Eavesdropping On the Electromagnetic Emanations of Digital Equipment:
The Laws of Canada, England and the United States (1993)

This document is a rough draft. The Legal Sections are overviews. They will be significantly expanded in the next version.

We in this country, in this generation, are -- by destiny rather than choice -- the watchmen on the walls of world freedom.[1] -President John F. Kennedy

In the novel 1984, George Orwell foretold a future where individuals had no expectation of privacy because the state monopolized the technology of spying. The government watched the actions of its subjects from birth to death. No one could protect himself because surveillance and counter- surveillance technology was controlled by the government. This note explores the legal status of a surveillance technology ruefully known as TEMPEST[2]. Using TEMPEST technology the information in any digital device may be intercepted and reconstructed into useful intelligence without the operative ever having to come near his target. The technology is especially useful in the interception of information stored in digital computers or displayed on computer terminals. The use of TEMPEST is not illegal under the laws of the United States[3], or England. Canada has specific laws criminalizing TEMPEST eavesdropping but the laws do more to hinder surveillance countermeasures than to prevent TEMPEST surveillance. In the United States it is illegal for an individual to take effective counter-measures against TEMPEST surveillance. This leads to the conundrum that it is legal for individuals and the government to invade the privacy of others but illegal for individuals to take steps to protect their privacy. The author would like to suggest that the solution to this conundrum is straightforward. Information on protecting privacy under TEMPEST should be made freely available; TEMPEST Certified equipment should be legally available; and organizations possessing private information should be required by law to protect that information through good computer security practices and the use of TEMPEST Certified equipment.


Spying is divided by professionals into two main types: human intelligence gathering (HUMINT) and electronic intelligence gathering (ELINT). As the names imply, HUMINT relies on human operatives, and ELINT relies on technological operatives. In the past HUMINT was the sole method for collecting intelligence.[4] The HUMINT operative would steal important papers, observe troop and weapon movements[5], lure people into his confidences to extract secrets, and stand under the eavesdrip[6] of houses, eavesdropping on the occupants. As technology has progressed, tasks that once could only be performed by humans have been taken over by machines. So it has been with spying. Modern satellite technology allows troop and weapons movements to be observed with greater precision and from greater distances than a human spy could ever hope to accomplish. The theft of documents and eavesdropping on conversations may now be performed electronically. This means greater safety for the human operative, whose only involvement may be the placing of the initial ELINT devices. This has led to the ascendancy of ELINT over HUMINT because the placement and monitoring of ELINT devices may be performed by a technician who has no training in the art of spying. The gathered intelligence may be processed by an intelligence expert, perhaps thousands of miles away, with no need of field experience. ELINT has a number of other advantages over HUMINT. If a spy is caught his existence could embarrass his employing state and he could be forced into giving up the identities of his compatriots or other important information. By its very nature, a discovered ELINT device (bug) cannot give up any information; and the ubiquitous nature of bugs provides the principle state with the ability to plausibly deny ownership or involvement. ELINT devices fall into two broad categories: trespassatory and non-trespassatory. Trespassatory bugs require some type of trespass in order for them to function. A transmitter might require the physical invasion of the target premises for placement, or a microphone might be surreptitiously attached to the outside of a window. A telephone transmitter can be placed anywhere on the phone line, including at the central switch. The trespass comes either when it is physically attached to the phone line, or if it is inductive, when placed in close proximity to the phone line. Even microwave bugs require the placement of the resonator cone within the target premises.[7] Non-trespassatory ELINT devices work by receiving electromagnetic radiation (EMR) as it radiates through the aether, and do not require the placement of bugs. Methods include intercepting[8] information transmitted by satellite, microwave, and radio, including mobile and cellular phone transmissions. This information was purposely transmitted with the intent that some intended person or persons would receive it. Non-trespassatory ELINT also includes the interception of information that was never intended to be transmitted. All electronic devices emit electromagnetic radiation. Some of the radiation, as with radio waves, is intended to transmit information. Much of this radiation is not intended to transmit information and is merely incidental to whatever work the target device is performing.[9] This information can be intercepted and reconstructed into a coherent form. With current TEMPEST technology it is possible to reconstruct the contents of computer video display terminal (VDU) screens from up to a kilometer distant[10]; reconstructing the contents of a computer's memory or the contents of its mass storage devices is more complicated and must be performed from a closer distance.[11] The reconstruction of information via EMR, a process for which the United States government refuses to declassify either the exact technique or even its name[12], is not limited to computers and digital devices but is applicable to all devices that generate electromagnetic radiation.[13] TEMPEST is especially effective against VDUs because they produce a very high level of EMR.[14]

ELINT is not limited to governments. It is routinely used by individuals for their own purposes. Almost all forms of ELINT are available to the individual with either the technological expertise or the money to hire someone with the expertise. Governments have attempted to criminalize all use of ELINT by their subjects--to protect the privacy of both the government and the population.


In the United States, Title III of the Omnibus Streets and Crimes Act of 1968[15] criminalizes trespassatory ELINT as the intentional interception of wire communications.[16] As originally passed, Title III did not prohibit non- trespassatory ELINT,[17] because courts found that non-wire communication lacked any expectation of p2IIIrivacy.[18] The Electronic Communications Privacy Act of 1986[19] amended Title III to include non-wire communication. ECPA was specifically designed to include electronic mail, inter- computer communications, and cellular telephones. To accomplish this, the expectation of privacy test was eliminated.[20] As amended, Title III still outlaws the electronic interception of communications. The word "communications" indicates that someone is attempting to communicate something to someone; it does not refer to the inadvertent transmission of information. The reception and reconstruction of emanated transient electromagnetic pulses (ETEP), however, is based on obtaining information that the target does not mean to transmit. If the ETEP is not intended as communication, and is therefore not transmitted in a form approaching current communications protocols, then it can not be considered communications as contemplated by Congress when it amended Title III. Reception, or interception, of emanated transient electromagnetic pulses is not criminalized by Title III as amended.


