Natanael wrote on 12/05/2015 12:50 AM:
Den 4 dec 2015 23:49 skrev "U.Mutlu" <[email protected]>:
Martin Dehnel-Wild wrote on 12/04/2015 09:58 PM:
Yes. Having a pre-shared public key definitely allows you to prevent MITM
attacks. (Where by 'attack' I assume you mean 'the adversary learns the
agreed key')
Yes, indeed that's what I'm meaning by attacks.
But I have a hard time to see how the use of a public key can help here,
because the public key is by definition known to everybody, so also to
the MITM, but then he can easily replace the encrypted message by his
own message encrypted with the same public key --> bingo!
Or, where is my lack of understanding here?
Thanks for the info and links below, I'm going to study them.
This is where you tell them to reply encrypted to your public key, inside
the encrypted message, and sign it. So they got a message from somebody
else? If they know you already, they'll see the signature failed. If they
don't, you'll be the one who notices the total lack of response, and you'll
try again until you get one (which is signed).
This introduces signing, but in the wikipedia article I had quoted
in the OP signing is not mentioned:
https://en.wikipedia.org/wiki/Diffie–Hellman_key_exchange#Public_key
If I might summarize:
Using DH protocol and adding to it the use of say RSA certificates
(for signing, enc, dec) will make the DH session MITM-secure,
for example for subsequently sending a new password (for something else)
over to the other side.
Is that conclusion right?
That would be what I need, ie. a safe way to send the other side a
new/initial password (for a different purpose), but without any human
interaction as the participants are devices or apps but which already
have their own certificates.
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