CN113132052A

CN113132052A - Nondestructive detection method for radio frequency eavesdropping

Info

Publication number: CN113132052A
Application number: CN202110308577.9A
Authority: CN
Inventors: 张骞允; 施继婷; 吴比翼
Original assignee: Beihang University; Beijing Institute of Technology BIT
Current assignee: Beihang University; Beijing Institute of Technology BIT
Priority date: 2021-03-23
Filing date: 2021-03-23
Publication date: 2021-07-16
Anticipated expiration: 2041-03-23
Also published as: CN113132052B

Abstract

The invention provides a nondestructive detection method aiming at radio frequency eavesdropping, which utilizes the scattering characteristics of an eavesdropping antenna and a radio frequency circuit thereof to detect a hidden eavesdropper and establishes a nondestructive detection system framework with good robustness; and judging whether a hidden eavesdropper exists or not by judging and detecting the change degree of the power and the phase of the signals received by the antenna. The method utilizes the scattering characteristic of the radio frequency circuit to overcome the defect of local oscillator leakage to a certain extent; in the detection process, whether a hidden eavesdropper exists in a certain frequency band of the radio frequency circuit can be judged more effectively by reasonably selecting system parameters and configuring a system environment, and the test accuracy is improved.

Description

Nondestructive detection method for radio frequency eavesdropping

Technical Field

The invention belongs to the technical field of communication safety, and particularly relates to a nondestructive testing method for radio frequency eavesdropping.

Background

In terms of network security, the occurrence of eavesdropping events for wireless networks is always present; the eavesdropper steals the user data by utilizing the characteristics of passively receiving signals and passively transmitting signals, and the detection of the eavesdropper is very difficult, so how to effectively detect the eavesdropper in the equipment is an important means for protecting the privacy data of the user.

The main principle of the existing eavesdropper detection method is to judge whether a hidden eavesdropper exists or not by tracking the unique characteristics of a radio frequency eavesdropper in a wireless channel. The method utilizes the influence of near-field inductive coupling on the change of the channel state to judge whether an eavesdropper exists or not; and a more common characteristic is the local oscillator leakage level (LO leakage).

The main principle of using the local oscillator leakage level to detect the eavesdropper is that, since the wireless receiver must use the local oscillator to convert the modulated signal from the carrier to the baseband for subsequent digital sampling or further processing, even if the wireless eavesdropper passively receives information and does not actively transmit signals, the sinusoidal signal generated by the local oscillator still leaks into the channel through the eavesdropping antenna, so that the eavesdropper inevitably leaks radio frequency signals.

In the detection method based on the local oscillator leakage level, due to the weak characteristic of local oscillator leakage, a high-sensitivity and expensive detector is generally required, and a certain limit is also caused to the detection range; meanwhile, how to distinguish an eavesdropper from a legal receiver based on the local oscillator leakage level also has certain difficulty; finally, related studies have shown that human adjustments to local oscillator leakage may degrade detector performance.

In summary, the detection scheme based on local oscillator leakage has certain limitations in robustness, effectiveness and other aspects, and therefore a scheme for detecting the hidden eavesdropper more robustly, more effectively, more conveniently and more accurately is needed.

Disclosure of Invention

In view of this, the present invention provides a nondestructive testing method for a radio frequency eavesdropper, which has the characteristics of being lossless, efficient, convenient and fast, and high in robustness.

A method for non-destructive testing of a radio frequency eavesdropper, comprising:

irradiating the equipment to be detected by adopting an antenna with set working frequency, and receiving a reflected signal of the equipment to be detected under the power-on and power-off conditions by using a same-frequency receiving antenna; respectively obtaining set parameters of a received signal under the power-on and power-off conditions, and obtaining a set parameter difference value of the signal during power-on and power-off; and when the difference value is larger than the set threshold value, judging that the radio frequency eavesdropping exists in the equipment to be detected.

Preferably, the set parameter is at least one of level, power, phase, error rate and eye pattern, the parameter after power-on is compared with the parameter value before power-on, and when the fluctuation is greater than the set threshold, an eavesdropper exists in the device to be detected.

Preferably, when the number of the parameters is more than two, one parameter fluctuation is larger than a set threshold value, and an eavesdropper exists.

Preferably, the receiving antenna and the transmitting antenna are at the same position or different positions.

Preferably, the included angle between the receiving antenna and the equipment to be detected and between the receiving antenna and the transmitting antenna is smaller than 90 °.

Preferably, the distance L between the receiving and transmitting antennas and the device under test should satisfy the far field test condition, i.e.

