KR102549074B1 - Method and apparatus for generating secret key in wireless communication network - Google Patents

Abstract

Obtaining a random sequence using reciprocity of a radio channel;
Generating a security key for secure communication based on a random sequence, and stopping generation of the security key when the flatness measured from the measurement result of the radio channel exceeds a predetermined threshold. A method and apparatus for generating are provided.

Description

Method and apparatus for generating secret key in wireless communication network

The present disclosure relates to an apparatus and method for generating a security key for secure communication between terminals using characteristics of a radio channel of a wireless communication network.

In general, in wireless communication, two terminals share the same secret key in order to perform secure communication in which a secret message is exchanged. In order for two terminals to share the same security key, public key cryptography may be used. Public key cryptography requires infrastructure for key management, and public key cryptography can be used only when the computing power of a terminal trying to steal confidential messages is limited.

However, distributed wireless communication systems generally do not have such an infrastructure. In addition, the conventional public key encryption method, which limits the computing power of a terminal trying to eavesdrop on a confidential message, is difficult to apply to a distributed wireless communication system.

One embodiment provides an apparatus for generating a security key using characteristics of a radio channel.

Another embodiment provides a method of generating a security key using characteristics of a radio channel.

According to one embodiment, a method of generating a security key for secure communication is provided. The security key generation method includes obtaining a random sequence using reciprocity of a radio channel, generating a security key based on the random sequence, and based on the flatness measured from the measurement result of the radio channel. When it is determined that the radio channel is flat, stopping the generation of the security key.

The obtaining of the random sequence in the security key generation method may include quantizing a strength indicator of a received signal.

In the security key generation method, the received signal may be a received probe request or a probe response received for the transmitted probe request.

In the security key generation method, the received signal may be a received request to send (RTS) message or a received clear to send (CTS) message for the transmitted request to send message.

Obtaining a random sequence in the security key generation method may include quantizing an impulse response for a radio channel.

The quantization step in the security key generation method may include quantizing an impulse response of a dominant path among impulse responses for multiple paths when a radio channel is composed of multiple paths.

The obtaining of the random sequence in the security key generation method may include quantizing a frequency response for a radio channel.

The step of stopping the generation of the security key in the security key generation method is the inverse peak-to-average power ratio (IPAPR) obtained from the frequency response for the wireless channel, the peak-to-average power ratio (peak- It may include measuring at least one of a to-average power ratio (PAPR), a spectral flatness measure (SFM), or a coherence bandwidth as flatness.

The step of generating a security key in the security key generation method includes removing a difference between a random sequence and a random sequence obtained by a counterpart device of secure communication, and removing a difference between the two random sequences. It may include removing information about randomness from the random sequence.

In the security key generation method, the step of removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences is leaked in the process of removing the difference between the two random sequences using the universal hash function. It may include removing information about possible randomness from the random sequence.

According to another embodiment, it includes at least one processor, a memory, and a wireless communication unit, and the at least one processor executes at least one program stored in the memory to generate a random sequence using reciprocity of a wireless channel. Obtaining, generating a security key for secure communication based on the random sequence, and stopping generation of the security key when it is determined that the radio channel is flat based on the flatness measured from the measurement result of the radio channel. Provided is a security key generating device that performs the steps.

In the secure key generating apparatus, at least one processor may perform a step of quantizing a strength indicator of a received signal when performing the step of obtaining a random sequence.

In the security key generating device, the received signal may be a received probe request or a probe response received for the transmitted probe request.

In the security key generation device, the received signal may be a received request to send (RTS) message or a received clear to send (CTS) message for the transmitted request to send message.

In the security key generating apparatus, at least one processor may perform a step of quantizing an impulse response for a radio channel when performing the step of obtaining a random sequence.

In the secure key generation device, when performing the quantization step, at least one processor may perform the step of quantizing the impulse response of the dominant path among the impulse responses for the multi-path when the radio channel is composed of multiple paths. .

In the secure key generating apparatus, at least one processor may perform a step of quantizing a frequency response for a radio channel when performing the step of obtaining a random sequence.