In England the Interception of Communications Act 1985[21] criminalizes the tapping of communications sent over public telecommunications lines.[22] The interception of communications on a telecommunication line can take place with a physical tap on the line, or the passive interception of microwave or satellite links.[23] These forms of passive interception differ from TEMPEST ELINT because they are intercepting intended communication; TEMPEST ELINT intercepts unintended communication. Eavesdropping on the emanations of computers does not in any way comport to tapping a telecommunication line and therefore falls outside the scope of the statute.[24]


Canada has taken direct steps to limit eavesdropping on computers. The Canadian Criminal Amendment Act of 1985 criminalized indirect access to a computer service.[25] The specific reference to an "electromagnetic device" clearly shows the intent of the legislature to include the use of TEMPEST ELINT equipment within the ambit of the legislation. The limitation of obtaining "any computer service" does lead to some confusion. The Canadian legislature has not made it clear whether "computer service" refers to a computer service bureau or merely the services of a computer. If the Canadians had meant access to any computer, why did they refer to any "computer service". This is especially confusing considering the al- encompassing language of (b) 'any function of a computer system'. Even if the Canadian legislation criminalizes eavesdropping on all computers, it does not solve the problem of protecting the privacy of information. The purpose of criminal law is to control crime.[26] Merely making TEMPEST ELINT illegal will not control its use. First, because it is an inherently passive crime it is impossible to detect and hence punish. Second, making this form of eavesdropping illegal without taking a proactive stance in controlling compromising emanations gives the public a false sense of security. Third, criminalizing the possession of a TEMPEST ELINT device prevents public sector research into countermeasures. Finally, the law will not prevent eavesdropping on private information held in company computers unless disincentives are given for companies that do not take sufficient precautions against eavesdropping and simple, more common, information crimes.[27]


TEMPEST ELINT is passive. The computer or terminal emanates compromising radiation which is intercepted by the TEMPEST device and reconstructed into useful information. Unlike conventional ELINT there is no need to physically trespass or even come near the target. Eavesdropping can be performed from a nearby office or even a van parked within a reasonable distance. This means that there is no classic scene of the crime; and little or no chance of the criminal being discovered in the act.[28] If the crime is discovered it will be ancillary to some other investigation. For example, if an individual is investigated for insider trading a search of his residence may yield a TEMPEST ELINT device. The device would explain how the defendant was obtaining insider information; but it was the insider trading, not the device, that gave away the crime. This is especially true for illegal TEMPEST ELINT performed by the state. Unless the perpetrators are caught in the act there is little evidence of their spying. A trespassatory bug can be detected and located; further, once found it provides tangible evidence that a crime took place. A TEMPEST ELINT device by its inherent passive nature leaves nothing to detect. Since the government is less likely to commit an ancillary crime which might be detected there is a very small chance that the spying will ever be discovered. The only way to prevent eavesdropping is to encourage the use of countermeasures: TEMPEST Certified[29] computers and TEMPEST Certified equipment is theoretically secure against TEMPEST eavesdropping. terminals. In merely making TEMPEST ELINT illegal the public is given the false impression of security; they lulled into believing the problem has been solved. Making certain actions illegal does not prevent them from occurring. This is especially true for a TEMPEST ELINT because it is undetectable. Punishment is an empty threat if there is no chance of being detected; without detection there can be no apprehension and conviction. The only way to prevent some entity from eavesdropping on one's computer or computer terminal is for the equipment not to give off compromising emanation; it must be TEMPEST Certified. The United States can solve this problem by taking a proactive stance on compromising emanations. The National Institute of Standards and Technology (NIST[30]) is in charge of setting forth standards of computer security for the private sector. NIST is also charged with doing basic research to advance the art of computer security. Currently NIST does not discuss TEMPEST with the private sector. For privacy's sake, this policy must be changed to a proactive one. The NIST should publicize the TEMPEST ELINT threat to computer security and should set up a rating system for level of emanations produced by computer equipment.[31] Further, legislation should be enacted to require the labeling of all computer equipment with its level of emanations and whether it is TEMPEST Certified. Only if the public knows of the problem can it begin to take steps to solve it. Title III makes possession of a surveillance device a crime, unless it is produced under contract to the government. This means that research into surveillance and counter-surveillance equipment is monopolized by the government and a few companies working under contract withthe government. If TEMPEST eavesdropping is criminalized, then possession of TEMPEST ELINT equipment will be criminal. Unfortunately,this does not solve the problem. Simple TEMPEST ELINT equipment is easy to make. For just a few dollars many older television sets can be modified to receive and reconstruct EMR. For less than a hundred dollars a more sophisticated TEMPEST ELINT receiver can be produced[32]. The problem with criminalizing the possession of TEMPEST ELINT equipment is not just that the law will have little effect on the use of such equipment, but that it will have a negative effect on counter-measures research. To successfully design counter-measures to a particular surveillance technique it is vital to have a complete empirical understanding of how that technique works. Without the right to legally manufacture a surveillance device there is no possible way for a researcher to have the knowledge to produce an effective counter-measures device. It is axiomatic: without a surveillance device, it is impossible to test a counter-measures device. A number of companies produce devices to measure the emanations from electrical equipment. Some of these devices are specifically designed for bench marking TEMPEST Certified equipment. This does not solve the problem. The question arises: how much radiation at a particular frequency is compromising? The current answer is to refer to NACSIM 5100A. This document specifies the emanations levels suitable for Certification. The document is only available to United States contractors having sufficient security clearance and an ongoing contract to produce TEMPEST Certified computers for the government. Further, the correct levels are specified by the NSA and there is no assurance that, while these levels are sufficient to prevent eavesdropping by unfriendly operatives, equipment certified under NACSIM 5100A will have levels low enough to prevent eavesdropping by the NSA itself. The accessibility of supposedly correct emanations levels does not solve the problem of preventing TEMPEST eavesdropping. Access to NACSIM 5100A limits the manufacturer to selling the equipment only to United States governmental agencies with the need to process secret information.[33] Without the right to possess TEMPEST ELINT equipment manufacturers who wish to sell to the public sector cannot determine what a safe level of emanations is. Further those manufacturers with access to NACSIM 5100A should want to verify that the levels set out in the document are, in fact, low enough to prevent interception. Without an actual eavesdropping device with which to test, no manufacturer will be able to produce genuinely uncompromising equipment. Even if the laws allow ownership of TEMPEST Certified equipment by the public, and even if the public is informed of TEMPEST's threat to privacy, individuals' private information will not necessarily by protected. Individuals may choose to protect their own information on their own computers. Companies may choose whether to protect their own private information. But companies that hold the private information of individuals must be forced to take steps to protect that information. In England the Data Protection Act 1984[34] imposes sanctions against anyone who stores the personal information[35] on a computer and fails to take reasonable measures to prevent disclosure of that information. The act mandates that personal data may not be stored in any computer unless the computer bureau or data user[36] has registered under the act.[37] This provides for a central registry and the tracking of which companies or persons maintain databases of personal information. Data users and bureaux must demonstrate a need and purpose behind their possession of personal data. The act provides tort remedies to any person who is damaged by disclosure of the personal data.[38] Reasonable care to prevent the disclosure is a defense.[39] English courts have not yet ruled what level of computer security measures constitute reasonable care. Considering the magnitude of invasion possible with TEMPEST ELINT it should be clear by now that failure to use TEMPEST Certified equipment is prima facie unreasonable care. The Remedies section of the act provides incentive for these entities to provide successful protection of person data from disclosure or illicit access. Failure to protect the data will result in monetary loss. This may be looked at from the economic efficiency viewpoint as allocating the cost of disclosure the persons most able to bear those costs, and also most able to prevent disclosure. Data users that store personal data would use TEMPEST Certified equipment as part of their computer security plan, thwarting would-be eavesdroppers. The Data Protection Act 1984 allocates risk to those who can bear it best and provides an incentive for them to keep other individuals' data private. This act should be adopted by the United States as part of a full-spectrum plan to combat TEMPEST eavesdropping. Data users are in the best position to prevent disclosure through proper computer security. Only by making them liable for failures in security can we begin to rein in TEMPEST ELINT.