Where D is the maximum size of the receiving or transmitting antenna and λ is the wavelength to which the antenna operates.

The invention has the following beneficial effects:

Drawings

FIG. 1 is a system model of a detection scheme of the detection method of the present invention;

FIG. 2 is a diagram of a radio frequency circuit employed in an embodiment of the present invention;

FIG. 3(a) is a power variation curve of a detecting receiving antenna under different conditions; fig. 3(b) is a phase variation curve of the detecting receiving antenna under different conditions;

FIG. 4(a) is the power difference of the received signal with and without power supply to the DUT facing the aperture of the transmitting antenna, and FIG. 4(b) is the power difference of the DUT with and without power supply to the Device Under Test (DUT) rotated 30 °; FIG. 4(c) is a graph of the power difference of the DUT with and without power supply for a 60 rotation of the DUT.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

The invention provides a method for detecting an eavesdropper possibly existing in equipment by using the change of the scattering characteristic of an eavesdropper antenna.

The antenna of the radio frequency receiver is used to capture electromagnetic signals in the wireless medium, and the radio frequency signals intercepted by the eavesdropping antenna typically need to be further processed by radio frequency filters, amplifiers, and mixers with local oscillators before the signals are down-converted from a carrier frequency to a base frequency. For active components in radio frequency circuits, such as amplifiers and mixers, their input impedances are quite different in the presence or absence of a supply bias.

Meanwhile, the scattering characteristics of the antenna are determined by the geometry of the antenna and the load impedance. The change of the input impedance of the active element can cause the loaded impedance of the antenna feed port to change; when the load impedance of the eavesdropper antenna is different, the scattering characteristics of the antenna may change. Therefore, the invention can observe the scattering characteristic of the equipment by controlling the power supply condition of the equipment to be detected, thereby judging whether the eavesdropping device exists or not.

In the present invention, in order to extract the variation of the scattering characteristics and identify the presence of a hidden eavesdropper, a device to be tested (DUT) is first illuminated by the incident wave of a transmitting antenna for detection, and the scattered field in the other direction is measured by a receiving antenna for detection. If the measured fringe field amplitude/power or phase changes significantly when the DUT is powered on and off, then a hidden eavesdropper is present.

(1) Principle of detection scheme

The model setting, the relevant technical principle and the formula of the detection scheme provided by the invention are as follows:

the system model of the test apparatus is shown in FIG. 1 and essentially comprises a transmitting antenna for illuminating the DUT; a receive antenna for receiving a measurement of the field scattered by the DUT; a DUT is placed on the turntable so that it scatters incident waves irradiated from the transmitting antenna at different angles.

In the system model, both the transmit and receive antennas are highly directional to avoid test errors due to multipath scattering effects.

In antenna theory, with a load impedance Z_LThe scattering electric field E of the antenna of (1) can be represented by:

wherein E^s(0) When short-circuiting the antenna (Z)_L0) scattering electric field, E^tFor the radiation of the electric field of the antenna in the transmitting mode, I_sIs the port current on the short-circuited antenna caused by the incident field, I_tIs the port current, Z, of the antenna when operating in the transmit mode_AIs the input impedance of the antenna.

As can be seen from the formula, there is a load impedance Z_LThe scattering electric field of the antenna of (1) can be divided into two components, the first component depending on the incident wave and the second component depending on the load impedance Z_LAnd antenna radiation characteristics E_tThis component provides a potential mechanism for detecting eavesdroppers in the present invention.

All active radio frequency components in the circuit are biased after being connected with a power supply, the load impedance of the antenna is changed, and the change affects the total scattered field through the second component of the formula (1) when matching is carried out.

(2) Detailed description of the preferred embodiment

In the embodiment, to control the relevant variables, the verification of the validity and the relevant performance of the scheme is performed according to fig. 1, and the specific steps are as follows:

1. placing the DUT on a rotating platform facing the aperture of the transmitting antenna, and recording the power and the phase of a signal received by a receiving antenna;

2. switching on a DUT power supply, repeating the measurement process in the step 1, and recording the power and the phase of a signal received by a receiving antenna;

3. comparing the power difference and the phase difference in the step 1 and the step 2, and if the difference between the power difference and the phase difference is small, determining that no eavesdropper exists on the frequency band to be researched; otherwise, a hidden eavesdropper is deemed to be present on the frequency band under study.

(3) Examples of the embodiments

To verify the validity of the scheme and to check the correlation performance, full-wave numerical simulation results are given in this example according to the correlation step in (2).

