JP5904718B2 - COMMUNICATION DEVICE, COMMUNICATION DEVICE CONTROL METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to a communication device, a communication device control method, and a program, and more particularly, to a communication device that performs cryptographic communication by WPA in an ad hoc network, a communication device control method, and a program.

  Communication data is encrypted to prevent eavesdropping and tampering. In particular, since wireless communication is easy to wiretap, it is important to secure a safe communication path.

  In the wireless LAN infrastructure mode, the communication device (STA) and the access point (AP) implement standards such as wired equivalent privacy (WEP) or Wi-Fi protected access (WPA). WEP guarantees security by setting an encryption key in advance for STA and AP and using the encryption key for communication. However, it has been pointed out that in this method, the encryption key is always fixed, and the strength of the encryption algorithm adopted by WEP is not high, so there is a situation where safety cannot be guaranteed. Thus, in WPA, the strength of the encryption algorithm is improved, and the security is further improved by generating the encryption key every time the network joins the network from information set in advance for the STA and AP.

  In the infrastructure mode, the STA transmits data to other STAs via the AP. In other words, since the STA communicates directly only with the AP, it is only necessary to guarantee the safety of communication with the AP.

  On the other hand, in the ad hoc mode, there is no AP and the STA communicates directly with the communication partner. Therefore, when communicating with a plurality of STAs, it is necessary to consider the safety of communication with the plurality of STAs. Although the network configuration is different, it is desirable to change the encryption key for each communication session in order to ensure security as in the infrastructure mode. However, when communicating in an ad hoc mode using a commercially available wireless LAN device, the same encryption key is set in advance to all STAs participating in the network, and the encryption key is used. As a result, the security issues of concern in infrastructure mode remain.

  IEEE 802.11i, which has been standardized after WPA for these problems, proposes to dynamically generate an encryption key for each communication session even in the ad hoc mode. In IEEE 802.11i, the two communication STAs exchange messages each other called a 4-way handshake, and generate and share a unicast key PTK (pairwise transient key) and a group key GTK (group temporal key).

  The feature of this method is that communication is performed by switching the encryption key for each communication partner, and that different keys are set for transmission and reception. One group key for transmission is determined so that all STAs on the network can receive, and a group key for reception is held for each STA.

  On the other hand, wireless LAN devices often have a limited number of unicast keys and group keys. This is because in wireless LAN devices that require high-speed packet processing, packets are often encoded / combined within the wireless LAN chip, and it is necessary to maintain a unicast key and group key in the wireless LAN chip. Because there is.

  At this time, the upper limit of the number of unicast keys and group keys that can be held by each wireless LAN device (the upper limit number of key holdings) differs depending on the device.

  When ad hoc communication using WPA is performed between devices with different key retention upper limit numbers, devices that have already reached the upper limit number that can hold keys and devices that have not yet reached the upper limit number that can hold keys are in the same network. Can occur. In other words, there are cases where there are devices that communicate and devices that do not communicate within the same ad hoc network, and an algorithm that ensures communication between devices even when the key holding upper limit number does not match for each device. Is needed.

  Patent Document 1 discloses an algorithm for performing ad hoc communication using WPA between a device having a key retention upper limit number of 1 and a device having a key retention upper limit number of 2 or more.

JP 2007-336010 JP

  However, when two or more communication devices with a key retention upper limit number of 2 construct an ad hoc network using WPA, the communication service can be provided because the number of ad hoc network components exceeds the device key retention upper limit. There is a problem of disappearing.

  In view of the above problems, an object of the present invention is to make it possible to cope with the case where the number of devices constituting an ad hoc network exceeds the key holding upper limit of the device.

