Re: double encyphering with an enigma

From: Michael Amling (nospam_at_nospam.com)
Date: 02/27/04 

Date: Fri, 27 Feb 2004 15:14:56 GMT

John A. Malley wrote:
>
> I'd assume cascading two ENIGMA machines with independent key settings
> results in a longer periodic polyalphabetic key sequence than that from
> a single ENIGMA machine stage.
>
> Cascading two independent involutions can map a PT character to itself
> in the final CT output - simplest example - using 1 and 2 to designate
> stage 1 and stage 2, let pi^1_i() = pi^2_i(). Both are the same
> involution, so the second stage decrypts the first stage, and what goes
> in comes out. Other involution cacades might map a subset of the PT
> alphabet to the same characters in the CT. The cascade results in a
> substitution on the PT alphabet that is no longer restricted to
> involutions.

   IIRC, the OP didn't specify two independent encryptions, just two
encryptions. While they could be independent, that would require a
larger indicator and fiddling by the operator in mid-message.
   I had assumed the OP meant to run the plaintext through the first
encryption, then without changing anything, type in the ciphertext from
the first encryption. The indicator remains the same. And I think even
this simpler procedure makes Bletchley Park's work significantly harder.
The bombe needs at least double the number of wheels needed for single
encryption.

--Mike Amling

Loading