Linux Journal: The 101 Uses of OpenSSH: Part I

“This month we’ll cover ssh’s background and architecture,
how to build and/or install OpenSSH, how to use ssh as an encrypted
replacement for Telnet, how to set some basic ssh configuration
options and how to use scp for encrypted file transfers.
month I’ll cover RSA/DSA authentication, local port-forwarding,
remote-command-execution and other more advanced, and extremely
powerful functions of ssh/OpenSSH.”

“…a few years ago Finnish über-hacker Tatu Ylonen created
a mind-blowingly cool thing called the Secure Shell, or ssh. ssh is
a suite of tools that roughly correspond to Sun’s rsh, rcp and
rlogin commands, but with one very important difference: paranoia.
ssh lets you do everything rsh, rcp and rlogin do, using your
choice of libertarian-grade encryption and authentication methods.
But wait–there’s a catch–ssh version 1 relies heavily on RSA, an
excellent, but as we say, encumbered (patented) technology that
requires any application that uses it to be licensed (paid for)
unless it’s used in noncommercial settings (even in noncommercial
use ssh’s legality has always been murky, especially in the US).
But wait, you say, RSA’s US patents expired in September
2000–problem solved, right? Almost: Tatu’s got to earn a living,
so by the time RSA became less encumbered, ssh itself had become
more so as his company F-Secure tightened the licensing reins. In
fact, beginning with ssh version 2.0, unlicensed/free commercial
use (regardless of RSA issues) was no longer permitted. All this
despite Tatu’s sincere desire that ssh become an Internet standard,
one of the requirements of which is that at least one free
implementation be available.”

“Enter Theo de Raadt and the OpenBSD team. OpenBSD, of course,
is the ultra-secure offshoot of NetBSD, a free version of BSD UNIX.
Theo and our open-source brethren in the OpenBSD project wanted to
include ssh in OpenBSD 2.6 but were wary of ssh’s various
encumbrances. When they learned that the Swedish programmer Bjoern
Groenvall had released an improved version of ssh, 1.2.12 (the last
completely free-except-for-RSA version of Ylonen’s ssh), the
OpenBSD guys rapidly got to work on updating and adapting it for a
larger audience. OpenSSH has been part of OpenBSD ever since and is
now portable to most versions of UNIX.”


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