A communication device according to the present invention that achieves the above object is as follows.
A communication device for communicating with a plurality of other communication devices in a wireless network,
Storage means for storing an encryption key used for communication in the wireless network;
Receiving means for receiving, from the other communication device, a start packet for starting a process of sharing an encryption key with the other communication device;
First determination means for determining whether or not the number of encryption keys stored in the storage means is greater than a predetermined number;
A notification unit that performs a predetermined notification to a user when the first determination unit determines that the number of the encryption keys is larger than the predetermined number;
Have
If the number of other communication devices constituting the wireless network has not decreased even after a predetermined time has elapsed since the notification by the notification unit, the storage unit is already stored by the storage unit. And deleting a new encryption key shared based on the start packet in place of the deleted encryption key.

  According to the present invention, it is possible to cope with the case where the number of devices constituting the ad hoc network exceeds the key holding upper limit of the device.

FIG. 3 is a diagram illustrating a configuration of a printer. Explanatory drawing of the key overflow state in a WPA ad hoc network. The flowchart which shows the procedure of a key holding | maintenance upper limit determination process. The figure which shows the example of the warning screen to a user. The figure which shows group key standby mode. The figure which shows the ad hoc network which performs group key standby mode. FIG. 6 is a sequence diagram illustrating a group key standby mode printing service. The flowchart which shows the procedure of the process in group key waiting mode. The flowchart which shows the procedure of registration of a group key. The flowchart which shows the procedure of registration of a unicast key. The figure which shows the example of the screen which shows that the operation mode is switching. The sequence diagram of group key update.

(First embodiment)
As an embodiment for effectively functioning the wireless communication apparatus of the present invention, an application example to an ad hoc network including a printer will be described below.

  A functional configuration example in which the system of the present embodiment is applied to the printer 13 will be described with reference to FIG. The printer 13 includes a printer engine 102, a print processing unit 103, a wireless communication function unit 104, an RF unit 105, a display unit 106, a display processing unit 107, a memory card I / F 108, and a memory card 109. An operation unit 110, a system controller 111, a USB I / F 112, a flash memory 113, a parallel I / F 114, a CPU 115, a ROM 116, and a RAM 117.

  The printer engine 102 prints an image on recording paper based on the image signal output from the print processing unit 103. The print processing unit 103 outputs an image signal to the printer engine 102. The wireless communication function unit 104 performs wireless communication with other wireless communication devices, and executes packet framing, response to data, data encryption / decryption processing, and the like based on the wireless standard. The RF unit 105 transmits and receives wireless signals to and from other wireless communication devices. Note that the wireless communication function unit 104 and the RF unit 105 may be realized as one functional block. The display unit 106 displays information to the user by LCD display, LED display, audio display, or the like. The display processing unit 107 controls the display content of the display unit 106. The memory card I / F 108 is an interface to which the memory card 109 is connected. The memory card 109 stores various information. The operation unit 110 includes various keys and is connected to the CPU 115 via the system controller 111.

  Note that user operations such as selecting information displayed on the display unit 106 are performed in conjunction with the operation unit 110. That is, the display unit 106 and the operation unit 110 constitute a user interface. The USB I / F 112 provides a serial bus interface for connection to an external device. The flash memory 113 is a nonvolatile memory, and stores wireless communication setting information. The parallel I / F 114 provides a parallel interface for connection to an external device. The CPU 115 uses the RAM 117 or the flash memory 113 as a work memory, executes a program stored in the ROM 116 or the flash memory 113, and controls each component. In general, the ROM 116 stores a program for starting the wireless communication function unit 104 and the RF unit 105 in accordance with an application instruction.

  The wireless communication function unit 104 has a function of holding an encryption key for each STA that is a communication partner. Although the maximum number of cryptographic keys held depends on the implementation depending on the apparatus, the maximum number of keys held by the printer 13 is 3 in this embodiment. The maximum holding number represents the number of connectable devices. In this case, the specification is such that a total of six keys including three unicast keys and three group keys can be held.

  Next, an example of a WPA ad hoc network including the printer of the present embodiment will be described with reference to FIG. The wireless network shown in FIG. 2 includes a PC 10 (PC 1), a camera 11 (camera 2), a camera 12 (camera 1), a printer 13, and a PC 14 (PC 2). That is, there are a plurality of communication devices other than the printer 13. Here, each of T20 to T24 represents a WPA key table corresponding to each device.

