The Enigma Machine - Bletchley Park takes a closer look at how it works

Bletchley Park's Outreach Learning Officer Andrew Fryer and Exhibitions Manager Erica Munro take a closer look at an Enigma machine and how it works.

0:52 - What is an Enigma machine?
1:07 - How does an Enigma machine work?
2:02 - How do the Enigma rotors work?
3:04 - How do you set up an Enigma machine?
3:14 - Enigma settings sheet
11:34 - Enigma plugboard set up
14:34 - Enigma three letter password

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Bletchley Park Podcast

About Bletchley Park

Bletchley Park is a vibrant heritage attraction and museum, open daily to visitors.

It was the home of British World War Two codebreaking; a place where technological innovation and human endeavour came together to make groundbreaking achievements that have helped shape the world we live in today.

This unique site was previously a vast Victorian estate, where parts including the Mansion still survive, expanding during wartime to accommodate Codebreakers Huts and Blocks.

During World War Two, the Government Code and Cypher School (GC&CS), now known as the Government Communications Headquarters (GCHQ), was based at Bletchley Park. It grew from a small team of specialists to a vast intelligence factory of thousands of dedicated women and men. This extraordinary combination of brilliant and determined people and cutting-edge technology contributed significantly to Allied victory. In tough conditions, they provided vital intelligence and developed pioneering technological innovation that had a direct and profound influence on the outcome of the war.

The site continues to reveal secrets and tell fascinating stories of our national legacy.

[timgluckman]

In the last five minutes of the film, the music is so loud that one either (a) cannot hear what's being said; OR b) music distracts from comprehension. A surprising beginner's error in a film made with a budget. The positive aspect is that is a v clear explanation.

[AlanCanon]

I visited in 2003, and volunteered to stand in the parlor of the mansion, as the docent told us of how a volunteer from each incoming set of recruits would stand with a loaded pistol leveled at their head as the Official Secrets Act was read out to the class. Visiting Bletchley Park was a tremendously moving experience, and I would encourage all to visit, and to support the Bletchley Park Trust. Greetings from Kentucky.

[pamelaclark]

Clearly explained, thank you. However, please 'be mindful of your likely audience' (who are probably of an age when hearing is not quite so clear) when using background music. It became frantic, intrusive and rather spoilt an otherwise excellent video. Probably not necessary at all. Will look forward to further Bletchley videos.

[jamestulk]

An interesting feature of the Enigma machine is that it is “reversable”. As explained, when an operator types in a plaintext message, they get an encrypted (scrambled) sequence of letters. Now. If the recipient of this encrypted message sets their machine to exactly the same initial settings, then types in the scrambled letter sequence, the plaintext message emerges! Pretty cool, since it meant that the operator had both an encryption machine and decryption machine in the same box. This is why a code breaker’s main task was to discover the setup parameters. The “bomba” machines functioned by systematically disqualifying setups that would not have been capable of producing the intercepted encrypted letter sequence.

[robertgoss]

Excellent video, on a very difficult subject. I have done a lot of reading about the Enigma machine, and this program does a good job of explaining the device. I knew Enigma machines were old when adopted by the military, but I didn't know how old.

[denvan]

The daily code sheet had an initial setting for the three letters visible in the rotor window. But the person sending a new message would first instruct the person receiving to change the window setting to an intermediate arrangement and with the rotors in that new setting the first operator would send a new set of letters in which the message would be encoded. The operators got sloppy and fell into using combinations of letters the code breakers could identify, like HIT & LER, BER & LIN, LON & DON, MAD & RID. So it was easy to guess from HIT the second set of letters was LER. Operators sometimes used their initials and their girlfriend’s initials. It didn’t much matter to the operators because, as they were told by their superiors, the Enigma coding system was unbreakable.

[snivesz]

I think it’s interesting how at the beginning of each message a key (Spruchschlüssel) must be sent to seed that messages start rotor position. And how over time this procedure needed to change because it weakened the encryption. e.g. they would simply type a randomly selected 3 letter key but type it twice to avoid errors. But doing so created a relationship between the two sets of encrypted letters helping code breakers identify the correct rotor positions for the day.

[CZPODUTY]

Nicely done Ms Munro. You brought this all together. Thanks

[mariusgnheimer]

What a fascinating machine! Thank you for this close-up look :) The Backgroud Music at 15:00 was a bit too loud in my opinion, but nevertheless a great video. Keep it up

[barbarawitte]

Thank you so much. I have plans to visit Bletchley Park as soon as we are clear of Covid.

[darcynog]

Great explanation. However, have I missed the function of the 3-letter sequences identified as Kenngruppen in the settings sheet?

[rhhmunro]

Blimey that guy with the hat is hard work. Getting him to answer questions is like extracting teeth.

[jplietar]

Why make it difficult to hear especially as you reaching the end of your presentation? I am very interested in this machine and couldn't quite catch all of it.

[robertroche]

This is the first video / information that I've been able to find about how the daily settings were arrived at and communicated - this question has been bugging me for a while, so many thanks! Presumably if the day setting sheet was captured or made known to the allies this would completely defeat the enigma process - assuming the allies had the same version working model to use to decode. I then presume the German forces would need to re-issue and distribute new day settings to all users if / when they discovered the day settings had been captured / compromised.? I'd imagine if that ever happened it would be extremely disruptive. I'm not sure that I quite understood the bit about the individual user passwords that had to be thought up quickly and what the need was for them, other than to identify the user / coder / decoder sender / receiver? I really enjoyed this video and will be looking at the others. Thanks again.

[mikesforays]

Getting information out of Mr. Fryer, is like getting Enigma to give up it's secrets.

[Goldstone]

The first rotor turns once per key press, the second rotor turns once every 26 rotations of the first rotor, and the third rotor turns once every 26 rotations of the second rotor.

[PeteBlack]

This is the exact explanation I use when I get busted by the girlfriend smuggling new tech into the house.

[dmartin]

A suggestion "for the next presentation video"? Demonstrate a short example - maybe a sentence such as "Good morning, how are you?" Anything really. Demonstrate how the initial rotor settings would be set, how the code book interacted - and then demonstrate how it would be received, if possible. A short "tutorial", if you will.

[MrDsalomon]

See "The Code Book" by Simon Singh (2011) for much more info and history

[davidadams]

Great explanation. Thank you. Please tell me was the turnover position for each rotor different to each of the other four from manufacture? That is, at a fixed point on every rotor but at a different place for each of the 5 rotors?