CN115835188B - Concealed time channel method and system based on independent basic service combination - Google Patents
Concealed time channel method and system based on independent basic service combination Download PDFInfo
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Abstract
The invention discloses a hidden time channel method and a system based on independent basic service combination, wherein the method comprises the steps that in the independent basic service combination, a hidden information sender identifies a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol; after handshake is completed between a hidden information sender and a hidden information receiver, the hidden information sender encodes the hidden information, the encoded hidden information is mapped into a time delay code block through the additional time delay of a time delay codebook, the time delay code block is overlapped on a beacon frame sequence to obtain a time delay beacon frame sequence, and the hidden information sender sends the time delay beacon frame sequence; the hidden information receiver counts the time slots of the time delay beacon frame sequence, calculates the time delay through a time delay estimation algorithm, and decodes the codeword obtained by calculation to obtain hidden information. By adopting the technical scheme, the detection device has higher concealment and higher detection reliability and stability.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a method and a system for a hidden time channel based on independent basic service combinations.
Background
The wireless hidden communication is a special communication mode which takes the hidden property as main pursuit, and has important application prospect in the fields of military communication in complex countermeasure environment, information communication in physical isolation environment and the like.
Common covert communication methods include three methods of concealing a large capacity channel (Covert Storage Channel), concealing a time channel (Covert Timing Channel), and wireless covert channel (Wireless Covert Channel).
The hidden high-capacity channel is usually inserted with the reserved field or the spare field in the wireless channel data frame or the management frame, and the hidden information is decoded and received by the hidden communication receiver according to the convention, and the hidden data of the hidden high-capacity channel is still reserved in the transmitted data packet, so that the existence of the hidden channel can be easily checked by a secondary checking and related statistical method.
The wireless hidden channel mainly hides the modulated hidden data in the redundant field of the physical layer or the MAC layer protocol, and the method has better concealment but higher operation difficulty. The modulation and demodulation equipment of the transmitter and the receiver of the hidden communication are required to be modified respectively, and the defects of lower reliability, higher receiving difficulty and the like of the hidden information exist.
The hidden time channel uses the time difference between time intervals for transmission, such as inter-packet delay or packet retransmission. However, since the hidden time channel may violate the related communication protocol specifications due to inter-packet delay or packet retransmission, interruption of communication by a legitimate user may be caused, and there is a risk of detection.
Disclosure of Invention
The invention aims to: the invention provides a hidden time channel method and a hidden time channel system based on independent basic service combination, which are based on the time delay of a transmission request identification and superposition on a beacon frame of a handshake protocol, have higher concealment and have higher detection reliability and stability.
The technical scheme is as follows: the invention provides a hidden time channel method based on independent basic service combination, which comprises the following steps: in the independent basic service combination, a hidden information sender identifies a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol; the hidden communication handshake protocol flow comprises the following steps: the method comprises the steps that a first detection request frame is sent to all communication equipment in a communication environment by a hidden information receiving party, wherein the first detection request frame comprises first information predetermined between a hidden information receiving party and a hidden information sending party; the method comprises the steps that a hidden information sender sends a first beacon frame, second information predetermined between a hidden information receiver and the first beacon frame is removed, and the hidden information receiver detects second information change in the received first beacon frame; the hidden information receiver sends a second detection request frame, wherein the first information is not included in the second detection request frame; the hidden information sender sends a second beacon frame, and adds the second information in the sent second beacon frame, and the hidden information receiver detects the second information change in the received second beacon frame; after handshake is completed between a hidden information sender and a hidden information receiver, the hidden information sender encodes the hidden information, the encoded hidden information is mapped into a time delay code block through the additional time delay of a time delay codebook, the time delay code block is overlapped on a beacon frame sequence to obtain a time delay beacon frame sequence, and the hidden information sender sends the time delay beacon frame sequence; the hidden information receiver receives the time delay beacon frame sequence, counts time slots of the time delay beacon frame sequence, calculates time delay through a time delay estimation algorithm, and decodes the codeword obtained through calculation to obtain hidden information.
Specifically, the first information is an extended support rate, and the extended support rate field includes additional transmission rate information.
Specifically, the second information is a temporary storage frame.
