SSH is a secure protocol that is used to connect to remote Linux servers.
SSH server must have the SSH daemon running on it and the client machine must have SSH client installed on it to connect to a remote Linux server.
SSH keys provide a more secure way to authenticate into a Linux-based server as compared to a regular username-password combination. SSH keys are of three types- RSA, DSA and ECDSA.
OpenStack supports RSA keys as RSA is more universal than DSA and ECDSA.