[GTALUG] Netgear 5-port Gigabit switch -- $10 ?

[D. Hugh Redelmeier]

| From: Lennart Sorensen <lsorense at csclub.uwaterloo.ca>

| It is not that simple.  DH key exchange works and has been used for a
| long time now because it works.

Yes, but it doesn't prevent man-in-the-middle attacks.  For that you
need authentication.

SSH does a few things for authentication.

SSH hosts have keys.  An SSH client warns the user if a hosts key has
changed since the last time they talked.  This puts little burden on
the user and yet gives some security.  But it won't detect a
man-in-the-middle that was there from first contact.

Users can authenticate with a client via passwords or via a public
key.  Both require out-of-band installation of credentials.

I think that the password will travel over the wire when authenticating, but
encrypted.  But a spoofing server could collect passwords.

With a public key system (like RSA), only a signature goes over the
wire.  So a spoofing server could not collect the key.  Things get a
little more intricate when you use ssh-agent for forwarding authenticaton.