[Cryptography] Imitation Game: Can Enigma/Tunney be Fixed?

Phillip Hallam-Baker phill at hallambaker.com
Wed Jan 7 13:11:40 EST 2015

On Tue, Jan 6, 2015 at 2:45 PM, Philip Gladstone <
pjsg-cryptography at nospam.gladstonefamily.net> wrote:

> On 1/6/15 03:54, Ray Dillinger wrote:
>> On 01/05/2015 09:41 AM, Tony Arcieri wrote:
>>  Enigma is fatally flawed in its current design, AFAIK. Due to the nature
>>> of
>>> how its rotors operate, it can't encrypt a letter to itself, introducing
>>> a
>>> statistical bias into the ciphertext.
>>> Enigma would need to be modified so all letters have equal probabilities.
>>> Someone who knows the intricacies of these rotor machines better than me
>>> might know what's involved.
>> The Enigma actually had two fatal weaknesses.  First, as you
>> correctly point out, the allies exploited the can't-map-to-
>> itself property to great effect; t was how the Bombes
>> eliminated possibilities in great quantities once they were
>> started.
>>  My impression was that the steckerboard did not significantly help
> against cryptanalysis (contrary to what the Germans thought). The closures
> (or cycles) that were used to drive the bombes were independent of the
> steckering.

That is my understanding as well. It took me a long time to work out what
the steckering did because I could not really see what the point was. They
could have achieved a lot more bang for the buck if the steckering had some
sort of interaction with the reflector. As it was they just had two
orthogonal ciphers, a rotor cipher and a Ceasar cipher that was easily
stripped off with a meet in the middle approach.

In addition to what Jon raised, one of the biggest operational defects was
the habit of sending out 'test' messages of a single letter repeated. that
combined with the reflector no letter maps to itself defect made it really
easy to spot cribs.
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