[radlad]

I'm confused by this. I know that HTTPS is supposed to be fixing this problem too supposedly. But I don't understand how. If an attacker fully replicates a SSH server, and responds to all client messages with the victim correctly, while then relaying their commands to the real SSH server, and acting as a full SSH client, isn't there still an issue?

The attacker just has to authenticate with the correct signature to each, but if it's an attacker, why would it just pass along the victim's data anyway? The whole point of an MITM is that you can modify data before it hits its target.

[asdfaoeu]

In the hypothetical scenario the attacker doesn't have the client's private key so it can't authenticate to the server. It can pass along the session key from the server but then it won't be able to read the data.

[jrochkind1]

Ah, I get it now. It's not just the authentication step, it's the fact that the data is encrypted so only the original client can read it? That's right?