SSH Key-Based Authentication on Linux Servers

I want to login from one Linux server to another Linux server without the need to enter a password.

Create SSH keys

# Login to server 1


Generating public/private rsa key pair.
Enter file in which to save the key (/home/'USERNAME'/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/'USERNAME'/.ssh/id_rsa
Your public key has been saved in /home/'USERNAME'/.ssh/
The key fingerprint is:
SHA256:27U2nApZQLSwS1UVh2Lw4aDM/B9/gR0Uum1ppRrqjpg 'USERNAME'@server1
The key\'s randomart image is:
+---[RSA 3072]----+
|    +o+ .o       |
| + . Bo+o .      |
|  = o.*...       |
|   o + o .       |
|    + o S   .    |
|     . X * +     |
| .    * @ O      |
|E . .. B * .     |
| ..+..o o        |

The utility will prompt to select a location for the keys that will be generated. By default, the keys will be stored in the ~/.ssh directory within user’s home directory. The private key will be called id_rsa and the associated public key will be called

Now we have a private and public key that we can use to authenticate.

Copy keys to server 2

We will use the same keys on server 2:

scp ~/.ssh/id_rsa     USERNAME@server2ip:~/.ssh
scp ~/.ssh/ USERNAME@server2ip:~/.ssh

Create authorized_keys on both servers:

ssh-copy-id USERNAME@localhost
ssh-copy-id USERNAME@server2ip

Connect to server 2

ssh USERNAME@server2ip
# or just
ssh server2ip

Now we SHOULD connect to server2 without the need to enter a password.

Failing - But why?

Unluckily in my case I still have to enter a password. But why?

# Login to server 2
ssh server2ip

# check auth.log
less /var/log/auth.log
rexec line 15: Deprecated option RSAAuthentication

# check sshd_config
less /etc/ssh/sshd_config
RSAAuthentication no

So in my case the RSA-Authentication has been disabled.
As the default is enabled by purpose, this has been done by purpose.
Unfortunatly I am not the admin or manager of the server, so I can not change this settings.