What is SSH or Security SHell
SSH, which is an acronym for Secure SHell. Shell means command line and security shell means the process by which shell is accessed remotely in a network using a secured way.
Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client .
Why it is so important concerning security
I think many of you already have heard about Telnet. Telnet is used to access shell account remotely in a network. But Telnet is not a great idea since every data of receiving and sending in Telnet system happens in a plain text format which is easily visible or understandable to your local area network or any device connected to this network.
This means any devil who sniff in-between can get your user name, password easily. It may possible for him to read email what you have read and commands that you run. Its a serious security breach.
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| The above picture courtesy from suso.com show how a telnet session can be viewed by anyone on the network by using a sniffing program like Ethereal (now called Wireshark) or tcpdump. This type of security breach is called MITM or man in the middle attack. The first diagram shows user jsmith or suppose you logging in to a remote server through a telnet connection. He or you type his/your username jsmith and password C0lts06!, which are viewable by anyone who is using the same networks that he or you are using. |
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| The second picture is showing how the data in an encrypted connection like SSH is encrypted on the network and so cannot be read by anyone who doesn't have the session-negotiated keys or authentication to access. In this case at the second picture you are seeing some random encrypted code instead of username: jsmith and passwrd: COlts06! Remember what I said before ! In Telnet Username and password are visible in a plain text so you were seeing username: jsmith and passwrd: COlts06! But at SSH, username and pass are encrypted so you are seeing not any visible plain text but encrypted codes. |
For more understanding you can visit
http://en.wikipedia.org/wiki/Secure_Shell
http://www.openssh.org
http://www.ssh.com
My intention was to give clear idea about SSH. Therefore if you really understand this article, a thank you is much appreciated.
