JP2010056917A - Wireless communication system, wireless communication device, and method for generating key - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for generating a key of which an original communication function can be used for generating key information and the key information can be generated regardless of whether or not devices are stationary or move. <P>SOLUTION: In the method for generating the key, a digital modulation signal having the same carrier frequency is transmitted and received between two wireless communication devices. Each wireless communication device performs quadrature demodulation of the digital modulation signal, extracts constellation feature information according to the result of quadrature demodulation, and generates key information to be used for encryption based on the extracted constellation feature information. As a result, two wireless communication devices share the same key information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, and a key generation method, and can be applied to, for example, a wireless LAN to which encrypted communication is applied.

  Conventionally, in wireless communication, there is a risk of wiretapping from other wireless stations. As a countermeasure for this, an encryption method using a certain key is common.

  However, the key must be known in advance between those who communicate. When the key is transferred by wireless communication, the key itself may be wiretapped there. Although a method of exchanging the key by other than wireless communication, for example, by wired communication, can be considered, it is not practical because two communication paths must be secured. In addition, there is a method that a person who uses a communication device has a module that generates random numbers periodically and inputs it, but it must be input to both communication devices, which is not practical. . As described above, although there are many methods for key generation and key exchange, there are respective problems.

  In order to solve the problems as described above, Patent Document 1 and Patent have disclosed a method in which both communication devices can independently generate the same key using the characteristics of the wireless propagation path without exchanging the key. Proposed in Document 2.

  The methods disclosed in these documents are based on the following idea. When viewed from a certain communication device (referred to as communication device A), the other communication devices (referred to as communication devices B to D) execute wireless communication via propagation paths having different conditions for each installation location. is there. That is, the propagation path characteristic from the communication apparatus A to the communication apparatus B is different from the propagation path characteristic from the communication apparatus A to the communication apparatus C. On the other hand, the transmission path through which the communication device A and the communication device B communicate is the same if the surrounding environment does not change at the same frequency. That is, the propagation path characteristic from the communication apparatus A to the communication apparatus B and the propagation path characteristic from the communication apparatus B to the communication apparatus A are the same.

  That is, if the propagation path characteristic can be converted into a numerical value so that it becomes a key, the same key can be shared only with the other party with which communication is desired without exchanging the key with another means.

Patent Document 1 discloses that the characteristic of a propagation path that can be used for key generation is the electric field strength measured while rotating the directivity of a communication antenna. Further, Patent Document 2 describes that a fading pattern is used as a characteristic of a propagation path that can be used for key generation.
JP 2005-333438 A JP 2006-222817 A

  The technique described in Patent Document 1 has a problem that it is not practical because it is necessary to have more functions than a communication device such as a function of rotating the directivity of an antenna.

  In the technique described in Patent Document 2, since fading used for key generation does not change unless it moves, communication between fixed stations and between mobile stations whose positions are fixed when key generation is required There is a problem that it cannot be used for communication.

  Therefore, a wireless communication system, a wireless communication device, and a key generation method that can use the original communication function for generating key information and that can generate key information without being fixed or moved between devices is desired. Yes.

  The key generation method according to the first aspect of the present invention includes (a) exchange of digital modulation signals having the same carrier frequency between the first wireless communication device and the second wireless communication device, and (b) the first wireless communication device. Each of the wireless communication device and the second wireless communication device performs quadrature demodulation of the digital modulation signal, extracts constellation feature information related to the orthogonal demodulation result, and uses a key used for encryption based on the extracted constellation feature information And (c) the first wireless communication device and the second wireless communication device share the same key information.

  According to a second aspect of the present invention, in a wireless communication apparatus that performs encrypted communication with an opposing wireless communication apparatus, (a) a digital demodulation unit that orthogonally demodulates a digital modulation signal that has arrived from the opposing wireless communication apparatus; (B) constellation analysis means for extracting constellation feature information related to the orthogonal demodulation result; and (c) key information generation / storage for generating and storing encryption key information based on the extracted constellation feature information. Means.

