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'[OT]: Enigma (was Sensing a current - diving rods'
2004\10\28@140344 by Howard Winter

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Russell,

On Thu, 28 Oct 2004 13:34:25 +1300, Russell McMahon wrote:

> >> During the wolf pack days of WWII there was a technique, which worked
> >> better than anyone hoped, for finding german u-boats.
> >> Basically, they asked everyone where they thought the u-boats were.
> >> Where everything overlapped, that's where they frequently found them.
>
> > Was this the official cover for their being able to *really* tell where
> > they were, knowing that Enigma had been broken by that time ?

It may have been, along the lines of "Cats' eyes Cunningham", the night-fighter ace who was said to eat a lot
of carrots to improve his night vision.  The airborne interception radar was useful too, but they didn't
mention that!  :-)

Similarly, the fact that we were finding and sinking U-boats on the surface was "leaked" to be due to
infra-red detection of the paint on the conning-tower (the Germans changed the type of paint they used) and
then to detecting spurious radiation from their radio equipment - and when they checked they found that there
was indeed some of this, so they worked at eliminating it.  All of this lengthened the time before they
realised that we were (a) using airborne radar (again) to detect them and (b) reading some of their coded
messages.  They never did believe the latter.

> The German's naval enigma code was never broken in the manner that the other
> enigma codes were.

Not as often and not as quickly, but there were times when we were indeed reading their messages within a
useful timeframe.  In one case it is known that we read the message *before* the intended recipient - our
interception was "clean" (and it was a cipher-setup that we'd cracked so it was deciphered in minutes) but the
recipient station had it garbled and requested a retransmission!

> The navy used a more complex and flexible version of the basic machine which
> gave them about 1000 times better message security, used better key handling
> procedures and took far greater care with message content.

I'm not sure where you get the 1000 from - it had more rotors to choose from and an extra rotor installed, and
that complicates the initial setup, but I have a feeling it didn't turn like the others, or if it did it would
only have been one step every 17576 letters (26^3).  Since most messages weren't this long, it didn't add to
the scrambling.  But it did indeed increase the number of possible setups - I'm just not sure about the 1000.

> The Allies only
> managed to access their codes by contriving to steal code books without the
> Germans' knowledge - no easy task. Ian Fleming of James Bond fame contrived
> a plan to crash a German aeroplane near a German ship and then have the
> rescued "Germans" take over the ship. This was put into action but cancelled
> before implementation. They finally managed to raid light ships and similar
> and hide the loss of the code books by destroying the vessel afterwards.

Yes, the capture of the machine and settings-books from U110 (somewhat like the ficticious story in the film
U571) and not letting on that we had, was a major breakthrough, but there were many other techniques used to
produce "cribs" - guesses at the plain text that were a major part of cracking any version of Enigma.  One was
known as "harvesting", where something was done deliberately to elicit a message of known contents, like
sowing mines in a harbour-channel.  Having done so you then wait for the message(s) warning about the fact and
since a lot of German messages were in a prescribed form, you had your crib.  Some messages were sent with the
same plain text if different codes - weather reports for example - and by cracking the "easy" one you then
have a crib for the "difficult" one.  I don't know if the (controversial) technique that was shown in the film
"Enigma" ever was used - waiting for a wolfpack to assemble before attacking a convoy, and using the "sighting
reports" from the assembling U-boats to deduce the settings, but it's entirely possible to do that, given
enough messages.

> Sound too strange to be true? War tends to be like that. Information (true
> or not) from Simon Singh's  fascinating "The code book - the secret history
> of codes and code-breaking". Worth reading.

Indeed!  Next time you're over here I can heartily recommend a visit to Bletchley Park (weekends are best).  
It's fascinating to hear the various stories, and see some of equipment and the places where all of these
things happened.  I go there two or three times a year and learn something new every time (the people running
it are still discovering things that have lain unknown for sixty years!).

Cheers,


Howard Winter
St.Albans, England


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2004\10\28@150010 by Russell McMahon

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>> The navy used a more complex and flexible version of the basic machine
>> which
>> gave them about 1000 times better message security, used better key
>> handling
>> procedures and took far greater care with message content.

> I'm not sure where you get the 1000 from - it had more rotors to choose
> from and an extra rotor installed, and
> that complicates the initial setup, but I have a feeling it didn't turn
> like the others, or if it did it would
> only have been one step every 17576 letters (26^3).  Since most messages
> weren't this long, it didn't add to
> the scrambling.  But it did indeed increase the number of possible
> setups - I'm just not sure about the 1000.

All from Singh:

Scramblers:    Std = 5    Naval  = 8
Possible arrangements increased by factor of ~= 8

Reflector:
Std = fixed. Naval = movable to 26 positions.
Increases combinations by factor of 26

26 x 8 ~= 200

Specific instructions and practice to not send standardised messages.
Factor = ?

More secure message key transfer system = ?

Hard to put factors on latter 2 - probably far more than 5:1 in practice.

Overall they never cracked the naval version in the sense that they had done
the others.
Obtaining the code books was their breakthrough.

> since a lot of German messages were in a prescribed form, you had your
> crib.

This was the sort of thing the naval people were smart enough to avoid.
Amazing that it did not apply to all services. (Grand admiral Raeder ran a
tight ship ).


       Russell McMahon

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2004\10\29@045041 by Alan B. Pearce

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>Some messages were sent with the same plain text if
>different codes - weather reports for example - and
>by cracking the "easy" one you then
>have a crib for the "difficult" one.

One of the cribs they realised early on, was the reports from the weather
ships. These were often among the first messages using the new coding for
the day, and were typically of a prescribed format, likely to be using a
limited set of words, including the source position of the message. These
often gave a rapid decode hence finding the rotor setting for the day.

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