JP2007110487A - Lan system and its communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a LAN system capable of making encrypted data communicate between LAN devices through a wired or a wireless communication line and maintaining LAN security, and to provide its communication method. <P>SOLUTION: When a wireless LAN terminal 18 makes an encrypted data transmission communicate with a wireless LAN base station 14 in a wireless LAN system 10, the wireless LAN terminal 18 usually generates a secret key based on a random number acquired by a random number exchange means such as a 4WAY handshake. If the wireless LAN terminal 18 has made an encrypted data transmission communicate with the wireless LAN base station 14 before, the wireless LAN terminal 18 generates a new secret key based on the last secret key used in the last transmission, and makes data encrypted communicate using the new secret keys PTK. By this arrangement, the number of times is decreased when a random number of plaintext is sent out in a wireless manner, and a risk can be reduced that secret keys may be decoded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a LAN system and a communication method for maintaining LAN security by communicating encrypted data between LAN devices such as a LAN (Local Area Network) terminal and a LAN base station via a wired or wireless communication line. is there.

  Conventionally, in LAN systems, as a security function, when LAN devices such as LAN terminals and LAN base stations communicate with each other, a secret key known only to both parties is shared, and encrypted data using this secret key is stored. Communication is possible via a wired or wireless communication line.

  For example, in a wireless LAN system, a random key such as a 4-way handshake defined in the IEEE802.11i standard is exchanged, and a secret key can be generated based on the acquired random number. According to this wireless LAN system, communicating devices share a pre-shared key in advance at the start of connection, and share a random number by sending parameters (random numbers) necessary for generating a secret key by a 4-way handshake. Thus, a secret key PTK (Pairwise Transient Key) can be generated and shared by both devices based on a random number and a pre-shared key.

  In addition, in wireless LAN systems, when communication data is communicated with communication devices connected for a long time, a 4-way handshake is performed every time the secret key PTK is valid to prevent the secret key PTK from being decrypted. Thus, a random number can be acquired, and a new secret key PTK can be generated and updated based on the random number.

  In the wireless LAN system described in Patent Document 1, a secret key is shared between an access point and a terminal by a secret key sharing procedure, the access point generates a secret key, and the secret is generated using an encryption function. The key can be encrypted with the secret key and supplied to the terminal, and the encrypted secret key supplied by the terminal can be decrypted with the secret key, so that the secret key can be shared between the access point and the terminal. Further, in this wireless LAN system, predetermined data is encrypted using a shared secret key to generate an encrypted data stream, and communication data transmitted / received between the access point and the terminal is transmitted using this encrypted data stream. Can be encrypted and decrypted.

JP 2004-56762 A

  However, in a conventional wireless LAN system, random number exchange such as 4WAY handshake is performed when a communication device sends a random number over the air in plain text, and when connection is started, that is, when connection and authentication processing are performed. In other words, the eavesdropper has a high risk of eavesdropping on a random number because it needs to be performed every time re-association processing is performed. Further, the pre-shared key shared in advance between the communication devices may be known by other than both, and if the eavesdropper learns, the secret key PTK will be decrypted based on the wiretapped random number.

  In addition, in such a conventional wireless LAN system, 4WAY handshaking is frequently performed, so that the communication amount and processing time increase.

  Furthermore, in a conventional wireless LAN system, when a communication device connects for a long time and performs encrypted data communication, if a 4-way handshake is performed every time the valid time of the private key PTK elapses, plaintext random numbers are transmitted over the air. Opportunities to send out increase, increasing the risk of decoding.

  It is an object of the present invention to provide a LAN system and a communication method therefor that can eliminate the disadvantages of the conventional technique, reduce the risk of secret key decryption, and reduce the communication volume and processing time. .

  In order to solve the above-mentioned problems, the present invention provides a LAN system including a plurality of LAN devices that communicate data encrypted using a secret key via a wired or wireless communication line. When communicating encrypted data with a LAN device, including a secret key generating means for generating this secret key used for encrypting data to be communicated based on a pre-shared key previously shared with the opposite LAN device, This secret key generation means determines whether or not encrypted data communication with this opposite LAN device has been performed before, and if it has not communicated, exchanges random numbers with this opposite LAN device to generate a random number. If the first secret key is acquired based on the random number and the pre-shared key and has been communicated, the last secret key used in the previous encrypted data communication is used as a random number. And this pre-share And generating a new second secret key based on.

