Using ssh

Using ssh

If you understand the concepts revolving around telnet and how to use it, then you will have absolutely no problem understanding secure shell, commonly referred to as ssh and invoked with the ssh command. Secure shell is primarily used to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another just as you would with telnet. The difference is, ssh does it securely.

There are serious flaws in the telnet program as it is based on the telnet protocol, which is part of the TCP/IP protocol suite. Without getting too involved with what the suite is, remember that you had an IP address before that you needed to connect to a remote system. Well, IP is a protocol and it has weaknesses because the version of it in use (version 4) has been around just as long as Unix has. That being said, IP wasn't made for today's script kiddie/hacker/cracker/exploiter, and does not satisfy the need for greater security.

A newer version was created to replace the older version 4, but the newer version is harder to implement. Also, because of the disruption it may cause, and issues it may bring up, version 6 of the IP protocol hasn't gained the steam it should have. So, what is the solution? This is where ssh comes in. ssh in its simplest definition is encrypted telnet. It provides strong authentication and secure communications over insecure channels, namely the Internet, or your current network, which, believe it or not, could have a sniffer on it which could capture your packets and see your unencrypted data. Although this is highly unlikely, it is completely possible. It is a replacement for telnet and rlogin and some other unsecure protocols that conform to the same cleartext model. We will cover rlogin next. Before we do, let's look at how to use ssh:

 > ssh 10.1.1.1 > ssh pr1 

Remember that ssh protects you only if you use it. The ssh command comes standard on most systems, but if you do not have it, ask your system administrator to set it up for you, especially if you frequently use Unix remotely.

ssh Usage Using the ssh command can be tricky if you have never used it. Telnet is straight forward; you enter the command and then specify the host. With ssh, it may be that easy if it is set up already. If not, you may get errors back. You may also need to set up encryption information on your Unix system before you use it. Just be aware of this and ask your Unix systems administrator for help if you are in a jam.