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Download Day Day Up > Classic Shell Scripting By Nelson H.F. Beebe
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secure exchange of a randomly generated lengthy encryption key for use with any of several simpler and faster encryption algorithms. No user data is transmitted until the encrypted channel is established, and the standard encryption methods are well studied and believed to be quite secure; an attacker sees an apparently random stream of bytes in your packets, although source and destination address are still visible, and can be used for traffic analysis. Secure shell also creates a secure channel for X Window System data, protecting input keystrokes and window output from attackers. Of course, this won't help if the attacker sits between you and your computer: Internet cafes, keyboard sniffers, wireless networks, and thin clients can all open up avenues of attack that even the secure shell cannot protect against. Even the varying reflection of a monitor against a wall has been demonstrated to permit the screen image to be read by an attacker 80 meters away.[27] [26] See, for example, http://www.columbia.edu/kermit/, http://www.ssh.com/, and http://www.openssh.org/. For an indepth treatment of this important software SSH, The Secure Shell: The Definitive Guide(O'Reilly). [27] Markus Kuhn, Optical Time-Domain Eavesdropping Risks of CRT Displays, Proceedings: 2002 IEEE Symposium on Security and Privacy, 12-15 May, 2002, Berkeley, California, IEEE Computer Society Press, 2002, pp. 3-18, ISBN 0-7695-1543-6. Also available at http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf. < Day Day Up >