Specifically, in a static communication environment, a first time delay codebook is adopted, and in a time delay fluctuation communication environment, a second time delay codebook is adopted; if the environment time delay is lower than the standard time delay, the static communication environment is determined, otherwise, the time delay fluctuation communication environment is determined; the additional delay of the first delay codebook is less than the additional delay of the second delay codebook.
Specifically, the first delay codebook includes: codeword 0 additional delay 0, codeword 1 additional delay T 1 。
Specifically, the second delay codebook includes: codeword 0 additional delay-T 2 Codeword 1 with additional delay T 2 。
Specifically, in the sampling period, based on the value obtained after discrete fourier transform is performed on the signal received by the hidden information receiver and the signal sent by the hidden information sender, a nonlinear least square function is established to fit the signal received by the hidden information receiver, and the time delay of each beacon frame in the time delay beacon frame sequence is calculated by minimizing the nonlinear least square function, so that the actually sent time delay codeword is calculated.
The invention also provides a hidden time channel system based on independent basic service combination, which comprises: the device comprises a handshake establishment unit, a hidden information sending unit and a time delay estimation unit, wherein: the handshake establishment unit is used for identifying a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol in the independent basic service combination; the hidden communication handshake protocol flow comprises the following steps: the method comprises the steps that a first detection request frame is sent to all communication equipment in a communication environment by a hidden information receiving party, wherein the first detection request frame comprises first information predetermined between a hidden information receiving party and a hidden information sending party; the method comprises the steps that a hidden information sender sends a first beacon frame, second information predetermined between a hidden information receiver and the first beacon frame is removed, and the hidden information receiver detects second information change in the received first beacon frame; the hidden information receiver sends a second detection request frame, wherein the first information is not included in the second detection request frame; the hidden information sender sends a second beacon frame, and adds the second information in the sent second beacon frame, and the hidden information receiver detects the second information change in the received second beacon frame; the hidden information sending unit is used for encoding the hidden information by the hidden information sender after handshake is completed between the hidden information sender and the hidden information receiver, mapping the encoded hidden information into a time delay code block through a time delay codebook, and superposing the time delay code block on a beacon frame sequence to obtain a time delay beacon frame sequence, wherein the hidden information sender sends the time delay beacon frame sequence; the delay estimation unit is used for receiving the delay beacon frame sequence by the hidden information receiver, counting time slots of the delay beacon frame sequence, calculating the delay through a delay estimation algorithm, and decoding the codeword obtained through calculation to obtain hidden information.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages: the transmission request based on the handshake protocol identifies and overlaps the delay of the beacon frame, has higher concealment and higher detection reliability and stability.
Drawings
Fig. 1 is a schematic diagram of the composition of a beacon frame;
fig. 2 is a schematic diagram of a four-way handshake process according to the present invention;
FIG. 3 is a workflow diagram provided by the present invention;
fig. 4 is a schematic diagram of a delay estimation provided by the present invention;
fig. 5 is a block diagram of a received beacon frame signal interval estimation using a first codebook according to the present invention;
fig. 6 is a diagram of a received beacon frame signal interval estimation using a second codebook provided by the present invention;
fig. 7 is a block diagram of received beacon frame signal interval estimation at the end or termination of a communication provided by the present invention.
Description of the embodiments
The technical scheme of the invention is further described below with reference to the accompanying drawings.
The target scenario of the present invention is a stand-alone network, also known as stand-alone basic service set (IBSS, independent Basic Service Set). In an IBSS, the workstations can communicate directly with each other, and the distance between the two must be within a range that can communicate directly. The minimum 802.11 network is an IBSS consisting of two workstations. In general, IBSS is a temporary network consisting of a small number of workstations for a particular purpose, and such temporary networks are more common in conflict zones and sensitive areas. It is common for actions or deployments to begin with the participants forming an IBSS to communicate data. IBSS is sometimes referred to as ad hoc BSS (ad hoc BSS) or ad hoc networks (ad hoc networks) because of the short duration, small size, and special purpose.
