
Technical Details of the Enigma Machine - ergot
http://users.telenet.be/d.rijmenants/en/enigmatech.htm
======
Animats
The number of rotors was limited by the keyboard effort. All those spring-
loaded contacts between the rotors make advancing the rotors hard. Enigmas
have a huge key travel, almost an inch, to provide extra leverage. You can't
actually "type" on one; you push the keys down firmly, one at a time. Somebody
has to write down which lamp came on, anyway, so that's not the limit on
speed.

The keyboard-driven rotor machines didn't scale up well. Beyond three rotors,
motor drive was usually needed, although the cute little M-209 used a wheel
and lever for input, rather than a keyboard. The next step up was the Lorenz
SZ-40/42, a six-rotor machine set up as a peripheral for a Teletype. That was
cracked with the Colossus electronic key-tester.

The Germans built the T-52 Geheimschreiber, with 10 rotors, but that had a
built-in Teletype machine and was too heavy to be portable. The Allies didn't
crack that one.

That was the original limit on key length. The longer the key, the bigger and
heavier the machine.

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ChuckMcM
The Enigma is a neat machine. I wrote a Java iButton applet that emulated one
and in doing research for that came across the rotor patent
([https://www.google.com/patents/US3984922](https://www.google.com/patents/US3984922))
this patent was _filed_ in 1944 but it _issued_ in 1976. October 12th to be
precise. One month before the Data Encryption Standard (DES) came out as a
FIPS standard. How Enigma worked had remained classified for decades after the
war ended, that is a pretty strong endorsement for this remarkable machine.

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cyberferret
Like most, I always thought that the allies were desperate to get their hands
on these machines during the war.

I was lucky enough to get to play with one of these things when a lecturer
from the Bletchley Park foundation toured here some years back. She gave a
fascinating and riveting talk on the history of the device.

I was surprised to hear that these were actually commercially available before
the war, and that the allies had quite a few of them in store already. The
crucial thing they were after were the booklets with the daily rotor and
plugboard settings - far more valuable than the machines themselves.

~~~
SteveNuts
I thought the commercially available models did not include the pegboard,
which was crucial for the higher # of possibly combinations?

~~~
cyberferret
I think you are correct. Also, the Kriegsmarine version had an extra rotor,
plus they also used a secondary code book to encode keywords before encrypting
on the Enigma.

Those were, from what I hear, much harder to break, thus the efforts to
capture the code books and devices from the U-boats.

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ddt_Osprey
All things considered, 84 bit encryption is pretty impressive, considering DES
was still considered "okay" even into the late 1990's.

[https://en.wikipedia.org/wiki/Data_Encryption_Standard](https://en.wikipedia.org/wiki/Data_Encryption_Standard)

[https://en.wikipedia.org/wiki/Deep_Crack](https://en.wikipedia.org/wiki/Deep_Crack)

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devindotcom
It really was quite a remarkable device, and if I remember correctly offered
much more security than was strictly "necessary" at that stage of the crypto
wars, though of course we know how all that particular story ended.

~~~
cyberferret
Yes, but on that note, the 'reflector' in the Enigma, which essentially double
encrypted everything on the device was one of the features that the allies
managed to use to break the device.

The reflector essentially routed the signal path _back_ through the rotors
again, which the Germans thought made the device even harder to decrypt.
However, the wiring involved essentially meant that the same letter typed
could NEVER be represented by itself once encrypted. (e.g. a raw 'A' could
never come out encrypted as 'A' etc.).

This n-1 weakness meant that allied cryptographers could eliminate options by
a large factor when running decrypting routines.

Also, the Germans would routinely ask their field operators to send long
random garbage transmissions in order to soak up the time and energy of the
allied decrypting teams.

However, human nature took over, and a lot of operators were simply too lazy
to hit random keys on the device, but instead would repeatedly press the same
key (usually the 'L' key which was the lowest key on the right of the
keyboard) while chatting to their colleagues.

Thus when the allied cryptographers saw a long transmission which _never_
contained the letter 'L', they knew it was a 'dummy lazy transmission', and
they could use 'LLLLL...' as the crib which made cracking that day's Enigma
code so much simpler.

An astonishing example of when a tactic to try and make things harder to crack
actually made it easier to do so (with the assistance of human frailties).

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alblue
There's an Enigma Machine on display in the centre of Milton Keynes this
weekend
[https://twitter.com/alblue/status/823105879847370752](https://twitter.com/alblue/status/823105879847370752),
as part of the celebrations of MK's 50th anniversary. Bletchley is a suburb of
Milton Keynes. [http://mk50.co.uk](http://mk50.co.uk) has more if you're
interested :-)

Bletchley Park has a machine on display as well, and also hosts the Bombe
machine which was used to crack Enigma codes during the war. It used motors to
drive copies of the rotors in Enigma in order to find a "short circuit" (where
one letter coded back to itself) since this would indicate the starting point
was invalid. The rotors would then tick one over and start again. The reason
for so many columns was that each column of three was a different stating
point - in effect, base 26 counters where each 3-digit number was started from
a different number. To account for different rotor combinations and choices
there were 20 or so machines built each corresponding to a different rotor
choice (ABC, ABD, ABE, ACB, ACD etc). In fact it didn't just use the reflexive
lookup for short circuiting; the cryptanalysts produced "cribs" which were
hypothesised guesses of loops; if R-S, and S-T and T-R then this would be
another short circuit option. The bombe was "programmed" with such cribs
mechanically (leads plugged in to simulate connections) and then set to run.
Since this process changed at midnight each day they would do the same thing
day after day.

Round the corner from Bletchley Park is the National Museum of Computing
[http://tnmoc.org](http://tnmoc.org) which although on the same site is a
different organisation. They have the Colossus machine which was used to break
the Lorenz cypher, and was the first programmable electronic computer
(although the program was wired in in hardware, in effect a manual ROM).

It's well worth going to see both of these if you ever happen to be in the
Milton Keynes area, or if you're passing through London - it's half an hour
away by train.

------
sounds
After reading to the end (very enjoyable),be sure to find out what weaknesses
Bletchley Park exploited to break the encryption:

[http://users.telenet.be/d.rijmenants/en/enigmauboats.htm](http://users.telenet.be/d.rijmenants/en/enigmauboats.htm)

