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 (or uncommend):

     PubkeyAuthentication yes 

    
    

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

     usr/local/etc/ssh/sshd_config 

  • backup
    
    
• Restart the ssh server to re-read the configuration.
  • sudo /usr/local/etc/init.d/openssh restart
    
    

After configuring PuTTY or other terminal server to use Public Key Authentication with the new private key, you should be able to login directly as user tc using the phrase you used while generating the key pair.