  In the example shown in FIG. 2, the key table T23 of the printer 13 having the key holding upper limit number 3 holds keys for communication with the three opposing devices. On the other hand, the key tables T20, T21, T22, and T24 of the PC 10, the camera 11, the camera 12, and the PC 14 each hold a key for communication with the four opposing devices except the own device.

  That is, a phenomenon occurs in which the number of opposite devices that can be communicated by the printer 13 is different from the number of opposite devices that can be communicated by devices other than the printer 13, and the number of devices that can communicate while existing in the same ad hoc network is different. As a result, in a device having a small key holding upper limit number (holding upper limit number), a counter device that cannot hold a key is generated. In such a state, a device that can communicate with another device that exists in the same ad hoc network and a device that cannot communicate with each other are generated.

  In such a situation, a problem occurs when a protocol such as ARP (Address Resolution Protocol) that collects information in the wireless network is executed. This problem will be described with reference to FIG.

  Consider a case where the PC 14 tries to attach an IPv4 address used by the printer 13 to its own device. As the operation of the printer 13, since the IPv4 address designated by the ARP request from the PC 14 (PC2) is already the IPv4 address used by the own apparatus, it is expected that the duplication is notified by the ARP response. However, since the printer 13 does not own the group key of PC14 (PC2) in the key table T23, the ARP request packet cannot be decrypted and the packet is discarded. Therefore, it is impossible to notify the IPv4 address duplication to PC14 (PC2) by the ARP response. Accordingly, there are two devices having the same IPv4 address, the printer 13 and the PC 14 (PC2), in the ad hoc network of FIG. Therefore, a phenomenon occurs in which other devices in the wireless network such as the camera 12 cannot correctly transmit a packet to a desired device of either the printer 13 or the PC 14 (PC2). In order to deal with such a problem, the printer 13 determines whether or not the key holding number of its own device has reached the upper limit at the time of key exchange. If the upper limit has been reached, a warning screen is displayed and the user is prompted to reconfigure the network configuration. Encourage construction.

  A procedure in which the printer 13 that has reached the key holding upper limit displays a warning screen and prompts the user to reconfigure the network configuration will be described with reference to the flowchart of FIG.

  First, in S301, the wireless communication function unit 104 of the printer 13 receives an exchange start packet for starting key exchange. In S302, the CPU 115 performs a key holding upper limit number determination process when performing key exchange with a new apparatus. In S303, the CPU 115 determines whether or not the number of keys held in the key table T23 at that time has reached the key holding upper limit number, that is, whether or not the key holding number exceeds the key holding upper limit number due to the current key exchange. . When it is determined that the key holding number exceeds the key holding upper limit number by key exchange (S303; YES), the process proceeds to S304. If it is determined that the key holding number is equal to or less than the upper limit number of key holdings even after key exchange (S303; NO), the process ends. In S304, the CPU 115 prompts the user to reconfigure the network configuration by displaying a warning screen as shown in FIG. 4 on the display unit 106. Thus, the respective processes in the flowchart of FIG. 3 are completed.

  According to this embodiment, the user can recognize that the network has the number of devices exceeding the key holding upper limit. As a result, it is possible to improve the network environment and maintain the provision of communication services by the device.

(Second embodiment)
In the embodiment of the present invention shown in the first embodiment, there may be a case where the network environment is not reconfigured by the user after the user is prompted to reconfigure the network configuration. In such a case, in the present embodiment, the printer 13 operates in an operation mode called a group key standby mode, thereby improving the state in which communication as described in the first embodiment is interrupted between devices constituting the network. Suggest a way to do it. The functional configuration of the printer 13 is the same as the functional configuration described with reference to FIG.

