From jkwilli2@unity.ncsu.edu Wed Dec 17 23:17:14 2003 From: Ken Williams To: cypherpunks-legacy@lists.cpunks.org Subject: BEATING THE TEMPEST Date: Wed, 17 Dec 2003 23:17:14 +0000 Message-ID: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="===============9004081895485691474==" --===============9004081895485691474== Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable -----BEGIN PGP SIGNED MESSAGE----- BEATING THE TEMPEST: December 1998 Just because you're paranoid doesn't mean they aren't out to get you. Most co= mputer users would be startled to realize that somebody=20 parked outside their home with the right kind of (very expensive) receiving e= quipment can read the data that appear on their computer=20 screens. The receiver uses the monitor's radio emanations to reconstruct the = screen's contents. The U.S.=20 Department of State and other organizations spend a fortune buying shield= ed hardware to defeat these signals, known as Tempest radiation, after the code na= me for a government program aimed at tackling it. Now Ross Anderson, a computer scientist at the University of Cambridge, and g= raduate student Markus=20 G. Kuhn say they have developed methods for controlling Tempest radiation. Wh= at's different about their techniques is that they run in=20 software, making them much cheaper and easier to deploy. The story began, Anderson says, when Microsoft made its $20-million investmen= t in Cambridge's=20 computer science lab and said the company was particularly interested in ways= to control software piracy. Most approaches call for some=20 kind of copy protection; Anderson's idea was to design something that would e= nable detection of offenders rather than prohibit copying,=20 which is a nuisance loathed by consumers. Their concept was to make computer = screens broadcast the serial number of the software in use.=20 In principle, properly equipped vans could patrol business districts looking = for copyright infringements. In researching the broadcast=20 idea, Anderson and Kuhn came up with fundamental discoveries about Tempest. In particular, they observed that emissions relating to screen content are mo= stly found in the higher bands--above 30 megahertz, in the=20 UHF and VHF bands. So altering those frequencies could change the Tempest rad= iation. Anderson and his colleagues have fashioned a couple of prototypes that rely o= n different frequency-alteration methods. One of the lab's=20 prototypes, built using a black-and-white video display capable of monitoring= and receiving Tempest radiation, filters the top=20 frequencies. As a result, the fonts become unreadable to the eavesdropping re= ceiver. On-screen, the fonts look comfortably legible and=20 nearly normal. Filtering text requires display software that supports graysca= le representation of fonts, but most computers have this=20 ability. Therefore, Anderson believes this technology could be easily built i= nto existing machines, although the fonts' interference with=20 graphics makes it more likely they would be included in a security product th= an in, say, a general operating system. The second prototype takes advantage of the display technique known as dither= ing, a method of mixing extra colors from a limited palette=20 based on the principle that if the dots that make up the display are small en= ough, the human eye will perceive the mix as a solid color.=20 Given a monitor of today's high resolutions, the human eye cannot distinguish= between a solid medium gray and a pattern of=20 black-and-white pixels that adds up to the same gray. But the pattern of blac= k and white is much easier for the snooping receiver to=20 detect, one consequence being that the computer could be programmed to broadc= ast a different signal from the one that actually appears on=20 the screen. The demonstration on display at Anderson's lab serves as a nice e= xample, in which the word "Oxford" on the display appears as=20 "Cambridge" on the receiver. Aside from stemming electronic eavesdropping, these prototypes could open the= way to new types of security attacks on computers, Anderson=20 and Kuhn suggest. A virus could be designed to find and then broadcast inform= ation stored on a machine without a user's knowledge. The=20 game of spy versus spy goes on. WENDY M. GROSSMAN is a freelance writer based in London. - ---------- yeah, yeah....it's old news, but a new article, and from=20 "Unscientific Scamerican" no less. Regards, Ken Williams Packet Storm Security http://www.Genocide2600.com/~tattooman/ E.H.A.P. Head of Operations http://www.ehap.org/ ehap(a)ehap.org NC State CS Dept http://www.csc.ncsu.edu/ jkwilli2(a)unity.ncsu.edu PGP DSS/DH/RSA Keys http://www4.ncsu.edu/~jkwilli2/pgpkey/ _____________________________________________________________ Get Your Private, Free, Encrypted Email at http://www.nsa.gov -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 5.0i for non-commercial use Charset: noconv iQEVAwUBNlAdPZDw1ZsNz1IXAQFNNQf/Q23VtU0+xj6Cq4Eppm5TMqwd7DzE0k62 wR+hCqa7FXEEHbr+RSK7vdL3PmtaF6zUYAy9+Yn2C7lHnotVCRJ65hEIC+sDx5Rg AdF9Y8wCiGUenAeFr54uSz8amo6aKXB6eoAFxJSwqp2xsQMqn9rGcEMOUOLi/OtO b5Lj+e8gk9RREgjhPEIhHeVxqeJsKzB+A35FYr46T8du5+IYQyQucWGJEf/5zLga Cr1N/8oPOXU4x+o0eUQmafvWNTyvuScu9+QdLyKxhgeRQyOe7U/TljNcp6kJs0q8 D+qlEADpzbKdm8uNAv0e7xRDe5J+CCdEKhUzs0A76TgXR7g6c+Czjg=3D=3D =3DKXvR -----END PGP SIGNATURE----- --===============9004081895485691474==--