KR20200067739A - Common secret key generating system for secure wireless communication - Google Patents

Abstract

According to the present disclosure, disclosed are a system and method for generating a secret key for secure wireless communication. According to a specific embodiment of the present disclosure, a low key bit disagreement rate (KBDR) and a high key agreement rate (KAR) can be obtained by generating a spare key according to quantizing an autocorrelation sequence of channel coefficients in a time division duplex (TDD) wireless channel environment, performing information adjusting on the bit disagreement of the generated spare key using safety sketch or low density parity check (LDPC), and generating a secret key by performing privacy amplification using a hash function. In addition, according to the improvement of the channel condition, the performance of information adjustment can be improved with a safety sketch technique, and information of all generated keys can be adjusted when the signal-to-noise ratio (SNR) is 0 dB or more.

Description

SECOND KEY GENERATION SYSTEM FOR SECURE WIRELESS COMMUNICATION FOR SECURE WIRELESS COMMUNICATION

The present invention relates to a system and method for generating a secret key for secure wireless communication, and more specifically, as the secret key is generated with a channel gain derived from uplink and downlink channel coefficients between a transmitting node and a receiving node, security It relates to a technology that can be further improved.

The wireless device can communicate with other wireless devices within its power range due to the broadcasting characteristics of the wireless communication channel, and thus is very vulnerable to various frequency hacking attacks.

Therefore, recently, physical layer security has been proposed to secure the security of a wireless channel, and this physical layer security is implemented as a key-based system as a technology that proposes security between wireless systems by utilizing random attributes between wireless channels.

The key-based secret key generation system randomly generates a secret key from common channel information available between users of a legitimate wireless link, and the randomness and security of the secret key generated based on the physical layer security are time-correlated, It is determined by channel reciprocity and spatial correlation.

That is, since the channel state is randomly changed over time due to the movement of objects in the environment as well as the transmitting node and the receiving node, such an unpredictable change in the channel state is provided as a variable of the secret key generation system based on the physical layer security. do.

In addition, assuming that the channel fading at the transmitting node and the receiving node are the same, the channel response of the forward channel is the same as the reverse channel in the time division duplex (TDD) system, so the same secret is used using common random channel information. You can generate keys.

However, due to instability and measurement noise of wireless equipment, channel information obtained from uplink and downlink channels is asymmetric, making it difficult to implement secret key generation.

The present invention for solving this problem can improve the low key bit disagreement rate (KBDR: Key Bit Disagreement Rate) and the key agreement rate (KAR: Key Agreement Rate). It is an object of the present invention to provide a system and method for generating a common secret key for secure wireless communication that can improve the performance.

The object of the present invention is not limited to the above-mentioned object, other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by embodiments of the present invention. In addition, it will be readily appreciated that the objects and advantages of the present invention can be realized by means of the appended claims and combinations thereof.

According to an embodiment of the present invention for achieving the above object, a common secret key generation system for secure wireless communication is

A wireless device comprising a transmitting node and a receiving node performing bidirectional communication, and a wiretapping node for eavesdropping communication between the transmitting and receiving nodes,

A random extraction unit provided in the transmitting node and deriving channel coefficients between uplink and downlink between the transmitting node and the receiving node;

A channel pre-processor for deriving an autocorrelation sequence vector for the channel coefficients of the random extractor;

A pre-key generator for quantizing the auto-correlation sequence vector of the channel pre-processor into a binary vector to generate a pre-key;

An information adjusting unit that adjusts the bit mismatch of the generated spare key with LDPC (Low Density Parity Check); And

It characterized in that it comprises a secret key generating unit for generating a secret key by performing a privacy amplification on the pre-adjusted bit mismatch.

Preferably, the channel pre-processing unit,

It may be provided to derive an autocorrelation sequence vector through a fast Fourier transform and an inverse Fourier transform on the derived channel coefficients.

Preferably, the information adjustment unit,

At the transmitting node, the codeword to which LDPC (Low Density Parity Check) is added among the error correction codes is encoded, then modulated through BPSK (Binary Phase Shift Keying), and the modulated signal is transmitted to the receiving node using a public channel. ,

At the receiving node, the codeword to which the Low Density Parity Check (LDPC) is added is decoded by using the preliminary key received using the Sum Product Algorithm (SPA) for the modulated codeword, and the codeword is completely recovered. It can be provided to adjust the information until.

Preferably, the information adjustment unit,

At the transmitting node, a random codeword is selected from the error correction code, an exclusive OR is performed on the selected spare key and the selected codeword to calculate the syndrome, the syndrome is modulated by BPSK (Binary Phase Shift Keying) technique, and then the public channel is To the receiving node,

At the receiving node, an exclusive OR may be performed on the received syndrome and the generated spare key to output the codeword from which the syndrome has been removed, and then decode the codeword to adjust the information until the random codeword is completely recovered. have.

Preferably, the privacy amplification unit,

The hash function between the transmitting node and the receiving node may be provided to remove the information exposed to the eavesdropping node among the spare keys to generate a secret key.

According to another embodiment of the present invention, a method for generating a common secret key for secure wireless communication is

A method for generating a common secret key for secure wireless communication of a wireless device including a transmitting node and a receiving node performing bidirectional communication, and a wiretapping node for eavesdropping communication between the transmitting and receiving nodes,

A random extraction step provided in the transmitting node to derive channel coefficients between uplink and downlink between the transmitting node and the receiving node;

A channel preprocessing step of deriving an autocorrelation sequence vector for the derived channel coefficients;

A preliminary key generation step of generating a preliminary key by quantizing the autocorrelation sequence vector of the channel preprocessing unit into a binary vector

An information adjustment step of adjusting the bit mismatch of the generated spare key with LDPC (Low Density Parity Check); And

And a secret key generation step of generating a secret key by performing privacy amplification on the spare key in which the bit mismatch is adjusted.