  Here, the group key standby mode described above will be described with reference to FIG. FIG. 5 shows a WPA key table of the printer 13. The printer 13 is a device having a key holding upper limit number of 3. Normally, as indicated by the key table 501 in the normal key management mode, the number of group keys held is 3, and the number of unicast keys held is 3. When a transition from the normal key management mode to the group key standby mode is made, the breakdown of the key table becomes the key table 502. In the example of FIG. 5, the number of group keys held changes to 4, and the number of unicast keys held changes to 2. Thus, a state in which the number of group keys held is larger than the number of unicast keys held is defined as a group key standby mode.

  Next, with reference to FIG. 6, the operation when the printer 13 transitions to the group key standby mode will be described. The network shown in FIG. 6 includes a PC 10 (PC 1), a camera 11 (camera 2), a camera 12 (camera 1), a printer 13, and a PC 14 (PC 2). Here, each of T20 to T24 represents a WPA key table of each device. The printer 13 abandons the unicast key and secures group keys for four devices in order to secure communication with four devices while the upper limit number of key holdings is three. Is working with. As a result, the printer 13 can receive broadcast communication and multicast communication from any device in the network. When operating in the group key standby mode, the printer 13 receives a broadcast communication packet and a multicast communication packet from a device in the network, and then generates a unicast key with the device that issued the communication. The printer 13 supports unicast communication with a device that has issued broadcast communication and multicast communication by holding the unicast key for a predetermined time.

  Next, a print service sequence in the group key standby mode that provides the print service to the PC 14 when the printer 13 is operating in the group key standby mode will be described with reference to FIG. A method for the printer 13 to transition to the group key standby mode will be described later with reference to the group key standby mode transition chart of FIG. 8 and the group key registration chart of FIG.

  In S700, the CPU of the PC 14 broadcasts a printer discovery packet to any printer in the network.

  In S701, the CPU 115 having the group key of the PC 14 detects that the received packet is a broadcast packet, and the PC 14 and the 4-way handshake (4-way handshake) to acquire the unicast key of the broadcast packet transmission source device I do.

  In S702, the CPU 115 obtains a temporary unicast key, which is a key temporarily used for communication with the PC 14 after performing the 4-way handshake. This temporary unicast key is held in the key table T23 described with reference to FIG. A method for acquiring the temporary unicast key will be described later with reference to the unicast key registration chart of FIG.

  In S703, the CPU 115 transmits a discoveryAck packet, which is a response packet to the printer discovery packet S700, to the PC 14 using the temporary unicast key acquired in S702.

  Thereafter, in S704 to S707, print packet communication for printing is performed using the temporary unicast key. Specifically, the CPU of the PC 14 transmits a print instruction packet for executing printing to the printer 13, and the CPU 115 transmits a print Ack packet that is a response packet to the received print instruction packet to the PC 14.

  Thereafter, printing ends in S708.

  In S709, when the CPU 115 does not receive the unicast communication from the PC 14 for a predetermined time, the unicast key deletion trigger is driven and determines the temporary unicast key as an unnecessary key.

  In S710, the CPU 115 thereafter deletes the temporary unicast key from the key table T23. The process ends here.

  As described above, even in a network configured by the number of devices exceeding the key retention upper limit of the printer 13, the print service can be realized by the printer 13 shifting to the group key standby mode.

  With reference to the flowchart of FIG. 8, a procedure for transitioning to the group key standby mode after the wireless communication function unit 104 of the printer 13 receives the key exchange start packet through the RF unit 105 will be described.

  In S800, the CPU 115 receives the key exchange start packet. In S801, the CPU 115 analyzes the operation mode of the own device. In S802, the CPU 115 determines whether or not the own device is operating in the group key standby mode as a result of the analysis in S801. That is, it is determined whether or not the number of group keys held is larger than the number of unicast keys held (group key standby mode) in the key table holding the encryption keys (holding number determination process). When it is determined that the own apparatus is operating in the group key standby mode (S802; YES), the process proceeds to S811. On the other hand, when it is determined that the own apparatus does not operate in the group key standby mode (the state in which the number of group keys held is equal to or less than the number of unicast keys held) (S802; NO), the process proceeds to S803.

