The SSH (acronym for secure shell) is made of a set of tools for secure and encrypted connections between server and clients. The older tools such as telnet, rlogin, and rsh should be discarded as they are prone to hacks as they do not encrypt the login session thereby leaving your username and password vulnerable. SSH is different as it encrypts the connection and also it authenticates both ways.

The transport layer in the network stack is encrypted with a cryptographic handshake and hence the connection is secure. The authentication is via either user ID/password or a public/private key between the server and client.

Install the client and server in your machines using the following commands:

sudo apt-get install openssh-client
sudo apt-get install openssh-server

The server package needs to be installed only on those machines to which you want to log in to.