Preferably, the channel pre-processing step

It may be provided to derive an autocorrelation sequence vector through a fast Fourier transform and an inverse Fourier transform on the derived channel coefficients.

Preferably, the information adjustment step

At the transmitting node, the codeword to which LDPC (Low Density Parity Check) is added among the error correction codes is encoded, then modulated through BPSK (Binary Phase Shift Keying), and the modulated signal is transmitted to the receiving node using a public channel. ,

At the receiving node, the codeword to which the Low Density Parity Check (LDPC) is added is decoded by using the preliminary key received using the Sum Product Algorithm (SPA) for the modulated codeword, and the codeword is completely recovered. It can be provided to adjust the information until.

Preferably, the information adjustment step

At the transmitting node, a random codeword is selected from the error correction code, an exclusive OR is performed on the selected spare key and the selected codeword to calculate the syndrome, and the syndrome is modulated by BPSK (Binary Phase Shift Keying) technique, and then the public channel is To the receiving node,

At the receiving node, an exclusive OR may be performed on the received syndrome and the generated spare key to output the codeword from which the syndrome has been removed, and then decode the codeword to adjust the information until the random codeword is completely recovered. have.

According to an embodiment of the present invention, a TDD wireless channel environment quantizes an auto-correlation sequence of channel coefficients to generate a spare key, adjusts information using a safety sketch or a low density parity check (LDPC), and hash function As the secret key is generated by performing privacy amplification, a low key bit mismatch rate (KBDR) and a high key match rate (KAR) can be obtained. It can be improved, and if the signal-to-noise ratio (SNR) is more than 12dB, information of all the generated keys can be adjusted.

The following drawings attached in this specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description of the invention described below, and thus the present invention is described in such drawings. It is not limited to interpretation.
1 is a diagram illustrating a wireless device of one embodiment.
2 is a configuration diagram of a system for generating a secret key of a wireless device in one embodiment.
3 is a detailed configuration diagram of a random extraction unit of an embodiment.
4 is a detailed configuration diagram of a channel preprocessor of an embodiment.
5 is a detailed configuration diagram of an information adjustment unit using an LDPC in one embodiment.
6 is a conceptual diagram of a safety sketching technique of an information adjustment unit of an embodiment.
7 is a graph showing KBDR versus channel speed of 3Km in one embodiment.
8 is a graph showing KAR versus channel speed of 3 Km in one embodiment.
9 is a graph showing KBDR versus channel speed of 30Km in one embodiment.
10 is a graph showing KAR versus channel speed of 30 Km in one embodiment.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

Advantages and features of the present invention, and a method of achieving them will be apparent with reference to embodiments described below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention pertains. It is provided to completely inform the person having the scope of the invention, and the present invention is only defined by the scope of the claims.

Terms used in the specification will be briefly described, and the present invention will be described in detail.

The terminology used in the present invention has been selected, while considering the functions in the present invention, general terms that are currently widely used are selected, but this may vary according to the intention or precedent of a person skilled in the art or the appearance of a new technology. In addition, in certain cases, some terms are arbitrarily selected by the applicant, and in this case, their meanings will be described in detail in the description of the applicable invention. Therefore, the terms used in the present invention should be defined based on the meanings of the terms and the contents of the present invention, not simply the names of the terms.

When a certain part of the specification "includes" a certain component, this means that other components may be further included instead of excluding other components unless specifically stated to the contrary. Also, the term "part" as used in the specification means a hardware component such as software, FPGA, or ASIC, and "part" performs certain roles. However, "part" is not meant to be limited to software or hardware. The "unit" may be configured to be in an addressable storage medium or may be configured to reproduce one or more processors.

Thus, as an example, "part" refers to components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, Includes subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, database, data structures, tables, arrays and variables. The functionality provided within the components and "parts" may be combined into a smaller number of components and "parts" or further separated into additional components and "parts".

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains may easily practice. In addition, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted.

The communication system to which an embodiment is applied may include any dog in any suitable configuration for each component. In general, computing and communication systems appear in a wide variety of configurations, and the drawings do not limit the scope of the present disclosure to any particular configuration. Although the figure shows one operating environment in which various features disclosed in this patent document may be used, such features may be used in any other suitable system.

According to an embodiment, a self-correlation sequence of a channel estimate derived between an uplink and a downlink between a transmitting node and a receiving node is provided in a transmitting node, and the derived autocorrelation sequence is quantized and converted into a binary value to reserve a key. And adjust the bit mismatch with one of LDPC (Low Density Parity Check) codes, Turbo codes, cascades, or safety sketches of the generated spare key, and then, among the spare keys generated by the privacy amplification technique, the leaked part to the wiretap node Remove it to generate a secret key.

Accordingly, it is possible to provide a low key bit disagreement rate (KBDR) and a high key agreement rate (KAR), and the performance of the secret generation system may remain the same despite rapid channel changes. have.

1 is a view showing the configuration of a wireless device to which the secret key generation system of an embodiment is applied. Referring to FIG. 1, the wireless communication device of an embodiment includes a transmitting node Alice and a receiving node Bob capable of bidirectional communication, and It may include an eavesdropping node Eve that intercepts communication between nodes.