In the target system, there are several legitimate users (including a receiving side and a transmitting side), a covert communication detecting side (a supervisor set for preventing information leakage), and a covert communication user (including a covert communication receiving side and a covert communication transmitting side). The hidden communication receiver is for transmitting the hidden information and is not perceived by the hidden communication detector. Transmission of hidden information using Beacon (Beacon) frames in IBSS networks is contemplated. Beacon (Beacon) frames are an important network maintenance mechanism, mainly to announce the presence of a certain network. The Beacon, which is sent periodically, allows the user in the target environment to learn about the existence of the network, thereby adjusting the parameters necessary to join the network. In the basic network, all Beacon frames are sent by one base station, and a receiver cannot be far away from the base station, and is concerned and detected more, and can not be utilized to transmit hidden information. In an IBSS, stations may send Beacon signals in turn with each other.
The Beacon signal is transmitted in turn, which means that all users in the IBSS network can transmit information in turn, and the method also provides scene shielding for a hidden sender to transmit hidden information by using Beacon frames, improves detection difficulty and enables information transmission to be more hidden.
Beacon (Beacon) is not a communication behavior in nature, is a non-target broadcasting behavior, does not need target reply, only transmits basic information of information source equipment such as WIFI, base stations and other equipment, and is convenient for users in a target scene to find themselves, such as a mobile phone to find WIFI and the like. Beacon does not have a fixed transmission time, a fixed transmission interval is generally reserved, but the fixed transmission interval is not reserved, so that other devices can not find and receive Beacon signals, because Beacon signals of a plurality of different devices are usually present in a communication scene, hidden information is transmitted by using the Beacon, and the communication protocol is not violated by the communication.
As shown in fig. 1, a schematic diagram of the composition of a Beacon frame is shown. Wherein the BSS identification code, typically the MAC address of the sender of the information, is typically unique and fixed in a typical IBSS network. According to the BSS identification code, the hidden communication receiver can accurately locate the target hidden communication sender, and parameters such as network name, rate information and the like can be modified and repeated. In order to maintain the stability of the IBSS network, the detection party is prevented from detecting, and the hidden information is not directly added into the Beacon frame, but the information is transferred through the delay change of the Beacon frame. The hidden communication receiver can combine the Beacon frame interval to detect the delay of the Beacon frame, and the data is to-be-transmitted information (Traffic Indication Map), when the hidden communication sender receives the transmission request of the hidden communication receiver, the hidden communication receiver can be used for carrying out a hidden communication protocol handshake, namely, the hidden information sender identifies the hidden communication transmission request of the hidden information receiver through the hidden communication handshake protocol.
As shown in fig. 2, in order to implement the process of the hidden communication handshake protocol, the four-way handshake is included altogether, before the handshake, the hidden communication receiver does not collect and decode the information (Beacon frame), the hidden communication receiver works as a legal BSS, sends Beacon information according to the rated time, and fixes additional real-time communication TIM (Traffic Indication Map) elements, namely temporary storage frames in the conventional communication process.
First handshake:
and (5) a hidden information receiving party: and sending a detection Request (Probe Request) frame, and specifically sending a detection Request frame containing a broadcast SSID (service set identifier), a Supported transmission rate (Supported Rates) and an extended support rate (Extended Supported Rates) to ensure that all IBSS in the area receive the detection Request. The extended support rate field is a first information predetermined between the hidden information receiver and the hidden information sender, and only contains one additional transmission rate information.
Second handshake:
hidden information sender (some IBSS device): maintaining a silent state, transmitting Beacon information (first Beacon frame) in a normal sequence, and removing second information predetermined between the receiving sides of the hidden information, namely TIM (Traffic Indication Map) elements, namely temporary storage frames in the conventional communication process, in the transmitted Beacon frame; and (5) a hidden information receiving party: and detecting a Beacon signal transmitted by the target IBSS equipment, confirming the change of the TIM element state (removing the TIM element), and confirming the completion of the secondary handshake.
Third handshake:
and (5) a hidden information receiving party: and sending the detection request frame again, wherein the transmission content is consistent with the detection request frame sent for the first time, and stopping sending the additional transmission rate information, namely sending only the support rate field and not transmitting the expansion support rate field (first information).