  The wireless communication system of the third aspect of the present invention has two wireless communication apparatuses of the second aspect of the present invention, and exchanges digital modulation signals having the same carrier frequency between the two wireless communication apparatuses. Two wireless communication apparatuses share the same key information.

  According to the present invention, since the key information is generated based on the constellation information obtained from the digital demodulation result, the original communication function can be used for the generation of the key information, and the fixing and movement between the devices are possible. It is possible to provide a wireless communication system, a wireless communication apparatus, and a key generation method that can generate key information without conditions such as the above.

(A) First Embodiment Hereinafter, a first embodiment of a wireless communication system, a wireless communication apparatus, and a key generation method according to the present invention will be described with reference to the drawings.

(A-1) Configuration of First Embodiment FIG. 1 is a block diagram showing a configuration of one of two opposing wireless communication devices (also referred to as communication devices as appropriate) that generate keys. FIG. 1 shows the components related to key generation. Both of the two facing radio communication apparatuses need to have the configuration shown in FIG.

  In FIG. 1, a wireless communication device 10 includes a key generation code generation unit 11, a BPSK (Binary Phase Shift Keying) modulation unit 12, a BPSK demodulation unit 13, a constellation analysis unit 14, a key generation / storage unit 15, and a transmission / reception changeover switch 16. And an antenna 17 and a key generation control unit 20.

  The key generation code generation unit 11 generates a data code for key generation in accordance with an instruction from the key generation control unit 20. The code length of the data code for generating the key is arbitrary, but the constellation analyzer 14 described later may have a code length that can accurately obtain the positions of the codes “0” and “1” in the constellation map. preferable. The data code for key generation may be dedicated for key generation, but a code used during normal communication such as a frame sequence may also be used as a data code for key generation.

  The BPSK modulator 12 applies BPSK modulation to a carrier having a predetermined frequency using a data code for key generation.

  When the wireless communication device 10 performs a transmission operation for key generation under the control of the key generation control unit 20, the transmission / reception changeover switch 16 connects the BPSK modulation unit 12 to the antenna 17, and When the communication device 10 performs a receiving operation for key generation, the BPSK demodulator 13 is connected to the antenna 17.

  The antenna 17 is used for both transmission and reception. At the time of transmission, a carrier (BPSK modulation signal) BPSK modulated by the BPSK modulation unit 12 is radiated to the space as an electromagnetic wave. Is to capture.

  The BPSK demodulator 13 BPSK-demodulates a reception signal (BPSK modulation signal) captured by the antenna 17 and given through the transmission / reception changeover switch 16. In the case of the first embodiment, the BPSK demodulator 13 demodulates the received signal (BPSK modulated signal) by orthogonal demodulation using locally generated orthogonal carriers.

  The constellation analysis unit 14 analyzes the constellation of the received signal (symbol) and obtains information representing the characteristics of the constellation. The constellation reflects the characteristics (for example, noise characteristics) of the propagation path between the two communication devices used for communication.

  The key generation / storage unit 15 directly stores the constellation feature information obtained by the constellation analysis unit 14 as key information, or uses the constellation feature information obtained by the constellation analysis unit 14 as an input value to a predetermined function or conversion algorithm. The function and the output value of the conversion algorithm are stored as key information. The key information stored in this way is used for subsequent encrypted communication.

  The key generation control unit 20 controls the entire flow when generating key information in cooperation with the key generation control unit (20) in the opposite radio. The key generation control unit 20 of the two radios controls each unit so that the digital modulation signal (BPSK modulation signal) related to the data code for key generation is exchanged in a time-division manner within a short time for both directions. The same key information is stored in the key generation / storage unit 15 of each wireless device.

