JP2018036552A - Electromagnetic information restoration evaluation device, electromagnetic information restoration evaluation method, and electromagnetic information restoration evaluation processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately evaluate easiness of screen restoration in a frequency band of an electromagnetic wave including screen information.SOLUTION: An electromagnetic information restoration evaluation device acquires, if a frequency having a predetermined electromagnetic field intensity level higher than noise is present in the vicinity of a first frequency indicated by a product of resolution and refresh rate of the screen information in a horizontal direction, or in the vicinity of a second frequency indicated by a product of resolution and refresh rate of the screen information in a vertical direction, in a frequency spectrum based on an electromagnetic wave radiated from a display device serving as evaluation object for easiness of screen information restoration, a screen signal component obtained by summing a frequency component in the vicinity of the existing frequency and an integrated value of harmonic component signal strength and a noise component obtained by summing integrated values of signal strength of the frequency components other than the frequency of the screen signal component, and calculates an evaluation value for evaluating the easiness of restoring screen information on the basis of a ratio of a value of the screen signal component to a value of the noise component.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an electromagnetic information restoration evaluation device, an electromagnetic information restoration evaluation method, and an electromagnetic information restoration evaluation processing program.

  The threat of electromagnetic wiretapping that obtains information from weak electromagnetic waves radiated from electronic devices has been pointed out. For example, the threat of screen snooping using leaked electromagnetic waves from display devices has been a concern. This threat of screen snooping is particularly a concern for stationary displays with relatively high electromagnetic wave strength.

  When the interface for transferring screen information to a display device is a conventional analog interface, the screen is displayed as a bit string of analog voltage values including luminance information in the device or in the wiring connecting the display device and the electronic device. Information is transmitted. When there is a color change or color shading on the screen, the above-mentioned analog voltage value changes, so that there is a possibility that an electromagnetic field is generated and is radiated to the outside as a so-called electromagnetic wave.

  In most cases, the leakage electromagnetic wave radiated to the outside (far) is a harmonic component of an electromagnetic field generated by the change in the analog voltage value. For this reason, a leaked electromagnetic wave is received by an antenna, detected, and demodulated, whereby a bit string of analog voltage values including the original screen information can be obtained. Furthermore, this bit string is input to the RGB input terminal of the monitor corresponding to the analog interface, and the vertical synchronization signal and the horizontal synchronization signal specific to the display device to be screened are simultaneously input, so that the display screen contents can be changed. Can be reproduced (see, for example, Non-Patent Document 1).

  The analog interface is an interface for a CRT display (CRT display) that performs drawing by a raster scan method. Even in the mainstream LCD displays (liquid crystal displays), many displays have an analog interface in order to maintain interface compatibility.

  In addition, even in LCD displays and tablet terminals using digital interfaces, if there is a part where data is serially processed and transmitted in the device, electromagnetic waves including screen information may be leaked from the liquid crystal drive unit. As with displays equipped with an interface, there is concern about the threat of screen snooping (see Non-Patent Document 2, for example).

  Usually, an electromagnetic wave radiated from an electronic device including a display includes a signal component generated in the electronic device and its harmonic component, and often has a wideband frequency component. Therefore, when evaluating the threat of information leakage from electromagnetic waves, a method to check whether the screen information has been reproduced by actually receiving the leaked electromagnetic waves of all frequency bands in order and trying to restore the screen information so far. I took it.

Suzuki Yasunao, Tajima Kimihiro, Masugi Masao, Yamane Hiroshi, "Technology for Information Leakage due to Electromagnetic Waves Eradiated from PC", NTT Technical Journal (August 2008), p.11-15, August 10, 2016 Search, Internet <URL: http://www.ntt.co.jp/journal/0808/files/jn200808011.pdf> Y. Hayashi, N. Homma, M. Miura, T. Aoki, H. Sone, "A Threat for Tablet PCs in Public Space: Remote Visualization of Screen Images Using EM Emanation," 21st ACM Conference on Computer and Communications Security (CCS '14), PP.954-965, 2014., searched on August 10, 2016, Internet <URL: http://dl.acm.org/citation.cfm?id=2660292>

  However, since the screen information restoration method requires advanced technology and screen information is restored one by one, it takes a very long time to identify which frequency band contains the screen information, and It is impossible to quantitatively evaluate how much screen information is included.

  An object of the present invention is to provide an electromagnetic information restoration evaluation device, an electromagnetic information restoration evaluation method, and an electromagnetic information restoration evaluation process capable of appropriately evaluating the ease of screen restoration in the frequency band of electromagnetic waves including screen information. Is to provide a program.

