster/F2130683?thread=8298176
- Between Silk and Cyanide, p.452
- Leo Marks (1998), Between Silk and Cyanide: A Codemaker's Story 1941-1945. HarperCollins. ISBN 0-684-86780-X
- Philippe Ganier-Raymond (1968), The Tangled Web, (Arthur Barker; [reprint]: Warner Paperback ISBN 0-446-65934-7, originally published in French as Le Réseau Étranglé). One of the central stories in Marks's book, the betrayal of the SOE Dutch network, told from the Dutch and German points of view.