An absolutely safe wired frequency hopping secret communication system and method

Abstract

The application relates to the technical field of wired communication, and discloses an absolutely safe wired frequency hopping secret communication system and method, which comprises Alice nodes and Bob nodes. The two nodes of Alice and Bob in the whole system can carry out full-duplex wired secret communication, which is beneficial to use. A signal generating circuit is mainly used for modulating and up-converting a voice signal, generating a noise signal, modulating and up-converting the noise signal, and then adding the two signals together to send to an applying end of a 2 / 4 conversion circuit. A signal receiving circuit is mainly used for extracting a voice signal of a target node from a telephone line and demodulating and outputting the voice signal. The receiving circuit is connected to a receiving end of the 2 / 4 conversion circuit. Based on the 2 / 4 line conversion circuit, the receiver can be instantaneously demodulated, and thus the signal-to-noise ratio of an eavesdropper is far lower than that of the receiver. Frequency hopping modulation is adopted, the carrier frequency is periodically changed, and thus the anti-interference ability of the communication system is improved, frequency conflicts are avoided, and the concealment and security of communication are increased.

Description

Technical Field

[0001] This invention relates to the field of wired communication technology, specifically to an absolutely secure wired frequency-hopping secure communication system and method. Background Technology

[0002] Traditional communication systems often achieve confidentiality through key encryption. This method of communication is vulnerable to eavesdropping, and the keys can be easily cracked by others, leading to information leakage.

[0003] Currently, encryption keys are mainly classified as symmetric keys and asymmetric keys. Symmetric key encryption uses the same key for both encryption and decryption. This method offers fast encryption / decryption speeds and is suitable for encrypting large amounts of data, but key management is difficult. Asymmetric key encryption requires different keys for encryption and decryption. The sender uses a public key for encryption, while the receiver uses a private key for decryption. This method offers greater security, but encryption and decryption are slower than symmetric key encryption. Furthermore, the advancement of computing power has made encrypted communications more vulnerable to cracking. Therefore, designing more secure secure communication systems has become a hot research topic and a pressing technical problem.

[0004] To address the aforementioned problems, this invention proposes an absolutely secure wired frequency-hopping secure communication system and method to resolve the potential danger of key decryption or theft and loss of confidentiality in traditional secure communication systems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an absolutely secure wired frequency hopping secure communication system and method that addresses the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an absolutely secure wired frequency hopping secure communication system, including Alice node and Bob node, which are connected by a telephone line to achieve full-duplex communication;

[0007] Each node includes a signal generation circuit, a signal receiving circuit, and a 2 / 4 line conversion circuit;

[0008] The signal generation circuit includes a microphone, a noise source, a modulation device for processing the signals generated by the microphone and the noise source respectively, an upconversion device for upconverting the modulated speech signal and the noise signal respectively, as well as an adder circuit, an ADC and a DAC. The signal generation circuit is mainly used to modulate and upconvert the speech signal, generate a noise signal, modulate and upconvert the noise signal, and then add the two together and send them to the signal application terminal of the 2 / 4 line conversion circuit.

[0009] The signal receiving circuit includes a bandpass filter, a demodulator, a DAC, and a speaker. It is used to receive the signal from the receiving end of the 2 / 4 line conversion circuit, and demodulate the target speech signal after filtering out noise through the bandpass filter. The processed data is output by the speaker.

[0010] The 2 / 4 line conversion circuit has an application terminal connected to the signal generation circuit, a receiving terminal connected to the signal receiving circuit, and a common terminal connected to the telephone line. It is used to inject locally generated noise signals and voice signals into the telephone line and separate the mixed signals from the remote node to the signal receiving circuit.

[0011] The 2 / 4 line conversion circuit is used to add the noise and voice signals generated by Alice and Bob nodes into the telephone line and separate the voice and noise signals generated by Bob node in the telephone line and send them to the receiving end of Alice node.

