martin f krafft  wrote:
>David Wagner <[EMAIL PROTECTED]> writes:
>> You're absolutely right.  Quantum cryptography *assumes* that you
>> have an authentic, untamperable channel between sender and
>> receiver. The standard quantum key-exchange protocols are only
>> applicable when there is some other mechanism guaranteeing that
>> the guy at the other end of the fibre optic cable is the guy you
>> wanted to talk to, and that noone else can splice into the middle
>> of the cable and mount a MITM attack.
>
>Uh, so if I have a channel of that sort, why don't I send cleartext?

Quantum cryptography doesn't assume the channel is immune from
eavesdropping.  It does assume you know who is on the other end, and
no one can splice themselves in as a man-in-the-middle.  (Even though
we have an authentic channel, eavesdropping on the channel might still
be possible.)

One could reasonably ask how often it is in practice that we have a
physical channel whose authenticity we trust, but where eavesdropping
is a threat.  I don't know.

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