A PROTECTIVE DEVICE FOR COMPUTERS AND THE LIKE, ADAPATED TO PREVENT THE PICK UP, THE RECORDING AND THE UNAUTHORIZED USE OF DATA FROM THE COMPUTERS DURING THE WORKING THEREOF, AND TO PROTECT THEM AGAINST HIGH ENERGY TRANSIENT DISTURBANCES TAKING PLACE ON THE MAIN A.C. POWER LINE

Abstract: In order to protect computers and the like against the pick up, the recording and the unauthorized use of data from the computers during the working thereof, and to protect them against high energy transient disturbances taking place on the main A.C. power line, a filter unit (1) is foreseen comprising a plurality of sections (19) comprising inductances (21) and capacitances (23), between which it is interposed at least a gas-discharge surge arrester (25) and varistors (27), and a masking unit (3) comprising a power supply (31), a white noise generator (33) and an amplifier (35) emitting from the antenna circuit (61) said properly amplified white noise which is completely random and unpredictable, and therefore impossible to be decoded.

Description: A PROTECTIVE DEVICE FOR COMPUTERS AND THE LIKE, ADAPTED TO PREVENT THE PICK UP, THE RECORDING AND THE UNAUTHORIZED USE OF DATA FROM THE COMPUTERS DURING THE WORKING THEREOF, AND TO PROTECT THEM AGAINST HIGH ENERGY TRANSIENT DISTURBANCES TAKING PLACE ON THE MAIN A.C. POWER LINE The present invention relates to a protective device for computers and the like, adapted to prevent the pick up, the recording and the unauthorized use of data from the computers during the working thereof, and to protect them against high energy transient disturbances taking place on the main A.C. power line. It is known that normally operating electronic devices can behave both as sources and receivers of electromagnetic waves. More particularly the computers, when considered as receivers can be disturbed or in case damaged by sudden high energy transients (natural lightnings, voltage switchings, switching noises due to transitions in low and medium voltage substa¬ tions by the supplying company, radiowaves generated by indus¬ trial installments, sporadic disturbances caused by house ap¬ pliances or motorcars, etc.) that can take place on the A.C. power line to which they are connected; when considered as sources, computers can radiate information carrying elec¬ tromagnetic waves that can nullify the data privacy when prop¬ erly picked up. The electromagnetic waves generated from computers and their peripheral equipments (video terminals, printers peripheral disk drivers, tape drivers, etc. ) can be either directly radiated through air or guided through the power supply cables and hence along the power distribution network, thus turning this latter in a sort of radiating antenna having quite extended size and easy to be reached by people aiming to unauthorized data gathering. More precisely, the signals within a data processing system can produce undesired emission through the following mechanisms: A) - The information can be found recovered as an amplitude or phase modulation of the current adsorbed from the electric main. This may happens since the power supply has to feed also the current for the signal processing circuit and the inter¬ face circuits preparing for and adapting the same to the dif¬ ferent periheral devices. When using a switching power supply, the information sig¬ nal can be present in form of a modulation of carriers at a rather high frequency. Indeed, any change of the current drawn from the switching power supply by the load causes a change in the duty cycle of the device acting as a switch (chopper) , this latter in turn has switching times quite short and consequentely generates high frequency spectrum components. It is evident that such signals generated in the feeder circuit propagate more easily as signals guided through the power network. B) - The radiated emission that is more easily reduced to the information caused by the data processing can originate either from sources within the system or actuated by phoenomena in the outer environment but anyhow strictly re¬ lated to the electronic circuits controlling the generation of the image for a video terminal and the interfacing circuits, circuitry and wirings connected thereto (graphic boards, color boards, etc. ) . Namely, these circuits besides forming the baseband video signals (more than 5 MHz wide) , are a source of spurious sig¬ nals that contains the video signal in form of amplitude modulation, and therefore the confidential information that is the result of the processing system at the precise moment. The drive for these undesired emission can take place by means of a "beating" with electromagnetic fields present in the environment (circular video channel