  In order to achieve the above object, the first aspect of the electromagnetic information restoration evaluation apparatus in the embodiment of the present invention inputs an electromagnetic wave radiated from a display device that is an evaluation target of ease of restoration of screen information. An antenna unit, a bandpass filter unit that outputs a signal of a frequency component of a predetermined band for the electromagnetic wave input by the antenna unit, a detection demodulator unit that detects and demodulates the signal output by the bandpass filter unit, A frequency characteristic confirmation unit that obtains a frequency spectrum by performing a fast Fourier transform on a signal output from the detection demodulation unit; and a horizontal resolution of screen information displayed on the display device and a refresh of the screen information in the frequency spectrum. The vicinity of the first frequency indicated by the product of the rate or the vertical resolution of the screen information displayed on the display device When a frequency having a predetermined electromagnetic field intensity level higher than a noise floor exists in the vicinity of the second frequency indicated by the product of the refresh rate, a frequency component near the existing frequency in the frequency spectrum, and A screen signal component obtained by combining the integrated values of the signal strengths of the harmonic components and a noise component obtained by combining the integrated values of the signal strengths of frequency components other than the frequency of the screen signal component in the frequency spectrum are obtained. There is provided an apparatus having a calculation unit that calculates an evaluation value for evaluating ease of restoration of screen information based on a ratio between a component value and a noise component value.

  According to a second aspect of the electromagnetic information restoration evaluation apparatus configured as described above, in the first aspect, the bandwidth of the screen signal component is determined by a ratio based on the existing frequency.

  According to a third aspect of the electromagnetic information restoration evaluation device configured as described above, in the first aspect, the evaluation value of the screen information is a correlation coefficient based on a ratio between the value of the screen signal component and the value of the noise component. Provide a device that is a value.

  In order to achieve the above object, an electromagnetic information restoration evaluation method according to an embodiment of the present invention inputs an electromagnetic wave radiated from a display device to be evaluated for ease of restoration of screen information from an antenna unit. A frequency spectrum signal is output by outputting a signal of a frequency component of a predetermined band with respect to the input electromagnetic wave by a bandpass filter unit, detecting and demodulating the output signal, and performing fast Fourier transform on the detected and demodulated signal. The frequency spectrum is displayed in the vicinity of the first frequency indicated by the product of the horizontal resolution of the screen information displayed on the display device and the refresh rate of the screen information, or displayed on the display device. A location higher than the noise floor in the vicinity of the second frequency indicated by the product of the vertical resolution of the screen information and the refresh rate. When there is a frequency having the electromagnetic field intensity level, a screen signal component that combines the frequency component in the vicinity of the existing frequency in the frequency spectrum and the integrated value of the signal intensity of the harmonic component, and the frequency spectrum A noise component obtained by combining integrated values of signal intensities of frequency components other than the frequency of the screen signal component is obtained, and screen information can be easily restored based on a ratio of the value of the screen signal component and the value of the noise component. Provided is a method for calculating an evaluation value for evaluating the thickness.

  According to a second aspect of the electromagnetic information restoration evaluation method described above, in the first aspect, the bandwidth of the screen signal component is determined by a ratio based on the existing frequency.

  According to a third aspect of the electromagnetic information restoration evaluation method described above, in the first aspect, the evaluation value of the screen information is a value of a correlation coefficient based on a ratio between the value of the screen signal component and the value of the noise component. To provide a way to be.

  In order to achieve the above object, an aspect of the electromagnetic information restoration evaluation processing program in the embodiment of the present invention is a program used for a computer that operates as a part of the electromagnetic information restoration evaluation apparatus in the first aspect, A program for causing the computer to function as the antenna unit, the bandpass filter unit, the detection demodulation unit, the frequency characteristic confirmation unit, and the calculation unit is provided.

  According to the present invention, it is possible to appropriately evaluate the ease of screen restoration in the frequency band of electromagnetic waves including screen information.

The figure explaining the structure of the electromagnetic information decompression | restoration evaluation apparatus in embodiment of this invention. The figure explaining the structure of the frequency characteristic confirmation part of the electromagnetic information decompression | restoration evaluation apparatus in embodiment of this invention. The flowchart which shows an example of the processing operation by the electromagnetic information decompression | restoration evaluation apparatus in embodiment of this invention. The figure which shows an example of the image displayed on the object display used as restoration evaluation object of the screen information by the electromagnetic information restoration evaluation apparatus in embodiment of this invention. The figure which shows an example of the frequency characteristic of the electromagnetic waves containing the information of the screen displayed on the object display used as the object of restoration evaluation of the screen information by the electromagnetic information restoration evaluation apparatus in the embodiment of the present invention. The figure which shows an example of the relationship between the image and correlation coefficient which are displayed on the object display used as the restoration | recovery evaluation object of the screen information by the electromagnetic information restoration evaluation apparatus in embodiment of this invention.