[0012] The addition circuit at nodes Alice and Bob adds the up-converted microphone signal and noise signal, and then sends them to the telephone line via a 2 / 4 conversion circuit. The signal on the telephone line at a certain moment is:

[0013] Sum = S a1 (t)+N a2 (t)+S b2 (t)+N b1 (t)

[0014] The signal at a certain moment at the Alice node's input end is:

[0015] S Alice =S a1 (t)+N a2 (t)

[0016] The signal received by the Alice node at a certain moment is:

[0017] S bob =S b2 (t)+N b1 (t)

[0018] Among them, S a1 (t) and S b2 (t) represent the upper sideband signals of the speech signals of Alice node and Bob node, respectively, N a2 (t) and N b1 (t) represents the upper sideband signal of the noise signal of Alice node and Bob node, respectively;

[0019] The system employs frequency hopping modulation technology, where the carrier frequencies of the voice signal and the noise signal periodically change within a preset range based on an orthogonal pseudo-random sequence, and the power of the noise signal is higher than that of the voice signal, making the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

[0020] Preferably, the system is based on the Wyner principle, which releases noise of the same frequency and distribution into the circuit, making it impossible for the eavesdropper to distinguish between the noise and the target signal. At the same time, it uses a 2 / 4-line conversion circuit to eliminate noise interference of the same frequency, and combines frequency hopping modulation technology to make the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

[0021] Preferably, the power of the noise signal is set to at least 30 times the power of the speech signal to meet the requirement of a signal-to-noise ratio ≤ -15dB.

[0022] Preferably, the noise signal is a narrowband noise signal processed by a low-pass filter from a uniformly distributed normal random sequence, and its spectral characteristics are similar to those of a speech signal.

[0023] Preferably, the 2 / 4-line conversion circuit extracts the target speech signal by eliminating locally injected noise signals, retaining only the mixed signal from the far-end node, and filtering out far-end noise signals through a bandpass filter.

[0024] Preferably, the modulation device employs frequency division multiplexing technology to separate the voice signal from the noise signal in the frequency domain, and the noise signal covers the frequency band that the eavesdropper may steal.

[0025] Preferably, the upconversion device uses an orthogonal pseudo-random sequence to control the carrier frequency jump, and the carrier frequencies of the voice signal and the noise signal always maintain an orthogonal relationship.

[0026] Preferably, the center frequency of the bandpass filter changes synchronously with the carrier frequency of the voice signal from the remote node, ensuring that only the target voice signal passes through.

[0027] Preferably, the carrier frequency range of the frequency hopping modulation is 1MHz to 2MHz, and the carrier frequencies of the voice signal and the noise signal are located in different frequency bands.

[0028] An absolutely secure wired frequency-hopping secure communication method includes the following steps:

[0029] S1. Information sending steps:

[0030] The node's microphone and noise source simultaneously generate both speech and noise signals, with the power of the noise source being much greater than the power of the speech signal.

[0031] The speech signal and the noise signal are frequency-hopping modulated separately to obtain the modulated speech signal and the noise signal;

[0032] The up-converted signals of the voice signal and the noise signal are mixed, and then converted into corresponding analog signals by a high-speed DAC before being sent to the signal application terminal of the 2 / 4 conversion circuit.

[0033] S2. Information Receiving Steps:

[0034] The signal emitted by itself is eliminated by a 2 / 4 conversion circuit, and the signal received from the remote end is transmitted to the signal receiving circuit.

[0035] By using a bandpass filter to filter out the noise signal of the other party node, the upper sideband signal of the speech of the other party node is obtained.

[0036] The audio signal is then demodulated by a demodulator and sent to a speaker for playback.