Fourth handshake:
hidden information sender (some IBSS device): maintaining the silence state, transmitting Beacon information (second Beacon frame) in a normal order, and fixedly attaching TIM (Traffic Indication Map) elements (second information) in the transmitted Beacon frame; and (5) a hidden information receiving party: and detecting a Beacon signal transmitted by the target IBSS equipment, confirming the change of the TIM element state (including the TIM element), and confirming the completion of the four-way handshake.
After handshake is completed between a hidden information sender and a hidden information receiver, the workflow of a time hidden channel can refer to fig. 3 for encoding the hidden information, the method adopts a BCH code for encoding the encoded hidden information, a time delay codebook is selected for mapping the hidden information into time delay information, and the specific mapping method comprises the following two codebooks:
table 1 codebook 1:
| |
0 | 1 |
| |
0 | +T1 |
Table 2 codebook 2:
| |
0 | 1 |
| Additional time delay | -T2 | +T2 |
In a quasi-static wireless environment, a codebook 1 (a first codebook) is adopted, and at the moment of larger fluctuation of environmental time delay, a codebook 2 (a second codebook) is adopted, wherein the difference between the two is the environmental time delay, if the environmental time delay is lower than the standard time delay, the static communication environment is considered, otherwise, the time delay fluctuation communication environment is considered, and the standard time delay can be set according to the actual application scene.
After generating a delay code (delay information) block according to a codebook, superposing the delay code block on a Beacon frame signal (delay Beacon frame sequence), taking the delay as a code word and a code block on the basis of the original system fixed delay, arranging a plurality of delay code words and delay code blocks according to the sequence to form a hidden delay sequence, wherein the Beacon original delay sequence is the fixed delay, namely, the Beacon is sent at fixed intervals, the hidden delay sequence is added on the original fixed delay, so that the non-fixed delay, namely, a new delay sequence is obtained, and a hidden information sender refers to the new delay sequence to send the Beacon frame (delay Beacon frame sequence). After receiving the Beacon signal (time delay Beacon frame sequence), the hidden information receiver can demodulate the Beacon information first and analyze the specific content of the Beacon frame information, and mainly comprises a BSS identification code, a Beacon interval and a TIM element. And after the handshake is judged to be completed, counting the Beacon time slots. And estimating the time delay of the code block by adopting a time delay estimation algorithm, performing BCH decoding on the estimated code word, correcting error information in the code block, and finally obtaining decoded hidden information.
Referring to FIG. 4, a schematic diagram of time delay estimation is shown, wherein T 0 For system fixed time delay, i.e. Beacon spacing in FIG. 1Typically at regular intervals. Assuming that n Beacon frame signals are received in total, the absolute interval between the signals is tau [ i ]]I=1, 2, …, n. The absolute signal interval can be obtained by direct detection, but the relative time slot cannot be obtained directly, and must be calculated by a delay estimation algorithm. Therefore, the invention provides a time delay estimation algorithm, which comprises the following specific procedures:
the concealment receiver signal may be expressed as:
wherein x=it 0 ，T 0 For a fixed interval of Beacon, x is the time of expected signal transmission, i is a sequence and i=1, 2, …, n represents transmission of n groups of signals, y (x) is a signal received by a receiver at x time, e (x) is additive gaussian noise in the environment, R is the total number of signals (the environment contains a plurality of base station devices transmitting Beacon signals and has multipath fading phenomenon, and the total number of signals is assumed to be R), β r For the amplitude gain (including complex gain and real gain) of the (r) th signal, s (x) is the signal transmitted by the information transmitter, (x-ti [, i ]]) For the actual transmission time of the signal, ti]To delay a relative time slot, consider that the system has multipath fading or other environmental changes, the relative time slot is mainly composed of two parts, expressed as:
t[i]=c[i]+η[i] （2）
wherein c [ i ] is a delay codeword actually transmitted, is an amount to be solved by a hidden information receiver, η [ i ] is an environmental delay coefficient, is generally approximately a fixed value in a flat fading environment, is a variable amount in a time fast fading channel, and considering that a sampling signal of the hidden information receiver contains n samples in total, one may contain n-1 sampling time slots, and for the kth sampling time slot, the above formula (1) may be rewritten as follows:
the time delay estimation problem can be expressed as a Nonlinear Least Square (NLS) fitting problem in a frequency domain (the time delay estimation is an important subject in the field of digital communication and is divided into single-path and multi-path time delay estimation, a nonlinear least square algorithm is widely applied to digital signal processing, the time delay parameter estimation by utilizing an iterative algorithm on the frequency domain by utilizing the nonlinear least square method is a common method, the calculation requirement on a hardware system is low, and the implementation is easy), and then a method based on weighted Fourier transform is provided, a nonlinear least square function is established to fit signals (comprising signals sent by an information sender and environmental noise) received by a hidden information receiver, and the method is used for minimizing a complex multi-mode NLS cost function (formula 4).