Embodiments according to the present invention will be described below.
In this embodiment, in order to evaluate the frequency component of the electromagnetic wave including screen information and the ease of screen restoration at that frequency, out of the frequency component of the electromagnetic wave radiated from the display device (display device), the screen information Only the frequency components of electromagnetic waves including are specified.
Further, in this embodiment, the ease of screen restoration with this frequency component is automatically evaluated.

  The outline of the procedure is to detect or demodulate leaked electromagnetic waves of any frequency radiated from the display device, and to specify specific frequency components that may contain screen information (specific periodic components of the baseband signal). ), And if there is this specific frequency component, determine the presence or absence of frequency components including screen information and the ease of restoration of screen information by calculating the intensity ratio of signals related to screen information. To do.

As described above, in this embodiment, an electromagnetic wave radiated from the display device is acquired, and the acquired electromagnetic wave is detected and demodulated to determine the presence or absence of a specific frequency component. When screen information is included in the acquired electromagnetic wave, a drawing frequency signal can be observed by detecting and demodulating the electromagnetic wave.
Data related to screen information displayed on the display device has a periodicity depending on the resolution. For this reason, in a frequency channel in which information is leaked, periodicity is observed in the demodulated data. Therefore, a frequency having this periodicity is called a drawing frequency. This drawing frequency corresponds to the horizontal synchronization signal of the analog interface.
Therefore, by analyzing the signal after detection and demodulation, and examining the frequency component near the frequency calculated from the resolution and refresh rate of the screen information in the analyzed signal, the screen information is included in the acquired electromagnetic wave. It can be estimated whether or not.

  As described above, when the signal after detection and demodulation does not include a frequency component having an electromagnetic field intensity level equal to or higher than a predetermined frequency near the calculated frequency, screen information is not included in the acquired electromagnetic wave. It can be determined that there is no leakage.

  On the other hand, when the signal after detection and demodulation includes a frequency component having a predetermined or higher electromagnetic field intensity level near the calculated frequency, it is easy to restore the screen in a frequency band including this frequency component. There is a difference in degree.

  Therefore, in the present embodiment, the screen signal component is controlled in such a manner that the character / graphic shape / color of the image displayed on the display device has quantitative regularity and the periodicity of the screen is grasped in advance. And other noise components are defined in the periodic spectrum, and the ratio of these is calculated to evaluate how much the screen information can be restored based on this ratio.

  In the present embodiment, for example, when a frequency having a high electromagnetic field strength in the vicinity of a tentative candidate frequency of a drawing frequency is aHz, the frequency component of aHz and the harmonic component of N times (integer multiple). When all harmonic components up to N times are observed, in the periodicity of the leaked electromagnetic wave of a certain frequency, for example, a constant frequency width (± bHz) in the vicinity of aHz and the above-mentioned observed A frequency component determined by a certain frequency width (± b Hz) near the harmonic component can be defined as a screen signal component, and a frequency component other than the screen signal component can be defined as a noise component. Thereby, a signal noise ratio (SN ratio) can be defined. In this embodiment, the ease of screen restoration can be estimated from the defined value.

That is, when a leaked electromagnetic wave of a certain frequency is an electromagnetic wave including a frequency component having a high electromagnetic field strength in the vicinity of the provisional candidate frequency of the drawing frequency, an SN ratio related to this frequency component is derived, and this SN ratio is derived. The ease of screen restoration is evaluated by using an image evaluation index related to the value of, and the result of this evaluation is output as a value.
About the degree of ease of restoration of screen information, for example, correlation coefficient r, SSIM (structural similarity), PSNR (peak signal to noise ratio) etc. are used. Since quantitative evaluation can be realized, these can be used as the image evaluation index.

Next, a specific example of the embodiment of the present invention will be described.
FIG. 1 is a diagram illustrating the configuration of an electromagnetic information restoration evaluation apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the electromagnetic information restoration evaluation device according to the embodiment of the present invention evaluates whether or not screen information is included in an electromagnetic wave radiated from a target display terminal 10 that is a restoration evaluation target of screen information. It includes an antenna unit 11, an amplifier unit 12, a band pass filter unit (BPF) 13, a detection demodulation unit 14, a frequency characteristic confirmation unit (spectrum monitor) 15, a control unit 16, and a storage device 17.