  For example, it is assumed that one of the two wireless devices (wireless communication devices) is a wireless LAN access point device 10-1, and the other wireless device is a wireless LAN terminal 10-2. Assume that the power of the wireless LAN terminal 10-2 is switched from OFF to ON, and the access point device 10-1 recognizes that the wireless LAN terminal 10-2 exists in its own area. At this time, the key generation control unit 20-1 of the access point apparatus 10-1 and the key generation control unit 20-2 of the wireless LAN terminal 10-2 firstly transmit from the access point apparatus 10-1 to the wireless LAN terminal 10-. 2 transmits a BPSK modulated signal related to the data code for key generation, stores the key information in the key generation / storage unit 15-2 of the wireless LAN terminal 10-2, and then immediately accesses from the wireless LAN terminal 10-2 The BPSK modulation signal related to the data code for key generation is transmitted to the point device 10-1, and the key information is stored in the key generation / storage unit 15-1 of the access point device 10-1.

  Note that the timing at which the key generation control unit 20 starts the key information generation process is not limited to the above example.

(A-2) Operation of the First Embodiment Next, the positional relationship between the two communication devices 10-A and 10-B used for communication and the wiretapping device 10-C is in the relationship of FIG. The key information generation operation will be described. Note that not only the communication devices 10-A and 10-B but also the wiretapping device 10-C has the internal configuration shown in FIG. 1 (however, cooperative control by the key generation control unit is not executed). Suppose that the communication device 10-A and the communication device 10-B are installed within a range where radio waves can be received.

  Now, it is assumed that the communication device 10-A has become a communication device on the transmission side for causing the communication device 10-B to generate key information. At this time, the key generation code generation unit 11-A in the communication device 10-A generates a key generation data code, and the BPSK modulation unit 12-A generates key generation data for a carrier having a predetermined frequency. BPSK modulation is performed by the code, and the obtained BPSK modulation signal is given to the antenna 17-A via the transmission / reception changeover switch 16-A and radiated to the radio space. As shown in the constellation diagram of FIG. 3A, the constellation of the signal transmitted from the communication device 10-A has both the constellations of “0” and “1” on the I axis.

  In the communication device 10-B, the antenna 17-B captures the BPSK modulation signal radiated from the communication device 10-A, and the captured BPSK modulation signal is transmitted through the transmission / reception changeover switch 16-B. After being supplied to 13-B and orthogonally demodulated, the constellation analyzer 14-B analyzes the constellation of the received signal. The characteristics of the propagation path between the two communication devices 10-A and 10-B used for communication are reflected in the constellation obtained by this analysis. For example, as shown in the constellation diagram of FIG. 3B, the constellation appears at a position rotated by an angle α from the constellation on the transmission side.

  For example, information on the angle α is given to the key generation / storage unit 15-B as constellation feature information. The key generation / storage unit 15-B quantizes the information of the angle α (for example, converts the angle α so that -5 ° or more and less than 5 ° becomes 0, and converts 5 ° or more and less than 10 ° to 1) and quantizes the information. The angle information is stored as key information as it is, or the quantized angle information is used as an input value to a predetermined function or conversion algorithm, and the output value of the function or conversion algorithm is stored as key information. The information on the angle α may be applied without being quantized.

  Also in the wiretapping device 10-C, the antenna 17-C captures the BPSK modulation signal radiated from the communication device 10-A, and the captured BPSK modulation signal is transmitted through the transmission / reception changeover switch 16-C. After being supplied to 13-C and orthogonally demodulated, the constellation analyzer 14-C analyzes the constellation of the received signal. The constellation obtained by this analysis reflects the characteristics of the propagation path between the communication devices 10-A and 10-C, and reflects the characteristics of the propagation path between the communication devices 10-A and 10-B. Is different. For example, as shown in the constellation diagram of FIG. 3C, the constellation appears at a position rotated from the transmitting constellation by an angle β (β is not equal to α).

  Therefore, even if the key generation / storage unit 15-C generates key information based on the information on the angle β, what is the key information generated by the key generation / storage unit 15-B based on the information on the angle α? It will be different. That is, the key information cannot be stolen in the wiretapping device 10-C.

