The Machine That Helped Win World War Two

This is the Enigma, the encryption machine the Nazis relied on in World War Two.

You can see the Nazi Party sigil right on the case, so this is the real thing.

Someone once asked Derek if Hitler himself ever used one of these machines.

I don't know, but Benedict Cumberbatch and Keira Knightley did.

Could we try encrypting a word?

I have just the word for us. You'd never guess what it is.

Letter by letter, the lamps lit up: V, J, E, F, M, and L.

Pure gibberish on the page. That is exactly the point.

To decrypt it, someone needs another Enigma set up in exactly the same way.

Trillions of possible combinations. One setting off, and the message stays locked forever.

And there it is. The plaintext appears: Veritasium.

By 1939, the Nazis were sending hundreds of encrypted messages across Europe every single day.

Today we rule Germany. Tomorrow, the world.

Every night at midnight, the Germans changed the settings on all their Enigma machines.

Any message the Allies cracked was useless by the next morning.

So British intelligence secretly assembled the country's greatest minds in one place.

Bletchley Park. An unsuspecting mansion in the English countryside.

Chess players, crossword fanatics, academics, and hundreds of women from the Royal Navy.

Do not talk at meals. Do not talk by your own fireside. Be careful even in your own hut.

At its peak, around 9000 people ran the most secret codebreaking operation in the world.

But here's the first surprise: the Enigma wasn't invented by the Nazis at all.

It was patented in 1918 by a German inventor named Arthur Scherbius, for banks and businesses.

The company was desperate for customers, so you could definitely go out and buy one.

Poland bought one. The British bought one. The Russians bought one. You name it.

What made Enigma superior? Press the L key once and the Y lamp lights up.

Press L again and you don't get Y. You get H. The substitution changes with every key press.

Inside are three rotors with 26 scrambled contacts each, and a reflector bouncing current back through.

The German military added revolving rings, a plug board, and completely rewired rotors.

The key space exploded to over seven times ten to the power of eighteen.

Every machine on a network followed daily settings from prearranged key sheets.

Without the key sheets, you were stuck. And the British were completely stuck.

But years earlier, another country had already launched a secret effort against Enigma.

In 1931, a German cipher office employee sold Enigma secrets to the French, who passed them to Poland.

Polish mathematicians spotted a flaw: operators encrypted their three letter setting twice.

A young genius named Marian Rejewski recognized it as a problem in permutation theory.

By 1933, the Poles had reconstructed the military Enigma's wiring without ever seeing one.

Then in 1939 the Nazis added two extra rotors and more plug board swaps.

The key space multiplied by 15,000, to over 100 sextillion combinations.

In July 1939, the Poles revealed everything they knew to British and French intelligence.

Just over a month later, Poland was invaded. Their codebreakers fled, leaving everything behind.

Our producer crafted an Enigma message. Now I'll try to crack it using the tricks Bletchley knew.

The Germans had fixed the double encryption flaw, but people are terrible at being random.

Operators often picked their girlfriend's name. Cilla became CIL. The codebreakers called them cillies.

This message starts with LON. So the operator probably just chose London.

The Herivel tip gave me the ring settings, because lazy operators barely shuffled their rotors.

Then the rotor order. Then the plug board. It was a lot of brute force guessing.

DON is supposed to come out as CNG. So the rotor order is one, three, two.

There we go. The message reads: James is a legend.

James the producer, everybody. And that took me one hour straight.

And that was an easy example. Real codebreakers trawled hundreds of messages a day by hand.