And the wireless device between the transmitting node Alice and the receiving node Bob in one embodiment is a time division TDD half duplex system operated at a carrier frequency of 2.4 GHz, and the eavesdropping node Eve has a distance greater than 1/2 wavelength at the transmitting/receiving node. Suppose you are in

That is, it is assumed that a wireless device between a transmitting node (Alice) and a receiving node (Bob) transmits channel information between a transmitting node and a receiving node, and there is an eavesdropping node (Eve) that attempts to eavesdrop on communication between the transmitting and receiving nodes. It is assumed that the node (Eve) is a passive attacker and can predict the key generation scheme between the transmitting node (Alice) and the receiving node (Bob) and channel characteristics between the transmitting and receiving nodes.

In addition, assuming that the transmitting node Alice and the receiving node Bob exchange the probing signal of the channel within a time shorter than the coherence time of the channel, the channel estimate derived by Alice and Bob is based on the principle of channel reciprocity and noise. It can be the same on the assumption that none. That is, the error of the channel estimate is caused only by noise.

For the secure communication of these wireless devices, each transmitting node Alice and receiving node Bob have a secret key generation system, respectively.

2 is a detailed configuration diagram of a secret key generation system according to an embodiment. Referring to FIG. 2, an embodiment derives channel coefficients derived between uplink and downlink between the transmitting node Alice and the receiving node Bob, Derive the autocorrelation sequence of the derived channel coefficients, quantize the derived autocorrelation sequence vector, convert it to a binary level to derive the preliminary key, adjust the bit mismatch of the preliminary key, and then generate the preliminary key based on the privacy amplification technique. The secret key is generated after removing some of the leaks from the intercepted node Eve. Here, in one embodiment, the bit mismatch of the spare key is described as an example of adjusting information by using a low density parity check (LDPC) code and a safety sketching technique, but a low density parity check (LDPC) code, a turbo code, and a cascade , Or various techniques such as safety sketching may be used, but is not limited thereto.

Accordingly, the transmitting node Alice encodes and compresses the raw signal of the transmitting node with the generated secret key, and then transmits it to the receiving node Bob. At this time, the spare key is used jointly between the transmitting node Alice and the receiving node Bob.

As shown in FIG. 2, the secret key generation system according to an embodiment is provided at each of the transmitting node Alice and the receiving node Bob of the wireless communication device, and the random extraction unit 100, the channel pre-processing unit 200, and the information quantization unit It may include at least one of the 300, the information adjustment unit 400, and the privacy amplification unit 500.

Here, the random extraction unit 100 extracts common channel characteristics that each node Alice and Bob can use. Here, the channel characteristics include received signal strength (RSS), channel impulse response (CIR), or channel frequency response (CFR). Because it is easily accessible from commercial wireless equipment, the most practical implementation of secret key generation is performed based on Received Signal Strength (RSS). In addition, the channel impulse response (CIR) or the channel frequency response (CFR) can be channel-probeed using a minimum mean squared error (MMSE) algorithm for pilot signals between transmitting and receiving nodes.

That is, channel estimation can be performed based on channel probing for a pilot signal provided through two-way communication between the transmitting node Alice and the receiving node Bob.

At this time, the channel coefficient hab of the receiving node Bob in the transmitting node Alice and the channel gain hba of the transmitting node Alice in the receiving node Bob are correlated due to hab = hba or noise based on the principle of channel reciprocity.

에 대해, 송신 노드(Alice) 및 수신 노드(Bob) 각각의 수신 신호

,

는 식 1으로 주어진다.Probe signal transmitted and received through a bidirectional channel

For, the receiving signal of each of the transmitting node (Alice) and the receiving node (Bob)

,

Is given by Equation 1.

[Equation 1]

는 송신 노드 Alice의 수신 신호이고,

는 수신 노드 Bob의 수신 신호이면,

,

는 백색 가우시안 잡음이며,

는 송신 노드 Alice와 수신 노드 Bob 간의 다중 경로 페이딩 채널이다.

Is the received signal from the transmitting node Alice,

Is the receiving signal of the receiving node Bob,

,

Is a white Gaussian noise,

Is a multipath fading channel between the transmitting node Alice and the receiving node Bob.

와 프로브 신호

간의 연산은 컨블루션(Convolution) 연산이다. Here, the multipath fading channel between the transmitting node Alice and the receiving node Bob

And probe signal

The operation of the liver is a convolution operation.

And, assuming that the half duplex switching time delay between channels is smaller than the coherence time of the channel environment, the channel information between the transmitting and receiving nodes Alice and Bob has a high correlation with the secret key generation.

On the other hand, assuming that the eavesdropping node Eve always eavesdrops at a distance of 1/2 or more of the system operating frequency (l = 2), the channel coefficient hae between the transmitting node Alice and the eavesdropping node Eve and the receiving node Alice and the eavesdropping node Eve The channel coefficient hbe is independent of the channel information of the transmitting node Alice or the receiving node Bob, so the eavesdropping node Eve cannot generate the same common secret key between the transmitting node Alice or the receiving node Bob.

In addition, a white Gaussian noise (FWGN) model and tap filtered to generate a fading channel considering channel change characteristics according to frequency generated by multipath channels as well as time-varying characteristics of channels generated by mobility of each node. A delay line (TDL) model is used.

Accordingly, the random extraction unit 100 of one embodiment performs a function of generating such a multipath fading channel.

는 부가 백색 가우시안 잡음으로 모델링된다.FIG. 3 is a diagram showing a process of generating a multipath fading channel h(t) between a transmitting node Alice and a receiving node Bob. The two white Gaussian noises are each filtered by a Doppler spectrum filter to form a complex number. Here, the Doppler spectrum filter performs a function such that the channel h(t) has time correlation characteristics. Meanwhile, channel estimation and hardware noise

Is modeled as additive white Gaussian noise.

