Assuming you’re using Secure Shell to SSH to a remote server, you can import identity files from the connection dialog.
Select the "Import...", select your private key and public
key from the file picker, for example "id_rsa" and "id_rsa.pub", for each identity.
If you have a key stored in a single ".pem" file, you must split it into two files before importing.
In my case, I had an openstack_keypair.pem, an Openstack Nova generated keypair as pem
file. Since I had a private key (openstack_keypair.pem), I needed to
generate a public key (openstack_keypair.pub) for it. To generate the public
key, I did:
ssh-keygen -y -f openstack_keypair.pem > openstack_keypair.pub
This command created the .pub file that I needed. With that, I renamed the openstack_keypair.pem file to openstack_keypair and went back to Secure Shell, select the “Import…” button, selected openstack_keypair and openstack_keypair.pub and connected