  In the communication device 10-B, when the generation and storage of the key information is completed, the communication device 10-B is switched to the transmission side and the communication device 10-A is switched to the reception side, and transmission using the same carrier frequency as described above is performed. Executed. Also in this case, since the propagation path at the time of transmission from the communication device 10-A to the communication device 10-B propagates in the reverse direction, the constellation analysis unit 14-A of the communication device 10-A causes the constellation on the transmission side. Analysis result that a constellation appears at a position that is rotated by an angle α, and the key information that is the same as the key information obtained by the key generation / storage unit 15-B is obtained by the key generation / storage unit 15-B. Generated and stored.

  As described above, the communication device 10-A and the communication device 10-B have the same key information, and subsequent encrypted communication is possible.

(A-3) Effect of First Embodiment According to the first embodiment, two communication devices generate key information using constellation feature information (phase rotation information) reflecting propagation path characteristics. Since it did in this way, the key information which a wiretap machine cannot know can be shared between communication apparatuses.

  In addition, the existing communication configuration can be applied to the generation of key information as it is, and a new additional circuit for generating the key information can be dispensed with, or can be suppressed to a slight extent.

  Furthermore, even if two communication devices that want to share key information are fixed or relatively moved at a moving speed that does not change the propagation characteristics, the above-described method for generating key information Can be applied.

(B) Second Embodiment Next, a second embodiment of the wireless communication system, the wireless communication apparatus, and the key generation method according to the present invention will be described with reference to the drawings.

  FIG. 4 is a block diagram showing extracted components related to key generation in the wireless communication apparatus (also referred to as a communicator as appropriate) of the second embodiment, and is a block diagram showing FIG. 1 according to the first embodiment. The same and corresponding parts are denoted by the same reference numerals.

  As is clear from comparison between FIG. 1 and FIG. 4, the wireless communication device 30 of the second embodiment replaces the BPSK modulation unit 12 in the wireless communication device 10 of the first embodiment with OFDM (Orthogonal Frequency Division Multiplexing). The modulation unit 31 is applied, and the OFDM demodulation unit 32 is applied instead of the BPSK demodulation unit 13 in the wireless communication apparatus 10 of the first embodiment. The OFDM scheme is a general multicarrier modulation scheme used in commercially available wireless LANs and the like.

  In the case of the second embodiment, in the communication device on the transmission side for generating key information (the code is 30-A), the OFDM modulation unit 31-A is the key generation code generation unit 11-A. OFDM modulation is performed based on the generated data code for key generation. On the other hand, in the communication device on the receiving side (the code is 30-B), the OFDM demodulator 32-B performs OFDM demodulation.

  Here, it is assumed that the OFDM modulation signal is a superimposed signal of a plurality of BPSK modulation signals having different frequencies (subcarriers). The OFDM demodulator 32-B orthogonally demodulates the BPSK modulation signal for each subcarrier.

  The constellation analyzer 14-B obtains constellation feature information for each subcarrier based on the orthogonal demodulation result for each subcarrier. For example, the angle (phase rotation amount) α (1), α (2),..., Α (n) for each subcarrier is obtained by the method described in the first embodiment (where n is the number of subcarriers). . Here, the angle information may be quantized as described above. The key generation / storage unit 15-B uses the angle series α (1), α (2),..., Α (n) for each subcarrier as key information or the angle series α (1 for each subcarrier. ), Α (2),..., Α (n) are applied to generate and store key information.

  Conversely, when key information is generated in the other communication device 30-A, the OFDM modulation signal is transmitted from the communication device 30-B to the communication device 30-A, as in the case of the first embodiment. You can do that.

  As is well known, encryption is performed by numerically calculating target data based on key information. Key information using a certain number of numerical sequences has a lower probability of being broken.

  According to the second embodiment, since the constellation feature information of each subcarrier is used for generation of key information by using the OFDM modulation scheme, it is more resistant to being stolen than the first embodiment. Strong key information can be generated, and the probability of breaking the encryption can be further reduced.

