EP0411917A1 - Sicherheit für Videomonitoren - Google Patents

Sicherheit für Videomonitoren Download PDF

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Publication number
EP0411917A1
EP0411917A1 EP90308448A EP90308448A EP0411917A1 EP 0411917 A1 EP0411917 A1 EP 0411917A1 EP 90308448 A EP90308448 A EP 90308448A EP 90308448 A EP90308448 A EP 90308448A EP 0411917 A1 EP0411917 A1 EP 0411917A1
Authority
EP
European Patent Office
Prior art keywords
information
monitor
line
dummy
random
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90308448A
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English (en)
French (fr)
Inventor
Raymond Gordon Fielding
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rank Brimar Ltd
Original Assignee
Rank Brimar Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rank Brimar Ltd filed Critical Rank Brimar Ltd
Publication of EP0411917A1 publication Critical patent/EP0411917A1/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G1/00—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data
    • G09G1/06—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data using single beam tubes, e.g. three-dimensional or perspective representation, rotation or translation of display pattern, hidden lines, shadows
    • G09G1/14—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data using single beam tubes, e.g. three-dimensional or perspective representation, rotation or translation of display pattern, hidden lines, shadows the beam tracing a pattern independent of the information to be displayed, this latter determining the parts of the pattern rendered respectively visible and invisible
    • G09G1/16—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data using single beam tubes, e.g. three-dimensional or perspective representation, rotation or translation of display pattern, hidden lines, shadows the beam tracing a pattern independent of the information to be displayed, this latter determining the parts of the pattern rendered respectively visible and invisible the pattern of rectangular co-ordinates extending over the whole area of the screen, i.e. television type raster
    • G09G1/165—Details of a display terminal using a CRT, the details relating to the control arrangement of the display terminal and to the interfaces thereto
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/18—Use of a frame buffer in a display terminal, inclusive of the display panel