The antenna unit 11 receives as wide an electromagnetic wave as possible radiated from the target display terminal 10. The amplifier unit 12 amplifies the radio wave signal received by the antenna unit 11 to a level sufficient for subsequent processing. The band pass filter unit 13 passes only a signal having a specific frequency component among the radio wave signals amplified by the amplifier unit 12.
The detection demodulation unit 14 detects and demodulates the signal that has passed through the band pass filter unit 13.
The frequency characteristic confirmation unit 15 obtains a frequency spectrum which is a signal in the frequency domain by performing FFT (Fast Fourier Transform) analysis on the signal input from the detection demodulation unit 14, and displays the frequency spectrum on a built-in monitor. .
FIG. 2 is a diagram illustrating the configuration of the frequency characteristic confirmation unit of the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention.
The frequency characteristic confirmation unit 15 includes an input unit 15a, an FFT analysis unit 15b, a drawing frequency candidate determination unit 15c, an image information evaluation value calculation unit 15d, a storage unit 15e, and an output unit 15f. The storage unit 15e is a storage medium such as a nonvolatile memory.

The control unit 16 controls the frequency band of the signal passing through the bandpass filter unit 13 and the frequency confirmed by the frequency characteristic confirmation unit 15, and records the measurement result and the measurement progress status in the storage device 17. The storage device 17 is a storage medium such as a nonvolatile memory.
The above-described configuration may be configured by either hardware or software, and may be configured by using functions of devices such as a spectrum analyzer and a personal computer.

Next, a procedure for specifying a candidate for an electromagnetic wave frequency including screen information and a candidate for a drawing frequency in the electromagnetic wave radiated from the target display terminal 10 will be described. FIG. 3 is a flowchart showing an example of processing operations performed by the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention.
First, the control unit 16 knows that the horizontal resolution of the screen of the target display terminal 10 is X (dpi), the vertical resolution is Y (dpi), and the screen refresh rate is Z (Hz). , The provisional candidate values of the drawing frequency of the screen information, that is, the frequencies f ₁ and f ₂ that are so-called rough candidate values, are calculated, and these calculated f ₁ and f ₂ are set in the frequency characteristic confirmation unit 15. In addition, it is recorded in the storage device 17 (A1).
f ₁ is obtained by X × Z, and f ₂ is obtained by Y × Z. For f ₁ and f ₂ , separately calculated values may be recorded in advance in the storage device 17 without depending on the control unit 16.

Next, the control unit 16 sets the lower limit value of the frequency range measured by the frequency characteristic confirmation unit 15, for example, a range of about 0 to several GHz, as f _min , and sets the upper limit value as f _max , and stores these values. 17 is recorded. f _min and f _max are set within a range supported by the electromagnetic information restoration evaluation apparatus as the measurement component device to be used.
Further, the control unit 16 sets the initial value of the center frequency fm in the frequency band of the electromagnetic wave radiated from the target display terminal 10 to pass through the band-pass filter unit 13 as the lower limit value f _min described above. They are set in the bandpass filter unit 13 and the frequency characteristic confirmation unit 15 and recorded in the storage device 17 (A2). The frequency fm is a center frequency of a frequency band having a predetermined width such as 10 MHz or 20 MHz and passing through the band pass filter unit 13.

  Next, the control unit 16 controls the image display by the target display terminal 10 to display an arbitrary image on the target display terminal 10 (A3). Note that the image displayed on the target display terminal 10 is not a white noise screen, but an image that can be determined to be significant by human vision, such as characters and figures.

FIG. 4 is a diagram illustrating an example of an image to be displayed on a target display which is a target for screen information restoration evaluation by the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention.
For example, as shown in FIG. 4, by using an image that divides the entire image at equal intervals in both vertical and horizontal directions using a combination of vertical lines, horizontal lines, or different color schemes, a frequency component that is an integral multiple of the drawing frequency is displayed on the screen signal. It can be controlled to be included in the ingredients. As a result, a strong electromagnetic field intensity peak can appear at a frequency depending on regularity, and the screen information can be easily recognized.

  The periodicity of the screen can be arbitrarily changed according to the line spacing and color scheme. As for the characters on the screen, it is possible to use a screen drawing method that uses only vertical and horizontal lines as much as possible, for example, alphabets “H” and “T” and katakana “e” and “co”. The difference between the vertical direction and the horizontal direction can be made as difficult as possible in terms of periodicity in the image. Hereinafter, as shown in FIG. 4, it is composed of a color scheme having the same vertical and horizontal periodicities, that is, a color scheme in which the number of color transitions is the same in both vertical and horizontal directions, and the letters “H” and “T” composed only of vertical and horizontal lines. A measurement procedure using an image will be described. In this case, the periodicity of the screen signal component concentrates on the drawing frequency component and its harmonic component.

  Next, the antenna unit 11 receives the electromagnetic waves radiated from the target display terminal 10. The received radio wave is amplified by the amplifier unit 12 and then passes through the bandpass filter unit 13 so that only the signal of the frequency component belonging to the band of the predetermined width from the center frequency fm set as described above. Is transmitted to the detection demodulator 14 (A4). The detection / demodulation unit 14 detects and demodulates the signal input from the bandpass filter unit 13 (A5).