  Since the digital modulation scheme used in the second embodiment is also an OFDM modulation scheme that is frequently used in wireless LANs, the existing communication configuration can be directly applied to the generation of key information. A new additional circuit can be dispensed with or can be suppressed to a slight extent.

  Furthermore, even if two communication devices that are to share key information are fixed or relatively moving at a moving speed that does not change the propagation characteristics, the key of the second embodiment The information generation method can be applied as in the case of the first embodiment.

(C) Other Embodiments In the first embodiment, the digital modulation scheme is the BPSK modulation scheme. In the second embodiment, the digital modulation scheme is the BPSK modulation for each subcarrier. Although the OFDM modulation method, which is a method, has been shown, other digital modulation methods in which the characteristics of the propagation path appear in the constellation information may be applied.

  For example, a QPSK (Quadri PSK) modulation method may be applied instead of the BPSK modulation method of the first embodiment. Further, for example, as a modulation scheme for each subcarrier, an OFDM modulation scheme to which the QPSK modulation scheme is applied may be applied instead of the modulation scheme of the second embodiment.

  In the first embodiment, the constellation feature information is an angle with respect to the I axis (phase rotation amount), but other values may be used. For example, a vector having an intersection of the I axis and the Q axis as a starting point and a code position as an ending point may be used as constellation feature information and used to generate key information. The same applies to the second embodiment.

  In the second embodiment, the OFDM modulation scheme is applied to perform communication with different carrier frequencies (subcarrier frequencies) at the same time. However, if the communication device has a carrier frequency variable function, the time division is used. Thus, communication with different carrier frequencies may be performed to obtain constellation feature information for each carrier frequency, which may be used to generate key information.

It is a block diagram which shows the component related to the production | generation of the key in the radio | wireless communication apparatus of 1st Embodiment. It is explanatory drawing which shows the example of the positional relationship of the radio | wireless communication apparatus (radio | wireless machine) of 1st Embodiment, and an eavesdropper. FIG. 3 is a constellation diagram illustrating constellations in the transmitting radio, the receiving radio, and the eavesdropper in FIG. 2. It is a block diagram which shows the component related to the production | generation of the key in the radio | wireless communication apparatus of 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 30 ... Wireless communication apparatus, 11 ... Key generation code generation unit, 12 ... BPSK modulation unit, 13 ... BPSK demodulation unit, 14 ... Constellation analysis unit, 15 ... Key generation / storage unit, 16 ... Transmission / reception changeover switch, 17 ... Antenna, 20 ... Key generation control part, 31 ... OFDM modulation part, 32 ... OFDM demodulation part.

Claims (5)

A digital modulated signal having the same carrier frequency is exchanged between the first wireless communication device and the second wireless communication device;
Each of the first wireless communication device and the second wireless communication device performs quadrature demodulation on the digital modulation signal, extracts constellation feature information related to the quadrature demodulation result, and performs encryption based on the extracted constellation feature information. Generate key information used in
The key generation method, wherein the first wireless communication device and the second wireless communication device share the same key information.   A superimposition signal of a plurality of digital modulation signals having different carrier frequencies is exchanged between the first wireless communication device and the second wireless communication device, constellation feature information is extracted for each carrier frequency, and key information The key generation method according to claim 1, wherein the key generation method is used for generation.   The key generation method according to claim 1, wherein the constellation feature information is a phase rotation amount. In a wireless communication device that performs encrypted communication with a facing wireless communication device,
Digital demodulation means for orthogonally demodulating a digital modulation signal coming from an opposing wireless communication device;
Constellation analysis means for extracting feature information of the constellation according to the orthogonal demodulation result;
A wireless communication apparatus comprising: key information generation / storage means for generating and storing encryption key information based on the extracted constellation characteristic information. Two wireless communication devices according to claim 4,
A wireless communication system characterized in that a digital modulation signal having the same carrier frequency is exchanged between the two wireless communication devices, and the two wireless communication devices share the same key information.

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