Definitions

  • This invention is concerned with security of a radiation-emitting display such as a video monitor, particularly employing a cathode-ray tube (CRT).
  • a radiation-emitting display such as a video monitor
  • CRT cathode-ray tube
  • a video signal is used to modulate the beam of a cathode ray tube as the beam is raster-scanned over the tube face. This presents a security problem, because the radiation given off by the tube and its circuitry can be detected from a distance, and it is possible to reconstruct the video image.
  • a monitor and/or an associated device can be caused to give off radiation, optionally of a random nature, in addition to that caused by the display of information by a CRT or other thermionic device and its circuitry.
  • the dummy radiation need not be random, and it may substantially complement that emitted by the monitor such that the combined radiation is substantially uniform. If such dummy radiation were sent to a CRT, its screen would show substantially a negative of the picture to be displayed by the monitor. Random in this specification includes substantially random.
  • the present invention provides a method of operation of a monitor, wherein video or other information is displayed on the monitor intermittently, characterised in that dummy radiation is generated during the non-display of information.
  • the invention also provides a method of operation of a monitor wherein a stream of video or other information is received in one order, characterised in that the stream of information is displayed on the monitor in a different order.
  • the two aspects of the invention may be combined, and the additional radiation given off during blank periods during display of a field and/or during the inter-line and inter-field periods of the raster-scanning by the electron beam.
  • a standard composite video signal is received on input line 10.
  • the video signal contains a series of video lines.
  • a sync separator 12 extracts from the video signal a field sync signal on line 14 and a line sync signal on line 16.
  • the video signal at line 18 is passed to the data inputs of two frame stores, store A 20 and store B 22 and also to a pixel sync separator 24, which produces a pixel sync signal on line 26.
  • the pixel sync signal on line 26 pulses with each input pixel;
  • the line sync signal on line 16 pulses with each line of input pixels;
  • the field sync signal on line 14 pulses with each field of input lines.
  • the pixel sync pulses on line 26 are counted by a pixel counter 28, which is reset by the line sync signal on line 16, and the output count value on bus 30 is used for X address selection of store A 20 and store B 22.
  • the pulses of the line sync signal on line 16 are counted by a line counter 32, which is reset by the field sync signal on line 14, and the output line count value on bus 34 is used for Y address selection for store A 20 and store B 22 during writing to the stores.
  • the field sync signal on line 14 is also supplied to a bistable flip-flop 36 which supplies read/write selection signals on lines 38A, 38B alternately and oppositely to store A 20 and store B 22 so that for one field period store A 20 is being written to and store B 22 is being read from, and for the next field period store B 22 is being written to, and store A 20 is being read from.
  • the video information for successive fields of the input video signal on line 10 is successively written to store A 20 and store B 22 and that while one of the stores is being written to, the other store is enabled for reading by the signal on the appropriate line 38A, 38B.
  • the input video lines are written into the stores in the order in which they arrive. the video lines are read out from the stores in random order, as described in detail below.
  • a random line number generator 40 is responsive to the field sync pulses on line 14 and the line sync pulses on line 16 and provides a random line number on bus 52. With each line sync pulse, a different line number is output on the bus 52, until all of the permissible line numbers have been output and a field sync pulse is received.
  • the random line number is supplied on bus 52 to the read address inputs of store A 20 and store B 22 and also to a digital-to-analogue converter 54.
  • data is read out on line 56A or 56B from that one of store A 20 and store B 22 which is enabled for reading by the signal on line 38A or 38B, the data corresponding to that one of the lines denoted by the random number on bus 52, and all of the pixels for that line are read out by virtue of incrementation of the value on the pixel count bus 30.
  • the output data on line 56A or 56B is input to a gate 58 and is supplied via an amplifier 60 to the grid or cathode of a cathode ray tube 62. Therefore, as the electron beam is raster-scanned across the tube, it is modulated by the output data.
  • the line sync signal on line 16 is supplied to a line generator circuit 64, which supplies a saw tooth driving signal to a horizontal deflection coil 66 of the cathode ray tube 62.
  • the output of the digital-to-analogue converter 54 is supplied to a field amplifier 68, which in turn drives a vertical deflection coil 70 of the cathode ray tube 62.
  • a circuit 72 is provided for supplying biassing, focussing and other control voltages to the cathode ray tube 62, and a power supply 74 is included for providing EHT to the tube 62.
  • the random line number generator 40 described above may be implemented by a microcomputer, as shown in figure 2, comprising a microprocessor 90 with associated ROM 92 storing programme data, RAM 94, and input-output port 96 connected to the field and line sync pulse lines 14, 16 and the line address bus 52.
  • the microprocessor 90 is programmed to perform the steps of operation illustrated by the flow diagram of figure 3.
  • a field sync pulse is awaited on line 14 indicating the beginning of a new field.
  • variables L(1) L(2)....L(N) are set to zero in step 102. These variables are used line flags, and when set to zero they indicate that the respective line has not been used in the current field, and when set to one, they indicate that the line has been used in the current field.
  • N is the number of lines in a field.
  • variable R is set to a random integer number between one and N the number of lines in a field.
  • step 108 the used line flag for line R is set to one, and in line 110 a line sync pulse on line 16 is awaited.
  • step 112 the output line address on bus 52 is set equal to the random number.
  • step 114 it is determined whether a field sync pulse is also present on line 14, and if so, then the routine returns to step 102. However, if there is no field sync pulse, then the routine returns to step 104.
  • step 196 if the used line flag for line R has already been set, then in step 116 the variable R is incremented by one.
  • step 118 the routine returns to step 106, unless it is determined in step 118 that the variable R is greater than the number N of lines in a field, in which case the variable R is set to one in step 120, before returning to step 106.
  • the routine returns to step 106, unless it is determined in step 118 that the variable R is greater than the number N of lines in a field, in which case the variable R is set to one in step 120, before returning to step 106.
  • an increment of one and a decrement of one may be used alternately in step 116 for successive random line numbers to be generated.
  • a random number generator 130 generates a random number on a bus 132 in response to a line sync pulse on line 16, the random number having a value between one and the maximum number of lines in a field.
  • the random number on bus 132 is added to the count in a ring counter 134.
  • the ring counter 134 employs modular arithmetic having a base equal to the maximum number of lines in a field.
  • the result of the addition is output on bus 136 to a latch circuit 138 which is enabled by the line sync signal on line 16 and also to a used line memory 140.
  • the used line memory provides a flag for each line of the field, and the flag for a particular line is set when that line number appears on the bus 136.