  In addition, a communication method for communicating data encrypted with a secret key in a LAN system including a plurality of LAN devices via a wired or wireless communication line is the same as that of the opposite LAN device. Including a secret key generation step of generating the secret key used for encryption of data to be communicated based on a pre-shared key previously shared with the opposite LAN device. If it is determined whether or not encrypted data communication with the opposite LAN device has been done before, if it is determined that this LAN device exchanges random numbers with this opposite LAN device, a random number is obtained, A first secret key is generated based on the random number and the pre-shared key. On the other hand, if it is determined that there is a random key, the previous secret key used in the previous encrypted data communication is used as a random number. New based on pre-shared key And generates a second secret key to.

  According to the LAN system of the present invention, when the LAN device is connected to the opposite LAN device that is the communication partner, if the opposite LAN device is the device that previously communicated encrypted data, it is used in the previous communication. The number of times plaintext random numbers are sent over the air, that is, the number of random number exchanges, to generate a new secret key based on the previous secret key and enable encrypted data communication using the new secret key Can reduce the risk of decryption of the secret key. In this way, in this system, since past information known only by both parties is used as a secret key generation parameter, an effect equivalent to concealing a random number transmitted over the air in plain text can be obtained.

  In the LAN system of the present invention, since the number of random number exchange processes is reduced, the connection time can be shortened to reduce the communication amount, and the required program processing can be reduced to reduce the processing time.

  In addition, in the LAN system of the present invention, when encrypted data communication is performed between LAN devices for a long time, a new secret key is generated and updated based on the previous secret key used immediately before. , The risk of decryption of the secret key can be reduced, and the traffic and processing time can be reduced.

  Next, an embodiment of a wireless LAN system according to the present invention will be described in detail with reference to the accompanying drawings. For example, as shown in FIG. 1, the wireless LAN system 10 of the present invention includes a plurality of wireless LAN terminals 18 and 20 with respect to any of a plurality of wireless LAN base stations 14 and 16 installed in a LAN 12. Each transmits / receives a wireless signal and connects to LAN 12 by wireless LAN. Note that portions not directly related to understanding the present invention are not shown and redundant description is avoided.

  In this embodiment, the wireless LAN system 10 can actually include a large number of wireless LAN base stations, but only a small number of wireless LAN base stations 14 and 16 are shown in FIG. 1 to avoid complication. Similarly, the wireless LAN system 10 may actually include a large number of wireless LAN terminals, but only a small number of wireless LAN terminals 18 and 20 are shown in FIG. 1 to avoid complication.

  In the present embodiment, the LAN 12 may be connected to an authentication server 22, and this server 22 authenticates that a plurality of wireless LAN terminals 18 and 20 are permitted to connect to the system 10.

  The plurality of wireless LAN base stations 14 and 16 receive wireless signals transmitted from the plurality of wireless LAN terminals 18 and 20, and access to wirelessly transmit response signals to the wireless signals to the corresponding wireless LAN terminals. It is a point.

  The plurality of wireless LAN terminals 18 and 20 wirelessly connect to any of the plurality of wireless LAN base stations 14 and 16, respectively, and communicate with other wireless LAN terminals and other terminals connected to the LAN 12 by wire. be able to. The wireless LAN terminals 18 and 20 may have the same function. In addition, the wireless LAN terminals 18 and 20 may operate in an ad hoc mode, for example, and directly exchange wireless signals to be interconnected.

  For example, the wireless LAN terminal 18 transmits an authentication request to a nearby wireless LAN base station 14, receives an authentication response indicating success from the base station, is authenticated, and the connection to the system 10 is guaranteed. . Further, the authenticated wireless LAN terminal 18 transmits a connection request to the nearby wireless LAN base station 14, receives a connection response indicating success from the base station, and establishes a wireless LAN connection.