[0037] The present invention, by adopting the above technical solution, can bring the following beneficial effects:

[0038] This absolutely secure wired frequency-hopping secure communication system and method utilizes two nodes, Alice and Bob, which can perform full-duplex wired secure communication, facilitating ease of use. The signal generation circuit primarily modulates and up-converts the voice signal, generates a noise signal, modulates and up-converts the noise signal, and then combines the two signals to the application terminal of the 2 / 4 conversion circuit. The signal receiving circuit primarily extracts the voice signal from the target node on the telephone line and demodulates it. The receiving circuit is connected to the receiving end of the 2 / 4 conversion circuit. Based on the 2 / 4 line conversion circuit, the receiver can demodulate instantaneously, resulting in a signal-to-noise ratio far lower than that of the eavesdropper. Frequency-hopping modulation is used to periodically change the carrier frequency, thereby improving the anti-interference capability of the communication system, avoiding frequency conflicts, and increasing the concealment and security of communication. By applying frequency division multiplexing and other technologies to the system, even if an eavesdropper is present in the system, they cannot correctly demodulate and obtain the signal related to the communication content, thus achieving secure communication. Attached Figure Description

[0039] Figure 1 This is a diagram showing the overall system framework of the present invention;

[0040] Figure 2 This is a schematic diagram of physical layer secure communication based on the Wyner principle of this invention;

[0041] Figure 3 This is a schematic diagram of the full-duplex secure communication model of the present invention;

[0042] Figure 4 This is a schematic diagram of the structure of signal source A of the present invention;

[0043] Figure 5 This is a schematic diagram of the narrowband noise signal obtained by direct low-pass filtering of the evenly distributed sequence according to the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Please see Figure 1-5 The technical solution of the present invention is: an absolutely secure wired frequency hopping secure communication system, including Alice node and Bob node, which are connected by a telephone line to achieve full-duplex communication;

[0046] Each node includes a signal generation circuit, a signal receiving circuit, and a 2 / 4 line conversion circuit;

[0047] The signal generation circuit includes a microphone, a noise source, a modulation device for processing the signals generated by the microphone and the noise source respectively, an upconversion device for upconverting the modulated speech signal and the noise signal respectively, as well as an adder circuit, an ADC and a DAC. The signal generation circuit is mainly used to modulate and upconvert the speech signal, generate a noise signal, modulate and upconvert the noise signal, and then add the two together and send them to the signal application terminal of the 2 / 4 line conversion circuit.

[0048] The signal receiving circuit includes a bandpass filter, demodulator, DAC, and speaker. It is used to receive the signal from the receiver of the 2 / 4 line conversion circuit, and demodulate the target speech signal after filtering out noise through the bandpass filter. The processed data is output by the speaker.

[0049] The 2 / 4 line conversion circuit has its application terminal connected to the signal generation circuit, its receiving terminal connected to the signal receiving circuit, and its common terminal connected to the telephone line. It is used to inject locally generated noise signals and voice signals into the telephone line and separate the mixed signals from the remote node to the signal receiving circuit.

[0050] It should be noted that the four-wire interface of the 2 / 4 converter circuit is connected to the signal generation circuit and the signal receiving circuit respectively, while the two-wire interface of the 2 / 4 converter circuit is connected to the telephone line. The 2 / 4 converter circuit includes a signal application end, a signal receiving end, and a telephone line end. The signal application end is used to receive signals from the signal generation circuit, the signal receiving end is used to receive remote signals and transmit them to the signal receiving circuit, and the telephone line end is connected to the telephone line via a sub-wire.

[0051] The 2 / 4 line conversion circuit is used to add the noise and voice signals generated by Alice and Bob nodes into the telephone line and separate the voice and noise signals generated by Bob node in the telephone line and send them to the receiving end of Alice node.