Next, the input unit 15a of the frequency characteristic confirmation unit 15 inputs the signal obtained in A5. The FFT analysis unit 15b obtains a frequency domain signal by performing FFT analysis on the input signal (A6), and converts this signal from the lower limit value f _min set as described above to the upper limit value f _max . Display on the built-in monitor within the range.

The drawing frequency candidate determination unit 15c of the frequency characterization unit 15, the signal of the frequency domain, in the vicinity of or near the frequency f ₂ of the set frequencies f ₁ in A1, as compared with the noise floor (Noise floor) It is determined whether there is a frequency component having a high predetermined electromagnetic field intensity level (A7). The noise floor level may be the electromagnetic field intensity level of another frequency band in which the frequency component of the high electromagnetic field intensity level is not observed, or the electromagnetic wave observed when the display of the target display terminal 10 is turned off. Refers to one of the field strength levels. The electromagnetic field intensity level in the other frequency band is a value obtained by averaging the electromagnetic field intensity levels in a predetermined frequency range from this frequency centered on a frequency separated from the frequency f ₁ or f ₂ by a predetermined frequency. Point to.

If a frequency component having an electromagnetic field intensity level higher than Adb in comparison with the noise floor exists in the vicinity of the frequency f ₁ or f ₂ (Yes in A7), the image information evaluation value calculation unit of the frequency characteristic confirmation unit 15 15d is
In the frequency spectrum, the integrated value of the signal intensity of the frequency component f ₁ or f _{2 in} the vicinity of the frequency component having an electromagnetic field strength level higher than the Adb, and the signal strength of the frequency component in the vicinity of the harmonic component. The screen signal component S is set together with the integrated value. Similarly, the image information evaluation value calculation unit 15d sets an integrated value of frequency components other than the screen signal component S in the frequency spectrum as a noise component N (A8). A is a detection threshold, and is set to a value that can be clearly distinguished from the noise floor, for example.

Here, a method for defining S and N will be described.
In order to define the values of the screen signal component S and the noise component N described above, it is necessary to determine the bandwidth of the screen signal component S. Regarding the determination of the bandwidth of the screen signal component S, the frequency component f ₁ or f _{2 in} the vicinity of the frequency component having an electromagnetic field strength level higher than the above-mentioned Adb and the frequency component in the vicinity of the harmonic component up to ± 5 kHz. Is considered to be the bandwidth of the screen signal component S.
At this time, if the screen signal component S appears in the frequency component having the electromagnetic field intensity level higher than the Adb and the harmonic component thereof, the frequency component having the electromagnetic field intensity level higher than the Adb is the display terminal. Accordingly, the intervals between the frequencies at which the screen signal component S appears are different. Therefore, regardless of the value of the frequency component having an electromagnetic field strength level higher than the above Adb, when the bandwidth of the screen signal component S is uniformly set to the above ± 5 kHz, the weight of this value changes for each display terminal. Therefore, it is impossible to perform absolute evaluation independent of the terminal.

  Therefore, in the embodiment of the present invention, the image information evaluation value calculation unit 15d sets the frequency bandwidth of the screen signal component S to a ratio based on a frequency component having an electromagnetic field intensity level higher than the above Adb (for example, the above-mentioned 1/100) of the frequency component having an electromagnetic field intensity level higher than Adb. Thereby, the fairness of evaluation between display terminals can be maintained, and more versatile evaluation can be realized.

FIG. 5 is a diagram illustrating an example of frequency characteristics of an electromagnetic wave including information on a screen displayed on a target display that is a target for restoration evaluation of screen information by the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention.
In the example shown in FIG. 5, the frequency component having an electromagnetic field intensity level higher than the above Adb is S1, the harmonic components are S2 to S8, and the frequency bandwidth of 1/100 of the frequency component S1 is the screen signal. The bandwidth of the component S is set, and the other frequency bands N1 to N8 are set as the noise component N.

In connection with the determination of the bandwidth of the screen signal component S described above, the determination of which frequency range in the frequency spectrum the screen signal component S (for example, S1 to Sn) and the noise component N are integrated is performed. I need it.
In order to calculate an accurate S / N (S / N ratio), it is desirable to widen the frequency range as much as possible and to integrate more screen signal components S and signal strengths of noise components N. Actually, assuming that the frequency component is about 100 times as high as the frequency component S1, and in the example shown in FIG. 4, the frequency component S1 is 0.12 MHz, the signal intensity is integrated for the frequency band of 12 MHz. The screen information evaluation value can be calculated. Further, by integrating the signal intensity in the frequency band about 50 times the frequency component having the electromagnetic field intensity level higher than the above Adb, it is possible to calculate the screen information evaluation value with a practically no problem.

