SSH Protocols and Secure Shell

  Secure Shell is the secure login program that revolutionized remote
management of networks hosts over the Internet.  It is a powerful,
very easy-to-use program that uses strong cryptography for protecting
all transmitted confidential data, including passwords, binary files,
and administrative commands.

  SSH Communications Security is the developer of the Secure Shell and
the SSH protocol, technologies that are the de-facto standard for
encrypted terminal connections on the Internet. The benefits of SSH
include 

o Automatic authentication of users, no passwords sent in cleartext to
  prevent the stealing of passwords.

o Multiple strong authentication methods that prevent such security
  threats as spoofing identity.

o Authentication of both ends of connection, the server and the client
  are authenticated to prevent identity spoofing, trojan horses, etc. 

o Automatic authentication using agents to enable strong
  authentication to multiple systems with a single-sign-on.

o Encryption and compression of data for security and speed.

o Secure file transfer.

o Tunneling and encryption of arbitrary connections.


See http://www.ssh.fi/ for more details.