  In S803, the CPU 115 compares the number of keys by key exchange with the number of key holding upper limits of the device. In step S804, the CPU 115 determines whether the number of keys exceeds the key holding upper limit number of the device due to key exchange. If it is determined that the number of keys exceeds the key holding upper limit number of the device (S804; YES), the process proceeds to S805. On the other hand, when it is determined that the number of keys is equal to or less than the key holding upper limit number of the device (S804; NO), the process is terminated. In S805, the CPU 115 displays a user warning screen 401 (see FIG. 4) on the display unit 106.

  In S806, the CPU 115 waits for a predetermined time after displaying the user warning screen 401. In S807, the CPU 115 analyzes whether or not the number of devices belonging to the WPA ad hoc network environment to which the printer 13 is connected has decreased after a predetermined time has elapsed.

  In S808, the CPU 115 determines whether or not the number of belonging devices has decreased as a result of the analysis, that is, whether or not the network environment has improved. If it is determined that the network environment has improved (S808; YES), the process ends. On the other hand, if it is determined that the network environment has not improved (S808; NO), the process proceeds to S809.

  In S809, the CPU 115 displays a screen 1101 indicating that the operation mode is being switched to the group key standby mode in which the number of group keys held in the key table is larger than the number of unicast keys held (see FIG. 11). Is displayed on the display unit 106. In S810, the process proceeds to S900 in the flowchart of FIG. In S811, the process proceeds to S902 in the flowchart of FIG. Thus, the process of the flowchart shown in FIG. 8 ends.

  Next, the procedure of the group key registration process when the printer 13 transitions to the group key standby mode will be described with reference to the flowchart of FIG.

  In S900, the CPU 115 determines a unicast key. The CPU 115 identifies a unicast key that can be deleted by this processing. In S901, the CPU 115 deletes the unicast key specified in S900. Here, the unicast key is not necessarily deleted, and may be saved in the memory space of the RAM 117 or the key cache storage area (primary storage area) on the flash memory 113.

  In S902, after deleting the unicast key, the CPU 115 confirms that there is a free space in the key table of the printer 13 by the deletion.

  In S903, the CPU 115 determines whether or not there is a predetermined number of spaces in the key table. If it is determined that there is a predetermined number of spaces (S903; YES), the process proceeds to S904. On the other hand, if it is determined that there is no predetermined number of empty spaces (S903; NO), the process proceeds to S903.

  In S904, the CPU 115 registers the group key in the key table T23. In S905, the CPU 115 ends the group key standby mode. Thus, the process of the flowchart shown in FIG. 9 ends.

  Furthermore, a procedure of unicast key registration processing representing an operation after the wireless communication function unit 104 of the printer 13 receives a multicast packet or a broadcast packet through the RF unit 105 will be described with reference to a flowchart of FIG.

  In S1000, the CPU 115 receives a broadcast packet or a multicast packet. In S1001, the CPU 115 analyzes the operation mode of the own device. In S1002, the CPU 115 determines whether or not the own device is operating in the group key standby mode. When it is determined that the own apparatus is operating in the group key standby mode (S1002; YES), the process proceeds to S1003. On the other hand, if it is determined that the own apparatus is not operating in the group key standby mode (S1002; NO), the process proceeds to S1010.

  In S1003, the CPU 115 analyzes the owned unicast key. In S1004, the CPU 115 determines whether or not it owns the unicast key of the transmission source of the packet received in S1000 (key ownership determination process). If it is determined that the transmission source unicast key is owned (S1004; YES), the process proceeds to S1010. On the other hand, if it is determined that the source unicast key is not owned (S1004; NO), the process proceeds to S1005.

  In S1005, the CPU 115 identifies a group key that can be deleted. In S1006, the CPU 115 deletes the erasable group key specified in S1005. In S1007, the CPU 115 confirms the availability of the key table T23. In S1008, the CPU 115 determines whether or not there is a predetermined number of empty spaces in the key table T23. If it is determined that there is a predetermined number of spaces (S1008; YES), the process proceeds to S1009. On the other hand, when it is determined that there is no predetermined number of empty spaces (S1008; NO), the process proceeds to S1010.