,

는 식 2로 모델링된다.Channel coefficients derived from the transmitting node Alice and the receiving node Bob due to the additional white Gaussian noise

,

Is modeled as Equation 2.

[Equation 2]

와

는 송신 노드 Alice와 수신 노드 Bob 각각의 불완전한 채널 추정치이다.

와

는 각각 제로 평균 복소수 가우시안 잡음

으로 정의되고,

는 분산이며, 다중 경로 페이딩 채널

는 탭 지연 라인 다중 경로 채널 시뮬레이터의 출력이다. Where channel coefficient

Wow

Is an incomplete channel estimate for each of the transmitting node Alice and the receiving node Bob.

Wow

Is zero mean complex Gaussian noise, respectively

Is defined as

Is distributed, multipath fading channel

Is the output of the tap delay line multipath channel simulator.

,

는 두 개의 송신 노드 Alice와 수신 노드 Bob 사이의 하드웨어 및 채널 잡음으로 인해 탭 지연 라인 다중 경로 페이딩 채널

에 제로 평균 복소수 가우시안 잡음

및

가 추가된다.Channel coefficient

,

Is a tap delay line multipath fading channel due to hardware and channel noise between the two transmitting nodes Alice and the receiving node Bob.

Zero mean complex Gaussian noise

And

Is added.

와

각각은 비대칭 부가 가우시안 노이즈 프로세서에 의해 도출될 수 있다. 이러한 키 생성을 위한 채널 추정을 위해, 송신 노드 Alice와 수신 노드 Bob 각각은 채널 정보를 획득하기 위해 파일롯 신호로 채널 프로브(Prove)한다.Also, zero mean complex Gaussian noise

Wow

Each can be derived by an asymmetric additive Gaussian noise processor. To estimate the channel for generating the key, each of the transmitting node Alice and the receiving node Bob probes the channel with a pilot signal to obtain channel information.

In an embodiment, in order to reduce nonreciprocity effects when extracting channels of the transmitting node Alice and the receiving node Bob, preprocessing is performed on the unstable raw channel coefficients. Irreversibility is indicated by the occurrence of asymmetry in hardware during non-communication measurement and transmission/reception. When the irreversibleness that occurs when extracting the channel of the transmitting node Alice and the receiving node Bob is reduced, the cross-correlation between the channel estimation values of the transmitting node Alice and the receiving node Bob is improved, so that the key generation performance can be improved.

Accordingly, for the channel coefficients derived from the random extraction unit 100, the channel pre-processing unit 200 may derive an autocorrelation sequence vector using a fast Fourier transform technique to reduce irreversible.

와

은 다음 식 3으로 주어진다.That is, the channel coefficient vector obtained by channel probe with the pilot signal from the transmitting node Alice and the receiving node Bob

Wow

Is given by the following equation 3.

[Equation 3]

Here, m is the number of acquired channel samples.

Accordingly, the channel pre-processing unit 200 uses the Wiener-Khintchine theorem to autocorrelate sequence vectors A(n), n composed of N samples for m incomplete channel samples measured by each of the transmitting node Alice and the receiving node Bob. =1,2, ..., N are calculated. Here, N may be a Fast Fourier Transform (FFT) size dependent on the channel sample length m.

와

를 입력으로 자기 상관 시퀀스 벡터 A(n)를 출력할 수 있다. 4 is a diagram for explaining the concept of channel pre-processing in one embodiment. Referring to FIG. 4, an embodiment is a channel coefficient vector obtained from the transmitting node Alice and the receiving node Bob.

Wow

Autocorrelation sequence vector A(n) may be output as an input.

,

에 대해 이산 푸리에 변환을 수행한 후 이산 푸리에 변환된 결과값에 대해 단계 5 및 6에서 역 푸리에 변환을 수행할 수 있다. 즉, 자기 상관 시퀀스 벡터 A(n)는 송신 노드 Alice와 수신 노드 Bob에서 획득된 채널 계수 벡터

와

에 대한 고속 푸리에 변환을 통해 도출될 수 있다.That is, in step 4, each node receives the received channel sequence vector

,

After performing a discrete Fourier transform on, the inverse Fourier transform may be performed in steps 5 and 6 on the result of the discrete Fourier transform. That is, the autocorrelation sequence vector A(n) is a channel coefficient vector obtained from the transmitting node Alice and the receiving node Bob.

Wow

It can be derived through fast Fourier transform for.

And each node Alice, Bob is the auto-correlation sequence vector A(n) of the channel coefficient vector derived through the channel pre-processing process is transferred to the information quantization unit 300, and the quantization unit 300 is auto-correlation sequence vector A(n). Quantization technique is performed on.

There are two types of well-known information quantization techniques: Lossy-Quantization and Lossless-Quantization. Lossy-Quantization's information quantization technique uses the median value of the RSS measurement as a threshold level and uses a channel gain sequence vector near the threshold level. This is a deletion technique.

In one embodiment, the information quantization unit 300 may convert the autocorrelation sequence vector A(n) into a binary vector based on a single threshold level.

That is, a preliminary key is generated by converting the autocorrelation sequence vector A(n) into a binary vector, and the quantization technique is given by Equation 4 below. At this time, the generated spare key is used equally between the transmitting node Alice and the receiving node Bob.

[Equation 4]

는 다음 식 5로 주어진다.Where a single threshold level

Is given by the following equation 5.

[Equation 5]

가 제어되며, σ는 A 의 샘플 값들의 표준 편차 값으로 정의된다.Here, α is a quantization parameter, and a threshold level using the quantization parameter α

Is controlled, and σ is defined as the standard deviation value of the sample values of A.