carriers or AM or FM radio stations carriers), or with electromagnetic fields pur¬ posely generated and transmitted by people interested to pick up the confidential information. It is an object of the present invention that of overcome the above drawbacks, providing a device adapted to protect the users of electronic apparatuses such as computers against the electrical disturbances coming from the outside world, and at the same time adapted to prevent the risk that guided signals coming out from the above electronic apparatuses are picked up through the power distribution network. The subject device substantially comprises two units: 1. a network filter unit; 2. a masking unit; 1. the network filter unit or "main unit" being made up by a number of sections comprising inductances and capacitances, interconnected with voltage gas-discharge surge arresters and metal oxide varistors; the gas-discharge arresters bypassing currents in the order of several kA when subjected to a volt¬ age higher than their conduction threshold; the metal oxide varistors being resistors whose resistance value is an inverse function of the voltage applied to their terminals, so that with the increase of the applied voltage their resistance be¬ comes smaller and smaller, thus conducting a larger and larger current; the sections comprising inductances and capacitances attenuating the high frequencies guided to the power distrib¬ ution network by 80 dB (i.e. about 10.000 times) in a band¬ width approximately extending from 1 MHz to 1.5 GHz; for exam¬ ple, a 1 kV/lμs transient surge in the first station is "clipped" at about 600 V in the second, at about 400 V in the third, and at about 255 V in the fourth; said filter unit being designed for different ratings, with the components properly dimensioned as a function of the A.C. values re¬ quested by the different user typologies. 2.- The masking unit or "ghost" unit in turn comprising three sections: 2.1 - a power supply; 2.2 - a white noise generator; 2.3 - a wide band amplifier and antenna circuit; 2.1 - the power supply comprising a transformer having a high insulation between the primary and the secondary wind¬ ings, which converts the mains voltage (220 V A.C.) in a proper low voltage (aboput 13 V A.C), a diode bridge and a capacitor adapted to rectify the A.C. voltage and convert it into a D.C. voltage; a transistor together with a Zener diode stabilizing the D.C. voltage at a proper value, e.g. 12 V D.C, adapted for the working of the successive stations; 2.2 - the white noise generator being obtained by means of the reverse biasing of at least three transistors through three resistors and a potentiometer; the dispersion of the characteristics of the three transistors generating a con¬ tinuous spectrum from about 1 MHz to about 1.5 GHz which is completely random and unpredictable, and therefore impossible to be decoded; said white noise being applied to the succes¬ sive section through three capacitors; 2.3 - the wideband amplifier and the antenna circuit, de- signed in such a way as to linearly amplify the signal from the preceding stage within the whole considered bandwidth, substantially comprising: 2.3.1 - at least three hybrid circuits being fed by the power supply through three resistors respectively; suitable capacitors being provided for eliminating possible spurious components; the radiofrequency output of the hybrid circuits being present at a terminal thereof, suitable inductors acting as choke coils to prevent the useful signal from propagating towards the power supply; additional capacitors coupling the outputs of the first and the second hybrid circuits to the in¬ puts of the second and third hybrid circuits, respectively; whereas another capacitor connects the output of the third hybrid circuit to the rest of the circuit; 2.3.2 - at least three transistors; the first of which biased by resistors, a capacitor providing a moderate feedback; the output of said transistor, linearized at radiofrequency by two oscillating circuits, being present on the capacitor acting as decoupling capacitor between this stage and the successive; a potenziometer being provided to adjust the level of the power radiated from the antenna cir¬ cuit within such limits as to comply with the rules en force; the other two transistors forming two cascaded amplifier cir¬ cuits to further amplify the signal and to match it to the above mentioned antenna circuit; choke coils being provided to prevent the useful signal from propagating towads the power supply; 2.3.3 - an antenna formed by a certain number of wires having proper lengths and freely disposed in the environment to be protected. The invention will now be described in