The absolute time slot of the signal is estimated by minimizing the NLS cost function:
wherein Y (z) is Y (kT) 0 ) (signal received by hidden information receiver in sampling period) value after discrete Fourier change, S (z) is S (kT) 0 ) The value after discrete fourier change (of the signal sent by the hidden information sender in the sampling period), z is the corresponding sequence, ωr is the signal imaginary part, the angular frequency of the sine and cosine signals is represented, j is j in the imaginary number, and e is the index.
To minimize
(i.e., cost function), fitting the target signal using a least squares method has the difficulty that for different system models, so designing a relaxation algorithm improves the accuracy of the fitting, and a relaxation algorithm is proposed to obtain a least squares coefficient estimate, defining a receiving matrix:
and transmitting a signal diagonal array:
and (3) matrix:
wherein Θ (ω) r ) The R-th group signal (including R groups) is represented by an imaginary matrix corresponding to the R-th group signal (including R groups), namely an angular frequency matrix of sine and cosine signals, Y (-n/2), Y (-n/2+1) to Y (-n/2-1) respectively represent discrete Fourier transformed values of signals received by a hidden information receiver, S (-n/2) represents discrete Fourier transformed values of signals sent by a hidden information sender, and an upper corner mark T represents transposition.
The following definitions are made:
wherein beta is r To be the Beacon signal amplitude, then, the formula (4) can be rewritten as:
Based on equation (9), the following estimation can be made for the delay of the ith signal in the Beacon signal:
s is the complex conjugate matrix of the S matrix (defined as equation 6), Θ H Representing the conjugate transformation, argmax is a mathematical function, which is a function of the parameters (set) of the function, the function being calculated so that the objective function is obtained
Maximum omega r 。
And at the moment of interruption or ending of the transmission of the hidden communication information, the hidden information sender resumes the legal IBSS equipment to work, sends Beacon information according to the rated time window of the system, and is attached with a TIM element, no additional operation is carried out, the hidden information receiver detects the Beacon signal of the target equipment for eight time windows, and if the Beacon sending time and the TIM element state are not changed, the default communication is ended or terminated.
The invention is based on a semi-physical simulation platform for verification, and particularly comprises two SDR devices of USRP B210 and a PC. And generating a Beacon signal, generating a hidden time delay Beacon signal sequence, regenerating a common Beacon signal sequence, and finally performing fitting synthesis on a PC (personal computer), wherein the specific results are shown in fig. 5, 6 and 7.
As shown in fig. 5, when codebook 1 is adopted, all IBSS devices received by the hidden information receiver send Beacon signal sequences, when codebook 1 is adopted, no operation is performed when codebook 0 is sent, and when codebook 1 is sent, time delay T is added 1 The setting is 5ms, and most signal intervals are obvious in the figure, but part of intervals cannot judge whether additional delay or channel delay occurs, such as a first Beacon signal interval and a 29 th Beacon signal interval. Therefore, the time delay estimation algorithm provided by the invention can be adopted to analyze and judge the time delay and then decode. 10000 groups of Beacon signals adopting codebook 1 are selected for decoding comparison in the experiment, and specific results are shown in the following table:
table 3 bit error rate versus value:
| | Codebook | 1 | |
| Direct decision delay | 64.24% | 92.32% | |
| Experimental estimation algorithm determination | 84.52% | 95.27% |
As shown in Table 3, by adopting the time delay estimation algorithm provided by the invention, the judgment accuracy of the codebook 1 is improved by 30%, and the reliability of the time hidden channel is obviously improved.
