Below steps assume you already have a Public Key Pair generated.
Using e.g. PuTTYgen (PuTTY Key Generator) you can generate a new key pair.
Just search the Internet for a recent howto for generating and saving a new key pair.

• For user tc add a public key to allow Public Key Authentication.
  • sudo su - tc
  • mkdir -p /home/tc/.ssh
  • sudo vi /home/tc/.ssh/authorized_keys
  • add:

     paste your generated public key (not the priviate key!!). 

    
    

• Configure the ssh server (sshd) to allow Public Key Authentication.
  • sudo vi /usr/local/etc/ssh/sshd_config
  • add:

     PubkeyAuthentication yes 

    
    

• Preserve the ssh server config at reboot.
  • sudo vi /opt/.filetool.lst
  • add:

     usr/local/etc/ssh/sshd_config 

  • backup