  In the wireless LAN system 10 of the present embodiment, the wireless LAN devices such as the plurality of wireless LAN base stations 14 and 16 and the plurality of wireless LAN terminals 18 and 20 are respectively encrypted with the opposing LAN device that is the communication partner. In order to perform communication, it is possible to generate a secret key that only the device and the opposite device know, and to communicate data encrypted using the secret key. These wireless LAN devices share a pre-shared key in advance for key distribution with the opposite device, and also exchange random numbers such as a 4-way handshake to obtain a common random number for both parties. A secret key can be generated based on the random number.

  For example, a wireless LAN device shares a PMK (Pairwise Master Key) as a pre-shared key with the opposite device in advance, receives a random number ANonce (Authentication Nonce) from the opposite device through a 4-way handshake, and a random number SNonce (Supplicant Nonce) And PTK (Pairwise Transient Key) is generated as a secret key based on PMK, ANonce and SNonce.

  In this embodiment, in particular, the wireless LAN device normally generates a secret key based on a random number obtained by random number exchange means such as a 4-way handshake, but the device to which the opposite device has previously communicated encrypted data. In this case, a new secret key can be generated based on the previous secret key used in the previous communication.

  For example, if a wireless LAN device normally disconnects encrypted data with the opposite device and then disconnects normally, the storage device such as the cache table 24 is paired with the MAC address of this opposite device and the secret key used in this communication. You may remember. When generating a secret key, the wireless LAN device refers to the cache table 24 to determine whether or not the opposite device's MAC address is stored, that is, the opposite device previously communicated encrypted data. It is possible to determine whether the device is a certain device.

  Next, with regard to the wireless LAN system 10 in the present embodiment, the operation of communication of encrypted data will be described with reference to the flowchart of FIG. 2 and the sequence charts of FIGS.

  In the present embodiment, first, in the wireless LAN terminal 18, authentication (Authentication) processing and connection (Association) processing are performed using the wireless LAN base station 14 as an opposite device (S102). At this time, in the wireless LAN terminal 18 of the present embodiment, the pre-shared key PMK is shared in advance with the opposing wireless LAN base station 14. The pre-shared key PMK may be shared at any time before the secret key is generated.

  Next, the wireless LAN terminal 18 acquires the MAC address included in the request signal and response signal exchanged with the opposite wireless LAN base station 14 in the authentication process or connection process of S102 (S104). In addition, this MAC address may be acquired at any time before the secret key is generated.

  Next, the wireless LAN terminal 18 searches for the MAC address of the wireless LAN base station 14 with reference to the cache table 24 (S106). Here, in the wireless LAN terminal 18, it is determined whether or not this MAC address is stored in the cache table 24, that is, whether or not the wireless LAN base station 14 is an opposite device that has previously performed encrypted data communication. To do. As a result, if not stored, the process proceeds to step S108 to generate a secret key by 4WAY handshake.If not stored, the process proceeds to step S112 to generate a new secret key based on the previous secret key. Is called.

In step S108, the wireless LAN terminal 18 first supplies a random number ANonce from the wireless LAN base station 14 by a 4-way handshake to generate a random number SNonce, and generates a new secret key PTK based on PMK, ANonce, and SNonce. The At this time, the secret key PTK uses information such as a pre-shared key PMK (Pairwise Master Key) distributed by an authentication server or the like that can be changed over time, the MAC address AA of the terminal 18, and the MAC address SA of the base station 14. Thus, it is calculated by the following equation (1) using the pseudorandom function PRF-X.
PTK = PRF-X (PMK, “Pairwise key expansion”, Min (AA, SA) || Max (AA, SA) || Min (ANonce, SNonce) || Max (ANonce, SNonce)) ・ ・ ・ (1 )
Here, X indicates the size of the key to be generated, which is 512 for the encryption method TKIP (Temporal Key Integrity Protocol) and 384 for the encryption method CCMP (Counter mode with CBC-MAC Protocol). . These random numbers ANonce and SNonce are generated with a random length of 32 bytes, for example, and Min (ANonce, SNonce) || Max (ANonce, SNonce) may be 64 bytes long. In this embodiment, PMK is used as the pre-shared key. However, PSK (Pre-Shared Key) that is set by manual input or the like and fixed in time may be used.

