www.dailytelegraph.com/obituary Leo Marks LEO MARKS, who has died aged 80, was the chief cryptographer of Special Operations Executive during the Second World War; later he wrote the script for Peeping Tom, the film which destroyed the career of its director Michael Powell. Between 1942, when he joined SOE, and 1946, when he rejected an offer of employment from MI6, Marks proved himself a code-maker and breaker of rare genius. While still in his early twenties he revolutionised the construction and security of SOE's cyphers. And by his re-invention of the "one-time pad" he eventually influenced code systems used by secret services the world over. In the latter stages of the war he was entrusted with devising encryption systems for, among others, the SAS and the Free French. Unbeknown to the latter, Marks had already cracked General de Gaulle's private cypher in a spare moment on the lavatory. He began his career as a cryptographer at the age of eight in his father's antiquarian bookshop in London, Marks & Co, later the subject of Helen Hanff's memoir 84 Charing Cross Road (1971). One morning his father Benjamin showed Leo a first edition of The Gold Bug by Edgar Allan Poe, which he had just bought for #6 10s. Knowing that it would interest American collectors, he intended to price it at #850. The book's tale of hidden treasure the whereabouts of which was concealed by a cypher entranced Leo, and he set about breaking his father's own secret pricing code, a series of letters pencilled inside the cover of each book. Within minutes he had found the key (the 10 letters of Marks Cohen, the two partners in the business, each corresponded to a number) and gained two ambitions: to become an expert on codes and, like Poe, to write horror stories. In January 1942, Marks was called up and went to Bedford to train as a cryptographer, an opening secured for him by a godfather in Special Branch. He was the only one of his intake not to be sent on to Bletchley Park; instead, having in an evening cracked a code intended to be spread as a group exercise across a week, he was labelled a misfit and dispatched to Baker Street, the headquarters of the recently formed Special Operations Executive. Marks almost contrived to fail his interview, taking all day to break a cypher that he had been expected to decode in only 20 minutes with the help of a key. SOE's head of codes had forgotten to give him the necessary piece of paper, and in his memoir Between Silk and Cyanide (1998) Marks drew a vivid and often angry portrait of an organisation capable of both brilliance and lethal carelessness. It was also one in which Marks, as a quick-witted Jew, often felt an outsider. The title of his book referred to the new codes Marks had devised and had had printed on silk squares, and the poison carried by agents - life and death. He had had to come up with new cyphers because when he inspected SOE's methods for communicating with its agents in the field he was horrified to discover that the traffic could be read by the Germans with ease. The agents were using well-known poems as the cyphers for encoding their messages, and these could either be guessed by an enemy armed with reference books, or simply tortured out of captured operatives. His initial solution was to use original poems instead as cyphers. Many of these he wrote himself, the best known being that which he gave to the agent Violette Szabo, The Life That I Have. He had actually written it for a girl with whom he was in love, the news of whose death in an air crash he heard on Christmas Eve 1943. The poem was subsequently used in the film made about Violette Szabo, Carve Her Name With Pride (1958), and generated an enormous response. Marks took great pains to get to know the agents he briefed, among them his close friend Forest Yeo-Thomas - "The White Rabbit" - and Noor Inayat Khan, who suffered from the handicap for a spy of having been brought up never to lie. It could be difficult, as happened to Marks, to brief a man and then hear two days later that the Gestapo had tortured him horribly. But it was vital for him to understand the temperament of each agent, as this helped him with the other important area of his work, deciphering the garbled messages transmitted by agents under stress. It was vital that any such "indecipherables" - up to 20 per cent of the daily traffic - should be read as quickly as possible so that, with the Gestapo on the prowl, the agent need not risk his life to resend it. As Marks knew the coding idiosyncrasies of each agent - an inability to spell a certain word or a habit of transposing two columns in a cypher - he was often able to decipher the signals himself, but he also recruited 400 young women from the First Aid Nursing Yeomanry (Fany) to help him break indecipherables. When interviewing these girls Marks did not look for mathematical ability but for an interest in music and an aptitude for crosswords, believing these were better pointers to cryptographic talent; he himself was already regularly setting crosswords for The Times. Marks's helpers, based at Grendon Underwood in Buckinghamshire, proved immensely proficient and