In the security key generation device, when at least one processor performs the step of stopping the generation of the security key, the inverse peak-to-average power ratio (IPAPR) obtained from the frequency response for the radio channel ), peak-to-average power ratio (PAPR), spectral flatness measure (SFM), or coherence bandwidth as flatness. there is.

In the security key generating device, at least one processor, when performing the step of generating the security key, removing the difference between the random sequence and the random sequence obtained by the counterpart device of secure communication, and the difference between the two random sequences A step of removing information about randomness that may be leaked in the process of removing is removed from the random sequence.

In the secure key generation device, when at least one processor removes information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences, the universal hash function is used to perform the step of removing the two random sequences. A step of removing information about randomness that may be leaked from the random sequence in the process of removing differences between sequences may be performed.

Each terminal can perform secure communication without the help of a security key management infrastructure by generating a security key using the opposite characteristics of the radio channel. In addition, using the flatness of the estimated wireless channel, it is possible to detect in advance a case in which the security of the security key may be lowered due to an increase in channel correlation with a third party attempting to eavesdrop on secure communication.

1 is a flowchart illustrating a security key generation method according to an embodiment.
2 is a graph showing a received signal strength indicator of a wireless channel according to an embodiment.
3 is a graph showing an impulse response of a wireless channel according to an embodiment.
4 is a graph showing a frequency response of a wireless channel according to an embodiment.
5 is a graph showing an upper limit on the amount of information that a third party can know about a final security key according to an embodiment.
6 is a block diagram illustrating a wireless communication system according to an embodiment.

Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present disclosure may be implemented in many different forms and is not limited to the embodiments described herein. In addition, in order to clearly explain the present description in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, a terminal includes a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), and a high reliability mobile station (HR-MS) ), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (UE), machine type communication device, MTC device), etc., and may include all or some functions of MT, MS, AMS, HR-MS, SS, PSS, AT, UE, etc.

1 is a flowchart illustrating a security key generation method according to an embodiment.

According to one embodiment, the user of the terminal can turn on/off the secure communication function of the terminal. When the secure communication function of the terminal is in an on state, preparation for secure communication may be performed. In addition, the user may determine start or stop of secure communication when the secure communication function of the terminal is in an on state. During a period before the secure communication function is turned on and the user starts secure communication, the terminal prepares for secure communication. As preparation for secure communication, the terminal may store randomness obtained based on non-secure communication.

The security key may be obtained using randomness of a radio channel. That is, two terminals performing secure communication share a security key remotely without the help of a key management infrastructure through a sequential key distillation method using channel reciprocity of a radio channel, They can send and receive confidential messages to each other. Hereinafter, a method of generating a security key of a terminal performed when a security communication function of the terminal is in an on state will be described in detail with reference to FIG. 1 .

Referring to FIG. 1 , a first terminal and a second terminal having a secure communication function turned on each acquire a random sequence by estimating a radio channel (S110). At this time, the random sequences obtained from the first terminal and the second terminal contain similar randomness, and thus, step S110 may be a randomness sharing step.

In order to sufficiently secure the randomness necessary for extracting the security key, each terminal transmits and receives a message to estimate a radio channel (S111), and uses the radio channel estimation result to acquire common randomness. At this time, the obtained common randomness may be continuously updated. Then, when a secure communication request is generated, each terminal can use the latest randomness that has already been obtained.

For example, a request to send (RTS) message and a clear to send (CTS) message exchanged between terminals prior to data transmission of the terminals may be used to estimate a radio channel. When the RTS message and the CTS message are used for radio channel estimation, each terminal updates a radio channel estimation result from the RTS message and the CTS message, and when secure communication starts, a random random number is obtained from the most recently updated radio channel estimation result. sequence can be obtained. Alternatively, each terminal may estimate a radio channel using a probe request and a probe response.

Thereafter, the terminal acquires a random sequence by quantizing the estimation result of the radio channel (S112).

According to an embodiment, as a radio channel estimation result, a received signal strength indicator (RSSI), an impulse response, or a frequency response of the radio channel may be used for quantization.

2 is a graph showing a received signal strength indicator of a wireless channel according to an embodiment.

