Linux HowTo: Secured Shell (ssh) for Starters

Secured Shell (ssh) for Starters:


-ssh uses the technology of public-key-cryptography as the base.
-it requires two keys to open a file (public + private); somewhat like a bank locker which req two keys (bank's + user's)
      -public   key is freely accessible.
      -private  key is strictly restricted.
      -The combination of public + private key is supposed to be unique.

-how it works?
            . both receiver and sender must have access to each others public key
            . sender encrypts:   sender priv key + receiver pub key + data
            . sender sends
            . receiver decrypts: sender pub key + receiver priv key + data

-ssh is a proprietary protocol owned by the Finnish company ssh communications security.
-although the source code for original ssh is open, varios restrictions are imposed about its use and distribution.
-openssh is the opensource version of ssh under the openbsd project and is more popular and secure than the original ssh.
-to be fully secure, all insecure connections in a network need to be eliminated.
-eg: host a connects to host b via telnet; host b connects to host c via ssh.
            due to the insecure a-b conn, the traffic bet b-c can be monitored and cracked.

-usefuls (on Red Hat Linux):
            # yum -y install openssh-server
            # rpm -qa | grep -i openssh
            # service sshd start | stop | status
            # ssh -6 user@server         [ ipv6 ]
            . /etc/ssh/sshd_config         [ server daemon ]
            . /etc/ssh/ssh_config           [ client   daemon ]
            . ~/.ssh/known_hosts         [ a directory of ssh hosts ]