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<New Page>
Eavesdropping On
the Electromagnetic Emanations
of Digital Equipment:
The Laws of Canada,
England and the United States
This document is a rough
draft. The Legal
Sections are overviews.
T h e y w i l l b e
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
_____________________
1. Undelivered speech of President John F. Kennedy, Dallas
Citizens Council (Nov. 22, 1963) 35-36.
<New Page>
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
_____________________
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.
<New Page>
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.
I. INTELLIGENCE GATHERING
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
_____________________
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).
<New Page>
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
_____________________
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.
<New Page>
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
_____________________
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
<New Page>
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]
_____________________
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.
<New Page>
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.
II. UNITED STATES LAW
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-
_____________________
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).
<New Page>
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.
III. ENGLISH LAW
In England the Interception of Communications Act
1985[21] criminalizes the tapping of communications sent over
_____________________
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.
<New Page>
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]
IV. CANADIAN LAW
Canada has taken direct steps to limit eavesdropping on
computers. The Canadian Criminal Amendment Act of 1985
_____________________
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).
<New Page>
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]
_____________________
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
<New Page>
V. SOLUTIONS
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
_____________________
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. TEMPEST Certified equipment is
theoretically secure against TEMPEST eavesdropping.
<New Page>
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 with
_____________________
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.
<New Page>
the 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
_____________________
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).
<New Page>
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
_____________________
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
<New Page>
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
_____________________
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)
<New Page>
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
<New Page>
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.
ust 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
_____________________
33. FTEMPEST-shielding
Preventing Electromagnetic Eavesdropping
---------
NOTE: Even though the author of this document uses the term "TEMPEST" at
various points, he certifies that his text consists of general
concepts to reduce electromagnetic emissions, and was not based on any
actual TEMPEST specifications or data. Further questions on this topic
should be directed to the author, "grady@netcom.com".
-- PRIVACY Forum Moderator
---------
Abstract
Eavesdropping on personal computers is not limited to looking over the
shoulder of the operator or physically tapping in to an Ethernet cable.
U.S. Government standards relating to the prevention of information capture
via the emission of electromagnetic radiation from computers and peripherals
are known as TEMPEST. However, actual TEMPEST specifications are classified.
TEMPEST aside, there are inexpensive and easily applied means for
individuals to minimize unintentional emissions from equipment. My document
"Preventing Electromagnetic Eavesdropping," discusses these techniques.
Grady Ward <grady@netcom.com>
---------
Preventing Electromagnetic Eavesdropping
A note discussing the prevention of electromagnetic eavesdropping
of personal computers.
Grady Ward <grady@netcom.com>
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.
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 600 2066 1274 11221 5603104744 6627
| kingsley@hip-hop.sbay.org (Kingsley G. Morse Jr.) said:
| In <2dq47c$rvb@charm.magnus.acs.ohio-state.edu> wvhorn@magnus.acs.ohio-state.
| u (William VanHorne) writes:
| >TEMPEST is nothing more than a way to
| >force manufacturers to do some rudimentary shielding of their devices
| >so as to cut down on RF emissions, and concerns stuff like making sure
| >that the cables are coax-like shielded and real high-tech stuff like
| >that.
| >Now, you, as Mr./Ms. Consumer, do not buy electronic items that have
| >*any* shielding in them.
Not correct: all consumer electronics that produce RF have *some*
shielding. There are many "leaky" spots, however, and most of these
involve cabling and ground loops.
| PGP is popular, and perhaps TEMPEST equipment would sell well also.
| Does anyone know of a distributor or catalog of TEMPEST rated shielding
| or equipment?
Shielding is not difficult or complex; anyone can do it. Pop down
to your local magazine rack and get a mag on Amateur radio, look up
a mail order ham book place, and order a book on the subject.
As for personal computers, here's a few starting things to consider:
o Get a case that's made of steel, on all 6 sides.
o Get the highest quality shielded cables you can find. The GOOD
commercial ones will have metal hoods on the connectors and
little grounding pigtails. (If you pay $4.95 for a serial cable
you have probably bought a good antenna).
o Ground the case and cables with SHORT ground wires, directly
to a 10' copper ground rod just outside the wall.
o In a well-shielded system, the keyboard will emit the most RF,
and it may be impossible to shield it adequately, tho the
heavier, steel-base keyboards like Focus and Northgate are
quieter than cheap plastic ones. The coily-cords radiate a
lot, too. Replace your keyboard cable with a quality, straight,
shielded one and ground it.
o Use a portable shortwave radio to check for leaks. Tune it first
to your buss speed, then to processor speed. Then scan around
for leaks on other frequencies. If you're *really* serious, drop
2 grand+ on an RF spectrum analyzer. That's what any snoop
would use to locate your emission frequencies.
