Securing Remote Logins with OpenSSH Server

OpenSSH is the open source version of SSH, or Secure Shell. Connectivity tools such as Telnet and FTP are well-known, but they send data in plain text format, which can be intercepted by someone using another system on the same network, including the Internet. On the other hand, all data transferred using OpenSSH tools is encrypted, making it inherently more secure. The OpenSSH suite of tools includes ssh for securely logging in to a remote system and executing remote commands, scp for encrypting files while transferring them to a remote system, and sftp for secure FTP transfers. OpenSSH uses a server-client relationship. The system being connected to is referred to as the server. The system requesting the connection is referred to as the client. A system can be both an SSH server and a client. OpenSSH also has the added benefits of X11 forwarding and port forwarding. X11 forwarding, if enabled on both the server and client, allows users to display a graphical application from the system they are logged in to on the system they are logged in from. Port forwarding allows a connection request to be sent to one server but be forwarded to another server that actually accepts the request. This section discusses how to use OpenSSH, both from the server-side and the client-side.

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