Step 1: generate the private and public RSA key pair in Xsheel/Centos as below:
ssh-keygen -t rsa
Enter file in which to save the key (/root/.ssh/id_rsa): /* press the Enter button */
Enter passphrase (empty for no passphrase): /* enter your password */
Enter same passphrase again: /* enter the password again */
Your identification has been saved in /root/.ssh/id_rsa. /* the private key is already */
Your public key has been saved in /root/.ssh/id_rsa.pub. /* the publick key is already */
Step 2: download the id_rsa. and id_rsa.pub as a copy before step 3
press the ctrl+alt+F to open the Xftp, when opened, input "/root/.ssh" to locate to the directory, now download the two files above and save them safely. When downloading finished delete the id_rsa. in the Xftp for safefy
Step 3: rename the pub key and make use of it at once(please exit the current connection firstly in Xshell by input "exit" and enter)
mv /root/.ssh/id_rsa.pub /root/.ssh/authorized_keys chmod 600 /root/.ssh/authorized_keys
Step 4: use the keys to login into the VPS
in Xsheel, choose the authentication method as RSA file and upload the id_rsa.(ofcourse you can rename the file as your will), now try to login again. If succeed, see the step 5 as below.
Step 5: forbid the password authentication
in Xftp,in "/etx/ssh/", find the file sshd_config and download it. Open it with tools such as the Notepad++, ctrl+F to find the "PasswordAuthentication yes", replace the "yes" with "no",then close and save it.Now upload it to /etc/ssh to over write itself.
Step 6: restart the sshd service in Xshell as below
service sshd restart
Ok, all is done and now you can only log into the VPS via the RSA file pair.