Due to channel reciprocity, a radio channel when the first terminal transmits a signal to the second terminal and a radio channel when the second terminal transmits a signal to the first terminal are very similar. That is, referring to FIG. 2 , the RSSI when the first terminal receives a signal transmitted by the second terminal and the RSSI when the second terminal receives the signal transmitted by the first terminal are very similar. However, RSSI between the first terminal and the second terminal and a third party shows different patterns. Therefore, by using the fact that the characteristics of a radio channel are inherently random but are uniquely determined by the positions of the transmitter and receiver, by quantizing the observation result of the radio channel, two users who want to perform secure communication can You can create and share random sequences.

3 is a graph showing an impulse response of a wireless channel according to an embodiment.

In order for the first terminal and the second terminal to share randomness, an impulse response of a radio channel may be used. This is because the impulse response of the radio channel from the first terminal to the second terminal and the impulse response of the radio channel from the second terminal to the first terminal have very similar patterns due to channel reciprocity.

At this time, in order for two users who want to perform secure communication to share randomness from the impulse response of the radio channel, a path with relatively large received power (ie, a dominant path) among multiple paths constituting the impulse response of the radio channel on the time axis A random sequence obtained from the impulse response of path)) may be used as a common random property.

4 is a graph showing a frequency response of a wireless channel according to an embodiment.

Alternatively, a common random characteristic may be obtained through a frequency response of a radio channel that is equivalent to an impulse response of the radio channel.

Thereafter, when secure communication starts (S120), the terminal determines whether a sufficient number of random sequences necessary for generating a security key are secured (S130). If the randomness obtained from the estimation result of the radio channel is less than the amount of randomness required for extracting the security key, each terminal performs the randomness sharing step again. For example, each terminal may further secure randomness by additionally transmitting and receiving an RTS message and a CTS message, or a probe request and a probe response. At this time, each terminal may stop acquiring randomness when it is determined that randomness for secure communication is sufficiently secured.

The terminal may determine whether randomness is sufficiently secured based on Equation 1.

Referring to Equation 1, n _i is the length of a random sequence obtained in the ith channel estimation, and N _seq is a length of a random sequence sufficient to obtain randomness. That is, when the sum of the lengths of all sequences obtained through channel estimation is longer than the predetermined sequence N _seq , the terminal may determine that the random sequence is sufficiently secured.

Referring back to FIG. 1 , each terminal performs post-processing based on the random sequence obtained through quantization (S140) to generate a security key (S150). Information reconciliation (S141) is a step of removing differences existing between random sequences obtained from each terminal. For example, error correcting codes can be used for information reconciliation. In addition, the first terminal and the second terminal transmit information on common randomness that may be leaked (ie, information likely to be acquired by a third party trying to eavesdrop/eavesdrop) (N _leak ) on shared randomness ( N _seq ) is removed (privacy amplification) (S143). In the information reconciliation process, some information of the common sequence transmitted and received between each terminal may be intercepted by a third party. By removing information leaked through the privacy amplification step from the common sequence, A security key unknown to a third party may be extracted. For example, a universal hash function can be used for privacy amplification.

Thereafter, each terminal performs secure communication using the generated security key (S160), and the secure communication is terminated by a user's selection (S170).

On the other hand, if the characteristics of the radio channel estimated for randomness extraction are not frequency selective, that is, if multiple paths are not sufficiently secured in the radio channel environment, the randomness shared by the first user and the second user A correlation between the surname X and the randomness Y acquired by the third party through wiretapping may increase. If the correlation coefficient between the result observed by the first terminal or the second terminal and the result observed by the third party is ρ, the third party based on the quantization result (eg, random sequence obtained through wiretapping) The amount of information I (X, Y) that can be known about the random sequence shared by the first user and the second user is expressed in Equation 2 below.

Then, the first user and the second user post-process (f(·)) the shared random sequence to finally obtain a security key. The amount of information that a third party can know about the final security key based on the randomness acquired through wiretapping has an upper limit as shown in Equation 3 due to data processing inequality.

5 is a graph showing an upper limit on the amount of information that a third party can know about a final security key according to an embodiment.