Meanwhile, the spare key generated based on channel reciprocity must be the same, but may be inconsistent due to non-concurrent transmission and hardware noise. Accordingly, the key mismatch at any point of time must be corrected through the information adjustment unit 400, and accordingly, the agreement rate of the secret key may be improved.

Accordingly, in one embodiment, the information adjustment unit 400 is a bit of a spare key as one of the information adjustment techniques of a low density parity check (LDPC) code, a turbo code, a cascade, or a safety sketch for a binary vector of the information quantization unit 300. The discrepancy can be adjusted.

First, the information adjustment unit 400 according to an embodiment describes a series of processes of correcting the bit mismatch of the spare key generated by the transmitting node Alice and the receiving node Bob by applying a low density parity check (LDPC) code. .

Information adjustment using LDPC (Low Density Parity Check) code

An error correction code is applied to correct the bit mismatch between the spare key generated by the transmitting node Alice and the receiving node Bob. That is, by adjusting the mismatched bits of the spare key using the LDPC (Low Density Parity Check) code among the error correction codes (ECC), the transmitting node Alice and the receiving node Bob have the same spare keys Ka and Kb. Is shared. At this time, the LDPC code is added to the spare key to be encoded.

FIG. 5 is a block diagram showing a process of adjusting information to remove a mismatch between the spare key generated by the information quantization unit 300 of FIG. 2. Referring to FIG. 5, the information adjusted spare key Ka is codeword c After encoding, it is modulated by BPSK and transmitted to the receiving node Bob through the public channel, and the receiving node Bob decrypts the codeword c with the received spare key Ka using the Sum Product Algorithm (SPA). If the initial Key Bit Disaggreement Rate (KBDR) is less than the error correction capability of the error correction code, the receiving node Bob can successfully decode the codeword with the received spare key.

는 k 비트의 블록을 인코더에 대한 입력으로 받아들이고 n 개의 코딩 된 비트의 블록을 출력한다. 여기서

인 경우,

는 오류 검출 및 정정에 사용되는 패리티 비트의 수이고,

은 코드 비율이며, 코드 비율은 1/2로 설정된다.In the linear block code, an error correction code is added to the extra bits in the transmitted information. The extra bits are called parity bits and are used to detect and correct errors in transmitted information. I.e. linear block code

Accepts a block of k bits as input to the encoder and outputs a block of n coded bits. here

If it is,

Is the number of parity bits used for error detection and correction,

Is the code rate, and the code rate is set to 1/2.

In FIG. 5, G is a generator matrix and H is each defined as a parity check matrix, and the parity check matrix H can be obtained from Gauss-Jordan Elimination, and the parity check matrix is represented by the following Equation 6.

[Equation 6]

의 2진 행렬이고,

는

의 아이덴티티 행렬이다. Where A is the size

Is the binary matrix of

The

Identity matrix.

The generator matrix G is given by Equation 7 below.

[Equation 7]

Here, the parity check matrix H is applied with the row echelon operation of H to make the number less than 1 smaller than 0, thereby reducing the decoding complexity of the LDPC code. The codeword c is generated as the product of the secret key bit K and the generator matrix G, and satisfies the following Equation 8.

[Equation 8]

After encoding the codeword c to which the LDPC (Low Density Parity Check) is added, the signal of the transmitting node is modulated using BPSK (Binary Phase Shift Keying), and the modulated signal is transmitted to the receiving node using a public channel.

Then, the receiving node Bob, which has received the modulated codeword, decodes the codeword c to which the Low Density Parity Check (LDPC) has been added using the preliminary key received using the Sum Product Algorithm (SPA).

이면 유효한 코드워드 c 가 수신되거나 전송된 코드워드 c가 수신된 코드워드와 동일하다. 따라서 일 실시 예에서는 소프트 결정 복호화를 사용하고, 이에 합계 산술 알고리즘(SPA: Sum Product Algorithm)을 수행한다.Decoding of LDPC is performed by one of two main iterative decoding algorithms, namely hard-decision decoding and soft-decision decoding. Parity check conditions

If it is, a valid codeword c is received or the transmitted codeword c is the same as the received codeword. Therefore, in one embodiment, soft decision decoding is used, and a Sum Product Algorithm (SPA) is performed.

The Sum Product Algorithm (SPA) is defined as follows.

여기서, c 및 p는 각각 송수신된 코드워드이다.(One)

Here, c and p are codewords transmitted and received, respectively.

(

또는

의 쌍)는 메시지 노드

에 의해 체크 노드

로 전송된 메시지이고

또는

는

가 비트 0 또는 1 인 양이다. (2)

(

or

Pair of message nodes

Checked by node

Is a message sent to

or

The

Is a bit with bit 0 or 1.

는 체크 노드

에 의해 변수 노드

로 전송된 메시지이고,

와

는

가 비트 0 또는 1 으로 현재 또는 업데이트된 양이다. (3)

Is a check node

By variable node

Message sent to,

Wow

The

Is the current or updated amount with bits 0 or 1.

Based on the definition of the Sum Product Algorithm (SPA), the Sum Product Algorithm (SPA) technique proceeds to the next step.

메시지를

로 전송한다.1) Step 1: All variable nodes

Message

Transfer to.

를 다음 식 9 및 10으로부터 도출될 수 있다.2) Step 2: The node's response

Can be derived from the following equations 9 and 10.

[Equation 9]

[Equation 10]

3) Step 3: The message node updates the response message to the check node using the following equations 11 and 12.

[Equation 11]

[Equation 12]

는

를 만족하는 상수이다.here,

The

Is a constant that satisfies.

4) Step 4: Estimate the probability that the bit of the codeword c is 0 or 1 and update the codeword c of the current state by selecting the bit with the higher probability.

