> Well, I think I agree with everything David said, and given
> his assumptions I believe he is correct. However, it appears
> that he did NOT carefully read what I had posted. He is
> assuming the existance of "the key" (see his first interjection)
> while my argument was in two parts:
>
> If there is NO key then a man in the middle attack succeeds.
> No matter WHAT medium the transmission is on.
Quantum encryption can ensure that the key is known to one and only one
other party. No other existing technology can do that. Consider, for
example, a stream of entangled particles. For any given pair of particles,
one is + and one is -, and nobody gets to choose which is which. If I shoot
such a stream at me and you, we both get the same bit stream (though yours
is inverted). While a MITM could *get* the key, if he has it, you do not.
Can you do that with any other technology?
> If there IS a key then quantum encryption provides no
> additional protection above and beyond conventional
> encryption using that key.
Again, false. Quantum encryption can secure a communication today
against
all conceivable improvements in computing power.
> I can split the second case into two parts:
>
> If there IS a key AND there are NO quantum computers then
> the key provides adequate protection
No, it doesn't future advances in compution *will* make any given key
insecure eventually. Your communications today *will* be known in the
future.
> If there IS a key AND there ARE quantum computers then
> there is no protection against a man in the middle attack
> (I guess other than making the key have more bits than
> the largest known quantum computer).
There is. The MITM must know the key at the time of the communication,
and
can't do any guessing or trials.
> In NONE of these three cases does the addition of quantum
> encryption increase the security.
>
> In short, David did not understand my argument.
Definitely. I still don't.
> I EXPLICITLY
> mentioned both the private key concept he assumes AND a
> PKI-based system, and acknowleged that in the case of the
> former there is a key transportation problem, while in the
> latter case you need to have a PKI in place.
>
> David, perhaps you could explain to me what, in absence of
> any prearranged shared secret, the legitimate recipient
> could POSSIBLY do that an interceptor cannot do, given that
> they have the same level of functionality in their equipment
> and the same knowlege of the protocols in use.
The legitimate recipient can decode the particular beam of particles
that I
am sending. While an interceptor can do this, it is impossible for both the
interceptor and the legitimate recipient to do this. In other words, quantum
encryption can ensure that a given message has one and only one recipient,
now and forever. Quantum encryption can generate a message that *cannot* in
principle be decoded and re-sent (although you can't choose the message,
just know what it is after the fact).
> I think my argument is a little deeper than you first might
> have realized, and while I'd be glad to acknowlege that you
> are right if indeed you are right, I don't even have the
> basic glimmering of an idea how I might be mistaken???
Do you agree that:
1) If there exists a shared secret, quantum encryption can provide
protection, now and in the future, against MITM attacks or passive
interception.
2) Streams of entangled particles can generate shared secrets where none
previously existed.
DS
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