VII Recommendations

Do not criminalize TEMPEST ELINT. Most crimes that TEMPEST ELINT would aid, such a insider trading, are already illegal; the current laws are adequate. The National Institute of Standards and Technology should immediately begin a program to educate the private sector about TEMPEST. Only if individuals are aware of the threat can they take appropriate precautions or decide whether any precautions are necessary. Legislation should be enacted to require all electronic equipment to prominently display its level of emanations and whether it is TEMPEST Certified. If individuals are to choose to protect themselves they must be able to make a informed decision regarding how much protection is enough. TEMPEST Certified equipment should be available to the private sector. The current ban on selling to non- governmental agencies prevents individuals who need to protect information from having the technology to do so.

Possession of TEMPEST ELINT equipment should not be made illegal. The inherently passive nature and simple design of TEMPEST ELINT equipment means that making its possession illegal will not deter crime; the units can be easily manufactured and are impossible to detect. Limiting their availability serves only to monopolize the countermeasures research, information, and equipment for the government; this prevents the testing, design and manufacture of counter-measures by the private sector. Legislation mirroring England's Data Protection Act 1984 should be enacted. Preventing disclosure of personal data can only be accomplished by giving those companies holding the data a reason to protect it. If data users are held liable for their failure to take reasonable security precautions they will begin to take reasonable security precautions, including the use of TEMPEST Certified equipment. 33.

FTEMPEST-shielding --------- Preventing Electromagnetic Eavesdropping

A note discussing the prevention of electromagnetic eavesdropping of personal computers. Grady Ward public key verification by PK server, finger, or by request Version 1.0 22 March 93 TEMPEST is the code name for technology related to limiting unwanted electromagnetic emissions from data processing and related equipment. Its goal is to limit an opponent's capability to collect information about the internal data flow of computer equipment. Most information concerning TEMPEST specifications is classified by the United States Government and is not available for use by its citizens. The reason why TEMPEST technology is particularly important for computers and other data processing equipment is the kinds of signals components in a computer use to talk to each other ("square waves") and their clock speeds (measured in megahertz) produce a particularly rich set of unintentional signals in a wide portion of the electromagnetic spectrum. Because the spurious emissions occupy so wide a portion of that spectrum, technologies used to block one portion of the spectrum (as pulling the shades closed on a window to stop the visible light portion) are not necessarily effective in another portion. Unintentional emissions from a computer system can be captured and processed to reveal information about the target systems from simple levels of activity to even remotely copying keystrokes or capturing monitor information. It is speculated that poorly protected systems can be effectively monitored up to the order of one kilometer from the target equipment. This note will examine some practical aspects of reducing the susceptibility of your personal computer equipment to remote monitoring using easily-installed, widely available after-market components. I One way of looking at TEMPEST from the lay person's point-of-view is that it is virtually identical to the problem of preventing electromagnetic interference ("EMI") by your computer system to others' radios, televisions, or other consumer electronics. That is, preventing the emission of wide-band radio "hash" from your computers, cabling, and peripherals both prevents interference to you and your neighbors television set and limits the useful signal available to a person surreptitiously monitoring. Viewing the problem in this light, there are quite a few useful documents available form the government and elsewhere attacking this problem and providing a wealth of practical solutions and resources.