  • the used line memory 140 also has the function of outputting on line 142 a signal in the case where the line number on bus 136 has already been flagged, and the signal on line 142 is used to increment to the ring counter by the value of one. All of the flags in the used line memory 140 are reset at the beginning of each field by the field sync pulse on line 14. It will thus be appreciated that the output from the latch 138 on the address line bus 52 will not be repeated during any particular field, and that within a particular field period a series of random line numbers will appear on a bus 52.
  • a pixel generator 76 is supplied with the pixel sync signal on line 26 and provides on line 78 a series of pixel signals which are combined with the data read out from the stores 20, 22 by a pair of gates 80, 82 so that a dummy pixel signal is output from the gate 82 when there is no pixel data being output from either store 20, 22.
  • the dummy pixel signal is then applied via an amplifier 84 to the cathode or grid of a dummy thermionic valve 86, which may be of similar construction to the gun of the cathode ray tube 62.
  • the dummy valve 86 is supplied with anode voltage from the EHT supply 74, and may also be supplied with bias and focussing voltages from the circuit 72.
  • dummy data is supplied to the valve 86 and dummy radiation is created.
  • the dummy valve 86 may be used with a conventional monitor in order to obscure the radiation given off by the monitor.
  • the dummy radiation may be randomised, or sone ordered pattern provided which together with the radiation from the CRT provides either no coherent information, or incorrect or different information.
  • the object of this proposal is a device which, although displaying information in the normal way, nevertheless radiates a full screen of dots.
  • less than a full screen of dots is radiated, random or ordered radiation is added to that resulting from the displayed dots such that the result conveys no information or other different information from that displayed.
  • the VDU may contain a first CRT for displayed information and a dummy or other tube (or other radiation emitter), which preferably has similar characteristics to the CRT.
  • the dummy could take the form of a thermionic valve, built using a normal CRT gun, but optionally with a solid anode instead of the CRT deflection system and screen, hence it could be small, and easily contained within the volume of a normal VDU.
  • the second tube could display a negative picture of that shown on the first CRT; a second full screen would in general not be preferred because of size etc.
  • Incoming information in the form of coherent pixels, is detected and used to synchronise a slave pixel generator inside the display.
  • This generator is used to provide video pulses which, if applied as video to the CRT, would result in a full screen of dots (or in a pattern not revealing the information to be displayed to the legitimate viewer) as described earlier.
  • the incoming video signal information carried by which is to be displayed by the monitor, causes respective pixel pulses to be sent selectively to the monitor or to the dummy thermionic device. In general only the pulses containing valid information would be routed to the CRT.
  • all the pixel signals are generated by the same clock, and are fed to as near as possible identical thermionic devices (CRT and dummy), and therefore it should not be possible for a would-be eavesdropper to discriminate between the two, hence he could detect only a full, blank, screen.
  • CRT and dummy identical thermionic devices
  • a further refinement may be desirable for the following reason.
  • the way that characters are formed and presented to the monitor by differing computer systems varies. Some represent straight horizontal lines (such as underlining or the composition of individual letters) as a series of individual pixels, and others as long, uninterrupted, video pulses.
  • Figure 5 shows an overall block diagram of a preferred system.
  • lt may comprise elements of a monitor such as sync separator, video and scan circuits, together with the CRT and necessary power supplies together with a pixel generator and means to switch "scrambler" pixels into a dummy or other second tube.
  • a monitor such as sync separator, video and scan circuits, together with the CRT and necessary power supplies together with a pixel generator and means to switch "scrambler" pixels into a dummy or other second tube.
  • the pixel generator provides a continuous stream of video pulses in synchronism with incoming information; synchronising is achieved as follows (see waveform diagrams Figures 6 and 7).
  • An internal clock is used to drive a counter (in this case, a shift register).
  • the counter is reset at the start of every scanned line (see Figure 6).
  • the number contained in the counter at that time is loaded into a simple number store and the counter is reset, whereupon it starts counting again.
  • a number comparator which is connected to both counter and store emits a pulse, which again resets the counter.
  • the comparator will emit pulses at regular intervals depending upon the clock rate and the number held in store.
  • the next video pulse to arrive will interrupt the count and shorten the cycle, and so on, until the number held in the store represents the minimum time interval between incoming video pulses; this number is held in store for as long as necessary.
  • the comparator at this time will emit a steady stream of pulses synchronously with incoming video, and representing the maximum pixel frequency.
  • Figure 6 shows a simplified version of this sequence.
  • the comparator output pulses are then delayed, as shown in Figure 7, and passed to the pixel shaper.
  • the pixel shaper determines the length of pulses forming the pixels on the VDU screen.
  • incoming video pulses are passed to a "gate shaper", which lengthens and shapes each pulse, such that it completely brackets the pulses generated by the pixel shaper.
  • a gate shaper which lengthens and shapes each pulse, such that it completely brackets the pulses generated by the pixel shaper.
  • the pulses generated by the pixel shaper may be switched cleanly between the CRT and the dummy, with no residual edges to betray the presence, in the emitted radiation, of a character.
  • the CRT and dummy are closely matched, in terms of electrical characteristics as possible, and are run from common supplies in order to make the radiation from each, as far as possible, indistinguishable.
  • CRT and dummy are preferably mounted as closely together as possible, and video drive leads should be routed together.
  • All video logic circuits should be screened since they will in general radiate differently, and care should be devoted to earthing since circulating earth currents might cause differential radiation.
  • a programme was carried out with the object of demonstrating the feasibility of scrambling the radiated emissions from a VDU in the way described above.
  • a dummy tube was constructed, using a CRT electron gun and this was mounted close to the gun of the display CRT.
  • a second video amplifier was introduced, of the same type as that used in the VDU.
  • a pixel generator and gating circuit was constructed, run from the pixel clock in the character generator, and the whole was screened as well as practicable.
  • An eavesdropping device was constructed from a second VDU driven from a very broad bandwidth oscilloscope amplifier.
  • the lower part of the bandwidth of the amplifier was restricted by means of a simple high-pass filter, in order to limit sensitivity to line-flyback frequencies.
  • the eavesdropping VDU was synchronised, line and field, to the character generator.
  • a character generator was used for these tests in preference to a PC, from the point of view of accessibility of tho pixel clock.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Television Systems (AREA)
  • Controls And Circuits For Display Device (AREA)
EP90308448A 1989-07-31 1990-07-31 Sicherheit für Videomonitoren Withdrawn EP0411917A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8917450A GB2237711A (en) 1989-07-31 1989-07-31 Security of video monitors.
GB8917450 1989-07-31

