ssh -i /path/to/key

It uses ssh(secure shell) protocol(encrypt communication between client and remote machine), so you can safely execute command. In addition, since the ssh command can use key authentication using secret key / public key, you can further improve security by using them.

ssh -i /path/to/key

Specify the private key file(identity file). In the initial setting, SSH version 1 is /.ssh/identity, ssh version 2 is /.ssh/id_rsa and /.ssh/id_dsa