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

Ray Dillinger bear at sonic.net
Thu Jan 8 00:30:02 EST 2015

On 01/07/2015 04:12 PM, Richard Outerbridge wrote:
> On 2015-01-06 (6), at 15:57:32, Ray Dillinger <bear at sonic.net> wrote:

>> I had another thought about securing Enigma (or designing
>> a rotor machine) last night.  This follows from thinking
>> about the ”not enough different rotors" problem.

> Google FIALKA.  Breathe deeply.  Then KL-7.
> __outer

heh.  Of course, other people had similar ideas.

It's simple enough to make a rotor that can easily be
reconfigured.  I mean, if even my little stack of wiring
sandwiches would be too challenging to manufacture, distribute,
and manage, it's easy to just make rotors with a 26x26 grid of
screw holes.  Screw in 26 machine screws in at the beginning
of the day and you've got a rewired (crossbar) rotor, whose
electrical map depends on which 26 holes you filled.

I think maybe the biggest problem with re-keying like that is
the risk of getting it wrong and broadcasting something with
a "related" key and then later rebroadcasting it verbatim with
the "correct" key.

Operationally, each key would need to come with a test vector.
So in addition to the key, it would need to say something like,
"If you have key set up correctly, then the message BLACK CROW
IS ASLEEP should encrypt as DREEX CDNVX TWKFF PI"  and people
should be able to check that their key setup is correct without
ever transmitting or receiving anything.


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