Sam Heywood wrote:
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On Tue, 11 Jan 2000 09:11:04 -0500, Roger Turk wrote:
> Let me give you my idea of public key/private key usage by going back about
> 40 years. This is in the day where encryption was performed by mechanical
> crypto machines that had a number of rotors that could each be assembled in
> various manners. As the encrypter typed the plain text message, the crypto
> machine would generate a letter, increment the rotor so that if the same key
> was typed, a different letter would be generated. There would be literally
> thousands of ways the rotors could be assembled. The message would be the 5
> character group messages that Sam Heywood mentioned.
<snip>
Hello Roger:
What you have described above is the type of machine that incorporates the
technology of the Nazi "enigma" machine, as I understand it. I did not
realize that many similar types of machines were in common use around that
time. According to my understanding, I believe the "enigma" machine used
private key encoding only. Instructions for the setup for the gears and
rotors would be sent by secure means, such as by dead drop or by courier.
I found the rest of your post concerning private and public keys also very
informative. Thanx.
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Hi Sam,
The machine that I described was, indeed, a German invention and used by the
Nazis. I wanted to refer to the machine as the "enigma" machine also, but
the more I thought about it the more I was less certain about the "name" of
it and the more certain that the "enigma" machine was the machine used by the
British to process the various rotor assemblies without actually assembling
the rotor. The world's first decoding computer!
The encrypting method used by these machines was, until computers became
readily available, a very secure process. More highly classified material
could, and was, double and triple encrypted and the private keys afforded
more security as the classification increased. As an old Navy man, I can
attest that machines similar to this were used by the U. S. Navy well into
the 1960's and I would not be surprised if some countries are still using
this machine today.
The instructions on how to set up the rotors *has* to be included in the
encoded message. If a troop position is overrun and the machine, rotors, and
keys captured, you can't wait to send new keys to all the other units by
courier, runner or swimmer. You have to have a way of changing the
encryption with each message, thus the "public key" that is sent with each
message. Also, all originators of messages would not use the same rotor
arrangement. Imagine the field day that would be had if *all* encrypted
messages sent in one day were based on the same rotor assembly and that code
was broken! The problem that the Nazis had was that they were so confident
that the code couldn't be broken that they did not change rotors very
frequently. Another thing is that most encrypted messages don't require
immediate action --- they have to do with planning or actions days or months
away, so that gives cryptographers time to "play" with encrypted messages.
There is a book published by the U. S. Naval Institute titled "Double-edged
Sword," about the Navy's code breaking efforts in the Pacific during World
War 2. Being successful in breaking someone's code is a double-edged sword
as you don't want to show up everywhere they are going, yet you want to
hinder their success.
Roger Turk
Tucson, Arizona USA