Here, the probability is given by the following equations 13 and 14.

[Equation 13]

[Equation 14]

이 되면, 코드워드 c는 1이고, 아니면 코드워드 c는 0이다.Where the probability value

In this case, codeword c is 1, or codeword c is 0.

인 지를 체크한다. 즉,

이면, 디코딩이 성공한 것으로 판단되고 그렇지 아니하면 제2 단계로 반복 진행하거나 반복 횟수가 기 정해진 설정치에 도달하면 디코딩이 실패한 것으로 판단된다.5) Step 5: Parity check

Check the recognition. In other words,

If this is the case, it is determined that the decoding is successful, otherwise, it is determined that the decoding has failed when iteratively proceeds to the second step or the number of repetitions reaches a predetermined set value.

Coordination of information using safety sketching techniques

FIG. 6 is a view showing the concept of the safety sketching technique. Referring to FIG. 6, in step 2, the transmitting node Alice in one embodiment selects a random codeword c from the error correction code C, and selects the reserved key Ka and the selected codeword. Syndrome s is computed by performing an exclusive OR on c, the syndrome s is modulated by BPSK (Binary Phase Shift Keying) technique, and then transmitted to the receiving node Bob using a public channel.

를 도출한다. 그리고 수신 노드 Bob은 예비키 Ka를 복호화한 다음 코드워드

와 신드롬 s와의 배타적 논리합을 통해 불일치가 조정된 예비키

를 도출한다. In step 3, the receiving node Bob in one embodiment outputs a codeword cb with the syndrome s removed by performing an exclusive OR on the received syndrome s and the generated spare key Kb, and then decodes the codeword cb to decode the random codeword c Codeword as it recovers

To derive. And the receiving node Bob decrypts the spare key Ka, and then the codeword

And key s are adjusted through an exclusive OR between the syndrome and s

To derive.

= c ) 완전하게 예비키의 불일치가 조정된다. 결과적으로 수신 노드 Bob은 송신 노드 Alice와 동일한 키를 추출하게 된다.When the receiving node Bob can recover the exact random code word used to calculate the syndrome of the sending node Alice (i.e.

= c) The mismatch of the spare key is completely adjusted. As a result, the receiving node Bob extracts the same key as the transmitting node Alice.

In one embodiment, the spare key in which the bit mismatch of the spare key is adjusted is transmitted to the privacy amplification unit 500.

In other words, the privacy amplification unit 500 has the entropy of the secret key generated with a reduced length as some information is leaked to the eavesdropping node (Eve) during information adjustment and the secret key is generated by removing the leaked information from the generated spare key. Is increased. The privacy amplification technique is performed using a well-known hash function.

Simulation results for the performance of the key generation system

In order to evaluate the performance of the secret key generation system, respective items for key agreement rate (KAR), key bit disagreement rate (KBDR), and randomness are required.

On the other hand, the key bit mismatch rate KBDR is the ratio of the number of bits mismatched between the secret key generated at the transmitting node Alice and the receiving node Bob and the length of the generated key, which is defined by Equation 15 below.

[Equation 15]

는 비밀키의 길이이고,

는 생성된 키의 총 수이다.]here,

Is the length of the secret key,

Is the total number of keys generated.]

Meanwhile, the key generation rate KAR is a probability of the same number of keys generated by nodes Alice and Bob.

The efficiency of the secret key generation system indicates the number of keys generated per unit time. The higher the key generation rate KAR, the faster the generation of the secret key for data protection. The key generation rate KAR is derived by the following equation (16).

[Equation 16]

는 송신 노드 Alice와 수신 노드 Bob에서 추출된 동일한 키의 수,

는 생성된 키의 총 수이다.here,

Is the number of identical keys extracted from the sending node Alice and the receiving node Bob,

Is the total number of keys generated.

And randomness is a test item indicating how random the generated key is, and the randomness test technique is provided by the National Institute of Standard and Technology (NIST), and NIST is used to measure the random numbers of Random Number Generators and Pseudo Random Number Generators. Used for testing. Therefore, since the key generation is also a form of a random number generator, randomness is obtained using the NIST test.

Accordingly, in one embodiment, the performance of two methods of directly quantizing a raw channel estimate without the channel pre-processing unit 200 and the autocorrelation sequence vector of the channel estimation using the channel pre-processing unit 200 and quantizing it are compared and evaluated. do. At this time, performance evaluation of the key generation algorithm is performed based on the key bit mismatch rate (KBDR) and the key agreement rate (KAR) obtained based on the Monte Carlo simulation in MATLAB.

To this end, assuming that the wireless communication equipment is a TDD communication system operating at a frequency of 2.4 GHz and the movement in the channel environment is speeds of 3 km/h and 30 km/h, the channel gain is 0.1 millisecond sample and for all channel measurements 100,000 keys are generated, and each parameter to generate keys is as shown in Table 1 below.

[Table 1]

,

를 생성하고, 여기서

는 다중 경로 페이딩 채널이다. In one embodiment, the channel coefficient between the transmitting node Alice and the receiving node Bob

,

Create, where

Is a multipath fading channel.

은 필터링 된 백색 가우시안 노이즈 (FWGN) 모델을 이용하여 서로 독립적인 (수평의 평균 전력으로) 여러 개의 주파수 비 선택적 (플랫) 페이딩 샘플을 생성하고, TDL 모델을 이용하여 독립적인 평탄한 페이딩 채널 샘플의 7 개의 탭에 대해 하기 표 2에 주어진 각각의 탭 전력을 곱한 다음 합산하여 도출된다. Tap delay line multipath fading channel

Generates multiple frequency non-selective (flat) fading samples that are independent of each other (with a horizontal average power) using a filtered white Gaussian noise (FWGN) model, and 7 of the independent flat fading channel samples using a TDL model. It is derived by multiplying each tap power given in Table 2 below for the taps and then adding them up.