Very useful for the lay person are: Radio Frequency Interference: How to Find It and Fix It. Ed Hare, KA1CV and Robert Schetgen, KU7G, editors The American Radio Relay League, Newington , CT ISBN 0-87259-375-4 (c) 1991, second printing 1992 Federal Communications Commission Interference Handbook (1991) FCC Consumers Assistance Branch Gettysburg, PA 17326 717-337-1212 and MIL-STD-188-124B in preparation (includes information on military shielding of tactical communications systems) Superintendent of Documents US Government Printing Office Washington, DC 20402 202-783-3238 Information on shielding a particular piece of consumer electronic equipment may be available from the: Electronic Industries Association (EIA) 2001 Pennsylvania Ave NW Washington, DC 20006 Preventing unintended electromagnetic emissions is a relative term. It is not feasible to reduce to zero all unintended emissions. My personal goal, for example, might be to reduce the amount and quality of spurious emission until the monitoring van a kilometer away would have to be in my front yard before it could effectively eavesdrop on my computer. Apartment dwellers with unknown neighbors only inches away (through a wall) might want to even more carefully adopt as many of the following suggestions as possible since signal available for detection decreases as approximately the inverse square of the distance from the monitoring equipment to your computer. II Start with computer equipment that meets modern standards for emission. In the United States, the "quietest" standard for computers and peripherals is known as the "class B" level. (Class A level is a less stringent standard for computers to be use in a business environment.). You want to verify that all computers and peripherals you use meet the class B standard which permits only one-tenth the power of spurious emissions than the class A standard. If you already own computer equipment with an FCC ID, you can find out which standard applies. Contact the FCC Consumers Assistance Branch at 1-717-337-1212 for details in accessing their database. Once you own good equipment, follow the manufacturer's recommendations for preserving the shielding integrity of the system. Don't operated the system with the cover off and keep "slot covers" in the back of the computer in place. III Use only shielded cable for all system interconnections. A shielded cable surrounds the core of control wires with a metal braid or foil to keep signals confined to that core. In the late seventies it was common to use unshielded cable such as "ribbon" cable to connect the computer with, say, a diskette drive. Unshielded cable acts just like an antenna for signals generated by your computer and peripherals. Most computer manufacturer supply shielded cable for use with their computers in order to meet FCC standards. Cables bought from third-parties are an unknown and should be avoided (unless you are willing to take one apart to see for yourself!) Try to avoid a "rat's nest" of wire and cabling behind your equipment and by keeping all cables as short as possible. You want to reduced the length of unintended antennas and to more easily predict the likely paths of electric and magnetic coupling from cable to cable so that it can be more effectively filtered. IV Block radiation from the power cord(s) into the house wiring. Most computers have an EMI filter built into their body where the AC line cord enters the power supply. This filter is generally insufficient to prevent substantial re-radiation of EMI voltages back into the power wiring of your house and neighborhood. To reduce the power retransmitted down the AC power cords of your equipment, plug them in to special EMI filters that are in turn plugged into the wall socket. I use a model 475-3 overvoltage and EMI filter manufactured by Industrial Communication Engineers, Ltd. P.O. Box 18495 Indianapolis, IN 46218-0495 1-800-ICE-COMM ask for their package of free information sheets (AC and other filters mentioned in this note are available from a wide variety of sources including, for example, Radio Shack. I am enthusiastic about ICE because of the "over-designed" quality of their equipment. Standard disclaimers apply.) This particular filter from ICE is specified to reduce retransmission of EMI by a factor of at least 1000 in its high-frequency design range. Although ideally every computer component using an AC line cord ought to be filtered, it is especially important for the monitor and computer CPU to be filtered in this manner as the most useful information available to opponents is believed to come from these sources. V Block retransmitted information from entering your fax/modem or telephone line. Telephone line is generally very poorly shielded. EMI from your computer can be retransmitted directly into the phone line through your modem or can be unintentionally picked up by the magnetic portion of the EMI spectrum through magnetic induction from power supplies or the yoke of your cathode ray tube "CRT" monitor. To prevent direct retransmission, EMI filters are specifically designed for modular telephone jacks to mount at the telephone or modem, and for mounting directly at the service entrance to the house. Sources of well-designed telephone-line filter products include ICE (address above) and K-COM Box 82 Randolph, OH 44265 216-325-2110 Your phone company or telephone manufacturer may be able to supply you with free modular filters, although the design frequencies of these filters may not be high enough to be effective through much of the EMI spectrum of interest. Keep telephone lines away from power supplies of computers or peripherals and the rear of CRTs: the magnetic field often associated with those device can inductively transfer to unshielded lines just as if the telephone line were directly electrically connected to them. Since this kind of coupling decreases rapidly with distance, this kind of magnetic induction can be virtually eliminated by keeping as much distance (several feet or more) as possible between the power supply/monitor yoke and cabling. VI Use ferrite toroids and split beads to prevent EMI from escaping on the surface of your cables. Ferrites