  In S1009, the CPU 115 acquires a unicast key. The unicast key may be acquired by performing a 4-way handshake, and the unicast key saved in the memory space of the RAM 117 or the flash memory 113 may be used again. In S1010, the CPU 115 executes normal packet processing. Thus, the process of the flowchart shown in FIG. 10 ends.

  Next, the group key update sequence will be described with reference to FIG. WPA has a function of updating a group key, but when a group key is updated, a unicast key is required because encrypted communication using a unicast key is performed. On the other hand, one of the features of the present invention is that the number of connectable devices exceeding the upper limit number of key holdings by temporarily abandoning the unicast key and temporarily holding the communication partner's unicast key in which broadcast communication or multicast communication has occurred Is to secure. Therefore, by implementing the present invention, there is a case where the group key update timing comes without having the unicast key of the target device for updating the group key. In order to solve this problem, a method is proposed in which a unicast key for updating a group key is newly acquired by performing a 4-way handshake, and a group key exchange is performed using the acquired unicast key.

  The example shown in FIG. 12 represents a sequence in which the printer 13 exchanges the group key with the PC 14 in accordance with the group key update timing.

  In S1200, the CPU 115 identifies a device that needs to update the group key. In the present embodiment, the CPU 115 identifies the PC 14 as the target device. In S1201, the CPU 115 transmits message 1 (MSG1) to the PC. This message frame conforms to a format according to a protocol called EAPOL. This message includes information (Unicast) that is a message for exchanging unicast keys and information on a random number (Anonce) generated by the printer 13. Note that EAPOL is an abbreviation for extensible authentication protocol.

  In S1202, the CPU of the PC 14 that has received MSG1 generates a PTK (Pairwies Trasient Key) and generates a random number (Snonce) different from that of the printer 13. In S1203, the CPU of the PC 14 transmits message 2 (MSG2) to the printer 13. This message frame conforms to a format according to a protocol called EAPOL. This message includes information (Unicast) that is a message for exchanging unicast keys and information on a random value (Snonce) generated by the PC 14. In S1204, the CPU 115 generates a PTK.

  A PTK can be generated from the information Anonce and Snonce and the information held in advance by the printer 13 and the PC 14. Thereby, in S1202 and S1204, both the printer 13 and the PC2 (PC14) can generate the PTK.

  In S1205, the CPU 115 transmits message 3 (MSG3) to the PC. In S1206, the CPU of the PC 14 transmits message 4 (MSG3) to the printer 13. MSG3 and MSG4 are messages representing an acknowledgment response to the successful generation of the PTK. In S1207, the CPU of the PC 14 sets PTK as a unicast key. In S1208, the CPU 115 sets the PTK as a temporary unicast key (unicast key acquisition process).

  Thereafter, with regard to unicast, encrypted data is transferred between the printer 13 and the PC 14. Although the method for setting a temporary unicast key by the 4-way handshake has been described so far, if the printer 13 already possesses the unicast key of the PC 14, the CPU 115 does not perform the 4-way handshake. May be used.

  Next, a group key sharing method will be described. In S1209, when the 4-way handshake from S1200 to S1206 is completed, the CPU 115 generates a GTK (Group Trasient Key). If the printer 13 already owns GTK, it may be used.

  In S1210, the CPU 115 transmits a message 5 (MSG5) indicating group key handshake to the PC. This message frame also conforms to a format according to a protocol called EAPOL, and this message includes information (Group) that is a message for exchanging GTK. Since the message 5 is encrypted with the unicast key that has already been exchanged, the message 5 is transmitted securely.

