In order to communicate between different processors and different instances of the operating system in each node, some form of authentication is required just as we usually log in to workstation to use them. When we log into workstations, we are required to submit the user ID as well as passwords. Because of the above-mentioned security concerns, it is not wise to send cleartext passwords or non-encrypted passwords.
With the help of RSA cryptography, ssh allows the authentication using public and private keys. Here are the series of LINUX commands to accomplish this under a certain account in the Linux or UNIX operating system with commonly mounted home directory (i.e. NFS mounted):
# generate public/private key pair # for simplicity, leave the passphrase empty ssh-keygen -t rsa # copy the public key to the authorized_keys cp ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys # confirm the shell in use, and add the private k ey to compare it to the public key ssh-agent $SHELL ssh-add
We will not discuss how this form of authentication works in detail, but simply to state that private key is used to identify oneself and it is confirmed by the list of public keys in the file authorized_keys will confirm the identity claimed. Upon confirmation, these keys allow users to log in without typing in a password or sending non-encrypted passwords over a public network.