The Enigma Machine

At first glance, the Engima looks like a fancy typewriter. But, when you press a letter on the keyboard then another letter flashes up.
Is it broken? No.
Enigma was used to encode messages. Essentially, it used a system where one letter is replaced by another.
It represented a new form of encryption using machines rather than codebooks or hand cyphers.

How does it work?

If you opened up Enigma, you would see three wheels, known as rotors. Each rotor has 26 different positions representing the 26 different letters of the alphabet. These rotors can be taken out and their position swapped.
The inputted letter tapped on the keyboard passes through these three rotors and bounces off a reflector at the end, before passing the letter back through all three rotors in the opposite direction.
The encrypted letter flashes up on the lamp board above the keyboard.
Once the letter has flashed up, the first of the three rotors clicks round one position. This means that the output has now changed.
So, even if you hit the same letter on the keyboard again, a different output letter would flash up.
When the first rotor has turned through all 26 positions, the second rotor clicks round. When that has gone through 26 clicks, the third rotor takes over.
Another component known as a "plugboard" swaps pairs of letters as they go into and out of the machine, adding another layer of complexity to the system.
The reflector means you can use Enigma to both encrypt and decrypt messages. It's the same process, just in reverse.
So, let's assume you have two Enigma machines in two different locations, set up with the same starting rotor positions and plugboard setup. Messages would be encrypted by one Enigma and passed by Morse code to the other Enigma, where the message would be deciphered.
It's a simple system to describe - but one that's incredibly complex to crack.

Why was Enigma so difficult to crack?

To crack Enigma, you needed to know the starting position and the order of the three rotors, plus the set up of the plugboard.
There were 159 million million million possible settings to choose from when you're setting up an Enigma machine.
Oh, and the settings were changed every day during WWII so you were constantly fighting against the clock. You'd have 24 hours to try out 159 million million million possible settings.
So, the Germans believed Enigma was unbreakable. They were wrong.

How was Enigma broken?

There were a couple of pitfalls to Enigma's design, which meant thousands of possible rotor positions could be eliminated.
First, no letter would ever be encoded on itself. Hit "A" and you'll never get another "A" out. Second, certain phrases were very common in the messages. Operator sloppiness also helped - the rotors may not have been reset at the start of a new day, for example.
The teams at Bletchley Park built their own machine to break the Enigma machine. Known as the Bombe, it further cut down on the number of combinations.
This meant the teams at Bletchley could fight against the clock and beat Enigma.
It didn't end there. Enigma was continually updated to make it more difficult to crack over the years - and then the Germans introduced the more complex Lorenz cypher machine. This was cracked using another Bletchley machine - Colossus.
It's estimated that the work done at Bletchley Park shortened the Second World War by two years.
With roughly 11 million people dying per year, that's 22 million lives saved.

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