VPNs Illustrated: Tunnels, VPNs, and IPsec

7. SSH

7.1 Introduction

Historically, telnet, ftp, and the BSD r-commands (rcp, rsh, rexec, and rlogin) have been used to handle interactive sessions and file transfers between a local and a remote host. Although these utilities are still popular and in widespread use, their severe security problems make them unsuitable for use in settings where security is a concern. For example, telnet and ftp provide no encryption or authentication services, so any data transferred using them is vulnerable to eavesdroppers using simple passive attacks. More seriously, these utilities send the user’s password as plaintext, allowing the attacker to recover it and subsequently log on to the remote system as the user.

The r-commands are even worse. They ...