are magnetic materials that, for certain ranges of EMI frequencies, attenuate the EMI by causing it to spend itself in heat in the material rather than continuing down the cable. They can be applied without cutting the cable by snapping together a "split bead" form over a thick cable such as a power cord or by threading thinner cable such as telephone several times around the donut-shaped ferrite form. Every cable leaving your monitor, computer, mouse, keyboard, and other computer peripherals should have at least one ferrite core attentuator. Don't forget the telephone lines from your fax, modem, telephone or the unshielded DC power cord to your modem. Ferrites are applied as close to the EMI emitting device as possible so as to afford the least amount of cable that can act as an antenna for the EMI. Good sources for ferrite split beads and toroids include Amidon Associates, Inc. P.O. Box 956 Torrance, CA 90508 310-763-5770 (ask for their free information sheet) Palomar Engineers P.O. Box 462222 Escondido, CA 92046 619-747-3343 (ask for their free RFI information sheet) and Radio Shack. VII Other practical remedies. Other remedies that are somewhat more difficult to correctly apply include providing a good EMI "ground" shield for your computer equipment and other more intrusive filters such as bypass capacitor filters. You probably ought not to think about adding bypass capacitors unless you are familiar with electronic circuits and digital design. While quite effective, added improperly to the motherboard or cabling of a computer they can "smooth out" the square wave digital waveform -- perhaps to the extent that signals are interpreted erroneously causing mysterious "crashes" of your system. In other cases, bypass capacitors can cause unwanted parasitic oscillation on the transistorized output drivers of certain circuits which could damage or destroy those circuits in the computer or peripherals. Also, unlike ferrite toroids, adding capacitors requires actually physically splicing them in or soldering them into circuits. This opens up the possibility of electric shock, damage to other electronic components or voiding the warranty on the computer equipment. A good EMI ground is difficult to achieve. Unlike an electrical safety ground, such as the third wire in a three-wire AC power system, the EMI ground must operate effectively over a much wider part of the EMI spectrum. This effectiveness is related to a quality known as electrical impedance. You desire to reduce the impedance to as low a value as possible over the entire range of EMI frequencies. Unlike the AC safety ground, important factors in achieving low impedance include having as short a lead from the equipment to a good EMI earth ground as possible (must be just a few feet); the gauge of the connecting lead (the best EMI ground lead is not wire but woven grounding "strap" or wide copper flashing sheets; and the physical coupling of the EMI into the actual earth ground. An 8 ft. copper-plated ground may be fine for AC safety ground, but may present appreciable impedance resistance to an EMI voltage. Much better would be to connect a network of six to eight copper pipes arranged in a six-foot diameter circle driven in a foot or two into the ground, electrically bonded together with heavy ground strap and connected to the equipment to be grounded via a short (at most, several feet), heavy (at least 3/4-1" wide) ground strap. If you can achieve a good EMI ground, then further shielding possibilities open up for you such as surrounding your monitor and computer equipment in a wire-screen Faraday cage. You want to use mesh rather than solid sheet because you must preserve the free flow of cooling air to your equipment. Buy aluminum (not nylon) screen netting at your local hardware store. This netting typically comes in rolls 36" wide by several feet long. Completely surround your equipment you want to reduce the EMI being careful to make good electrical bonds between the different panels of netting and your good earth ground. I use stainless steel nuts, bolts, and lock washers along with special non-oxidizing electrical paste (available from Electrical contractors supply houses or from ICE) to secure my ground strapping to my net "cages". A good Faraday cage will add several orders of magnitude of EMI attenuation to your system. VIII Checking the effectiveness of your work. It is easy to get a general feeling about the effectiveness of your EMI shielding work with an ordinary portable AM radio. Bring it very close to the body of your computer and its cables in turn. Ideally, you should not hear an increased level of static. If you do hear relatively more at one cable than at another, apply more ferrite split beads or obtain better shielded cable for this component. The practice of determining what kind of operating system code is executing by listening to a nearby AM radio is definitely obsolete for an well-shielded EMI-proof system! To get an idea of the power and scope of your magnetic field emissions, an ordinary compass is quite sensitive in detecting fields. Bring a compass within a few inches of the back of your monitor and see whether it is deflected. Notice that the amount of deflection decreases rapidly with distance. You want to keep cables away from magnetic sources about as far as required not to see an appreciable deflection on the compass. VIIII Summary If you start with good, shielded equipment that has passed the FCC level B emission standard then you are off to a great start. You may even be able to do even better with stock OEM equipment by specifying "low-emission" monitors that have recently come on the market in response to consumer fears of extremely low frequency ("ELF") and other electromagnetic radiation. Consistently use shielded cables, apply filtering and ferrite toroids to all cabling entering or leaving your computer equipment. Finally, consider a good EMI ground and Faraday cages. Beyond this there are even more effective means of confining the electrical and magnetic components of your system through the use of copper foil adhesive tapes, conductive paint sprays, "mu metal" and other less common components.