[0052] When the carrier frequency hopping range for Alice and Bob is 1M-2M, the design scheme for the secure telephone is as follows:

[0053] Assuming node Alice communicates with node Bob, describe node Alice, including the steps for sending and receiving information:

[0054] The steps for sending information include:

[0055] The microphone on node Alice simultaneously generates both speech electrical signals and noise signals from the noise source. Specifically, the microphone on node Alice converts human speech into a speech electrical signal S. a0 (t), the analog voice electrical signal S is converted by a slow ADC. a0 (t) is converted into a digital voice electrical signal S a0 (n), in the speech electrical signal S a0 At the same time that (t) is generated, the noise source will generate a noise signal N. a0 (n) The system sets the power of the noise signal source to be much greater than the power of the speech signal. The noise generation scheme involves directly filtering a normally distributed random noise sequence (fs = 50k) using an LPF to obtain narrowband noise. This noise will automatically be compared to the speech, such as... Figure 5 As shown in the figure, the constructed noise is quite similar to the real noise.

[0056] The speech signal and noise signal are frequency-hop modulated separately to obtain modulated speech and noise signals, respectively. c1 and f c2 The high-frequency carrier signals are multiplied to obtain the up-converted voice signal S. a1 (n) and up-conversion noise signal N a1 (n). Where f c1 and f c2 The two orthogonal pseudo-random sequences change periodically within a frequency range of 1M-2M, respectively.

[0057] Upconverting the speech signal and noise signal to a higher frequency, i.e., S a1 (n) and N a1 (n) The input adder circuit mixes the signals, and then the high-speed DAC converts them into the corresponding analog signal S. a1 (t) and N a1(t) is then sent to the signal application terminal of the 2 / 4 conversion circuit;

[0058] The system has two nodes, Alice and Bob. Therefore, the mixed signal Sum in the telephone line at a certain moment is:

[0059] Sum = S a1 (t)+N a2 (t)+S b2 (t)+N b1 (t)

[0060] Among them, S a1 (t) represents the upper sideband signal of the speech signal of the Alice node, with a center frequency of f. c1 S b2 (t) represents the upper sideband signal of Bob's speech signal, with a center frequency of f. c2 N a2 (t) represents the upper sideband signal of the noise signal at the Alice node, with a center frequency of f. c2 N b1 (t) represents the upper sideband signal of the noise signal at Bob node, with a center frequency of f. c1 .

[0061] The steps for receiving information are as follows:

[0062] Alice node's signal S a1 (t)+N a2 (t) The signal is transmitted to the 2 / 4 conversion circuit, and then through the sub-line to the telephone line bus. Due to the characteristic of the internal circuit of the Alice node's 2 / 4 conversion eliminating its own emitted signal, the receiving end of the 2 / 4 conversion circuit receives signal S. b2 (t)+N b1 (t); thus, the signal S received by the Alice node from the telephone line at a certain moment is... bob for:

[0063] S bob =S b2 (t)+N b1 (t)

[0064] First, the center frequency of the Alice node is f. c2 The bandpass filter filters out the noise signal N at Bob's node. b1 (t), to obtain the speech upper sideband signal S of Bob node. b2 (t).

[0065] The upper sideband signal of Bob's voice is then demodulated by the demodulator of Alice node and sent to the speaker of Alice node's built-in power amplifier for playback.

[0066] In the solution of this invention, when the Alice node communicates with the Bob node, the signal N in the Alice node signal receiving circuit of the system... b1 The effective power should be much greater than the signal S in the signal generation circuit. a1 The effective power of signal N makes the signal N b1 It can better interfere with signal S a1 The upper sideband signal N of the Alice node is noise. b1 The upper sideband signal S of the speech at the Alice node a1 A higher power ratio is better. Assuming the signal-to-noise ratio of the Alice node is greater than and / or equal to 15 dB, the following formula applies:

[0067]

[0068] in, The upper sideband signal S representing the speech signal of the Alice node a1 The power, P Nb1 The upper sideband signal N representing the noise signal of the Alice node. b1 The power. Even if signal S a1 If the transmission is unfortunately intercepted during transmission, the eavesdropper will only obtain the combined signal Sum of the entire system. This combined signal Sum contains up-conversion noise with relatively high effective power. The eavesdropper's signal-to-noise ratio is far greater than 15 dB, therefore the eavesdropper cannot demodulate and obtain the valid information S. a1 ;

