How Poles cracked Nazi Enigma secret
By Laurence Peter, BBC News
A silk scarf bearing the image of a horse
race was a suitably cryptic gift for a Polish mathematician to receive from a
British code-breaker.
The Poles had got there first - that
seemed to be the message.
Dillwyn "Dilly" Knox was
delighted with the Polish copy of an Enigma - a top secret German military
cipher machine.
But his meeting with code breakers
in Poland in July 1939 - just weeks before Hitler invaded their country - had
initially put him in a sour mood. He had been struggling to figure out the
machine's wiring - a key part of the complex jigsaw puzzle called Enigma.
Marian Rejewski, a talented Polish
mathematician, had guessed correctly that the wiring connections between the
machine's keyboard and encoding mechanism were simply in alphabetical order.
Of course, there were numerous other
problems to solve, but Rejewski had made a major breakthrough, by devising
equations to match permutations in the machine's settings.
Unsung heroes
For decades after the war the
contributions of Rejewski and other Polish cipher experts to the Allied victory
over Nazi Germany went unrecognised.
But Bletchley Park, the nerve centre
of Britain's wartime code breaking operations, has just held its annual Polish
Day - a celebration of the Polish achievements that laid the foundations for
British success in cracking German codes.
The fictional film Enigma, made in
2000, had dismayed Poles by neglecting these achievements and portraying a Pole
as a traitor.
It has taken a long time to
establish the historical facts, but the picture is much clearer now, in the
run-up to the 70th anniversary of the outbreak of World War II.
"This event is tremendous -
we're very pleased that the British remember the Poles," said Derek
Celinski, a Polish army veteran who survived the Nazi destruction of Warsaw.
One of the lessons the British
learned from the Polish experience was the importance of engaging the country's
best mathematicians in the code-breaking project.
While British code-breakers were
undoubtedly bright - Knox was a translator of ancient Greek poetry - they were
not necessarily mathematicians.
Polish historian Eugenia Maresch
says that Alastair Denniston, the first director of Bletchley Park, was
inspired by his meeting with the cryptologists at Pyry, the small Polish
decoding centre in woods outside Warsaw. There the Poles divulged their methods
and Enigma secrets to British and French intelligence.
The Poles were already deciphering
Enigma messages in 1933, Mrs Maresch explained, whereas the British did not
seriously turn their attention to Enigma until the Spanish Civil War in 1936,
when the Axis powers' aggression started threatening British interests in the
Mediterranean.
Polish expertise
Rejewski was the brightest of three
top Polish mathematicians who were recruited for code-breaking, Bletchley Park
historian Frank Carter says. The other two were Henryk Zygalski and Jerzy
Rozycki.
They had graduated from a University
of Poznan cryptology course, set up by Polish officer Maksymilian Ciezki, who
had been trained by the Germans before Poland became independent in 1918.
Although Zygalski and Rejewski were
smuggled out of fascist Spain by British agents during the war the veil of
secrecy meant they were not allowed to join the Bletchley Park team, Mr Carter
explained.
German changes to the Enigma
machines during the war meant much greater resources were required to crack
them, and that was where the inventiveness of Alan Turing and the other British
code-breakers was key.
The Enigma configurations changed
daily - and the "key for the day" could be any one of about 364,000
million possible settings.
"Many Enigma keys were never
found," Mr Carter told the BBC.
"Probably less than 25% of the
naval codes were broken, but it was still a significant success.
"The easiest was the German air
force - they weren't as security-minded and made blunders. They were broken
daily."
Turing created the "Bombe"
at Bletchley Park - a more sophisticated decoding machine than an earlier
Polish machine called the "Bomba".
The Polish machine exploited a
weakness in the German "indicators" - the starting positions for
sending Enigma messages. But when the Germans changed the indicator system in
May 1940 the Polish method became redundant.
The British "Bombes"
however did work, based on "cribs" - recurring patterns in German
secret messages, such as the words "special arrangements for".
The German naval codes were the
hardest to crack - and that mattered hugely while U-boats were wreaking havoc,
torpedoing Allied ships in the North Atlantic.
But Bletchley Park's work is
reckoned to have shortened the war by as much as two years.
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