1. Undelivered speech of President John F. Kennedy, Dallas Citizens Council (Nov. 22, 1963) 35-36.

2. TEMPEST is an acronym for Transient Electromagnetic Pulse Emanation Standard. This standard sets forth the official views of the United States on the amount of electromagnetic radiation that a device may emit without compromising the information it is processing. TEMPEST is a defensive standard; a device which conforms to this standard is referred to as TEMPEST Certified. The United States government has refused to declassify the acronym for devices used to intercept the electromagnetic information of non-TEMPEST Certified devices. For this note, these devices and the technology behind them will also be referred to as TEMPEST; in which case, TEMPEST stands for Transient Electromagnetic Pulse Surveillance Technology. The United States government refuses to release details regarding TEMPEST and continues an organized effort to censor the dissemination of information about it. For example the NSA succeeded in shutting down a Wang Laboratories presentation on TEMPEST Certified equipment by classifying the contents of the speech and threatening to prosecute the speaker with revealing classified information. [cite coming].

3. This Note will not discuses how TEMPEST relates to the Warrant Requirement under the United States Constitution. Nor will it discuss the Constitutional exclusion of foreign nationals from the Warrant Requirement.

4. HUMINT has been used by the United States since the Revolution. "The necessity of procuring good intelligence is apparent & need not be further urged -- All that remains for me to add is, that you keep the whole matter as secret as possible. For upon Secrecy, Success depends in Most Enterprises of the kind, and for want of it, they are generally defeated, however well planned & promising a favorable issue." Letter of George Washington (Jul. 26, 1777).

5. "... I wish you to take every possible pains in your powers, by sending trusty persons to Staten Island in whom you can confide, to obtain Intelligence of the Enemy's situation & numbers -- what kind of Troops they are, and what Guards they have -- their strength & where posted." Id.

6. Eavesdrip is an Anglo-Saxon word, and refers to the wide overhanging eaves used to prevent rain from falling close to a house's foundation. The eavesdrip provided "a sheltered place where one could hide to listen clandestinely to conversation within the house." W. MORRIS & M. MORRIS, MORRIS DICTIONARY OF WORD AND PHRASE ORIGINS, 198 (1977).

7. Pursglove, How Russian Spy Radios Work, RADIO ELECTRONICS, 89-91 (Jan 1962).

8. Interception is an espionage term of art and should be differentiated from its more common usage. When information is intercepted, the interceptor as well as the intended recipient receive the information. Interception when not used as a term of art refers to one person receiving something intended for someone else; the intended recipient never receives what he was intended to receive.

9. There are two types of emissions, conducted and radiated. Radiated emissions are formed when components or cables act as antennas for transmit the EMR; when radiation is conducted along cables or other connections but not radiated it is referred to as "conducted". Sources include cables, the ground loop, printed circuit boards, internal wires, the power supply to power line coupling, the cable to cable coupling, switching transistors, and high-power amplifiers. WHITE & M. MARDIGUIAN, EMI CONTROL METHODOLOGY AND PROCEDURES,

10.1 (1985). "[C]ables may act as an antenna to transmit the signals directly or even both receive the signals and re-emit them further away from the source equipment. It is possible that cables acting as an antenna in such a manner could transmit the signals much more efficiently than the equipment itself...A similar effect may occur with metal pipes such as those for domestic water supplies. ... If an earthing [(grounding)] system is not installed correctly such that there is a path in the circuit with a very high resistance (for example where paint prevents conduction and is acting as an insulator), then the whole earthing system could well act in a similar fashion to an antenna. ... [For a VDU] the strongest signals, or harmonics thereof, are usually between 60-250 MHz approximately. There have however been noticeable exception of extremely strong emissions in the television bands and at higher frequencies between 450-800 MHz. Potts, Emission Security, 3 COMPUTER LAW AND SECURITY REPORT 27 (1988). 10. The TEMPEST ELINT operator can distinguish between different VDUs in the same room because of the different EMR characteristics of both homo and heterogeneous units. "[T]here is little comparison between EMR characteristics from otherwise comparable equipment. Only if the [VDU] was made with exactly the same components is there any similarity. If some of the components have come from a different batch, have been updated in some way, and especially if they are from a different manufacturer, then completely different results are obtained. In this way a different mark or version of the same [VDU] will emit different signals. Additionally because of the variation of manufacturing standards between counties, two [VDUs] made by the same company but sourced from different counties will have entirely different EMR signal characteristics...From this it way be thought that there is such a jumble of emissions around, that it would not be possible to isolate those from any one particular source. Again, this is not the case. Most received signals have a different line synchronization, due to design, reflection, interference or variation of component tolerances. So that if for instance there are three different signals on the same frequency ... by fine tuning of the RF receiver, antenna manipulation and modification of line synchronization, it is possible to lock onto each of the three signals separately and so read the screen information. By similar techniques, it is entirely possible to discriminate between individual items of equipment in the same room." Potts, supra note

9. For a discussion of the TEMPEST ELINT threat See e.g., Memory Bank, AMERICAN BANKER 20 (Apr 1 1985); Emissions from Bank Computer Systems Make Eavesdropping Easy, Expert Says, AMERICAN BANKER 1 (Mar 26 1985); CRT spying: a threat to corporate security, PC WEEK (Mar 10 1987).

11. TEMPEST is concerned with the transient electromagnetic pulses formed by digital equipment. All electronic equipment radiates EMR which may be reconstructed. Digital equipment processes information as 1's and 0's--on's or off's. Because of this, digital equipment gives off pulses of EMR. These pulses are easier to reconstruct at a distance than the non-pulse EMR given off by analog equipment. For a thorough discussion the radiation problems of broadband digital information see e.g. military standard MIL-STD-461 REO2; White supra note 9, 10.2.

12. See supra note 2.

13. Of special interest to ELINT collectors are EMR from computers, communications centers and avionics. Schultz, Defeating Ivan with TEMPEST, DEFENSE ELECTRONICS 64 (June 1983).

