Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
  • H04K3/00—Jamming of communication; Counter-measures
  • H04K3/80—Jamming or countermeasure characterized by its function
  • H04K3/82—Jamming or countermeasure characterized by its function related to preventing surveillance, interception or detection
  • H04K3/825—Jamming or countermeasure characterized by its function related to preventing surveillance, interception or detection by jamming
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
  • H04K2203/00—Jamming of communication; Countermeasures
  • H04K2203/10—Jamming or countermeasure used for a particular application
  • H04K2203/14—Jamming or countermeasure used for a particular application for the transfer of light or images, e.g. for video-surveillance, for television or from a computer screen
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
  • H04K3/00—Jamming of communication; Counter-measures
  • H04K3/40—Jamming having variable characteristics
  • H04K3/42—Jamming having variable characteristics characterized by the control of the jamming frequency or wavelength
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
  • H04K3/00—Jamming of communication; Counter-measures
  • H04K3/40—Jamming having variable characteristics
  • H04K3/43—Jamming having variable characteristics characterized by the control of the jamming power, signal-to-noise ratio or geographic coverage area

Definitions

• Data security is today in focus at the same time as EDP is being increasingly introduced into new fields of use. Often there may be large amounts of information collected in a single system.
• the information contained in an electronic data processing plant is usually protected by conventional methods such as security zones, code words and restricted access.
• the only method employed today is screening, and such equipment is normally referred to as TEMPEST protected.
• TEMPEST protected There is today such equipment available on the market and this is accepted for defence use.
• a drawback is represented by the high expences connected with this protection. The price of most of the products is doubled thereby.
• German patent No.2838.600 To protecting against leakage or corruption of information being printed by a matrix printer, it is known from German patent No.2838.600 to employ a compensation signal generated in such a way that the sum of this compensation signal and the printing signal in the matrix printer, is constant. Accordingly the total emitted radiation from the equipment will be constant, which makes it difficult to detect the actual information signal.
• the compensation signal is generated by compensation units which electrically shall correspond to the separate circuits which serve to activate the individual needles in the printer mechanism.
• this known method is intimately related to the form -of matrix printer concerned, so that the method among other things is not useful in connection with screen terminals.
• European patent application No.0.069.831 relates to a method for the purpose of avoiding corruptive radiation from data equipment.
• the solution described is to a large extent analogous to what is described in the above German patent specification. Both methods involve significant intervention into the equipment concerned, for which protection is desired, or even a completely integrated or built-in protective device in the computer equipment.
• An object of the present invention is to obtain protection which can be provided comparatively easily in connection with existing data equipment at the same time as it can be integrated in a relatively simple and inexpensive manner into new equipment being produced. Moreover it is an object of the invention to provide a system which in a better and more flexible way affords protection against remote access to digital equipment which emits stray electromagnetic radiation.
• this invention provides for the masking of corruptive radiation from computer equipment by emitting a coded masking signal which together with the actual information-carrying and corruptive signal will form a modified corruptive signal which to a high degree makes it difficult to detect or remotely access the information.
• the masking signal has the same or similar characteristic properties as the unintentionally radiated signal, there is obtained a good protective effect.
• the masking comprises emissionof a series of random character and letter combinations selected from a set of characters being equal to or corresponding to at least a portion of the character set which is given and is used for information processing or presentations in the data equipment concerned, and which can have the same statistical properties as the corruptive signal.
• Figure 1 shows a simplified block diagram of a protection system according to the invention.
• Figure 2 shows examples of typical signal shapes with protection by means of a system according to figure 1, and
• Figure 3 illustrates signal shapes with an additional and advantageous amplitude modulation according to an embodiment of the invention.
• FIG 1 there is shown a digital unit or data equipment unit in the form of a terminal 1 and an associated system for protection against corruptive radiation from the terminal 1, in the form of a module generally denoted 10.
• the radiation from the terminal 1 is indicated at 2.
• the terminal 1 emits corruptive radiation 2 of a relatively broadband nature, from 50 Hz to several MHz. Since the signal propagation in the terminal is essentially synchronous the corruptive radiation from the various components will also be synchronous. Further the radiation is primarily radiated from the electronic circuits which generate characters on the screen.