  The image information evaluation value calculation unit 15d calculates a ratio between the value of the screen signal component S and the value of the noise component N set in A8, and substitutes the calculated S / N value as an input of the evaluation function of the screen information. (A9).

Next, details regarding the evaluation function of the screen information will be described.
The screen information evaluation function includes, for example, correlation coefficients r, ssim, and psnr, which are considered to have a correlation with a general signal-to-noise ratio. Especially for the correlation coefficient r, (1) a binary signal is transmitted at a constant signal ratio under specific conditions (2) the variance of the signal component and the noise component can be separated significantly, (3) an analog signal In the case of comparison with ideal original data), “It can be formulated by the following equation (1).

r = √ (s / n) / √ (s / n + 1) (1)
Here, s / n is a signal to noise ratio.

Therefore, the correlation coefficient r using the signal-to-noise ratio takes a value between 0 and 1, and the ease of screen restoration can be quantitatively evaluated based on the magnitude of this value.
Qualitatively speaking, when the signal-to-noise ratio value is small, it is difficult to restore the screen (it is difficult to see), and in the opposite case, that is, when the signal-to-noise ratio value is large, it is easy to restore the screen (easy to see). Show.

FIG. 6 is a diagram illustrating an example of a relationship between an image displayed on a target display, which is a target for screen information restoration evaluation by the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention, and a correlation coefficient.
In the example shown in FIG. 6, the higher the obtained correlation coefficient r, the easier the screen is restored, and the lower the correlation coefficient r, the harder the screen is restored. 6A is a display image when r = 0.711, FIG. 6B is a display image when r = 0.568, and FIG. 6C is a display image when r = 0.166. FIG. 6D shows a display sample image that is the original of the images shown in FIGS. 6A to 6C.

  Also, the electromagnetic information restoration evaluation device can perform classification of information leakage risk determination based on the value of the correlation coefficient r depending on the level of security level required. For example, the electromagnetic information restoration evaluation apparatus can determine that “measures against leakage are necessary” when r = 0.2 or higher in class A where the required security level is high, and is a general security level. In class B, when r = 0.5 or higher, and in class C where the required security level is low, when r = 0.7 or higher, it can be similarly determined that “measures against leakage are necessary”.

  The image information evaluation value calculation unit 15d obtains the output value of the evaluation function of the screen information, and uses this output value, the value of the center frequency fm set by the control unit 16, and the calculated S / N value for screen restoration. Output and record as the evaluation result of ease (A10).

As described above, if there is a frequency component having an electromagnetic field intensity level higher than Adb in the vicinity of the frequency f ₁ at A7, the image information evaluation value calculation unit 15d obtains the above acquisition. The center frequency fm set by the control unit 16 is estimated as a candidate for the frequency of the electromagnetic wave including the screen information, which is radiated from the target display terminal 10, and the storage unit 15e. To record. The output unit 15 f records the recorded frequency value in the storage device 17.

Further, as described above, if there is a frequency component having an electromagnetic field strength level higher than Adb in the vicinity of the frequency f ₁ at A 7, the image characteristic evaluation value calculation of the frequency characteristic confirmation unit 15 is performed. The unit 15d estimates the frequency having the peak electromagnetic field intensity level in the existing frequency component as a candidate for the drawing frequency of the screen information included in the electromagnetic wave radiated from the target display terminal 10, and records it in the storage unit 15e. . The output unit 15 f records the recorded frequency value in the storage device 17. At A7, in the vicinity of the frequency f _2, which is the same when the frequency component is present with a high field strength level or Adb compared to the noise floor.

Further, when the electromagnetic field intensity level of the frequency in the vicinity of the frequencies f ₁ and f ₂ is not higher than Adb compared to the noise floor (No in A7), the frequency characteristic confirmation unit 15 does not pass through A8 to A10. The drawing frequency candidate determination unit 15c regards the acquired electromagnetic wave as not including screen information and records information indicating this in the storage unit 15e. The output unit 15f notifies the control unit 16 of the recorded information.
Also after A10, the output unit 15f notifies the control unit 16 of the information recorded in the storage unit 15e in A10.

  Upon receiving the above notification, the control unit 16 changes the center frequency fm of the passband by the bandpass filter unit 13 to fm + α (A11). α may be arbitrarily determined. The control unit 16 sets the changed center frequency fm in the band pass filter unit 13 and the frequency characteristic confirmation unit 15 and records it in the storage device 17.