  Next, in the wireless LAN terminal 18, the generated SNonce is transmitted to the opposite wireless LAN base station 14, and the base station 14 also creates a new secret key using the pseudorandom function PRF-X based on PMK, ANonce, and SNonce. A PTK is generated. As a result, the secret key PTK is shared between the wireless LAN terminal 18 and the opposing wireless LAN base station 14 (S110), and the process proceeds to encrypted data communication (S116).

Incidentally, in step S112, the wireless LAN terminal 18 first obtains the secret key corresponding to the MAC address of the opposite wireless LAN base station 14 from the cache table 24, that is, the previous secret key PTK ′, and the previous secret key PTK. A new secret key PTK is generated based on PMK, with 'as a random number. At this time, the secret key PTK is calculated by the following equation (2) using the pseudorandom function PRF-X.
PTK = PRF-X (PMK, “Pairwise key expansion”, Min (AA, SA) || Max (AA, SA) || PTK ') ・ ・ ・ (2)
In the equation (2), information similar to the equation (1) used in step S108 is used except for the previous secret key PTK ′. The previous private key PTK 'may be 64 bytes in the case of the encryption method TKIP, 32 bytes in the case of the encryption method CCMP, and if it is less than 64 bytes as in the encryption method CCMP, for example, pass-phrase Correct to 64 bytes. The method for correcting the secret key length may be a method determined in advance between communication devices, and in this embodiment, the algorithm and other methods are not limited.

  Similarly, in the wireless LAN base station 14, the previous secret key PTK ′ is acquired, and the previous secret key PTK ′ is set as a random number using the pseudorandom function PRF-X based on PMK according to the equation (2). A new secret key PTK is generated. As a result, a new secret key PTK based on the previous secret key PTK ′ is shared between the wireless LAN terminal 18 and the opposing wireless LAN base station 14 (S114), and the process proceeds to encrypted data communication (S116). .

  Next, in step S116, the wireless LAN terminal 18 communicates data encrypted using the secret key PTK shared with the opposite wireless LAN base station 14. Further, in the wireless LAN terminal 18 of the present embodiment, it is determined whether the encrypted data communication has succeeded or failed (S118).

  Here, if the encrypted data communication is successful, the process proceeds to step S120, but if the encrypted data communication is unsuccessful, for example, if a response is not obtained even after a predetermined number of repeated transmissions of the encrypted data. Regardless of whether a secret key was generated by a 4WAY handshake or a new secret key was generated based on the previous secret key, the process proceeds to step S108 and a new secret key is generated by a 4WAY handshake. It's okay. For example, if the opposing wireless LAN base station 14 does not have the function of generating a secret key based on the previous secret key according to the present invention, the wireless LAN terminal 18 generates based on the previous secret key PTK ′. Even if data encrypted using the new secret key PTK is communicated, the base station 14 cannot decrypt the data and the encrypted data communication fails.

  By the way, in step S120, the encrypted data communication ends normally in the wireless LAN terminal 18, and the disconnection process from the opposite wireless LAN base station 14 is normally performed.

  Next, proceeding to step S122, in the wireless LAN terminal 18, the secret key used in the encrypted data communication and the MAC address of the opposite wireless LAN base station 14 are stored in the cache table 24. At this time, if the MAC address of the opposite wireless LAN base station 14 is already stored in the cache table 24, the new secret key may be overwritten and stored.

  Also in the wireless LAN base station 14, the secret key used in the encrypted data communication and the MAC address of the opposite wireless LAN terminal 18 are stored in the cache table.

  In this way, the wireless LAN terminal 18 that has been normally disconnected can enter a state where it can proceed to the authentication process and the connection process of step S102.

  As another embodiment, when the encrypted data communication continues for a long time, the wireless LAN terminal 18 can change the secret key every time a predetermined effective time elapses to increase the LAN security. When a predetermined secret key valid time elapses, a new secret key is updated based on the previous secret key used immediately before.

  Next, for the wireless LAN system 10 in this embodiment, the operation of encrypted data communication with the opposite wireless LAN base station 14 will be described with reference to the flowchart of FIG. 5 and the sequence chart of FIG.

  In the wireless LAN system 10 according to this embodiment, first, steps S102, S108, and S110 operate in the same manner as the sequence chart shown in FIG. 3 of the above embodiment, and then the process proceeds to step S210.

