218 Are the Androids Dreaming Yet?
by anyone but the intended recipient. However, wouldn't it be equally valuable to know if someone other than the recipient had intercepted and read the message? This is the trick quantum cryptography gives us.
Taking a measurement with a quantum device disturbs the system so measurements can be taken only once with the same results. By the same logic, I could send you a message and if someone else has read it in the meantime, you will know. I could arrange to meet with you in Berlin and if you detect the message has been intercepted, you could simply not show up.
I could use this same technique to send you a one-time pad. If you receive it without it being overheard, I could then safely send you an encrypted message. In 2007, this technique was used to transmit the results of a Swiss election from the polling booths to the central counting center.
Enigma
World War II accelerated the evolution of encryption from simple substitutions a human could perform to complex ciphers only a machine could calculate. You might wonder why everyone does not use a one- time-pad since it is a perfect code. The problem is distributing and maintaining the pads while keeping them secret. My daughter cracked my earlier code because she knows my laptop password, broke in, and read the answer. That’s the problem with codes — security. The pads could be sent out in sealed envelopes but it would be easy to intercept an envelope, copy the pad and reseal it. You would then have a perfect and undetectable way to break the code. Also, if I were an Admiral wanting to communicate with my fleet of submarines I would need a huge pad — one page for every message I want to send — and either a pad for each submarine or one pad for all submarines. If I use only one pad, then I cannot talk to a submarine privately, and if any pad were lost all security would be breached. One-time-pads were used by both sides during World War Two, and often printed on nitrocellulose — a chemical similar to the explosive nitroglycerine. This allowed users to burn the codebooks quickly if an enemy threatened to capture them.
Both the Americans and British captured Enigma machines and codebooks during the war. A Navy Enigma machine was a sought-after prize, as it was more complex than the Army version, with extra dials and plug settings. To crack the more sophisticated codes Bletchley Park
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