Next, the control unit 16 compares fm changed in A10 with f _max recorded in the storage device 17. If fm> f _{max is} not satisfied (No in A12), the operation proceeds to A4 and subsequent operations based on the center frequency fm changed in A11. If the currently set center frequency fm> f _max (Yes in A12), the control unit 16 ends the process.
At the time of this end, if the candidate of the frequency of the electromagnetic wave including the screen information and the candidate of the drawing frequency are not recorded in A10, the frequency characteristic confirmation unit 15 does not confirm the leaked electromagnetic wave including the screen information. May be displayed on a built-in monitor.

  As described above, the electromagnetic information restoration evaluation apparatus according to the embodiment of the present invention quantitatively and simultaneously restores the restoration level in the frequency band of the leaked electromagnetic wave including the screen information without restoring the screen information one by one. Highly reliable evaluation can be performed.

  Further, in the embodiment of the present invention, when evaluating the ease of screen restoration described above, the screen image component included in the leaked electromagnetic wave after intentionally giving the display image a geometric regularity. By controlling the periodic band, a stricter signal-to-noise ratio can be clarified. Note that the drawing frequency of the terminal can be estimated to some extent from the display resolution and refresh rate of the terminal, but the periodicity of screen signals including frequency components other than this drawing frequency varies depending on the display screen, and is generally Since the image displayed on is complicated in shape, it is difficult to define the signal-to-noise ratio as described above.

  In the embodiment of the present invention, when evaluating the signal-to-noise ratio, the bandwidth of the screen signal component is defined by the ratio based on the frequency component having a high electromagnetic field strength level, thereby having a high electromagnetic field strength level. The fluctuation of the signal-to-noise ratio due to the difference in frequency components can be reduced, and a highly fair signal-to-noise ratio evaluation that does not depend on the terminal can be realized.

  In this embodiment, the relationship between the signal noise ratio and the screen information evaluation is formulated by formulating this relationship using a screen information evaluation index such as a correlation coefficient r that has a strong relationship with the signal noise ratio. Since one-to-one correspondence is possible, quantitative evaluation can be realized.

(Modification)
In the above embodiment, various resolutions and refresh rates of the screen information of the target display terminal 10 are known, and based on these, provisional candidate values f ₁ and f ₂ are obtained as approximate values of the drawing frequency. It was. However, if the resolution of the screen information of the target display terminal 10 is unknown, even if the signal after detection and demodulation is subjected to FFT analysis and a high level frequency component is observed, whether or not this frequency component is related to the screen information. Therefore, the method described in the above embodiment cannot be used as it is.
Therefore, in the modification of the above-described embodiment, a database in which a plurality of types of patterns having general resolutions and refresh rates adopted by display terminals distributed in the market are registered in the storage device 17. Then, for each of the patterns registered in this database, by performing the method described in the above embodiment, the electromagnetic wave frequency candidates including the screen information and the drawing frequency candidates are estimated, and the screen information is restored. Evaluate ease of use.

Next, a specific example of a modification of the embodiment will be described.
First, in the modification of the embodiment, a database in which a plurality of resolution patterns including general resolutions and refresh rates of screen information used for display terminals distributed in the market are registered in advance is recorded in the storage device 17.

The control unit 16 can use the pattern registered in this database for evaluation of the electromagnetic wave frequency candidate including the screen information, the estimation of the drawing frequency candidate, and the ease of restoration of the screen information. Since the resolution of the display terminal is standardized, the types of patterns are limited. Therefore, it is easy to collect information in advance.
Information necessary for configuring a resolution pattern to be registered in the database is a vertical resolution, a horizontal resolution, and a refresh rate.

  The control unit 16 selects any one unselected resolution pattern among the resolution patterns A, B, C... Registered in the database.

In this case, the control unit 16 uses the horizontal resolution, the vertical resolution, and the refresh rate that belong to the selected resolution pattern, and a provisional candidate value for the drawing frequency of the screen information in the target display terminal 10. The calculated frequencies f ₁ and f ₂ are calculated in the same manner as in the above embodiment, and the calculated values are set in the frequency characteristic confirmation unit 15. Thereafter, A2 to A11 described in the above embodiment can be similarly performed.

  If A11 is set to Yes, that is, if the currently set center frequency fm> fh and before all the resolution patterns registered in the database have been selected, the resolution pattern is selected as described above. Return.

Moreover, if it is after having selected all the resolution patterns registered into the database, the control part 16 will complete | finish a process.
When the electromagnetic wave frequency candidate including the screen information in A10 and the drawing frequency candidate are not recorded at this time, the frequency characteristic confirmation unit 15 confirms that the leakage electromagnetic wave including the image information is not confirmed. A message or the like may be displayed on a built-in monitor.