  In step S210, the wireless LAN terminal 18 starts encrypted data communication with the opposite wireless LAN base station 14.

  Here, in the wireless LAN terminal 18 of this embodiment, it is detected that a predetermined secret key valid time has elapsed after the start of encrypted data communication (S202).

  Next, proceeding to step S204, the wireless LAN terminal 18 updates the new secret key PTK based on the previous secret key PTK ′ shared at step S110. At this time, the wireless LAN terminal 18 may generate a new secret key PTK by using the previous secret key PTK ′ as a random number and Equation (2) used in step S112.

  Further, in the wireless LAN terminal 18, the new secret key PTK generated in this way is stored in the cache table 24 in a pair with the MAC address of the opposite wireless LAN base station 14 (S206). At this time, if the MAC address of the base station 14 is already stored in the cache table 24, the new secret key may be overwritten and stored.

  In the wireless LAN terminal 18 in which the secret key has been updated in this way, the encrypted data communication is resumed (S208), and then waits until a predetermined secret key valid time elapses, and the process repeatedly proceeds to step S202. be able to.

  In the wireless LAN system 10 in this embodiment, in the opposite wireless LAN base station 14 as well, a new secret key PTK ′ used immediately before is newly generated every time a predetermined secret key valid time elapses. By generating a new secret key PTK and storing the new secret key PTK in the cache table together with the MAC address of the opposite device, the secret key may be repeatedly updated in long-time encrypted data communication.

  The generation of a new secret key based on the previous secret key according to the present invention is not only the encrypted data communication of the wireless LAN system 10 as in the above embodiment, but also other communication devices and communication that perform an equivalent key generation procedure. It can be applied to all of the means. For example, the present invention can be realized when wireless LAN devices are directly connected in ad hoc mode to perform encrypted data communication, or when encrypted data communication is performed between LAN devices in a wired LAN system.

1 is a block diagram showing an embodiment of a wireless LAN system according to the present invention. 2 is a flowchart illustrating an operation procedure of the wireless LAN system according to the embodiment illustrated in FIG. 1. 3 is a sequence chart for explaining an operation procedure of the wireless LAN system according to the embodiment shown in FIG. 1. 3 is a sequence chart for explaining an operation procedure of the wireless LAN system according to the embodiment shown in FIG. 1. It is a flowchart explaining the operation | movement procedure of the other Example of the wireless LAN system which concerns on this invention. It is a sequence chart explaining the operation | movement procedure of the other Example of the wireless LAN system which concerns on this invention.

Explanation of symbols

10 Wireless LAN system
12 LAN
14, 16 Wireless LAN base station
18, 20 Wireless LAN terminal
22 Authentication server
24 Cash table

Claims (18)

