[ale] [OT] speaking of british (motorcycle thread) - interesting crypto info circa 1940

[Ron Frazier (ALE)]

Hi all,

I may have mentioned this here before, years ago, but considering the 
nsa stuff, I thought it would be interesting to share.

Last night I dug up a movie from a rarely used box I have and watched 
it.  It's called Enigma.

http://www.amazon.com/Enigma-Dougray-Scott/dp/B00006FD9P

It's about the British and American cryptanalysis and code breaking 
project during WWII circa 1940 - 1945.  The movie is R rated, and I 
could do without the parts that make it so.  However, the other core 
content of the movie is fascinating, and is based on truth.  I am not a 
history buff, but I do like this movie.

After watching the movie, I read about 29 pages from the following 
wikipedia articles about Bletchly Park and Bombes.  Yes that last thing 
is spelled correctly, as I will explain.

http://en.wikipedia.org/wiki/Bletchly_Park
http://en.wikipedia.org/wiki/Bombe

The articles state that the efforts of the code breakers in Britain and 
the US reduced the length of the war by 2 - 4 years and that the outcome 
of the war without their efforts would have been in question.  A caption 
in the movie says these endeavors saved millions of lives.  None of this 
was disclosed to the public until the 1970's.

The main concern (relevant to this topic) of the British and later the 
US was the German Enigma machine.  This is a brilliant little piece of 
engineering.  It had an alphanumeric keyboard, a series of movable and 
rotatable rotors, and a plug board where wires could be attached in 
various combinations.  The operator would type a plaintext letter on the 
keyboard, and a corresponding ciphertext letter would light up on a lamp 
board.  That ciphertext would be transmitted by U-Boats, etc. by 
radiotelegraph.  Gears inside would rotate the rotors, so, the next time 
you pressed the same plaintext letter, you would get a different 
ciphertext letter.

Even though the allies had some captured enigma machines or clones of 
them, unless the rotor sequence, rotor position, and plug board wires 
were set up properly, they would not be able to decrypt the enemy's 
messages.  The 4 rotor Enigma machine had 18x10^19 different ways of 
being set up.  If my math is right, that's more than the permutations of 
a 66 bit binary key.  Decrypting the German U-Boat signals was critical 
to protect convoys of allied ships from being sunk by the U-Boats.  This 
was a VERY sophisticated cipher scheme for it's time.  There are 
comments in the articles to the effect that, if the system had been 
properly used, it would have probably been unbreakable.

Alan Turing, sometimes known as the father of computer science, helped 
the British develop the bombe machines, which were 1 - 2 TON 
electromechanical monsters which replicated the function of 2 or more 
enigma machines, with large numbers of rotating drums (or later relays), 
but which could be driven at high speed by motors.  If the British or 
American cryptanalysts could get a crib, a piece of known plaintext with 
a matching piece of known ciphertext, like a weather report where the 
format and data was known, they could use that as a baseline to set up 
the bombe.  Using the known data, the bombe machines would try various 
possible combinations of enigma setup sequences at high speed until a 
possible option was found that could possibly decipher the other 
ciphertext messages for which there was no crib.  The cryptanalysts 
would further analyze this data, and eventually select a few possible 
setup sequences.   Those would be tested by trying to decrypt the German 
communications.  If the result came out German, then the allies could 
read the German comm traffic FOR A DAY OR TWO.  The next day, they had 
to figure out the code again.  This went on for years, and the allies 
eventually decrypted thousands of German messages.  At one point in 
time, there were 12,000 employees at Bletchly Park.

So, you might say the Bitish and American code breakers saved our 
collective butts.

There is a simplified description of of how all this works, with 
examples, in the articles.  Now, I've never claimed to be a math 
wizard.  But, this stuff, even from 1940, makes my eyes cross.  I'm glad 
someone understands it, and I'm sure modern crypto systems are much more 
complex.

Anyway, hats off to the cryptographers for what they do, WHEN it's in 
the best interest of society.

I just thought you all would find this interesting, as I did, even 
though history is not usually my thing.

Sincerely,

Ron


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Ron Frazier
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