detail with parti¬ cular reference to the attached drawings, given as a non limiting example and showing a preferred embodiment of the in¬ vention, in which: - Fig. 1 is a schematic perspective view illustrating a computer connected to the units forming the subject device; - Fig. 2 is an external schematic perspective view of the network filter unit; - Fig. 3 is an external schematic perspective view of the masking unit; - Fig. 4 is a diagram showing the positioning of the fil¬ ter unit; - Fig. 5 is an electric diagram illustrating said filter unit; - Fig. 6 is an electric diagram illustrating the power supply of the masking unit; - Fig. 7 is an electric diagram of the masking unit, and more particularly of the white noise generator and of the suc¬ cessive amplifier. As it is evident from the figures, the subject device sub- stantially is made up by two units: a network or line filter unit 1 and a masking unit 3. Said units 1 and 3 are shown in Fig. 1 as applied to a conventional personal computer also shown in the figure and comprising a keyboard 5, a video display 7 and the computer 9. It has been deemed proper to represent said units 1 and 3 as connected to a computer in order to put in evidence their volumes and to roughly show the physical size thereof. In Fig.s 2 and 3 said filter and masking units 1 and 3 are represented as separate units for a better clearness. The network filter unit 1 is provided to protect all the electronic devices connected thereto from possible transients and surges in the power distribution network, at the same time drastically attenuating guided signals that might come out of the electronic devices themselves. Fig. 4 is a circuit diagram showing the allocation of a filter unit 1: in such diagram it is further shown the power supply circuit for such filter unit: 11 indicates a switch, 13 an indicator lamp, 15 a fuse, 17 a number of user connectors. Fig. 5 illustrates the circuit diagram of a filter unit 1. It comprises a number of inductors 21 and capacitors 23 (L-C) sections 19 interposed between gas-discharge valves or surge arresters 25 and metal oxide varistors 27. Some inductors 21 are individually wound on ferrite sticks whereas some other indicated at 29 are wound in pairs over tori; this construction provides a good attenuation of distur¬ bances, surges, interferences, etc., both common mode and dif¬ ferential mode. The gas-discharge arresters 25 are devices whose inner resistance becomes quite low when the voltage applied to their terminals exceed a predetermined conduction threshold, being able to bypass or short-circuit currents in the order of several kA and returning to the original status, ready for fu¬ ture events after the transient ceases. The metal oxide varistors are resistors the resistive value of which varies inversely with the voltage applied to their terminals and therefore exhibits an decreasing resistance value to an increasing voltage, thus allowing for the flow of a gradually increasing current. The purpose of the L-C sections 19 is that of attenuating the high frequencies guided towards the power distribution network, by about of 80 dB (about 10,000 times) in a bandwidth extending approximately from 1 MHz to 1.5 GHz. In the illustrated embodiment of the filter unit 1 four sections are provided, see Fig. 5. From the graphs of Fig. 8 it can be seen the way a hypothetical high power transient or surge is "treated" by said filter unit 1 in the different passages. In A it is illustrated a hypothetical voltage surge with a slope of about 1 kV/μs (Fig. 8a); in B said surge is "clipped" at about 600 V (Fig. 8b); in C at about 400 V (Fig. 8c); and in D at about 250 V (Fig. 8d) within a time delay in the order of 1 μs. The voltage level of the surge, now reduced to the indi¬ cated value, is no longer fearful, nor is able to damage the users apparatuses, of the type of a computer. It is evident that such filter unit can be designed for different rates, wherein the components are properly dimen¬ sioned as a function of the A.C values requested by the dif¬ ferent user typology. The masking unit 3 substantially comprises three sections: - a power supply 31 (Fig. 6) - a white noise generator 33 (Fig. 7) - a wide band amplifier 35 and antenna circuit (Fig. 7). The power supply 31 (Fig. 6) is a conventional power supp¬ ly comprising a transformer 37 having a high insulation be¬ tween the primary and the secondary windings (in the order of 4,000 V as a safety against dangerous discharges) which con¬ verts the mains voltage (220 V A.C) in a proper low voltage (about 13 V A.C), a diode bridge 39 and a capacitor 41 rec¬ tifying the A.C voltage and converting it into a D.C. volt¬ age. The transistor 43 together with the Zener diode 45 stabi¬ lize the D.C voltage at the proper value of 12 V D.C, at output 47, a value adapted for the working of the successive stations . 