These links started to be used in May 1941.
In August 1941, the Allies had a big break.
An operating was sending a message starting with the initial configuration.
These configurations came from code books.
The recipients at the other end needed to know that the configuration for that day was.
But these could be distributed securely and
were much smaller than needing to distribute the key sequence.
Once you had the starting configuration, you could transmit
an arbitrarily large message if this assumption that the key was
completely unpredictable was true.
In this case the operator sent the message.
The receiver did not receive it.
The receiver said, "Garbled transmission, please resend."
So the annoyed operator had to send the message again for the insecure channel,
and this time it was received okay.
If this is exactly what happened, it would have been fine.
These would be exactly the same.
We restarted the machine in the same configuration.
But what happened was a little different.
The operator got a little lazy the second time.
The operator was annoyed having to retransmit the message,
so instead of sending exactly the same message sent a slightly different message.
That meant that there was a slightly different ciphertext than we had the previous time.
Both of these messages were intercepted.
That means the Allies now had access to both C and C'.
They didn't know anything about the key.
They didn't know anything about the original messages.
Well, maybe they knew a little bit about the original message.
That's what's going to help them given these two ciphertexts to figure out both the key,
and, once they have the key, the structure of the Lorenz.
What is the result of XORing these two messages?
That means for each bit, we go through the bits to the messages XORing each bit.
I want to introduce a new variable here.
The key that the machine generates we'll call K.
That's the key that the machine generates starting from configuration C0.
Which one of these is the value that the interceptor would get
by XORing the two intercepted ciphertexts.