Publications (1)

Publication Number Publication Date
EP0411917A1 true EP0411917A1 (de) 1991-02-06

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ID=10660907

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90308448A Withdrawn EP0411917A1 (de) 1989-07-31 1990-07-31 Sicherheit für Videomonitoren

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EP (1) EP0411917A1 (de)
AU (1) AU6056290A (de)
GB (1) GB2237711A (de)
WO (1) WO1991002344A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2410754A3 (de) * 2010-07-19 2015-07-22 Samsung Electronics Co., Ltd. Vorrichtung und Verfahren zur Verarbeitung eines Bildes und Vorrichtung und Verfahren zu dessen Anzeige

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0168861A2 (de) * 1984-06-22 1986-01-22 Staat der Nederlanden (Staatsbedrijf der Posterijen, Telegrafie en Telefonie) Videoanzeigeterminal mit derangierten Bildzeilen
EP0235947A2 (de) * 1986-02-28 1987-09-09 International Computers Limited Videoanzeigegerät
EP0240328A2 (de) * 1986-04-03 1987-10-07 Datasafe Limited Rechnersicherheitsvorrichtung

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2067871A (en) * 1980-01-19 1981-07-30 Marconi Co Ltd Information Encoding Systems
GB2094587B (en) * 1981-03-11 1985-02-13 Sony Corp Data processing
GB2139843B (en) * 1983-05-11 1987-07-08 Sony Corp Digital video tape recorder apparatus
GB8619737D0 (en) * 1986-08-13 1986-09-24 Philips Electronic Associated Business management

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0168861A2 (de) * 1984-06-22 1986-01-22 Staat der Nederlanden (Staatsbedrijf der Posterijen, Telegrafie en Telefonie) Videoanzeigeterminal mit derangierten Bildzeilen
EP0235947A2 (de) * 1986-02-28 1987-09-09 International Computers Limited Videoanzeigegerät
EP0240328A2 (de) * 1986-04-03 1987-10-07 Datasafe Limited Rechnersicherheitsvorrichtung

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2410754A3 (de) * 2010-07-19 2015-07-22 Samsung Electronics Co., Ltd. Vorrichtung und Verfahren zur Verarbeitung eines Bildes und Vorrichtung und Verfahren zu dessen Anzeige

Also Published As

Publication number Publication date
WO1991002344A1 (en) 1991-02-21
GB2237711A (en) 1991-05-08
GB8917450D0 (en) 1990-10-10
AU6056290A (en) 1991-03-11

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