[0069] The system employs frequency hopping modulation technology, where the carrier frequencies of the voice signal and the noise signal periodically change within a preset range based on an orthogonal pseudo-random sequence, and the power of the noise signal is higher than that of the voice signal, making the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

[0070] The system is based on the Wyner principle. It releases noise of the same frequency and distribution into the circuit, making it impossible for the eavesdropper to distinguish between the noise and the target signal. At the same time, it uses a 2 / 4-line conversion circuit to eliminate interference from noise of the same frequency, and combines frequency hopping modulation technology to make the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

[0071] The power of the noise signal is set to at least 30 times the power of the speech signal to meet the requirement of signal-to-noise ratio ≤ -15dB.

[0072] The noise signal is a narrowband noise signal processed by a low-pass filter from a uniformly distributed normal random sequence, and its spectral characteristics are similar to those of a speech signal.

[0073] The 2 / 4-line conversion circuit extracts the target speech signal by eliminating locally injected noise signals, retaining only the mixed signal from the far-end node, and filtering out far-end noise signals through a bandpass filter.

[0074] The modulation device uses frequency division multiplexing technology to separate the voice signal from the noise signal in the frequency domain, and the noise signal covers the frequency band that the eavesdropper may steal.

[0075] The upconversion device uses orthogonal pseudo-random sequences to control the carrier frequency jump, and the carrier frequencies of the voice signal and the noise signal always maintain an orthogonal relationship.

[0076] The center frequency of the bandpass filter changes synchronously with the carrier frequency of the speech signal from the remote node, ensuring that only the target speech signal passes through.

[0077] The carrier frequency range of frequency hopping modulation is 1MHz to 2MHz, and the carrier frequencies of the speech signal and the noise signal are located in different frequency bands.

[0078] By employing frequency hopping modulation based on a 2 / 4-line conversion circuit and utilizing carrier frequency division multiplexing (CDM) to achieve secure wired communication, this system ensures full-duplex communication between users. The signal-to-noise ratio (SNR) of an eavesdropper listening to information on any frequency band from any location on the telephone line is significantly lower than that of a legitimate recipient on the same channel. This achieves absolute security in the Wyner principle sense and offers advantages such as ease of integration, low cost, and high reliability.

[0079] An absolutely secure wired frequency-hopping secure communication method includes the following steps:

[0080] S1. Information sending steps:

[0081] The node's microphone and noise source simultaneously generate both speech and noise signals, with the power of the noise source being much greater than the power of the speech signal.

[0082] The speech signal and the noise signal are frequency-hopping modulated separately to obtain the modulated speech signal and the noise signal;

[0083] The up-converted signals of the voice signal and the noise signal are mixed, and then converted into corresponding analog signals by a high-speed DAC before being sent to the signal application terminal of the 2 / 4 conversion circuit.

[0084] S2. Information Receiving Steps:

[0085] The signal emitted by itself is eliminated by a 2 / 4 conversion circuit, and the signal received from the remote end is transmitted to the signal receiving circuit.

[0086] By using a bandpass filter to filter out the noise signal of the other party node, the upper sideband signal of the speech of the other party node is obtained.

[0087] The audio signal is then demodulated by a demodulator and sent to a speaker for playback.

[0088] The working principle and beneficial effects of this scheme are as follows: The entire system consists of two nodes, Alice and Bob, which can perform full-duplex wired secure communication, facilitating its use. The signal generation circuit is mainly used to modulate and up-convert the voice signal, generate a noise signal, modulate and up-convert the noise signal, and then combine the two signals and send them to the application terminal of the 2 / 4 line conversion circuit. The signal receiving circuit is mainly used to extract the voice signal from the target node on the telephone line and demodulate it. The receiving circuit is connected to the receiving terminal of the 2 / 4 line conversion circuit. Based on the 2 / 4 line conversion circuit, the receiver can demodulate instantly, thus the signal-to-noise ratio of the eavesdropper is much lower than that of the receiver. Frequency hopping modulation is used to make the carrier frequency change periodically, thereby improving the anti-interference capability of the communication system, avoiding frequency conflicts, and increasing the concealment and security of communication. By applying frequency division multiplexing and other technologies to the system, even if there is an eavesdropper in the system, they cannot correctly demodulate and obtain the signal of the relevant communication content, thus achieving secure communication.

