[CW] ENIGMA

[D.J.J. Ring, Jr.]

Emma Taylor‏ @emmataylorwords May 2
Posted a series of 29 tweets about Enigma.

How do I know so many made-up stories about how the Enigma code was
cracked and didn't know until yesterday how interesting the real story
is? A volunteer at the National Museum of Computing at Bletchley Park
just casually blew my mind with a bit of the story.

We asked how they came to have an Enigma machine at Bletchley Park,
and he said "the Polish postal service intercepted it just before the
Germans invaded". No U-Boats, no battles, no heroic Allied Officers -
a postman.

I looked it up when I got home and here's everything I could find.
There may be actual paper books that tell the story more coherently,
but on the internet I could only find little bits that all fitted
together - I'd love a recommended read if anyone knows one!

The Engima machine was commercially available for a decade or two
before WW2 - many countries used them. The machine itself couldn't
crack other people's codes unless you knew which settings they'd used
- otherwise just lengthy trial & error.

The commercial Enigma had 3 wheels, but in the 1930s the Nazis adapted
theirs to have 5 wheels, which meant they could communicate by radio
all across Europe without fear of interception. Useful, for what they
had in mind.

In June 1939, in anticipation of invading Poland, they wanted to send
an adapted 5-wheel Enigma machine to their embassy in Poland. SO THEY
POSTED IT.

They were on the verge of sending a massive invading force of tanks
and aeroplanes over the border, but wanted to make sure this vital
piece of military intelligence got the first, so they literally just
popped it in the basic civilian post.

The staff at the German embassy were hassling the postmaster at the
Polish depot: "we've got a very important parcel on the way, make sure
it gets to us immediately". He said "sorry, it's the weekend, we're
closed, we'll get it to you on Monday morning". The nerve of him!

Their haste made him suspicious, so he rang a friend who happened to
work for Polish military intelligence. They turned up and very
carefully unpacked the parcel, found the 5-wheel Enigma machine.
Realised what they'd got, and also that the Nazis must never know.

So over the weekend, they painstakingly took it to bits, photographed
it, drew circuit diagrams, then by Monday morning it was back in its
box looking untouched, delivered to the embassy. They had no idea, so
kept using the code for their military communication.

Polish military intelligence passed everything they had to UK
intelligence, shortly before the invasion. They were already decoding
most of the Nazis' messages, they were miles ahead of the British. The
British used info from the intercepted Enigma to build one of their
own.

But even with a machine, you needed a code sheet. The settings changed
every day, and the Nazis issued a month's settings, then assigned SS
officers the specific task to torture and murder anyone who let one
out of their hands. As a result, the Allies never got hold of one.

Also they were printed on paper that dissolved almost immediately on
contact with water, so very easy to dispose of them if you were
captured. Without the code sheets, UK military intelligence were just
guessing possible combinations.

With 5 wheels, a combination per second would take (according to the
museum volunteer) 14 billion years to work through. Not very
practical. But they had a few things on their side.

The main one being that the Nazi radio operators ended almost every
message with "Heil Hitler"! That gave the codebreakers a key in every
single message that they could use to decode the rest of it.

Even so, it was taking about 8 hours each day to work out the day's
Enigma settings, which would then change at midnight. So they built
the Welch-Turing Bombe, a massive proto-computer which is basically a
huge array of interconnected Enigma machines, to do it faster.

BUT! The Enigma was used by basic Nazis in the field. High Command -
Hitler and his generals - used an even more complicated machine that
they had commissioned specially - the Lorenz. The truly secret orders
were sent using that, and nobody else could decode them.

The UK built special radio receivers in Kent to pick up the
communications between Berlin and Nazi-occupied Paris, and special
machines to transcribe them, but they were just gibberish to the
Allies - they had the messages but no idea how to decode them.

Until one of the highly trained, highly trusted Nazi radio operators
made a mistake. He transmitted a 4000-character message on the Lorenz,
but due to reception problems, had to re-transmit the whole thing.

Apparently he couldn't quite be bothered to type the whole thing again
- to be fair the process was a bit of a faff. So he abbreviated some
of the words, meaning the new message started exactly the same but had
only 3100 characters.

The way these machines work is, every time you type a character, the
wheels turn, so the cipher for the next letter is different. So this
message contained large chunks where the original text was the same,
but encoded earlier in the machine's process.

They gave these two strings - 4000 and 3100 characters - to a
mathematician. Three months later he came back with a diagram. From
the two strings of gibberish, he had accurately deduced the Lorenz.

It had two sets of five wheels each, plus a set of two more, and the
settings on each wheel interacted to alter the code produced. Each of
the 12 wheels had a different number of pins. Each key press altered
the settings by a different amount. And he had worked it all out.

I'm in awe of the amazing human minds that solved these problems, and
the brave and selfless individuals who risked so much, and were often
not acknowledged (UK popular culture makes nearly zero mention of the
Polish codebreakers).

But what fascinates me is the basic humanness of it all. The person
who decided to stick an Enigma machine in the post. The ambassador
who, faced with a recalcitrant postmaster, went "yeah, that's what
postmasters are like, it sucks", and waited until Monday for his
parcel.

The high-level Nazi radio operator who sent Hitler's personal
communications across occupied Europe, who went "damn it, can't be
bothered to type all that again", and stuck in a bit of txtspk to make
his life a bit easier.

Even the people who created the code sheets, who thought "we'll be
fiendishly clever and never use the same wheels or settings two days
running", because to humans that looks "more random" but
mathematically it massively narrows down the options for cracking it.

It gives me a weird kind of hope that in the Nazi regime which was
explicitly trying to turn both humans and the state into perfect
machines, the war turned on a bunch of basic human flaws. The Allies
won the war because a coder wanted his lunch sooner.

Also, everyone should go to the UK National Museum of Computing @tnmoc
Whether you want code-breaking history or computer science or to play
retro computer games, it's packed full of interesting stuff and very
enthusiastic volunteers who will tell you amazing things. /end