There are two ways to generate a key pair. From a Linux system, generate the key pair with the ssh-keygen command:

ssh-keygen -t rsa -f cloud.key

This command generates a pair of keys: a private key (cloud.key) and a public key (cloud.key.pub).

From a Windows system, you can use PuTTYGen to create private/public keys. Use the PuTTY Key Generator to create and save the keys, then copy the public key in the red highlighted box to your .ssh/authorized_keys file.