dedicated. One message was deciphered with seconds to spare after 650,000 separate attempts. It was the lack of indecipherables in the traffic of SOE's Dutch section which first alerted Marks to the so-called Englandspiel, the most serious disaster to befall SOE. Marks deduced that since no signals from Holland were ever corrupted, the Germans must have penetrated the network and be controlling the transmitters. He was right, but his suspicions fell on deaf ears - or on those playing a longer game - and up to 50 Dutch agents went unnecessarily to their deaths. Thereafter Marks concentrated on perfecting codes that could not be discovered by the Germans. His solution was simple and brilliant - to use one-off cyphers, printed on silk which the agent then cut away and burnt so that he could not remember them. These "worked-out keys" not only reduced the incidence of garbling but, being random in origin, were much harder for the Germans to crack. Silk also had the advantage of being easily hidden in the lining of clothes, and if they were caught each agent was given a method of letting SOE know that he was transmitting under duress. By D-Day, when SOE's agents tied down thousands of German troops, Marks's silks were being used from Normandy to Sarawak. They were particularly gratefully received by the Free French, who routed all their traffic through SOE, allowing Marks to read politically sensitive material destined for de Gaulle. By then he had also refined the one-time pad, first invented by the Germans, in which a code was made by adding to numbers representing set phrases another pre-agreed series of numbers. The only copies of these were held by the agent and his masters, and used just once. Marks, who needed no invitation to demonstrate his intelligence, adapted the system to use letters instead of numbers, an idea already being used independently at Bletchley. But Marks's drive and determination ensured that the code became widely disseminated within the British secret services, and in time it became standard cryptographic technique. He retained discreet informal links with the Intelligence Service after the war and devised several other important new types of code; indeed, so central did his wartime work remain to modern cypher practice that he was unable to disclose much of it in his autobiography, the publication of which was delayed by the authorities for more than a decade after he had completed it. Leopold Samuel Marks was born in London on September 24 1920. An only child, he was educated at St Paul's and then helped out in his father's shop, where customers included Charlie Chaplin, Aleister Crowley and Sigmund Freud. After the war, Marks turned to writing for the stage and screen, and had some success in the West End with plays such as The Girl Who Couldn't Quite (1947) and The Best Damn Lie (1957), which made use of a lie detector. Indeed much of his literary work, which in truth was largely forgettable, seemed to hark back to his previous career. Thus the film Cloudburst (1951) was about a vengeful codebreaker; Sebastian (1967), with John Gielgud, concerned an academic code expert turned spy. Quite different from all these was Peeping Tom (1960). At its most superficial, it is the shocking story of a man, terrorised as a child by his father, who grows up obsessed with fear. He gets his kicks by filming young women as he murders them with a blade concealed within his camera. At a deeper level, the film is a meditation on the voyeuristic nature of cinema. Since the man's crimes are seen by the audience through his lens, they are in effect asked to identify themselves with his murderous acts. Marks's notably intelligent script, influenced by his lifelong interest in psychoanalysis, contains a number of in-jokes, notably that a director in the film is played by the blind actor Esmond Knight, and that the name Leo Marks gave his protagonist was Mark Lewis. Although now recognised as a strange but serious work, at the time the film proved too disturbing for audiences and critics. It was described as "evil and pornographic" and the reaction against it ended the illustrious career of its director, Michael Powell. Marks went on to work with the Boulting Brothers, whom he also almost finished with another film about a homicidal maniac, Twisted Nerve (1968). He never again reached the heights of Peeping Tom. So provocative is its reputation that it was not possible to show it on British television until 1997. The film is the primary influence on the cinema of the director Martin Scorsese; he acknowledged his debt in 1988 when he asked Marks to play the voice of Satan in his similarly controversial The Last Temptation of Christ. Marks's father died in 1968, but he was not tempted to take over the shop, living instead quietly in west London. He was good company, enjoyed showing that he knew more than he said, but kept secrets as well as any man. Though a natural cynic, he was also a romantic. In person he was short and powerful, with a grip of iron and a voice like new velvet. He was an habitue of the Special Forces Club. He married, in 1966 (dissolved 2000), the portrait painter Elena Gaussen.