As described above, in a modification of the embodiment of the present invention, for a display terminal whose resolution and refresh rate are unknown, electromagnetic wave frequency candidates including screen information and drawing frequency candidates are estimated in a short time, and screen information is displayed. It becomes possible to evaluate the ease of restoration. Therefore, it is possible to easily evaluate the risk and examine countermeasures against the threat of eavesdropping.
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  In addition, the method described in each embodiment is, for example, a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), optical disk (CD-ROM, etc.) as a program (software means) that can be executed by a computer (computer). It can be stored in a recording medium such as a DVD, MO, etc., semiconductor memory (ROM, RAM, flash memory, etc.), or transmitted and distributed by a communication medium. The program stored on the medium side includes a setting program that configures software means (including not only the execution program but also a table and data structure) in the computer. A computer that implements this apparatus reads a program recorded on a recording medium, constructs software means by a setting program as the case may be, and executes the above-described processing by controlling the operation by this software means. The recording medium referred to in this specification is not limited to distribution, but includes a storage medium such as a magnetic disk or a semiconductor memory provided in a computer or a device connected via a network.

  DESCRIPTION OF SYMBOLS 10 ... Target display terminal, 11 ... Antenna part, 12 ... Amplifier part, 13 ... Band pass filter part, 14 ... Detection demodulation part, 15 ... Frequency characteristic confirmation part, 16 ... Control part, 17 ... Memory | storage device.

Claims (7)

An antenna unit for inputting electromagnetic waves radiated from a display device to be evaluated for ease of restoration of screen information;
A band pass filter unit that outputs a signal of a frequency component of a predetermined band for the electromagnetic wave input by the antenna unit;
A detection and demodulation unit for detecting and demodulating the signal output by the bandpass filter unit;
A frequency characteristic confirmation unit that obtains a frequency spectrum by performing a fast Fourier transform on the signal output from the detection demodulation unit;
In the frequency spectrum, the vicinity of the first frequency indicated by the product of the horizontal resolution of the screen information displayed on the display device and the refresh rate of the screen information, or the screen information displayed on the display device When a frequency having a predetermined electromagnetic field strength level higher than the noise floor exists in the vicinity of the second frequency indicated by the product of the vertical resolution and the refresh rate, the frequency of the existing frequency in the frequency spectrum is present. A screen signal component that combines the integrated values of signal strengths of nearby frequency components and harmonic components, and a noise component that combines the integrated values of signal strengths of frequency components other than the frequency of the screen signal component in the frequency spectrum. And reconstructing the screen information based on the ratio of the value of the screen signal component and the value of the noise component. Electromagnetic information restoring evaluation device, characterized in that it comprises a calculation unit for calculating an evaluation value for evaluating of. The electromagnetic information restoration evaluation device according to claim 1, wherein the bandwidth of the screen signal component is determined by a ratio based on the existing frequency. 2. The electromagnetic information restoration evaluation apparatus according to claim 1, wherein the evaluation value of the screen information is a value of a correlation coefficient based on a ratio between the value of the screen signal component and the value of the noise component. A method applied to an electromagnetic information restoration evaluation device,
Input the electromagnetic wave radiated from the display device to be evaluated for ease of restoration of screen information through the antenna unit,
A signal of a frequency component of a predetermined band for the input electromagnetic wave is output by a bandpass filter unit,
Detecting and demodulating the output signal,
A frequency spectrum is obtained by fast Fourier transforming the detected and demodulated signal,
In the frequency spectrum, the vicinity of the first frequency indicated by the product of the horizontal resolution of the screen information displayed on the display device and the refresh rate of the screen information, or the screen information displayed on the display device When a frequency having a predetermined electromagnetic field strength level higher than the noise floor exists in the vicinity of the second frequency indicated by the product of the vertical resolution and the refresh rate, the frequency of the existing frequency in the frequency spectrum is present. A screen signal component that combines the integrated values of signal strengths of nearby frequency components and harmonic components, and a noise component that combines the integrated values of signal strengths of frequency components other than the frequency of the screen signal component in the frequency spectrum. And reconstructing the screen information based on the ratio of the value of the screen signal component and the value of the noise component. Electromagnetic information restoring evaluation method and calculates an evaluation value for evaluating of. 5. The electromagnetic information restoration evaluation method according to claim 4, wherein the bandwidth of the screen signal component is determined by a ratio based on the existing frequency. The evaluation value of the screen information is
The electromagnetic information restoration evaluation method according to claim 4, wherein the evaluation method is a correlation coefficient value based on a ratio between the value of the screen signal component and the value of the noise component. A program used in a computer that operates as a part of the electromagnetic information restoration evaluation device according to claim 1,
The computer,
An electromagnetic information restoration evaluation processing program for causing the antenna unit, the bandpass filter unit, the detection demodulation unit, the frequency characteristic confirmation unit, and the calculation unit to function.