14. The picture on a CRT screen is built up of picture elements (pixels) organized in lines across the screen. The pixels are made of material that fluoresces when struck with energy. The energy is produced by a beam of electrons fired from an electron gun in the back of the picture tube. The electron beam scans the screen of the CRT in a regular repetitive manner. When the voltage of the beam is high then the pixel it is focused upon emits photons and appears as a dot on the screen. By selectively firing the gun as it scans across the face of the CRT, the pixels form characters on the CRT screen. The pixels glow for only a very short time and must be routinely struck by the electron beam to stay lit. To maintain the light output of all the pixels that are supposed to be lit, the electron beam traverses the entire CRT screen sixty times a second. Every time the beam fires it causes a high voltage EMR emission. This EMR can be used to reconstruct the contents of the target CRT screen. TEMPEST ELINT equipment designed to reconstruct the information synchronizes its CRT with the target CRT. First, it uses the EMR to synchronize its electron gun with the electron gun in the target CRT. Then, when the TEMPEST ELINT unit detects EMR indicating that the target CRT fired on a pixel, the TEMPEST ELINT unit fires the electron gun of its CRT. The ELINT CRT is in perfect synchronism with the target CRT; when the target lights a pixel, a corresponding pixel on the TEMPEST ELINT CRT is lit. The exact picture on the target CRT will appear on the TEMPEST ELINT CRT. Any changes on the target screen will be instantly reflected in the TEMPEST ELINT screen. TEMPEST Certified equipment gives off emissions levels that are too faint to be readily detected. Certification levels are set out in National Communications Security Information Memorandum 5100A (NACSIM 5100A). "[E]mission levels are expressed in the time and frequency domain, broadband or narrow band in terms of the frequency domain, and in terms of conducted or radiated emissions." White, supra, note 9, 10.1. For a thorough though purposely misleading discussion of TEMPEST ELINT see Van Eck, Electromagnetic Radiation from Video Display units: An Eavesdropping Risk?, 4 Computers & Security 269 (1985).

15. Pub. L. No. 90-351, 82 Stat. 197. The Act criminalizes trespassatory ELINT by individuals as well as governmental agents. cf. Katz v. United States, 389 U.S. 347 (1967) (Fourth Amendment prohibits surveillance by government not individuals.)

16. 18 U.S.C. 2511(1)(a).

17. United States v. Hall, 488 F.2d 193 (9th Cir. 1973) (found no legislative history indicating Congress intended the act to include radio-telephone conversations). Further, Title III only criminalized the interception of "aural" communications which excluded all forms of computer communications.

18. Willamette Subscription Television v. Cawood, 580 F.Supp 1164 (D. Or. 1984) (non-wire communications lacks any expectation of privacy).

19. Pub. L. No. 99-508, 100 Stat. 1848 (codified at 18 U.S.C. 2510-710) [hereinafter ECPA].

20. 18 U.S.C. 2511(1)(a) criminalizes the interception of "any wire, oral or electronic communication" without regard to an expectation of privacy.

21. Interception of Communications Act 1985, Long Title, An Act to make new provision for and in connection with the interception of communications sent by post or by means of public telecommunications systems and to amend section 45 of the Telecommunications Act 1984.

22. Interception of Communications Act 1985 1, Prohibition on Interception: (1) Subject to the following provisions of this section, a person who intentionally intercepts a communication in the course of its transmission by post or by means of a public telecommunications system shall be guilty of an offence and liable-- (a) on summary conviction, to a fine not exceeding the statutory maximum; (b) on conviction on indictment, to imprisonment for a term not exceeding two years or to a fine or to both.

*** 23. Tapping (aka trespassatory eavesdropping) is patently in violation of the statute. "The offense created by section 1 of the Interception of Communications Act 1985 covers those forms of eavesdropping on computer communications which involve "tapping" the wires along which messages are being passed. One problem which may arise, however, is the question of whether the communication in question was intercepted in the course of its transmission by means of a public telecommunications system. It is technically possible to intercept a communication at several stages in its transmission, and it may be a question of fact to decide the stage at which it enters the "public" realm. THE LAW COMMISSION,WORKING PAPER NO. 110: COMPUTER MISUSE, 3.30 (1988).

24. "There are also forms of eavesdropping which the Act does not cover. For example. eavesdropping on a V.D.U. [referred to in this text as a CRT] screen by monitoring the radiation field which surrounds it in order to display whatever appears on the legitimate user's screen on the eavesdropper's screen. This activity would not seem to constitute any criminal offence..." THE LAW COMMISSION, WORKING PAPER NO. 110: COMPUTER MISUSE, 3.31 (1988).

25. 301.2(1) of the Canadian criminal code states that anyone who: ... without color of right, (a) obtains, directly or indirectly, any computer service, (b) by means of an electromagnetic ... or other device, intercepts or causes to be intercepted, either directly or indirectly, any function of a computer system ... [is guilty of an indictable offence].

26. UNITED STATES SENTENCING COMM'N, FEDERAL SENTENCING GUIDELINES MANUAL (1988) (Principles Governing the Redrafting of the Preliminary Guidelines "g." (at an unknown page))

27. There has been great debate over what exactly is a computer crime. There are several schools of thought. The more articulate school, and the one to which the author adheres holds that the category computer crime should be limited to crimes directed against computers; for example, a terrorist destroying a computer with explosives would fall into this category. Crimes such as putting ghost employees on a payroll computer and collecting their pay are merely age-old accounting frauds; today the fraud involves a computer because the records are kept on a computer. The computer is merely ancillary to the crime. This has been mislabeled computer crime and should merely be referred to as a fraud perpetrated with the aid of a computer. Finally, there are information crimes. These are crimes related to the purloining or alteration of information. These crimes are more common and more profitable due to the computer's ability to hold and access great amounts of information. TEMPEST ELINT can best be categorized as a information crime.

