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. /1
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. /2
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!
4/ 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.
5/ 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.
6/ 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.
7/ 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.
8/ 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!
9/ 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.
10/ 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.
11/ 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.
12/ 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.
13/ 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.
14/ 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.
15/ 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.
16/ 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.
17/ 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.
18/ 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.
19/ 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.
20/ 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.
21/ 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.
22/ 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.
23/ 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.
24/ 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).
25/ 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.
26/ 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.
27/ 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.
28/ 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.
29/ 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
"Codebreakers- The inside story of Bletchley Park". Edited by Hinsley & Stripp is a good place to start. Paperback or Kindle
If you really get hooked on the Polish contribution, Dermot Turing's X, Y & Z is good.
but rather complex spy story, based around Polish contribution.
Geoff Sullivan 💙
Book recommendations from peoplewho know this stuff better than me (despite my extensive backgroun consisting of a day at a museum and half an hour on the internet :)) twitter.com/variousnick/st…