Referring to FIG. 5 , when a correlation between a main channel (a channel between a first user and a second user) and an eavesdropping channel (a channel between a first user or a second user and a third party) increases, the third party It is possible to have a large amount of information about a random sequence shared by the first user and the second user. In general, since the correlation between the main channel and the eavesdropping channel is unknown to the first user and the second user, information leaked to a third party in the randomness extraction process is difficult to remove through privacy amplification. Therefore, in this case, the third party can partially know about the security key finally obtained between the first user and the second user, and the security key cannot satisfy the required security.

In one embodiment, a case in which the security of the shared security key is determined to be insufficient is selectively detected, so that the user may be notified of the existence of a potential risk. For example, if multiple paths are not sufficiently secured in a wireless channel, the terminal may stop a process of generating a security key for secure communication and notify the user of this process. Alternatively, the terminal may ask the user whether to stop generating a security key for secure communication when a multipath is not sufficiently secured in a radio channel, and whether to continue secure communication may be determined according to the user's selection.

The correlation between the main channel and the tapped channel may be proportional to the flatness of the wireless channel and inversely proportional to the number of multipath fading constituting the wireless channel. Accordingly, the terminal according to an embodiment may measure the flatness from the estimation result of the radio channel and stop generating the security key when it is determined that the radio channel is flat. For example, when the flatness of the radio channel exceeds a predetermined threshold, generation of the security key may be stopped. Table 1 is a table showing scales for measuring the flatness of a radio channel frequency response.

Measure explanation Inverse peak-to-average power ratio
(Inverse Peak-to-Average Power Ratio, IPAPR)

(

,
x_i=i번째 부반송파에서의 주파수 응답)

(

,
x _i =frequency response at the ith subcarrier) Spectral Flatness Scale
(Spectral Flatness Measure, SFM)

(x _i = frequency response at the ith subcarrier) correlation bandwidth
(Coherence Bandwidth)

(

,
τ=multipath delay , A _c (τ)=gain of the delay path)

That is, a terminal according to an embodiment may measure at least one of PAPR, IPAPR, SFM, and correlation bandwidth as flatness of a radio channel. In addition, when the terminal determines that the radio channel is flat based on the flatness (ie, when the radio channel is flat because multipath is not sufficiently secured), the terminal may determine that the security of the security key to be generated is low. For example, when IPAPR is measured as flatness, the terminal determines that the security of the security key to be generated is low when IPAPR exceeds a predetermined threshold. Thereafter, each terminal may stop generating the security key and inform the user that secure communication cannot be performed.

As described above, each terminal can perform secure communication without the help of a communication infrastructure by generating a security key using the opposite characteristics of the radio channel. In addition, using the flatness of the estimated wireless channel, it is possible to detect in advance a case in which the security of the security key may be lowered due to an increase in channel correlation with a third party attempting to eavesdrop on secure communication.

6 is a block diagram illustrating a wireless communication system according to an embodiment.

Referring to FIG. 6 , a wireless communication system according to an embodiment includes a base station 610 and a terminal 620 .

The base station 610 includes a processor 611, a memory 612, and a radio frequency unit (RF unit) 613. The memory 612 is connected to the processor 611 and may store various information for driving the processor 611 or at least one program executed by the processor 611 . The wireless communication unit 613 may be connected to the processor 611 to transmit and receive wireless signals. The processor 611 may implement functions, processes, or methods proposed in the embodiments of the present disclosure. At this time, in the wireless communication system according to an embodiment of the present disclosure, the air interface protocol layer may be implemented by the processor 611. An operation of the base station 610 according to an embodiment may be implemented by the processor 611.

The terminal 620 includes a processor 621, a memory 622, and a wireless communication unit 623. The memory 622 is connected to the processor 621 and may store various information for driving the processor 621 or at least one program executed by the processor 621 . The wireless communication unit 623 may be connected to the processor 621 to transmit and receive wireless signals. The processor 621 may implement functions, steps, or methods proposed in the embodiments of the present disclosure. At this time, in the wireless communication system according to an embodiment of the present disclosure, the air interface protocol layer may be implemented by the processor 621. An operation of the terminal 620 according to an embodiment may be implemented by the processor 621.

