Server is not asking for keys to authenticate

Question

I am trying to configure an ssh server, so that it accepts only keys (so disabling the request of the password).

I have already generated the public and private key using PuTTY (under Windows). I have two users currently, root and amministratore.  I don't want root to be able to login using ssh, only amministratore can.

What I've modified and done until now is:

1. /etc/ssh/sshd_config – see https://pastebin.com/hp0EQ5hG

2. root@autoapi:~# ls -ld ~/.ssh
    
   drwx------ 2 amministratore amministratore 4096 May  5 16:22 /home/amministratore/.ssh

3. amministratore@autoapi:~/.ssh$ ls -l
    
   total 4
   -rw-r--r-- 1 amministratore amministratore 398 May  5 16:08 authorized_keys

4. root@autoapi:~/.ssh# ls
   authorized_keys

5. I HAVE REMOVED CHARS IN THE MIDDLE, OBVIOUSLY.

   root@autoapi:~/.ssh# cat authorized_keys
   ssh-rsa AAAA.....KKQ== rsa-key-20190504

What have I forgotten?

Answer 1

When you connect with SSH, the client first checks to see what will be acceptable to the server. That is it asks the whether a particular key is acceptable before it actually trys to login. This means that if a particular key isn't acceptable the client won't even try to use it.

From your evidence the most likely thing is that your authorized_keys file is set to publicly readable and your config specifies the default # StrictModes yes. It also specifies # PasswordAuthentication yes. So the key authentication is being rejected by the server and instead you are being asked for a password. To fix this change two things.

1 Change the permissions on authorized_keys:

chmod go-rwx ~/.ssh/authorized_keys

2 Disable password authentication in /etc/ssh/sshd_config:

PasswordAuthentication no

Answer 2

You have correctly set the config to not allow root login.

It looks like you need to set the permissions of the authorized_keys file of amministratore, to 600.