The files in
/etc/ssh are for the service on the server you are connecting to. it uses them to listen and exchanges keys with the client session so that the data is encrypted.
Your personal keys (as you know in
~/.ssh) provide the reverse.
When you request a connection (before signing on or anything) the server listening (default on port 22) will pass you its public key for the server. This key enables you to encrypt traffic that only the server can decrypt. You can also use this public key to verify that you have connected to the correct server. The first time, you open a connection, you will be asked to confirm the key provided by the server. If you accept, this is stored in
~/.ssh/knwon_hosts so that you can be sure you are connecting the the same server on a later occasion.
See this article for more information -
17.3. Event Sequence of an SSH Connection
I hope that this helps. If not, feel free to ask again.
Kind regards,
Robin