In an embodiment of the present description, the memory may be located inside or outside the processor, and the memory may be connected to the processor through various known means. Memory is a volatile or non-volatile storage medium in various forms, and may include, for example, read-only memory (ROM) or random access memory (RAM).

Although the embodiments have been described in detail above, the scope of rights is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts defined in the following claims also fall within the scope of rights.

Claims (20)

A method of generating a security key for secure communication, comprising:
Obtaining a random sequence using reciprocity of a radio channel;
generating the security key based on the random sequence; and
When it is determined that the radio channel is flat based on the flatness measured from the measurement result of the radio channel, stopping the generation of the security key;
Stopping the generation of the security key,
Obtained from the frequency response for the radio channel, inverse peak-to-average power ratio (IPAPR), peak-to-average power ratio (PAPR), spectral flatness measure, SFM), or a coherence bandwidth, as the flatness. In paragraph 1,
Obtaining the random sequence,
Quantizing the strength indicator of the received signal
Including, security key generation method. In paragraph 2,
The received signal is
A method for generating a security key, wherein a probe request is received, or a probe response is received for a probe request that is transmitted. In paragraph 2,
The received signal is
A method for generating a security key, which is a received request to send (RTS) message or a received clear to send (CTS) message for a received request to send message. In paragraph 1,
Obtaining the random sequence,
Quantizing the impulse response for the radio channel
Including, security key generation method. In paragraph 5,
In the quantization step,
quantizing an impulse response of a dominant path among impulse responses for the multi-path when the radio channel is composed of multi-paths;
Including, security key generation method. In paragraph 1,
Obtaining the random sequence,
Quantizing the frequency response of the radio channel
Including, security key generation method. delete In paragraph 1,
Generating the security key,
removing a difference between the random sequence and the random sequence obtained by the counterpart device of the secure communication; and
removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences;
Including, security key generation method. In paragraph 9,
In the process of removing the difference between the two random sequences, the step of removing information about randomness that may be leaked from the random sequence,
removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences using a universal hash function;
Including, security key generation method. at least one processor;
memory, and
radio communications department
including,
The at least one processor executes at least one program stored in the memory,
Obtaining a random sequence using reciprocity of a radio channel;
Generating a security key for secure communication based on the random sequence; and
When it is determined that the radio channel is flat based on the flatness measured from the measurement result of the radio channel, stopping the generation of the security key;
When the at least one processor performs the step of stopping the generation of the security key,
Obtained from the frequency response for the radio channel, inverse peak-to-average power ratio (IPAPR), peak-to-average power ratio (PAPR), spectral flatness Measure, SFM), or a security key generation device that performs the step of measuring at least one of a coherence bandwidth as the flatness. In paragraph 11,
When the at least one processor performs the step of obtaining the random sequence,
Quantizing the strength indicator of the received signal
To perform, secure key generation device. In paragraph 12,
The received signal is
An apparatus for generating a security key, which is a received probe request or a received probe response to a transmitted probe request. In paragraph 12,
The received signal is
A security key generating device, which is a received request to send (RTS) message or a received clear to send (CTS) message for a received request to send message. In paragraph 11,
When the at least one processor performs the step of obtaining the random sequence,
Quantizing the impulse response for the radio channel
To perform, secure key generation device. In clause 15,
When the at least one processor performs the quantization step,
quantizing an impulse response of a dominant path among impulse responses for the multi-path when the radio channel is composed of multi-paths;
To perform, secure key generation device. In paragraph 11,
When the at least one processor performs the step of obtaining the random sequence,
Quantizing the frequency response of the radio channel
To perform, secure key generation device. delete In paragraph 11,
When the at least one processor performs the step of generating the security key,
removing a difference between the random sequence and the random sequence obtained by the counterpart device of secure communication; and
removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences;
To perform, secure key generation device. In paragraph 19,
When the at least one processor performs the step of removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences,
removing information about randomness that may be leaked from the random sequence in the process of removing the difference between the two random sequences using a universal hash function;
To perform, secure key generation device.

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