[Cryptography] how to detect breakage -- lures etc.??

[Charles Jackson]

n Sat, Jan 4, 2020 at 2:24 AM Arnold Reinhold via cryptography <
cryptography at metzdowd.com> wrote:

>
> >  The SIGABA/ ECM-II sets, which by all accounts was never broken during
> the war,

In* Big Machines: Cryptographic Security of the German Enigma, Japanese
PURPLE, and US SIGABA/ECM Cipher Machines *Kelly states (IIRC) that in the
1970s, NSA deputy director Tordella (
https://en.wikipedia.org/wiki/Louis_W._Tordella) stated that they still
could not break SIGABA/ECM.

A paper by Stamp and Chan estimated that the SIGABA had a key of about 95
bits.  IIRC, they assume that the attacker knows the rotors.  If you assume
that the attacker has to recover the rotors from observing the traffic,
then the work required must be much greater.

> * five rotors in the alphabet maze, chosen from a set of ten
> * pseudo random stepping of the five rotors, at first controlled by an
> additional set of rotors
> * no reflector, eliminating the “no letter can encode to itself” weakness,
> at the expense of a bulky 26+ position encrypt/decrypt switch
>
> The rotors in the SIGAGA were reversible---adding another 2^10 bits to the
key.  The US issued new  rotors every year.  If the Germans had done that
with Enigma, the allies would have had a much harder time recovering
Enigma-coded message.

Chuck
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