Electronic Interference

Electronic Interference

by Matt Hoffman


Electromagnetic radiation is both an enabler and byproduct of modern information technology. The vast number of natural and man-made sources of electromagnetic radiation can, at times, emit signals that interfere with the normal function of electronic devices. This paper will examine the effects of electronic interference attacks by describing their sources, methods of action, and impacts on information systems.


Electromagnetic radiation is one form of energy characterized by its ability to transmit energy through open spaces. Electromagnetic radiation exists on a spectrum ranging from low frequency, low energy radio waves to high frequency, high energy gamma rays. While humans cannot directly sense many types of electromagnetic radiation, we are all intimately familiar with two forms: visible light, which occupies a small portion of the total spectrum, and heat, which originates from part of the infrared portion of the spectrum. [1] Modern technologies such as televisions, radios, cordless telephones, satellites, and wireless networking devices all utilize some form of electromagnetic radiation to transmit their signals from source to receiver. Electromagnetic radiation can also be emitted as a byproduct of electrical current (e.g. power transmission lines or any power-consuming device).

When unwanted electromagnetic energy disrupts the function of electronic devices, a condition known as electronic interference (EI) arises. Depending upon the source, electronic interference can be categorized as natural, incidental (man-made, but unintentional), or intentional (man-made and deliberate). Because each type has the potential to disrupt the electronic signals that drive our information systems, all three must be considered hazards to our information infrastructure. This paper will describe how electronic interference can disrupt electronic systems by examining the sources and impacts of natural, incidental, and intentional electronic interference.

Requirements and Effects of EI

In order for electronic interference to occur, there has to be a source of the interfering signal (an emitter), a device that is susceptible to the emitted radiation (a "victim"), and enough physical proximity between the two devices that allows them to share a common electromagnetic field. Two electronic devices that interfere with each other are said to lack electromagnetic compatibility, meaning that the emitter device produces interference on the same frequency that the victim device requires to operate. [2] The degree of physical proximity is a function of both the power of the emitter device and the sensitivity of the victim device. Two electronic devices may not have electromagnetic compatibility, yet if they are separated by a sufficient distance they will not interfere with each other.

One way that EI can disrupt electronic devices is through bit corruption. In this method, EI of the right frequency and power can alter individual bytes of data in an electronic transmission, causing the device that interprets the data stream to read the wrong data. While in many cases electronic devices use error-correction algorithms to reject corrupted data, if enough altered bytes are introduced or the error-correction system fails, the victim device will be flooded with false data. This may cause the device to misinterpret the intended transmission or "lock up" because it cannot perform an invalid operation. [2] Another example of bit corruption would be the introduction of EI that floods a transmission stream with a large amount of extraneous data, preventing the receiver from distinguishing the real data from the interference. [3] This technique has the same effect as bit alteration, and is commonly employed in jamming technologies (see below).

Electronic interference can also disrupt power supplies in electronic components. This event, called junction rectification, occurs when an interference signal interacts with the power semiconductors in an electronic device. Interference signals of sufficient strength can disrupt the semiconductors responsible for supplying a device with electricity, causing a shutdown of that circuit and of possibly the entire device. In addition to corrupting power supplies, junction rectification can also cause bit corruption in an electronic device. [2]

Natural EI

We are constantly surrounded by natural sources of electromagnetic radiation, some of which can act as sources of electronic interference. In addition to disabling information systems through power outages, lightning can also produce enough interference to temporarily disrupt communications. [4] The primary source of natural EI, however, comes from the sun. [5] The earth is constantly bombarded by all types of electromagnetic energy from the sun, and energy that is not filtered out by the atmosphere has the potential of causing interference. Under normal circumstances, the energy from the sun is not great enough to interfere with electronic equipment. However, solar flares (the release of magnetic energy on the sun's surface [6]) can send enough electromagnetic energy to the earth to disrupt all types of electronic devices on the sun-facing side of the earth. For example, in June 2000 a large solar flare disrupted several telecommunications services in China [7], and in 1996 another solar flare caused a widespread outage of shortwave radio services. [8] A particularly strong solar flare in March 1989 even disabled electrical generators and transmission lines in Quebec, Ontario, leaving over six million people without electricity. [9]

Incidental EI

In addition to natural sources, electromagnetic interference can also arise from regular use of electronic devices. Electrical interference can occur when the operation of certain electrical appliances causes power fluctuations in electrical components (junction rectification). A television displaying static while a hair dryer is in use is an example of this phenomenon. Also, any wire that carries electronic signals (e.g. speaker wire, monitor cables, internal wiring, etc.) can transmit interference if its protective covering, which prevents the signal from escaping the wire, is damaged. [10] Some electronic devices, such as fluorescent lights and laptop computers, emanate a small electromagnetic field during regular use that may interfere with nearby electronic equipment. Finally, signals from wireless devices such as mobile radios, radar systems, and cellular phones can also cause electronic interference. [4]