As shown in fig. 6, in order to receive the Beacon signal interval when the codebook 2 is adopted, compared with the codebook 1, the delay is obvious, the decoding is easier, the error rate is reduced by 50% by combining with the table 3, the improvement is obvious, and even if the delay estimation algorithm is used, the improvement is not obvious, but because the fluctuation of the transmitted Beacon interval is large, the Beacon interval is extremely easy to detect, the concealment of the covert communication is reduced, and therefore, the method is only used under the condition of higher safety of the covert communication environment.
As illustrated in fig. 7, is a sequence of Beacon signal intervals in the event of a covert communication termination or an emergency interrupt. Beacon signals transmitted by the target IBSS equipment last for eight time windows (namely eight times of Beacon signals are continuously transmitted), the Beacon transmission time and the TIM element state of the hidden information sender are not changed, and the communication is judged to be ended or terminated.
The present invention also provides a concealed time channel system based on a stand alone basic service set, comprising: the device comprises a handshake establishment unit, a hidden information sending unit and a time delay estimation unit, wherein: the handshake establishment unit is used for identifying a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol in the independent basic service combination; the hidden communication handshake protocol flow comprises the following steps: the method comprises the steps that a first detection request frame is sent to all communication equipment in a communication environment by a hidden information receiving party, wherein the first detection request frame comprises first information predetermined between a hidden information receiving party and a hidden information sending party; the method comprises the steps that a hidden information sender sends a first beacon frame, second information predetermined between a hidden information receiver and the first beacon frame is removed, and the hidden information receiver detects second information change in the received first beacon frame; the hidden information receiver sends a second detection request frame, wherein the first information is not included in the second detection request frame; the hidden information sender sends a second beacon frame, and adds the second information in the sent second beacon frame, and the hidden information receiver detects the second information change in the received second beacon frame; the hidden information sending unit is used for encoding the hidden information by the hidden information sender after handshake is completed between the hidden information sender and the hidden information receiver, mapping the encoded hidden information into a time delay code block through a time delay codebook, and superposing the time delay code block on a beacon frame sequence to obtain a time delay beacon frame sequence, wherein the hidden information sender sends the time delay beacon frame sequence; the delay estimation unit is used for receiving the delay beacon frame sequence by the hidden information receiver, counting time slots of the delay beacon frame sequence, calculating the delay through a delay estimation algorithm, and decoding the codeword obtained through calculation to obtain hidden information.
In the embodiment of the present invention, the first information is an extended support rate, and the extended support rate field includes additional transmission rate information.
In the embodiment of the present invention, the second information is a temporary storage frame.
In the embodiment of the invention, the hidden information sending unit is used for adopting a first time delay codebook in a static communication environment and adopting a second time delay codebook in a time delay fluctuation communication environment; if the environment time delay is lower than the standard time delay, the static communication environment is determined, otherwise, the time delay fluctuation communication environment is determined; the additional delay of the first delay codebook is less than the additional delay of the second delay codebook.
In an embodiment of the present invention, the first delay codebook includes:codeword 0 additional delay 0, codeword 1 additional delay T 1 。
In an embodiment of the present invention, the second delay codebook includes: codeword 0 additional delay-T 2 Codeword 1 with additional delay T 2 。
In the embodiment of the invention, the time delay estimation unit is configured to establish a nonlinear least square function to fit the signal received by the hidden information receiver based on the value obtained by performing discrete fourier transform on the signal received by the hidden information receiver and the signal transmitted by the hidden information transmitter in a sampling period, calculate the time delay of each beacon frame in the time delay beacon frame sequence by minimizing the nonlinear least square function, and further calculate the actually transmitted time delay codeword.