In a LAN system including a plurality of LAN devices that communicate data encrypted using a secret key via a wired or wireless communication line,
When the LAN device communicates encrypted data with the opposite LAN device, a secret for generating the secret key used for encrypting the data to be communicated based on the pre-shared key shared in advance with the opposite LAN device. Including key generation means,
The secret key generation means determines whether or not encrypted data communication with the opposite LAN device has been performed before, and if it has not communicated, exchanges random numbers with the opposite LAN device to obtain a random number. Obtaining a first secret key based on the random number and the pre-shared key;
If communication has occurred, the previous secret key used in the previous encrypted data communication is set as a random number, and a second secret key is newly generated based on the random number and the pre-shared key. LAN system. 2. The LAN system according to claim 1, wherein the LAN device acquires a MAC address of the opposite LAN device, and uses a first secret key as the previous secret key to pair with the MAC address, such as a cache table. Memorize it in the memory means,
The secret key generation means searches the MAC address of the opposite LAN device with reference to the storage means, and, as a result, if the MAC address is not stored in the storage means, It is determined that encrypted data communication has not been performed, and a first secret key is generated,
On the other hand, if the MAC address is stored in the storage means, it is determined that encrypted data communication has been performed with the opposite LAN device before, and the previous secret corresponding to the MAC address is stored from the storage means. A LAN system characterized by detecting a key and newly generating a second secret key using the previous secret key as the random number.   The LAN system according to claim 2, wherein the LAN device acquires the MAC address when performing authentication processing or connection processing with the opposing LAN device.   2. The LAN system according to claim 1, wherein when the encrypted data communication using the first or second secret key fails in the LAN device, the secret key generation means again sets the first secret. A LAN system characterized by generating a key.   2. The LAN system according to claim 1, wherein the secret key generation unit performs the predetermined valid time every time the predetermined valid time elapses while the LAN device performs encrypted data communication with the opposite LAN device. A LAN system, wherein a second secret key is newly generated and repeatedly updated with the previous secret key used immediately before as the random number. 6. The LAN system according to claim 5, wherein the LAN device acquires a MAC address of the opposite LAN device before the predetermined valid time elapses and uses it for encrypted data communication with the opposite LAN device. A secret key that is stored as a previous secret key in a storage means such as a cache table in a pair with the MAC address,
The secret key generation means detects the previous secret key corresponding to the MAC address with reference to the storage means when the predetermined valid time has elapsed, and newly sets the previous secret key as the random number. A LAN system characterized by generating a second secret key.   The LAN system according to claim 1, wherein the LAN device is a wireless LAN terminal, and the opposite LAN device is a wireless LAN base station.   The LAN system according to claim 7, wherein the random number exchange is a 4-way handshake.   The LAN system according to claim 1, wherein the LAN device and the opposite LAN device are different wireless LAN terminals. In a communication method in which data encrypted using a secret key is communicated via a wired or wireless communication line in a LAN system including a plurality of LAN devices, the method includes:
In the LAN device, including a secret key generation step of generating the secret key used for encryption of data communicated with the opposite LAN device based on a pre-shared key previously shared with the opposite LAN device,
The secret key generation step determines whether or not the LAN device has previously performed encrypted data communication with the opposite LAN device. A random number is obtained by exchanging a random number with, and a first secret key is generated based on the random number and the pre-shared key;
On the other hand, if it is determined that there is, the previous secret key used in the previous encrypted data communication is used as a random number, and a second secret key is newly generated based on the random number and the pre-shared key. A characteristic communication method. 11. The communication method according to claim 10, wherein the method includes a first step of acquiring a MAC address of the opposite LAN device in the LAN device, and a first secret key as the previous secret key. Including a second step of storing in a storage unit such as a cache table in pairs with the MAC address;
The secret key generation step searches the MAC address of the opposing LAN device with reference to the storage unit, and as a result, the LAN device determines whether the MAC address is stored in the storage unit. It is determined whether encrypted data communication with the opposite LAN device has been performed before. If not stored, it is determined that encrypted data communication has not been performed, and a first secret key is generated.
On the other hand, if stored, it is determined that encrypted data communication has been performed, the previous secret key corresponding to the MAC address is detected from the storage unit, and the previous secret key is used as the random number. A communication method, wherein a second secret key is newly generated.   12. The communication method according to claim 11, wherein the first step acquires the MAC address when performing authentication processing or connection processing with the opposing LAN device in the LAN device. .   11. The communication method according to claim 10, wherein when the encrypted data communication using the first or second secret key fails in the LAN device, the secret key generation step is performed again with a new one. And generating a first secret key.   The communication method according to claim 10, wherein the secret key generation step is performed every time a predetermined valid time elapses while the LAN device performs encrypted data communication with the opposite LAN device. A communication method comprising: a third step of generating a second secret key anew as a random number using the previous secret key used immediately before the predetermined valid time and repeatedly updating it. 15. The communication method according to claim 14, wherein the third step acquires a MAC address of the opposite LAN device at the LAN device before the predetermined valid time elapses, and A secret key used in encrypted data communication with a LAN device is stored as a previous secret key in a storage unit such as a cache table in pair with the MAC address,
The secret key generation step detects the previous secret key corresponding to the MAC address with reference to the storage unit when the predetermined valid time has elapsed, and newly sets the previous secret key as the random number. And generating a second secret key.   11. The communication method according to claim 10, wherein the method uses a wireless LAN terminal as the LAN device and a wireless LAN base station as the opposite LAN device.   17. The communication method according to claim 16, wherein the method uses a 4-way handshake as the random number exchange in the LAN device. 11. The communication method according to claim 10, wherein the method uses different wireless LAN terminals as the LAN device and the opposite LAN device.

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