How to verify if a public and private RSA SSH key match?

Question

How to verify if a public and private RSA SSH key match?

Answer

Warning: The commands below will show the contents of your SSH public and private keys. You should not share your SSH private keys with anyone, for any reason.

1. Access the server as root using SSH or the Terminal in WHM
2. Navigate to the folder that holds your SSH keys. By default, these are stored in the .ssh folder in a user's home directory. 

3. This folder will contain both the private and public keys, such as the following:

   # ls -alh /root/.ssh/id_*
   -rw------- 1 root root 2.6K Jul 31 00:02 /root/.ssh/id_rsa
   -rw-r--r-- 1 root root  580 Jul 31 00:02 /root/.ssh/id_rsa.pub

   Note: For cPanel users, SSH keys are stored in the user's home directory at: /home/USER/.ssh

4. Use the ssh-keygen command to test the files and print critical information:. The output of the command will contain the SHA256 signature for the key. 

   Private Key:

   #  ssh-keygen -l -f id_rsa
   2048 SHA256:abcdef123456789 user@domain.tld (RSA)

   Public Key:

   # ssh-keygen -l -f id_rsa.pub
   2048 SHA256:abcdef123456789 user@domain.tld (RSA)

   If the signatures match, then these SSH keys match.