> > 2) Streams of entangled particles can generate shared
> > secrets where none
> > previously existed.
>
> No, not really, since the scheme described on page 80 of the Jan 2005
> Scientific American looks vulnerable to a man-in-the-middle attack.
In that case, it generates two shared secrets. Either way, shared
secrets
are generated where none previously existed.
> I'm *fairly* sure that wrt shared secrets if "none previously existed"
> then there is NO way to prevent a man-in-the-middle attack, as there is
> no way to authenticate your correspondant, however, I am willing to
> listen to arguments.
In this case, it's not an attack. You have a secure channel to the MITM.
All that I said is that a shared secret is generated, not that you know who
you share that secret with. And, of course, either of the parties to a
secret can share it if they want.
You might wonder what good a shared secret is if you have no idea who
it's
with. The idea is that you authenticate the endpoint right after you
establish the shared secret, before you send any sensitive information. The
MITM cannot keep the shared secrets the same with both endpoints, so you
simply confirm equivalence at the endpoints as the next step.
For an example not involving any quantum encryption, consider using
anonymous DH to establish a connection. Then, over the connection, each end
sends the shared secret encrypted with its public key. Each end then
validates the signatures and that the shared secrets match. In other words,
you do MITM detection as a separate step.
The advantage over using ADH in this same application is the forward
security. You are protected against future compromises of the keys involved
and passive interception. This is a serious issue with public/private keys
because it is *always* possible to break such a key with sufficient
computational power in an automated, foolproof way.
DS
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