[0089] By employing physical layer noise injection and frequency division multiplexing techniques, eavesdroppers are unable to demodulate valid information due to the low signal-to-noise ratio, while legitimate users achieve secure communication by eliminating self-interference and using synchronization filtering. This invention eliminates the need for complex key management and boasts advantages such as strong anti-eavesdropping capabilities, simple hardware structure, low cost, and ease of integration. It is suitable for wired telephone communication and digital information exchange scenarios with high confidentiality requirements.

[0090] The theoretical basis and explanation of absolute safety:

[0091] In 1975, Wyner proposed the concept of physical layer secure communication, pointing out that when the legitimate receiver (Bob) has a channel capacity (C... B The channel capacity (C) is higher than that of the eavesdropper (Eve). E When the system's security capacity is greater than 0, an attacker will be unable to obtain any valuable information. The larger the system's security capacity, the faster the information transmission speed. Physical layer secure communication under the Wyner principle is as follows: Figure 2 As shown.

[0092] Based on Wyner's theoretical foundation, this paper proposes a full-duplex secure communication model in wired mode, such as... Figure 3As shown, information is transmitted using two frequency bands, 1 and 2. Signal source A transmits its information signal in frequency band 1 and its artificial noise signal in frequency band 2; signal source B transmits its information signal in frequency band 2 and its artificial noise signal in frequency band 1. When Eve eavesdrops on the coaxial cable, both frequency bands 1 and 2 are interfered with by artificial noise signals. Under a suitable signal-to-noise ratio (SNR), Eve will be unable to obtain valuable information. The legitimate receiver can use a 2 / 4 converter circuit to filter out its own transmitted information signal and artificial noise signal, receiving only the sender's information signal and artificial noise signal. Then, it can perform appropriate filtering and demodulation to obtain the target signal, achieving secure communication.

[0093] The structure of signal source A is as follows Figure 4 As shown. The signal generator in signal source A collects the "Alice sound source" and modulates it into S using signal modulator 1. A Information signal, then using carrier f C1 Up-converter 1 will S A Up-converter The information signal has a frequency within frequency band 1; the noise generator in signal source A collects artificial noise "Alice noise source" and modulates it into N using signal modulator 2. A Noise signal, then using carrier f C2 The up-converter 2 will N A Upconverting noise signals to The noise signal has a frequency within frequency band 2. Information signals and The noise signal is released to the coaxial cable through the adder and power amplifier, making the signal-to-noise ratio less than -15dB.

[0094] Signal source B is structurally similar to signal source A. Signal source B uses signal modulator 3 and carrier wave f. C2 The upconverter 3 obtains Information signal (located in frequency band 2); using signal modulator 4 and carrier f C1 The up-converter 4 obtains The noise signal (located in frequency band 1) is finally released to the coaxial cable through the adder and power amplifier, so that the signal-to-noise ratio is less than -15dB.

[0095] When Eve eavesdrops somewhere on the coaxial cable, the target signals he acquires in bands 1 and 2 are masked by noise, resulting in a very low signal-to-noise ratio and making it impossible to obtain any valuable signals. Meanwhile, Alice and Bob, at the two nodes, use a 2 / 4 converter circuit to eliminate self-interference signals, receiving only the information and noise signals transmitted by each other.

