SSH

SSH is a set of protocols which allow you to securely connect to remote systems either interactively or to transfer files. In doing so, SSH can use public/private key pairs for strong authentication, or at the discression of the remote administrator, it may allow the use of other methods including password entry, one time keys and others. However, unlike the programs rlogin and telnet and their historical protocols, the SSH protocol quickly shifts to an encrypted session before any sensitive data such as passwords are transferred. As a result, SSH sessions are more secure, but at the cost of the computational overhead necessary to encrypt and decrypt the session.

Also available with SSH is the possibility of doing port forwarding, where additional encrypted connections can be established from either a local IP port to a remote host/port, or from a remote port back to a local host/port. As a result, SSH can be used to access services which may otherwise be blocked by firewalls not necessarily controlled by the user, but to do so in a way much more secure and flexible than just establishing rules on the interveining firewalls.

Many different implementations of SSH are available. Almost all versions of *NIX, such as the several flavors of BSD, and the many more numerous versions of Linux come with SSH as a part of the base installation. In many cases, these are derived from OpenSSH. In addition, PuTTY is a free and open implementation is available for Win32 platforms.