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

Ray Dillinger bear at sonic.net
Fri Jan 9 23:51:54 EST 2015

On 01/09/2015 10:34 AM, Dave Horsfall wrote:
> On Thu, 8 Jan 2015, Ray Dillinger wrote:
>> [...] gives an alphabet of 28 symbols, which encompasses the 26 letters 
>> and gives you two more - to use probably for "switch to numbers" and 
>> "switch to numbers then look up the number in a codebook" respectively.
> No; you'd need a symbol to get back to letters again.  In the old Teletype 
> days using the 5-bit Murray/Baudot code, one symbol was LTRS and another 
> was FIGS, both of which were state-independent and dropped you into the 
> appropriate alphabet.
> Made for amusing times if LTRS/FIGS were not decoded properly due to
> noise; no ARQ or FEC back then...
> Either that, or your FIGS would act on the following symbol only, which I 
> suppose is do-able.

The "numbers" are digits 0-9, mapped to some set of ten symbols.
The first character that's not part of that set signals that
you're dropping back to letters. If you need to type a letter
that would otherwise be mapped to a number, you just insert a
space (well, an X since that's the way they did that) first.

Seriously, no other comment on the redesign?  I thought that
running both the positive and the negative connections through
the rotors via different electrical paths encoding the letter
by combination, and then using 18 of the electrical paths
through the rotors for feedback, was really clever!

It preserves the desirable property that the encryption depends
on (at least) two different paths through the rotors that the
reflector was intended to provide, and it does it while
keeping the parts count, mass, volume, and cost down. It
requires no new mechanical technology, and demolishes both of
the two greatest weaknesses of Enigma - the cyclometric attack
and the cant-map-to-itself property!

The fact that most of the time one or both of the paths will
go through some random-ish number *more* trips through the
rotors is a bonus!


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