11 The white noise generator 33 is obtained by means of the reverse biasing of three transistors 49 (49.1, 49.2, 49.3) through three resistors 51 (51.1, 51.2, 51.3) and a potentiometer 53.1. Due to the dispersion of the characteristics of the three transistors 49, a continuous spectrum from about 1 MHz to about 1.5 GHz is generated which is completely random and un¬ predictable, and therefore impossible to be decoded. The so generated white noise is applied to the successive section 35 through the capacitors 55 (55.1, 55.2, 55.3) The wideband amplifier and antenna circuit 35 is designed in such a way as to linearly amplify the signal from the preceding stage within the whole considered bandwidth. The amplifier circuit 35 substantially comprises: - three hybrid circuits 57 (57.1, 57.2, 57.3) being fed by the power supply through the resistors 51.4, 51.5, 51.6, respectively; the capacitors 55.4, 55.6 and 55.8 being pro¬ vided for eliminating possible spurious components. The radiofrequency output of the hybrid circuits 57 is present at the terminal 8 thereof, the inductors 59.5, 59.6 and 59.7 acting as choke coils to prevent the useful signal from propagating towards the power supply. The capacitor 55.5 couples the output of the hybrid cir¬ cuit 57.1 to the input of the circuit 57.2; the capacitor 55.7 couples the output of 57.2 to the input of 57.3, and finally the capacitor 55.12 couples the output of 57.3 to the rest of the circuit. - three transistors 49.4, 49.5, 49.6; the transistor 49.4 being properly biased by resistors 51.7, 51.8, 51.10, 51.15, 51.16; the capacitor 55.14 providing a moderate feedback. The oscillating circuits formed by resistor 51.9, inductor 59.1 and capacitor 55.24, and by capacitor 55.13 and inductor 59.2, respectively, serving to linearize the radiofrequency output from transistor 49.4 that is present on capacitor 55.15 acting as a decoupling capacitor between this stage and the succes¬ sive. The potenziometer 53.2 is used to adjust the level of the power radiated from the antenna circuit 61 within such limits as to comply with the rules en force (Rules CENELEC) . The transistors 49.5 and 49.6 are substantially the core of two cascaded amplifier circuits adapted to further amplify the signal and to match it to the above mentioned antenna cir¬ cuit 61. The inductors or inductance coils 59.3 and 59.4 are chokes to prevent the useful signal from propagating towads the power suppl . - an antenna 61 externally formed by a certain number of wires 63 having proper lengths and freely disposed in the en¬ vironment to be protected. As already indicated, all the users must be connected to the filter unit 1 (including the masking unit 3) in order to be protected against the electrical disturbances and surges from outside, thus preventing at the same time the risk of guided signals outcoming from the electronic apparatuses being picked up by the power distribution network. The masking unit 3 must be located as near as possible to the system video terminal 7 to be protected. This way the emission of white noise over an extended spectrum of frequencies by said unit 3 hides also the emission in a certain frequency which is typical of the system. In other words, a person attempting to pick up at any dis¬ tance the signals radiated by the video terminal (or the computer), by means of an antenna of the TV type (in case properly modified) or by means of any other trick, simultaneously receives on the same wavelenght also the white noise signal emitted by the masking unit. Since this signal is isofrequential and completely random it cannot be discrimined from the signal coming from the data processing system, and the pick up thereof is rendered use¬ less. Although the external appearance of the filter unit 1 is substantially a technical one, so that it is not very dif¬ ferent from a distribution box with a plurality of outlet con¬ nectors, the masking unit 3 can be associated to or camouflaged as one of the objects usually present on desks, such as a pen-holder a paper-weight, containers for various items, table-clock, etc. All the above is rendered possible and easier since the volume required by the electronics is about § cubic decimeter. Of course the material of the outer envelope can be of any type, this latter being of no relevance to the proper working ' of the device. It is evident that the invention is not limited to the de¬ scribed and illustrated embodiment, but several modifications and additional improvements can be carried out within the scope of the invention.