• the protection module 10 shown comprises as main components a micro-processor 13 and a store 14 containing one or two tables to be described more closely below.
• a digital-analog converter 15 In the module 10 there is further included a digital-analog converter 15, a modulator 16 and a high frequency generator 18 which emits protective or masking radiation through an antenna 19.
• the units or circuits 15, 16 and 18 can be considered to constitute the drive means for digital signals to be radiated from the antenna 19.
• a synchronizing unit 12 which through a connection 11 is adapted to receive a reference signal from the terminal 1, and which on the other hand supplies a clock signal to the micro-processor 13.
• the module 10 is controlled by the reference clock signal taken from the terminal 1.
• this signal is converted to the clock signal in the protection module.
• the clock signal can be phase-shifted so that both signals are in phase.
• the protection module is built up around the micro ⁇ processor 13 which quite at random selects which character the protective signal shall represent, modulates the signal and administrates the emission of the protective radiation 20.
• the signature of all characters which can be presented by the terminal 1" on its screen are stored in a register, i.e. the store 14 in the form of a so-called character table I containing codes for the choice of characters concerned.
• the processor 13 will then read out one of these codes when a protective signal is to be emitted.
• the most important property of the protective signal in additional to being analagous or identical in nature to the corruptive radiation, is that the characters emitted are selected in a completely random order or have a statistical distribution of characters corresponding to the radiated signal. This is obtained thereby that the micro-processor 13 in its programme table has stored an algorithm which generates a random sequence, which can take place in a manner which is known per se. If it is desired to avoid the repetition of the same sequence each time the equipment is started up, there can be utilized a circuit for generating a statistically random starting point.
• a second table II for generating (modulating) the strength, of the signal emitted.
• the masking signal be amplitude modulated. This is done by entering into the second table II and reading out the signal strength of the character to be emitted. This is sensed by the micro-processor 13 and when this information has been associated with the selected character, the micro-processor is ready to emit the protective signal.
• the signal is supplied in a digital form to the digital-analog converter 15 which generates a modulation signal.
• the modulator 16 serves to have the signal from the RF generator 18 amplitude modulated and emitted from the antenna 19.
• the RF generator 18 can be a small solid-state source with tuned output power adjusted to the radiation of the terminal.
• the protective signal 20 is radiated for example from an omnidirectional antenna 19 integrated into the protection module 10.
• the output power is matched to the radiation level of the corruptive radiation from the terminal 1.
• Figure 2 shows signal shapes as a function of time for illustrating the manner of operation of a system as shown in figure 1.
• the amplitudes AMP are shown in arbitrary units.
• the modulation of the signal reflects the binary character levels. More closely there is shown at 2A an example of an unintentionally radiated high frequency signal from data equipment such as the terminal 1 in figure 1, whereas at 2B there is illustrated a typical masking signal included in the protective radiation 20 from the module 10.
• This masking signal contains random character combinations which together with the signal mentioned above, results in a total radiated signal as shown at 2C. In this total signal the two signals mentioned above are combined in such a manner that even the most advanced remote detection equipment will hardly be able to detect the actual information for which protection is desired.
• the masking signal is emitted continuously when the digital equipment, possibly data equipment, is turned on. Even though such equipment is not in operation a continuous stream of randomly selected masking signals will bring any remote detection system to saturation, and thereby more or less make it impossible to detect the information for which protection is desired. With such utilization of this system there will be obtained a mutual protection when several different data equipment units in the same premises or location are provided with systems according to the invention. In many cases there will then be need for only a couple of masking systems in order to protect several data plants or units, even though these are not operating synchronously.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Signal Processing For Digital Recording And Reproducing (AREA)
• Storage Device Security (AREA)
• Emergency Protection Circuit Devices (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19891043

Family Applications (1)

Country Status (6)

Cited By (8)

Families Citing this family (25)

Citations (3)

Family Cites Families (5)

• 1988
  • 1988-07-05 NO NO882982A patent/NO165698C/no unknown
• 1989
  • 1989-07-03 AU AU38356/89A patent/AU3835689A/en not_active Abandoned
  • 1989-07-03 WO PCT/NO1989/000070 patent/WO1990000840A1/en active IP Right Grant
  • 1989-07-03 EP EP89907333A patent/EP0424415B1/en not_active Expired - Lifetime
  • 1989-07-03 DE DE89907333T patent/DE68912941T2/de not_active Expired - Fee Related
• 1991
  • 1991-01-03 US US07/623,815 patent/US5165098A/en not_active Expired - Fee Related

Patent Citations (3)

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