[Table 2]

Here, all seven channel paths are modeled as motion in a multipath environment using Jake's classical Doppler spectrum.

The classical Doppler spectrum is defined by Equation 17 below.

[Equation 17]

는 채널의 최대 도플러 주파수이다.here,

Is the maximum Doppler frequency of the channel.

In one embodiment, all channel coefficient vectors are converted into an autocorrelation sequence vector, and then the transformed autocorrelation sequence vector is quantized to generate a preliminary key of the binary vector, and a safety sketch is performed on the generated preliminary key to perform bit mismatch. Adjust.

This safety sketching technique is used to recover the sending node Alice's key from the receiving node Bob with the correct secret key of the sending node Alice. That is, the codeword c is randomly selected from the error correction code C, and is exclusively logically combined with the initial secret key of the transmitting node Alice to generate the syndrome s. This codeword c is BPSK modulated and transmitted to the receiving node Bob through the public channel. The syndrome s received at the receiving node Bob is decoded and used to recover the spare key generated at the transmitting node Alice.

7 is a graph showing a carrier terminal 2.4 GHz and a relative terminal speed of 3 Km/h, and a KBDR between each node Alice and Bob when the quantization parameter α=0.3, referring to FIG. 7, the KBDR of an embodiment is a preprocessed channel It can be seen that the preliminary key generated from the coefficient is improved over the existing KBDR that quantizes the raw channel coefficient into the preliminary key, and it can be seen that the KBDR is greatly reduced after correcting the information using the safety sketching technique.

8 is a graph showing a KAR between each node Alice and Bob when the carrier frequency is 2.4 GHz and a relative terminal speed of 3 Km/h, and the quantization parameter α=0.3. Referring to FIG. 8, safety using an open channel AWGN It can be seen that the KAR of an embodiment in which a bit mismatch of a spare key is performed by performing a sketching technique is improved than when transmitted through an existing Rayleigh multipath fading channel.

For example, for a carrier frequency of 2.4 GHz and a relative terminal speed between each node Alice and Bob at 3 km/h, the KAR in one embodiment can be achieved at 70% at an SNR of 20 dB, which means that each node Alice and Bob at 20 dB. It means that communication can be secured using 70 keys out of 100 keys generated during operation. In addition, 100% KAR can be achieved even in the 0 dB SNR environment when both the pre-processing and the information adjustment process are performed.

9 and 10 are graphs showing KAR and KBDR between each node Alice and Bob when the carrier frequency is 2.4 GHz and a relative terminal speed of 30 Km/h, and the quantization parameter α = 0.3. Referring to FIGS. 9 and 10, It can be seen that the carrier frequency shown in FIGS. 7 and 8 is a relative terminal speed of 2.4 GHz and 30 Km/h, and is somewhat deteriorated compared to when the quantization parameter α=0.3, but this is more due to high mobility or channel fluctuation. This is due to the small channel coherence time.

Accordingly, an embodiment generates a spare key by quantizing an auto-correlation sequence of channel coefficients in a TDD radio channel environment, adjusts the information of the bit mismatch of the generated spare key using a safety sketch or a low density parity check (LDPC), and hash function. As the secret key is generated by performing privacy amplification, a low key bit mismatch rate (KBDR) and a key match rate (KAR) can be obtained, and the performance of information adjustment is improved by the safety sketching technique according to the improvement of channel conditions. If the signal-to-noise ratio (SNR) is 0 dB or more, information on all the generated keys can be adjusted.

A method for generating a common secret key for secure wireless communication of a wireless device including a transmitting node and a receiving node performing bidirectional communication, and a wiretapping node for eavesdropping communication between the transmitting and receiving nodes is provided in the transmitting node and is provided between the transmitting node and the receiving node. A random extraction step of deriving channel coefficients between links and downlinks; A channel preprocessing step of deriving an autocorrelation sequence vector for the derived channel coefficients; A pre-key generation step of quantizing the auto-correlation sequence vector of the channel pre-processor into a binary vector to generate a pre-key; An information adjustment step of adjusting the bit mismatch of the generated spare key with LDPC (Low Density Parity Check); And a secret key generation step of generating a secret key by performing a privacy amplification on the spare key in which the bit mismatch is adjusted, wherein the channel pre-processing step performs fast Fourier transform and inverse Fourier transform on the derived channel coefficients. It may be provided to derive an autocorrelation sequence vector, and the information adjustment step encodes a codeword to which an LDPC (Low Density Parity Check) is added among error correction codes in a transmitting node, and then performs BPSK (Binary Phase Shift Keying). LDPC (modulated signal) is transmitted to the receiving node using a public channel, and the received node is used as a preliminary key received using a Sum Product Algorithm (SPA) for the modulated codeword. Low Density Parity Check) may be provided to decode the added codeword and adjust the information until the codeword is completely recovered.

In addition, the information adjustment step selects a random codeword from the error correction code at the transmitting node, performs an exclusive OR on the selected spare key and the selected codeword to calculate the syndrome, and the syndrome is a BPSK (Binary Phase Shift Keying) technique. After modulating to, it is transmitted to the receiving node using a public channel, and the receiving node performs an exclusive OR on the received syndrome and the generated spare key to output the codeword from which the syndrome is removed, and then decodes the codeword. It may be provided to adjust the information until the random codeword is completely recovered, each step of the secret key generation method described above is the random extraction unit 100, the channel pre-processing unit 200, the spare key generation unit 300 , The information adjustment unit 400, and the function performed by the privacy amplification unit 500, the detailed reference is omitted.