Claims (8)
1. A concealed time channel method based on a stand alone basic service set, comprising:
in the independent basic service combination, a hidden information sender identifies a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol;
the hidden communication handshake protocol flow comprises the following steps:
the method comprises the steps that a first detection request frame is sent to all communication equipment in a communication environment by a hidden information receiving party, wherein the first detection request frame comprises first information predetermined between a hidden information receiving party and a hidden information sending party;
the method comprises the steps that a hidden information sender sends a first beacon frame, second information predetermined between a hidden information receiver and the first beacon frame is removed, and the hidden information receiver detects second information change in the received first beacon frame;
the hidden information receiver sends a second detection request frame, wherein the first information is not included in the second detection request frame;
the hidden information sender sends a second beacon frame, and adds the second information in the sent second beacon frame, and the hidden information receiver detects the second information change in the received second beacon frame;
after handshake is completed between a hidden information sender and a hidden information receiver, the hidden information sender encodes the hidden information, the encoded hidden information is mapped into a time delay code block through the additional time delay of a time delay codebook, the time delay code block is overlapped on a beacon frame sequence to obtain a time delay beacon frame sequence, and the hidden information sender sends the time delay beacon frame sequence;
the hidden information receiver receives the time delay beacon frame sequence, counts time slots of the time delay beacon frame sequence, calculates time delay through a time delay estimation algorithm, and decodes the codeword obtained through calculation to obtain hidden information.
2. The method of blind time channel based on a stand alone basic service set of claim 1 wherein the first information is an extended support rate, and wherein the extended support rate field includes additional transmission rate information.
3. The method of blind time channels based on a stand alone basic service set of claim 2 wherein the second information is a buffered frame.
4. The method of blind time channel based on independent basic service set according to claim 3, wherein the coded blind information is mapped into a delay code block by an additional delay of a delay code book, comprising:
in a static communication environment, a first time delay codebook is adopted, and in a time delay fluctuation communication environment, a second time delay codebook is adopted; if the environment time delay is lower than the standard time delay, the static communication environment is determined, otherwise, the time delay fluctuation communication environment is determined; the additional delay of the first delay codebook is less than the additional delay of the second delay codebook.
5. The free-standing basic service set-based hidden time channel method according to claim 4, wherein the first time delay codebook comprises: codeword 0 additional delay 0, codeword 1 additional delay T 1 。
6. The free-standing basic service set-based hidden time channel method according to claim 4, wherein the second time delay codebook comprises: codeword 0 additional delay-T 2 Codeword 1 with additional delay T 2 。
7. The method of blind time channel based on free standing basic service set according to claim 4, wherein said calculating the time delay by a time delay estimation algorithm comprises:
and in the sampling period, based on the value obtained after discrete Fourier change is carried out on the signal received by the hidden information receiver and the signal transmitted by the hidden information transmitter, a nonlinear least square method function is established to fit the signal received by the hidden information receiver, the time delay of each beacon frame in the time delay beacon frame sequence is calculated through the minimum nonlinear least square method function, and then the actually transmitted time delay codeword is calculated.
8. A concealed time channel system based on a stand alone basic service set, comprising: the device comprises a handshake establishment unit, a hidden information sending unit and a time delay estimation unit, wherein:
the handshake establishment unit is used for identifying a hidden communication transmission request of a hidden information receiver through a hidden communication handshake protocol in the independent basic service combination; the hidden communication handshake protocol flow comprises the following steps: the method comprises the steps that a first detection request frame is sent to all communication equipment in a communication environment by a hidden information receiving party, wherein the first detection request frame comprises first information predetermined between a hidden information receiving party and a hidden information sending party; the method comprises the steps that a hidden information sender sends a first beacon frame, second information predetermined between a hidden information receiver and the first beacon frame is removed, and the hidden information receiver detects second information change in the received first beacon frame; the hidden information receiver sends a second detection request frame, wherein the first information is not included in the second detection request frame; the hidden information sender sends a second beacon frame, and adds the second information in the sent second beacon frame, and the hidden information receiver detects the second information change in the received second beacon frame;
the hidden information sending unit is used for encoding the hidden information by the hidden information sender after handshake is completed between the hidden information sender and the hidden information receiver, mapping the encoded hidden information into a time delay code block through a time delay codebook, and superposing the time delay code block on a beacon frame sequence to obtain a time delay beacon frame sequence, wherein the hidden information sender sends the time delay beacon frame sequence;
the delay estimation unit is used for receiving the delay beacon frame sequence by the hidden information receiver, counting time slots of the delay beacon frame sequence, calculating the delay through a delay estimation algorithm, and decoding the codeword obtained through calculation to obtain hidden information.
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