Grounding and Shielding -- Misconceptions & things to know:
o A DC ground and an RF ground are not the same thing. A ground
wire that is longer than 1/4 wavelength is an antenna, not a
ground (regardless of what you ground it to). For example, a
ground wire longer than 4.6 feet is an antenna at 50MHz.
At 8 MHz, wires approaching 29 feet become antennas.
Use 234/f (in mhz), then keep it quite a bit shorter than that.
Obviously, you can't use your house grounding system, or cold
water pipes, as RF grounds -- they're too long.
o Shielded multiconductor cables, and coax, are not really designed
to stop all emissions of RF. They are designed to stop electrical
interference from getting *into* the cable. If the shield of
a cable is carrying RF (either by direct feed or induction from the
wires within), it will radiate it at certain lengths, just like
any other wire.
o Twists: The most effective way to stop cable RF radiation is to
use cables that contain tightly twisted pairs of wires. This
results in near-total phase cancellation. But it doesn't stop
"common-mode" radiation. This is where RF at some frequency
treats all wires in the cable as one. For example, 8 MHz buss
noise may travel in-phase down your printer cable, to your
printer chassis, to house ground, and back to your computer
chassis. If this whole loop is => 29 feet, you'll radiate
buss noise. The shield radiates either because it is carrying
RF, or because the pairs inside are radiating and inducing
RF on the shield.
o Ferrite toroids are available in a variety of sizes, and don't
cost much. You probably already have some small ones in your
power supply, on the input leads. These doughnuts will "eat"
common-mode RF induction. You wrap several turns of the wire in
question thru the doughnut. You can add these to your power supply
(AC side), and all other wires leaving the computer case,
including ground wires, keyboard, video, serial, parallel,
LAN, and even speaker wires.
Notwithstanding all of the above, it is probably impossible to
pick up any *useful* information off of keyboards and monitors.
Networks, with their loooong data cables, are another matter.
Users needing tight security on networks should use fiber optics,
then apply all the stuff above to all pieces of hardware in the network.
(Continued to next message)
* QMPro 1.02 41-7176 * This is an egg. This is an egg in a skillet.
e to locate your emission frequencies.
Grounding and Shielding -- Misconceptions & things to know:
o A DC ground and an RF ground are not the same thing. A ground
wire that is longer than 1/4 wavelength is an antenna, not a
ground (regardless of what you ground it to). For example, a
ground wire longer than 4.6 feet is an antenna at 50MHz.
At 8
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.
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 600 2066 1274 11221 5603104744 6627
| kingsley@hip-hop.sbay.org (Kingsley G. Morse Jr.) said:
| In <2dq47c$rvb@charm.magnus.acs.ohio-state.edu> wvhorn@magnus.acs.ohio-state.
| u (William VanHorne) writes:
| >TEMPEST is nothing more than a way to
| >force manufacturers to do some rudimentary shielding of their devices
| >so as to cut down on RF emissions, and concerns stuff like making sure
| >that the cables are coax-like shielded and real high-tech stuff like
| >that.
| >Now, you, as Mr./Ms. Consumer, do not buy electronic items that have
| >*any* shielding in them.
Not correct: all consumer electronics that produce RF have *some*
shielding. There are many "leaky" spots, however, and most of these
involve cabling and ground loops.
| PGP is popular, and perhaps TEMPEST equipment would sell well also.
| Does anyone know of a distributor or catalog of TEMPEST rated shielding
| or equipment?
Shielding is not difficult or complex; anyone can do it. Pop down
to your local magazine rack and get a mag on Amateur radio, look up
a mail order ham book place, and order a book on the subject.
As for personal computers, here's a few starting things to consider:
o Get a case that's made of steel, on all 6 sides.
o Get the highest quality shielded cables you can find. The GOOD
commercial ones will have metal hoods on the connectors and
little grounding pigtails. (If you pay $4.95 for a serial cable
you have probably bought a good antenna).
o Ground the case and cables with SHORT ground wires, directly
to a 10' copper ground rod just outside the wall.
o In a well-shielded system, the keyboard will emit the most RF,
and it may be impossible to shield it adequately, tho the
heavier, steel-base keyboards like Focus and Northgate are
quieter than cheap plastic ones. The coily-cords radiate a
lot, too. Replace your keyboard cable with a quality, straight,
shielded one and ground it.
o Use a portable shortwave radio to check for leaks. Tune it first
to your buss speed, then to processor speed. Then scan around
for leaks on other frequencies. If you're *really* serious, drop
2 grand+ on an RF spectrum analyzer. That's what any snoop
would use to locate your emission frequencies.
Grounding and Shielding -- Misconceptions & things to know:
o A DC ground and an RF ground are not the same thing. A ground
wire that is longer than 1/4 wavelength is an antenna, not a
ground (regardless of what you ground it to). For example, a
ground wire longer than 4.6 feet is an antenna at 50MHz.
At 8
