ssh (Secure Shell) and stelnet

ssh and stelnet are suites of programs that allow you to login to remote systems
and have a encrypted connection.
openssh is a suite of programs used as a secure replacement for rlogin, rsh and rcp.
It uses public-key cryptography to encrypt communications between two hosts, as
well as to authenticate users. It can be used to securely login to a remote host or copy
data between hosts, while preventing man-in-the-middle attacks (session hijacking)
and DNS spoofing. It will perform data compression on your connections, and secure
X11 communications between hosts.

There are several ssh implementiations now. The original commercial
implementation by Data Fellows can be found at The ssh home page can be found
at http://www.datafellows.com.
The excellent Openssh implementation is based on a early version of the datafellows
ssh and has been totally reworked to not include any patented or proprietary pieces.
It is free and under a BSD license. It can be found at: http://www.openssh.com.
There is also a open source project to re-implement ssh from the ground up called
"psst...". For more information see: http://www.net.lut.ac.uk/psst/
You can also use ssh from your Windows workstation to your Linux ssh server.
There are several freely available Windows client implementations, including the
one at http://guardian.htu.tuwien.ac.at/therapy/ssh/ as well as a commercial implementation
from DataFellows, at http://www.datafellows.com.
SSLeay is a free implementation of Netscape’s Secure Sockets Layer protocol, developed
by Eric Young. It includes several applications, such as Secure telnet, a module
for Apache, several databases, as well as several algorithms including DES, IDEA
and Blowfish.
Using this library, a secure telnet replacement has been created that does encryption
over a telnet connection. Unlike SSH, stelnet uses SSL, the Secure Sockets Layer protocol
developed by Netscape. You can find Secure telnet and Secure FTP by starting
with the SSLeay FAQ, available at http://www.psy.uq.oz.au/~ftp/Crypto/.
SRP is another secure telnet/ftp implementation. From their web page:
“"The SRP project is developing secure Internet software for free worldwide use.
Starting with a fully-secure Telnet and FTP distribution, we hope to supplant weak
networked authentication systems with strong replacements that do not sacrifice
user-friendliness for security. Security should be the default, not an option!" ”
For more information, go to http://www-cs-students.stanford.edu/~tjw/srp/