Claims: C I M S 1. A protective device for computers and the like, adapted to prevent the pick up, the recording and the unauthorized use of data from the computers during the working thereof, and to protect them against high energy transient disturbances taking place on the main A.C. power line, characterized in that it substantially comprises two units: 1. a network filter unit (1) ; 2. a masking unit (3) ; 1. the network filter unit (1) or "main unit" being made up by a number of sections (19) comprising inductances (21) and capacitances (23), interposed between gas-discharge surge arresters (25) and metal oxide varistors (27); the gas- discharge arresters (25) bypassing currents in the order of several kA when subjected to a voltage higher than their con¬ duction threshold; the metal oxide varistors (27) being resistors whose resistance value is an inverse function of the voltage applied to their terminals, so that with the increase of the applied voltage their resistance becomes smaller and smaller, thus conducting a larger and larger current; the sec¬ tions (19) comprising inductances (21) and capacitances (23) attenuating the high frequencies guided to the power distrib¬ ution network by about 80 dB (i.e. about 10.000 times) in a bandwidth approximately extending from 1 MHz to 1.5 GHz; for example, a 1 kV/lμs transient surge in the first station (A) is "clipped" at about 600 V in the second (B) , at about 400 V in the third (C), and at about 255 V in the fourth (D) ; said filter unit (1) being designed for different ratings, with the components properly dimensioned as a function of the A.C. values requested by the different user typologies; 2.- The masking unit (3) or "ghost" unit in turn compris¬ ing three sections: 2.1 - a power supply (31); 2.2 - a white noise generator (33); 2.3 - a wideband amplifier (35) and antenna circuit; 2.1 - the power supply (31) comprising a transformer (37) having a high insulation between the primary and the secondary windings, which converts the mains voltage (220 V A.C.) in a proper low voltage (about 13 V A.C), a diode bridge (39) and a capacitor (41) adapted to rectify the A.C. voltage and con¬ vert it into a D.C. voltage; a transistor (43) together with a Zener diode (45) stabilizing the D.C. voltage at a proper value, at (47), e.g. 12 V D.C, adapted for the working of the successive stations; 2.2 - the white noise generator (33) being obtained by means of the reverse biasing of at least three transistors (49.1, 49.2, 49.3) through three resistors (51.1, 51.2, 51.3) and a potentiometer (53.1); the dispersion of the character¬ istics of the three transistors (49.1, 49.2, 49.3) generating a continuous spectrum from about 1 MHz to about 1.5 GHz which is completely random and unpredictable, and therefore impos¬ sible to be decoded; said white noise being applied to the successive section through three capacitors (55.1, 55.2, 55.3); 2.3 - the wideband amplifier (35) and antenna circuit, de¬ signed in such a way as to linearly amplify the signal from the preceding stage within the whole considered bandwidth, substantially comprising: 2.3.1 - at least three hybrid circuits (57.1, 57.2, 57.3) being fed by the power supply through three resistors, (51.4, 51.5, 51.6) respectively; suitable capacitors (55.4, 55.6, 55.8) being provided for eliminating possible spurious components; the radiofrequency output of the hybrid circuits (57.1, 57.2, 57.3) being present at a terminal (8) thereof, suitable inductors (59.5, 59.6, 59.7) acting as choke coils to prevent the useful signal from propagating towards the power supply (31); additional capacitors (55.5, 55.7) coupling the outputs of the first (57.1) and the second (57.2) hybrid cir¬ cuits to the inputs of the second (57.2) and third (57.3) hybrid circuits, respectively; whereas another capacitor (S5.12) connects the output of the third hybrid circuit (57.3) to the rest of the circuit; 2.3.2 - at least three transistors (49.4, 49.5, 49.6); the first (49.4) of which biased by resistors (51.7, 51.8, 51.10, 51.15 and 51.16), a capacitor (55.14) providing a moderate feedback; the output of said transistor (49.4), linearized at radiofrequency by two oscillating circuits (51.9, 59.1, 55.24) (55.13, 59.2), being present on the capacitor (55.15) acting as decoupling capacitor between this stage and the successive; a potenziometer (53.2) being provided to adjust the level of the power radiated from the antenna circuit (61) within such limits as to comply with the rules en force; the other two transistors (49.5, 49.6) forming two cascaded amplifier cir¬ cuits to further amplify the signal and to match it to the above mentioned antenna circuit (61); choke coils (59.3, 59.4) being provided to prevent the useful signal from propagating towads the power supply; 2.3.3 - an antenna (61) formed by a certain number of wires (63) having proper lengths and freely disposed in the environment to be protected. 2. A protective device as claimed in claim 1, character¬ ized in that the filter unit (1), provided for different rates having the components dimensioned as a function of the A.C. values requested by the different user typologies, is con¬ nected to the masking unit (3) in order to protect the com¬ puter or the like both against transient coming from outside and against the escape of data through the network. 3. A protective device as claimed in claims 1 and 2, char¬ acterized in that the masking unit (3) , connected to the fil¬ ter unit (1) , is adapted to protect the computer or the like against the escape of data both through the air and the network, with the aid of the filter unit (1).

Inventors: GILARDI GIOVANNI, SCARAZINI SEVERINO, GILARDI, GIOVANNI, SCARAZINI, SEVERINO
Applicants: DATA PROTECTION SRL, DATA PROTECTION S.R.L.
Application year: 1990
Main classification: H02H9
IPC codes: G06F21, H02H9