  In S1211, the CPU of the PC 14 transmits to the printer 13 a message 6 (MSG6) for confirming that the message 5 has been received. In S1212, the CPU 115 sets GTK as a group key. In S1213, the CPU of the PC 14 sets GTK as a group key. As a result, the broadcast packet is encrypted. In S1214, after the group key update is completed, the CPU 115 deletes the temporary unicast key for group key exchange that is no longer necessary. Thus, the sequence process shown in FIG. 12 is completed.

  According to this embodiment, even when there is no improvement in the communication environment by the user, a communication service can be provided by preferentially holding the group key and generating a unicast key when necessary.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (15)

A communication device for communicating with a plurality of other communication devices in a wireless network,
Storage means for storing an encryption key used for communication in the wireless network;
Receiving means for receiving, from the other communication device, a start packet for starting a process of sharing an encryption key with the other communication device;
First determination means for determining whether or not the number of encryption keys stored in the storage means is greater than a predetermined number;
A notification unit that performs a predetermined notification to a user when the first determination unit determines that the number of the encryption keys is larger than the predetermined number;
Have
If the number of other communication devices constituting the wireless network has not decreased even after a predetermined time has elapsed since the notification by the notification unit, the storage unit is already stored by the storage unit. A communication device that stores a new shared encryption key based on the start packet instead of the deleted encryption key.   The communication apparatus according to claim 1, wherein the predetermined number is an upper limit value of an encryption key that can be held by the communication apparatus.   The communication device according to claim 1, wherein the notification unit performs the predetermined notification by displaying a warning on a display unit.   The encryption key includes a unicast key used for communication with the other communication device and a shared group key used for communication with the plurality of other communication devices belonging to the wireless network. The communication apparatus according to claim 1, wherein the communication apparatus is characterized. A second determination means for determining whether the number of retained group keys is greater than the number of retained unicast keys;
5. The determination by the first determination unit is performed when the second determination unit determines that the number of retained group keys is smaller than the number of retained unicast keys. The communication apparatus as described in.   A first deletion that deletes the unicast key if the number of the other communication devices constituting the wireless network has not decreased even after a predetermined time has elapsed since the notification by the notification means. 6. The communication apparatus according to claim 4, further comprising means.   The communication apparatus according to claim 6, further comprising a holding unit that holds the group key newly shared according to the start packet after deletion by the first deletion unit. Third determination means for determining whether or not a unicast key used for communication with the other communication device is included;
A second deleting unit that deletes the group key when the third determining unit determines that the unicast key used for communication with the other communication device is not included; The communication apparatus according to claim 4, wherein:   When the group key is deleted by the second deletion unit, the system further comprises a first acquisition unit that acquires a unicast key used for communication with the other communication device as a temporary unicast key. The communication device according to claim 8.   The communication device according to claim 9, wherein the second deletion unit deletes the temporary unicast key when communication using the temporary unicast key is not performed for a predetermined time. Second acquisition means for acquiring an update key used to update the group key;
Updating means for updating the group key using the update key;
The communication apparatus according to claim 4, further comprising:   The communication apparatus according to claim 11, further comprising a third deletion unit that deletes the update key when the update by the update unit is completed.   The communication device according to claim 11 or 12, wherein the second acquisition unit acquires the update key by performing a 4-way handshake with the other communication device. A method of controlling a communication device that communicates with a plurality of other communication devices in a wireless network,
A storage step of storing an encryption key used for communication in the wireless network in a storage means;
A receiving step of receiving a start packet for starting a process of sharing an encryption key with the other communication device from the other communication device;
A determination step of determining whether the number of encryption keys stored in the storage means is greater than a predetermined number;
A notification step of performing a predetermined notification to a user when it is determined that the number of the encryption keys is larger than the predetermined number;
If the number of other communication devices constituting the wireless network has not decreased even after a predetermined time has elapsed since the notification by the notification step, the encryption key already stored in the storage means is deleted. And storing a newly shared encryption key based on the start packet instead of the deleted encryption key;
A control method characterized by comprising:   A program for causing a computer to operate as the communication device according to any one of claims 1 to 13.

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