As described above, although the embodiments have been described by a limited embodiment and drawings, those skilled in the art can make various modifications and variations from the above description. For example, the described techniques may be performed in a different order than the described method, and/or components such as the described system, structure, device, circuit, etc. may be combined or combined in a different form from the described method, or other configurations. Appropriate results can be achieved even if replaced or substituted by urea or equivalent. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims to be described later, but also by the claims and equivalents.

In a TDD radio channel environment, a self-correlation sequence of channel coefficients is quantized to generate a spare key, and the bit mismatch of the generated spare key is adjusted with information using a safety sketch or low density parity check (LDPC), and privacy amplification using a hash function. By performing the secret key generation, it is possible to obtain a low key bit mismatch rate (KBDR) and a key match rate (KAR), and according to the improvement of channel conditions, the safety sketching technique can improve the performance of information coordination. If the noise ratio (SNR) is more than 12dB, it can bring a great improvement in terms of the accuracy and reliability of operation of the secret key generation system and method for secure wireless communication that can adjust the information of all generated keys. In addition, it is an invention with industrial applicability since it is not only sufficient or commercially available for commercial or commercial operation of a system for providing wireless communication services.

Claims (9)

A wireless device comprising a transmitting node and a receiving node performing bidirectional communication, and a wiretapping node for eavesdropping communication between the transmitting and receiving nodes,
A random extraction unit provided in the transmitting node and deriving channel coefficients between uplink and downlink between the transmitting node and the receiving node;
A channel pre-processor for deriving an autocorrelation sequence vector for the channel coefficients of the random extractor;
A pre-key generator for quantizing the auto-correlation sequence vector of the channel pre-processor into a binary vector to generate a pre-key;
An information adjusting unit that adjusts the bit mismatch of the generated spare key with LDPC (Low Density Parity Check); And
And a secret key generator configured to generate a secret key by performing a privacy amplification on the spare key in which the bit mismatch is adjusted. The method of claim 1, wherein the channel pre-processing unit,
A secret key generation system for secure wireless communication, characterized in that it is provided to derive an autocorrelation sequence vector through a fast Fourier transform and an inverse Fourier transform on the derived channel coefficients. The method of claim 2, wherein the information adjustment unit,
At the transmitting node, the codeword to which the LDPC (Low Density Parity Check) is added among the error correction codes is encoded and then modulated through BPSK (Binary Phase Shift Keying), and the modulated signal is transmitted to the receiving node using a public channel. ,
At the receiving node, the codeword to which the Low Density Parity Check (LDPC) is added is decoded by using the preliminary key received using the Sum Product Algorithm (SPA) for the modulated codeword, and the codeword is completely recovered. Secret key generation system for secure wireless communication, characterized in that provided to adjust the information until. The method of claim 2, wherein the information adjustment unit,
At the transmitting node, a random codeword is selected from the error correction code, an exclusive OR is performed on the selected spare key and the selected codeword to calculate the syndrome, the syndrome is modulated by BPSK (Binary Phase Shift Keying) technique, and then the public channel is To the receiving node,
The receiving node is provided to adjust the information until the random codeword is completely recovered by outputting the codeword from which the syndrome has been removed by performing an exclusive OR on the received syndrome and the generated spare key. A secret key generation system for secure wireless communication. The method of claim 3 or 4, wherein the privacy amplification unit,
A secret key generation system for secure wireless communication, characterized in that it is provided to generate a secret key by removing information exposed to a wiretapping node from a spare key by using a hash function between a transmitting node and a receiving node. A method for generating a common secret key for secure wireless communication of a wireless device including a transmitting node and a receiving node performing bidirectional communication, and a wiretapping node for eavesdropping communication between the transmitting and receiving nodes,
A random extraction step provided in the transmitting node to derive channel coefficients between uplink and downlink between the transmitting node and the receiving node;
A channel preprocessing step of deriving an autocorrelation sequence vector for the derived channel coefficients;
A preliminary key generation step of generating a preliminary key by quantizing the autocorrelation sequence vector of the channel preprocessor into a binary vector
An information adjustment step of adjusting the bit mismatch of the generated spare key with LDPC (Low Density Parity Check); And
And a secret key generation step of generating a secret key by performing a privacy amplification on the bit mismatch adjusted spare key. The method of claim 6, wherein the channel pre-processing step
A method of generating a secret key for secure wireless communication, characterized in that it is provided to derive an autocorrelation sequence vector through a fast Fourier transform and an inverse Fourier transform on the derived channel coefficients. The method of claim 7, wherein the information adjustment step
At the transmitting node, the codeword to which LDPC (Low Density Parity Check) is added among the error correction codes is encoded, then modulated through BPSK (Binary Phase Shift Keying), and the modulated signal is transmitted to the receiving node using a public channel. ,
At the receiving node, decode the codeword to which the Low Density Parity Check (LDPC) is added by using the preliminary key received using the Sum Product Algorithm (SPA) for the modulated codeword, and the codeword is completely recovered. Secret key generation method for secure wireless communication, characterized in that provided to adjust the information until. The method of claim 7, wherein the information adjustment step
At the transmitting node, a random codeword is selected from the error correction code, an exclusive OR is performed on the selected spare key and the selected codeword to calculate the syndrome, the syndrome is modulated by BPSK (Binary Phase Shift Keying) technique, and then the public channel is To the receiving node,
The receiving node is provided to adjust the information until the random codeword is completely recovered by outputting the codeword from which the syndrome has been removed by performing an exclusive OR on the received syndrome and the generated spare key. A method of generating a secret key for secure wireless communication.

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