Incidental EI is a major concern with both medical devices and airplane electronics. Hospitals today contain hundreds of electronic devices that may not be electromagnetically compatible with each other. The interference produced by these devices can do anything from simply flickering nearby video screens to disrupting the function of life support systems. Between 1979 and 1993, the FDA received over 100 reports of equipment disruptions thought to be caused by EI. [11,12] Electronic interference has even prompted some hospitals to ban the use of cellular phones and two-way radios in certain areas. [13] Hospitals, however, are not the only place EI can affect medical equipment. In 1993, a Denver area man was injured when his electric wheelchair malfunctioned and drove over the edge of a cliff, reportedly because of EI from a nearby radio tower. [11,14] The FDA has also released advisories warning implant patients about the effects of metal detectors, anti-theft devices, and cellular phones on their implants. [15,16]

Although relatively rare, electronic interference can also significantly disrupt information systems in airplanes. Since 1976, electronic interference from passenger electronic devices has caused in-flight disruptions at least 52 times in the US alone [17]. Airline passengers are routinely told to refrain from using electronic devices during takeoff and landing because electromagnetic fields generated by such devices can interfere with a plane's communication and navigation systems. There have been several well-documented cases of personal electronic devices causing in-flight navigation problems [18,19,20]. Electronic interference is also thought to have been the cause of the 1996 TWA Flight 800 explosion off of Long Island, NY that killed all 230 passengers and crew members on board. [21,22]

Intentional EI/Jamming

The third category of interference, and likely the one most important to information security professionals, is intentional EI. Intentional EI, also known as jamming, involves the deliberate radiation, reradiation, or reflection of electromagnetic energy in order to disrupt the function of electronic devices. [3] Jamming is very similar to incidental EI, except that jamming employs more powerful transmitters to generate electrical interference. These transmitters can broadcast interference over a broad range of electromagnetic frequencies for general targets (barrage jamming) or over a narrow set of frequencies for a specific target (spot jamming). [23]

Jamming is commonly utilized in military operations to disrupt enemy communication and radar systems. Every branch of the U.S. Armed Forces has several pieces of mobile and stationary equipment capable of emitting very powerful broadband and narrowband jamming signals. [24] Military aircraft also contain jamming equipment to disable enemy radio transmissions and missile targeting systems. [25] Jamming technology has played an important role in warfare since World War II; a role that is likely to increase in future conflicts as military equipment becomes more reliant on electronic components. In the future, non-lethal weapons that target only electronic devices may be used to disable enemy electronics. One such weapon concept, the electromagnetic pulse (EMP) bomb, would be able to temporarily or irreversibly disable all electronic devices in a given area by releasing a powerful discharge of electromagnetic energy. Unlike nuclear weapons, which release electromagnetic energy as a byproduct of their explosions, EMP bombs would be non-lethal and non-destructive means to disable electronic systems. Although there has been no official confirmation of the existence of such a device, some defense analysts have begun research and discussion about the subject. [26,27]

Civilian operation of any jamming device is currently prohibited in the United States [28] and over 140 other countries. [29] Although these laws have been in place for some time, the FCC still received over 1200 complaints of jamming in 1999 alone. [30] Jamming equipment can be built relatively cheaply by anyone with some experience with radio equipment, and at least one online hacker journal provides guidelines for building jamming devices. [31] Enforcement of anti-jamming laws can be difficult because jamming transmitters can be difficult to locate without the proper equipment. Because tracking is difficult and jamming technology is becoming cheaper and more mobile, new concerns have arisen over the use of electronic jamming in terrorist actions against airliners or GPS systems [32,33]. Despite these concerns, ironically, there has also been some discussion about legalizing jamming in certain public places (e.g. movie theaters, libraries, etc.) to crack down on cellular phone disturbances. [34]

Summary, Conclusions, and Further Work

In summary, electronic interference can arise from a variety of sources and can significantly disrupt unprotected electrical devices. Since each source of EI has the potential of causing damage to information systems, information security personnel must consider each type of interference as an attack. Further research into methods of reducing incidental electromagnetic emanations (e.g. better wire shielding materials) may decrease the amount of background EI present in the environment. Incorporating materials that block electromagnetic energy into electronics designs can reduce the susceptibility of these devices to interference. Since electronic interference is often hard to detect and link to equipment failures, new detection technologies and experimental designs can help system engineers and administrators understand the complex interactions among electronic devices. These steps may result in electronic interference playing a lesser role in electronics equipment failure in the future.


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