[0096] This invention provides an absolutely secure wired frequency-hopping secure communication system and method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. An absolutely secure wired frequency-hopping secure communication system, characterized in that, This includes Alice and Bob nodes, which are connected via telephone lines to achieve full-duplex communication; Each node includes a signal generation circuit, a signal receiving circuit, and a 2 / 4 line conversion circuit; The signal generation circuit includes a microphone, a noise source, a modulation device for processing the signals generated by the microphone and the noise source respectively, an upconversion device for upconverting the modulated speech signal and the noise signal respectively, as well as an adder circuit, an ADC and a DAC. The signal generation circuit is mainly used to modulate and upconvert the speech signal, generate a noise signal, modulate and upconvert the noise signal, and then add the two together and send them to the signal application terminal of the 2 / 4 line conversion circuit. The signal receiving circuit includes a bandpass filter, a demodulator, a DAC, and a speaker. It is used to receive the signal from the receiving end of the 2 / 4 line conversion circuit, and demodulate the target speech signal after filtering out noise through the bandpass filter. The processed data is output by the speaker. The 2 / 4 line conversion circuit has an application terminal connected to the signal generation circuit, a receiving terminal connected to the signal receiving circuit, and a common terminal connected to the telephone line. It is used to inject locally generated noise signals and voice signals into the telephone line and separate the mixed signals from the remote node to the signal receiving circuit. The system employs frequency hopping modulation technology, where the carrier frequencies of the voice signal and the noise signal periodically change within a preset range based on an orthogonal pseudo-random sequence, and the power of the noise signal is higher than that of the voice signal, making the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

2. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The system is based on the Wyner principle. It releases noise of the same frequency and distribution into the circuit, making it impossible for the eavesdropper to distinguish between the noise and the target signal. At the same time, it uses a 2 / 4-line conversion circuit to eliminate interference from noise of the same frequency, and combines frequency hopping modulation technology to make the signal-to-noise ratio of the eavesdropper lower than that of the legitimate receiver.

3. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The power of the noise signal is set to at least 30 times the power of the speech signal to meet the requirement of signal-to-noise ratio ≤ -15dB.

4. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The noise signal is a narrowband noise signal processed by a low-pass filter from a uniformly distributed normal random sequence, and its spectral characteristics are similar to those of a speech signal.

5. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The 2 / 4-line conversion circuit extracts the target speech signal by eliminating locally injected noise signals, retaining only the mixed signal from the far-end node, and filtering out far-end noise signals through a bandpass filter.

6. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The modulation device employs frequency division multiplexing technology to separate the voice signal from the noise signal in the frequency domain, and the noise signal covers the frequency band that the eavesdropper may steal.

7. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The upconversion device uses orthogonal pseudo-random sequences to control the carrier frequency jump, and the carrier frequencies of the voice signal and the noise signal always maintain an orthogonal relationship.

8. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The center frequency of the bandpass filter changes synchronously with the carrier frequency of the voice signal from the remote node, ensuring that only the target voice signal passes through.

9. The absolutely secure wired frequency-hopping secure communication system according to claim 1, characterized in that: The carrier frequency range of the frequency hopping modulation is 1MHz to 2MHz, and the carrier frequencies of the voice signal and the noise signal are located in different frequency bands.

10. An absolutely secure wired frequency-hopping secure communication method, characterized in that, Includes the following steps: S1. Information sending steps: The node's microphone and noise source simultaneously generate both speech and noise signals, with the power of the noise source being much greater than the power of the speech signal. The speech signal and the noise signal are frequency-hopping modulated separately to obtain the modulated speech signal and the noise signal; The up-converted signals of the voice signal and the noise signal are mixed, and then converted into corresponding analog signals by a high-speed DAC before being sent to the signal application terminal of the 2 / 4 conversion circuit. S2. Information Receiving Steps: The signal emitted by itself is eliminated by a 2 / 4 conversion circuit, and the signal received from the remote end is transmitted to the signal receiving circuit. By using a bandpass filter to filter out the noise signal of the other party node, the upper sideband signal of the speech of the other party node is obtained. The audio signal is then demodulated by a demodulator and sent to a speaker for playback.

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