Re: double encyphering with an enigma

From: John A. Malley (102667.2235_at_compuserve.com)
Date: 02/26/04 

Date: Thu, 26 Feb 2004 10:27:23 -0800

Peter Fairbrother wrote:

> John A. Malley wrote:
>
>
>>I'd assume cascading two ENIGMA machines with independent key settings
>>results in a longer periodic polyalphabetic key sequence than periodic
>>
> polyalphabetic key sequence that from
>
>>a single ENIGMA machine stage.
>>
>
> Why? The overall periods of each machine would be the same, 17,576 letters
> for a 3-rotor machine.
>
> I may be making assumptions about what you mean by a "periodic
> polyalphabetic key sequence" though.
>

Argh! You are correct! I was thinking of toggling the second ENIGMA's
rotors as a function of one complete cycle (period) of the first
ENIGMA's rotors, and it can't work that way when we cascade two ENIGMAs
as-is. Each ENIGMA machine increments its rotor settings with each
keyboard key press, so there is no way to keep the rotor settings fixed
on the second machine while cycling through all of the rotor settings on
the first machine.

John A. Malley
102667.2235@compuserve.com