Generate pub/priv key

NSA recommends RSA key lenght of 3072 bits or longer.

SSH-KEYGEN

-t : algorithm (rsa, dsa, ecdsa) -b : key size in bits -f : filename where the key will be stored (normally, it prompts you)

ssh-keygen -t rsa -b 3072

The command above will generates 2 files, one will contains the private key and the other the public key that you can identify because it ends with .pub