28. Compare, for example, the Watergate breakin in which the burglars were discovered when they returned to move a poorly placed spread spectrum bug.

29. TEMPEST Certified refers to the equipment having passed a testing and emanations regime specified in NACSIM 5100A. This classified document sets forth the emanations levels that the NSA believes digital equipment can give off without compromising the information it is processing. NACSIM 5100A is classified, as are all details of TEMPEST. To obtain access to it, contractor must prove that there is demand within the government for the specific type of equipment that intend to certify. Since the standard is classified, the contractors can not sell the equipment to non-secure governmental agencies or the public. This prevents reverse engineering of the standard for its physical embodiment, the Certified equipment. By preventing the private sector from owning this anti- eavesdropping equipment, the NSA has effectively prevented the them from protecting the information in their computers.

30. Previously the Bureau of Standards. The NIST is a division of the Commerce Department.

31. In this case computer equipment would include all peripheral computer equipment. There is no use is using a TEMPEST Certified computer if the printer or the modem are not Certified.

32. The NSA has tried to limit the availability of TEMPEST information to prevent the spread of the devices. For a discussion of the First Amendment and prior restraint See, e.g. The United States of America v. Progressive, Inc. 467 F.Supp 990 (1979, WD Wis.)(magazine intended to publish plans for nuclear weapon; prior restraint injunction issued), reh. den. United States v. Progressive Inc. 486 F.Supp 5 (1979, WD Wis.), motion den Morland v. Sprecher 443 US 709 (1979)(mandamus), motion denied United States v. Progressive, Inc. 5 Media L R (1979, 7th Cir.), dismd. without op. U.S. v. Progressive, Inc 610 F.2d 819 (1979, 7th Cir.); New York Times, Co. v. United States, 403 U.S. 713 (1971)(per curium)(Pentagon Papers case: setting forth prior restraint standard which government was unable to meet); T. EMERSON, THE SYSTEM OF FREEDOM OF EXPRESSION (1970); Balance Between Scientific Freedom and NAtional Security, 23 JURIMETRICS J. 1 (1982)(current laws and regulations limiting scientific and technical expression exceed the legitimate needs of national security); Hon. M. Feldman, Why the First Amendment is not Incompatible with National Security, HERITAGE FOUNDATION REPORTS (Jan. 14, 1987). Compare Bork, Neutral Principles and Some First Amendment Problems, 47 IND. L. J. 1 (First Amendment applies only to political speech); G. Lewy, Can Democracy Keep Secrets, 26 POLICY REVIEW 17 (1983)(endorsing draconian secrecy laws mirroring the English system).

33. For example, the NSA has just recently allowed the Drug Enforcement Agency (DEA) to purchase TEMPEST Certified computer equipment. The DEA wanted secure computer equipment because wealthy drug lords had were using TEMPEST eavesdropping equipment.

34. An Act to regulate the use of automatically processed information relating to individuals and the provision of services in respect of such information. -Data Protection Act 1984, Long Title.

35. "Personal data" means data consisting of information which relates to a living individual who can be identified from that information (or from that and other information in the possession of the data user), including any expression of opinion about the individual but not any indication of the intentions of the data user in respect of that individual. -Data Protection Act 1984 1(3)

36. "Data user" means a person who holds data, and a persons "Holds" data if -- (a) the data form part of a collection of data processed or intended to be processed by or on behalf of that person as mentioned in subsection (2) above; [subsection (2) defines "data"] and (b) that person (either alone or jointly or in common with other persons) controls the contents and use of the data comprised in the collection; and (c) the data are in the form in which they have been or are intended to be processed as mentioned in paragraph (a) above or (though not for the time being in that form) in a form into which they have been converted after being so processed and with a view to being further so processed on a subsequent occasion. - Data Protection Act 1(5).

37. Data Protection Act 1984, 4,5.

38. An individual who is the subject of personal data held by a data user... and who suffers damage by reason of (1)(c) ... the disclosure of the data, or access having been obtained to the data without such authority as aforesaid shall be entitled to compensation from the data user... for any distress which the individual has suffered by reason of the ... disclosure or access. - Data Protection Act 1984 23.

39. ... it shall be a defense to prove that ... the data user ... had taken such care as in all the circumstances was reasonably required to prevent the... disclosure or access in question. Data Protection Act 1984 23(3)

Copyright (c) 1993 by Grady Ward. All Rights Reserved. Permission is granted for free electronic distribution. ought to be filtered, it is especially important for more-on-TEMPEST


From:cjs%cwru@cwjcc.ins.cwru.edu (Christopher J. Seline (CJS@CWRU.CWRU.EDU)) The following is a prepublication draft of an article on TEMPEST. I am posting it to this news group in the hope that it will: (1) stimulate discussion of this issue; (2) expose any technical errors in the document; (3) solicit new sources of information; (4) uncover anything I have forgotten to cover. I will be unable to monitor the discussions of the article. Therefore, PLEASE post your comments to the news group BUT SEND ME A COPY AT THE ADDRESS LISTED BELOW. I have gotten a number of mail messages about the format of this article. Some explanation is in order: The numbered paragraphs following "____________________" on each page are footnotes. I suggest printing out the document rather than reading it on your CRT. Thanks you in advance.

Christopher Seline cjs@cwru.cwru.edu cjs@cwru.bitnet (c)
1990 Christopher J. Seline