Assume that there is a hidden eavesdropper in the DUT that intercepts Wi-Fi signals in space using an archimedes spiral antenna operating at 2.4 GHz. The RF circuit is shown in FIG. 2, the antenna is directly connected to a single-ended commercial RF amplifier, and the impedance matching is provided by element L_gAnd L_SAnd (5) realizing. Starting from the model diagram of fig. 1, in the process of detecting an eavesdropper, a horn antenna is used as a transmitting antenna and a receiving antenna, the horn antennas are both placed 5 meters away from a rotating platform for installing a DUT, the angle theta is 10 degrees, and the receiving power mainly comes from a scattered field of the DUT.

Due to the side lobes of the transmit antenna and the scattering of the rotating stage itself, the receive antenna can still capture relatively low signal power even without the DUT. In this case, as a result of the simulation, as shown in fig. 3(a), the signal received power is about-62 dBw in the frequency band of 2.35GHz to 2.45GHz, and it can be seen from fig. 3 that the phase curve is linear with the frequency.

As shown in fig. 3, after the DUT is placed on the turntable, the power and phase of the signal received by the horn receiving antenna will oscillate within the same frequency band. From a comparison of the power curves, fig. 3(a), the amplitude of the received signal power oscillation increases significantly after the DUT power is turned on. Meanwhile, the minimum signal power received by the receive antenna for detection after the DUT is powered on is about 15dB less than the corresponding power if the DUT was not powered on over the frequency range under study. It can also be seen in fig. 3(b) that the amplitude of the phase oscillation of the received signal increases significantly after the DUT is powered on.

As can be seen from the simulation results in fig. 3, the signal reception power and the phase change of the detection reception antenna are significant when the DUT is powered on or off. Therefore, in actual measurement, the difference can be easily observed, thereby being used for judging whether an illegal eavesdropper exists.

To further systematically test the performance of the proposed eavesdropping detection method, θ was made 10 ° to 180 °, the position of the receiving antenna was changed and the test was performed. The test results are shown in fig. 4.

As can be seen from fig. 4(a), a significant power difference can be observed only when θ is less than 60 °; continued increases in θ will result in the receive antenna being insensitive to power, phase variations from the DUT's scattered field. From this, it can be concluded that: to improve the accuracy and sensitivity of the detection scheme, the effect of coupling between the transmitting and receiving antennas is minimized.

The influence of the incident angle on the variation of the scattering properties of the DUT is taken into account by rotating the DUT with the rotary stage, taking into account the fact that the scattering fields of the incident waves from different directions are different.

The turntable is rotated 30 and 60 in the x-z plane of the model diagram of fig. 1, and the received signal power difference over the same frequency and theta range is shown in fig. 4(b) and (c).

FIG. 4(b) is similar to FIG. 4(a) and it can be seen that when θ is greater than 60, the power variation is not significant; at θ less than 60 °, the received power difference can be greater than 10dB, which difference can also be clearly perceived in actual measurements in the presence of a certain noise level. In fig. 4(c), when the DUT is further rotated to 60 °, the power difference is insignificant for the different power states, with the maximum power difference being less than 2 dB.

In summary, if the measured received power and phase difference are small when the DUT is powered on or not powered on, it can be confirmed that there is no eavesdropper on the frequency band under study; otherwise, a hidden eavesdropper is deemed to be present on the band.

In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for non-destructive testing of a radio frequency eavesdropper, comprising:

2. A nondestructive testing method for a radio frequency eavesdropper as recited in claim 1, wherein the setting parameter is at least one of level, power, phase, error rate and eye pattern, the parameter after power-on is compared with the parameter before power-on, and when the fluctuation is larger than a setting threshold, the eavesdropper is present in the device to be tested.

3. A non-destructive testing method for a radio frequency eavesdropper as recited in claim 2, wherein when the number of parameters is two or more, one of the parameters fluctuates more than a predetermined threshold, and the eavesdropper is present.

4. A method of non-destructive testing for a radio frequency eavesdropper as recited in claim 1, wherein the receiving antenna is located at the same location as or a different location than the transmitting antenna.

5. A nondestructive testing method for a radio frequency eavesdropper as claimed in claim 1 wherein the angle between the receiving antenna to the device to be tested and then to the transmitting antenna is less than 90 °.

6. A non-destructive testing method for a radio frequency eavesdropper as claimed in claim 1, wherein the distance between the receiving and transmitting antennas and the device under testL should satisfy the far field test condition, i.e.