Editing Leo Marks (section)

==Work in cryptography==
Marks was conscripted into the [[British Army]] in January 1942<ref>[https://spartacus-educational.com/SOEmarks.htm Leo Marks] [[Spartacus Educational]]. Retrieved February 24, 2024.</ref> and trained as a cryptographer; apparently he demonstrated the ability to complete one week's work in decipherment exercise in a few hours.<ref name =guardian/> Unlike the rest of his intake, who were sent to the main British codebreaking centre at [[Bletchley Park]], Marks was regarded as a misfit and he was assigned to the newly formed [[Special Operations Executive]] (SOE) in [[Baker Street]],<ref name =telegraph/> which was set up to train agents to operate behind enemy lines and to assist [[Resistance during World War II|local resistance groups]] in [[German-occupied Europe|occupied Europe]].  SOE has been described as "a mixture of brilliant brains and bungling amateurs".<ref name =guardian/> Marks wrote that he had an inauspicious arrival at SOE when it took him all day to decipher a code he had been expected to finish in 20 minutes, because, not atypically, SOE had forgotten to supply the cipher key, and he had to break the code which SOE had regarded as secure.<ref name =guardian/>

Marks briefed many Allied agents sent into occupied Europe, including [[Noor Inayat Khan]], the Grouse/Swallow team of four Norwegian [[Norwegian heavy water sabotage|Telemark]] saboteurs and his own close friend [[F. F. E. Yeo-Thomas|'Tommy' Yeo-Thomas]], nicknamed "the White Rabbit."<ref name =telegraph/> In an interview which accompanied the DVD of the film ''[[Peeping Tom (1960 film)|Peeping Tom]]'', Marks quoted [[Dwight D. Eisenhower|General Eisenhower]] as saying that his group's work shortened the war by three months, saving countless lives.

Marks was portrayed by [[Anton Lesser]] in [[David Morley (writer)|David Morley]]'s [[BBC Radio]] drama ''A Cold Supper Behind Harrods''. The fictional play was inspired by conversations between Marks and [[David Morley (writer)|David Morley]] and real events in SOE. It featured [[David Jason]], and [[Stephanie Cole]] as [[Vera Atkins]].<ref>{{cite web |url=http://www.bbc.co.uk/programmes/b01mkztj |title=A Cold Supper behind Harrods |website=[[BBC]]}}</ref><ref>{{Cite web |url=https://archive.org/details/ACOLDSUPPERBEHINDHARRODS |title=A Cold Supper behind Harrods |website=Archive.org |access-date=15 July 2018}}</ref>

===Developments of cryptographic practice===
One of Marks's first challenges<ref name ="HCN1">{{Cite book |last=Marks |first=Leo |title=Between Silk and Cyanide: A Codemaker's Story 1941–1945 |year=1998 |publisher=Harper Collins |location=London |isbn=0-00-255944-7 |page=5}}</ref> was to phase out double [[transposition cipher]]s using [[key (cryptography)|keys]] based on poems. These [[poem code|poem ciphers]] had the limited advantage of being easy to memorise, but significant disadvantages,<ref name ="HCN1"/> 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.<ref>{{Cite book |title=Between Silk and Cyanide: A Codemaker's War, 1941-1945 |last=Marks |first=Leo |publisher=Simon & Schuster |year=2001 |page=250}}</ref>

===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 [[cryptanalyst]] 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;<ref>{{cite web |url=http://h2g2.com/dna/h2g2/alabaster/F2130683?thread=8298176 |title=The Long Life of a Poem |first=Dmitri |last=Gheorgheni |date=17 November 2012 |website=H2G2 Forum}}</ref> supposedly the god-daughter of the head of SOE, Sir [[Charles Jocelyn Hambro]].<ref>''Between Silk and Cyanide,'' p. 452.</ref>

<blockquote>
The life that I have <br />
Is all that I have <br />
And the life that I have <br />
Is yours. <br />
<br />
The love that I have <br />
Of the life that I have <br />
Is yours and yours and yours. <br />
<br />
A sleep I shall have<br />
A rest I shall have <br />
Yet death will be but a pause. <br />
<br />
For the peace of my years <br />
In the long green grass <br />
Will be yours and yours and yours.<br />
</blockquote>

===Gestapo activities and "Indecipherables"===
[[Gestapo]] signal tracers endangered clandestine radio operators, and their life expectancy in occupied France averaged about six weeks.<ref>{{Cite book |last=Marks |first=Leo |url=https://www.worldcat.org/oclc/40776827 |title=Between Silk and Cyanide : A Codemaker's War, 1941-1945 |date=1998 |publisher=Free Press |isbn=978-0-684-86422-8 |location=New York |page=602 |oclc=40776827}}</ref> 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 [[cryptanalysis|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 claims that he became convinced (but was unable to prove) that their agents in the [[Netherlands]] had been compromised by the German counter-intelligence [[Abwehr]].<ref name =telegraph/> The Germans referred to their operation as "a game"—[[Das Englandspiel]]. Marks's warnings fell on deaf ears and perhaps as many as 50 further agents were sent to meet their deaths in Holland.<ref name =telegraph/> The other side of this story was published in 1953 by Marks's German opposite number in the Netherlands, [[Hermann Giskes]], in his book ''London Calling North Pole''.

===Reporting to Brigadier Gubbins===
In his book (pp.&nbsp;222–3), Marks describes the memorandum he wrote detailing his conviction that messages from the Netherlands were being sent either by Germans or by agents who had been turned. He argued 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]]:

{{blockquote| 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):

{{blockquote| There was a warning gleam in those forbidding eyes. 'What did you tell Colonel Tiltman about the Dutch situation?'<br />
'Nothing, sir, I was instructed not to discuss the country sections.'<br />
'And you always obey your instructions?'<br />
'No, sir. But in this instance I did.'<br />
There was silence as Celt met Jew on the frontier of instinct. We then went our separate ways.}}

[[File:Leopold (Leo) Samuel Marks Historical Marker.jpg|thumb|center|Leopold (Leo) Samuel Marks Historical Marker]]