this post was submitted on 06 Oct 2024
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Cybersecurity
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The CA just signs the certificate. They don’t have access to the private key, and thus can’t decrypt the key exchange.
The key exchange is the only thing decrypted by the private keys. From that point on, everything is encrypted and decrypted by the agreed upon cipher using the exchanged key, which is randomly generated for each session.
Surely they can do a man-in-the-middle attack and gemerate the required private keys and certs on the fly.
this only works, if the client doesn't know the server yet or disregards an already known key (you know, like SSH or web browsers telling you the key has changed)
I don't think that browsers do that. There is HSTS but I think that it only checks if the connection is using TLS.
They could pretend to be any domain, yes, but you asked about inspecting a TLS stream, and afaik, there’s no way to do that without the private key. Once the TLS handshake begins, there wouldn’t be a chance for a man in the middle, so that kind of attack would have to be done before the connection is established.
Not that it really matters to this conversation but seems like you would know, so I’ll ask because I’m curious…
Is that randomly generated per session key generated by the remote host ssh server? Is it a symmetric key (maybe for performance purposes)?
Technically, either side can request that the other generate a key and use that one, and it will cost an additional round trip. But generally in practice, each side generates their own key and tells the other side that it will be using that key.
Yes, those keys are for symmetric encryption, and yes, it’s for performance. It’s way faster to just exchange keys with asymmetric encryption rather than do the whole stream.
Also, I think you meant SSL, not SSH. SSH Uses a different key exchange protocol.
I love cryptography. :)