[rescue] The Ultimate rescue - Colossus Lives Again?

ross-sunhelp at lonsteins.com ross-sunhelp at lonsteins.com
Sun Nov 18 16:15:05 CST 2007

On Thu, Nov 15, 2007 at 10:10:07PM +0200, Geoffrey S. Mendelson wrote:
> The Enigma code was broken by several methods. One of them was
> that the operators often sent the encryption key in encrypted

>From Simon Singh's "The Code Book", the machine itself was known-
there was a commercial version and the French had acquired by
espionage a German military unit and operations manual. The day key-
the arrangement of plugs and scramblers- was not known but its
structure was known and described in the manual. The day key was used
to encrypt the message key which should have been secure.

> text, but often sent that encryption key in open text.

I don't believe this was done except by mistake. The real mistake was
that there were structures to the sending of the message key and
regular structures in the German military messages. For example, the
message key was encoded twice and sent before the message encoded with
the key was sent. Occasionally, an operator would reuse the previous
day's key or send the same text on different days.

Also from Singh's book, before the war, code breakers in Poland worked
out patterns produced by the machine given particular scrambler
settings and then could brute-force the plugboard settings. Given what
they knew about the message structure, they could run multiple
machines in parallel to find the plaintext.

- Ross

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