JP2010272951A - Method and server for managing distribution of shared key - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that when an encryption key shared among users belonging to a group is distributed from a key distribution server, loads of the key distribution server and its peripheral networks are increased and the distribution may be delayed. <P>SOLUTION: When an inquiry about a network address of a client terminal or a key distribution server already holding a shared key is received from a client terminal in a case in which the shared key is shared among a plurality of client terminals, a connection table registering the network addresses of terminals holding the shared key is referred to. Then, one or more network addresses are selected from the connection table and transmitted to the client terminal which is a network address inquiring source. Then, the network address of the client terminal being the network address inquiring source is registered in the connection table referred to beforehand. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a mechanism for quickly distributing a shared key shared among users managed as a group to users belonging to the group. The present invention relates to a method and a server for managing, for example, shared key distribution.

  In recent years, it is required to ensure the confidentiality of files stored in a storage device. Encryption technology is widely used to ensure confidentiality. The encryption key used to encrypt the file must be strictly stored by the user who owns the encryption key so that the encrypted file (hereinafter also referred to as “encrypted file”) is not decrypted illegally. .

  Incidentally, an encrypted file may be shared by a plurality of users belonging to a group. In this case, a method of sharing an encryption key used for file encryption (hereinafter also referred to as a “file key”) among users in the group or a method of encrypting a file key with a shared key shared by users in the group. Is used.

  For example, in Patent Literature 1, encrypted data is shared among users belonging to a group by distributing a public key and a private key unique to the group to users belonging to the group and using them for data encryption and decryption. The mechanism is disclosed.

JP 2006-345261 A

OASIS KMIP Technical Committee, “KMIP-Key Management Interoperability Protocol Draft Version 0.98”, OASIS KMIP Technical Committee, February 10, 2009

  By the way, in actual operation, it is necessary to assume a case where a user leaves the group or a case where a shared key shared by users in the group is leaked to a third party who does not belong to the group. In these cases, it is necessary to take measures to protect the encrypted file shared within the group from unauthorized decryption. Specifically, it is necessary to newly generate a shared key and distribute it to the users in the group, and to decrypt the shared encrypted file with the old shared key and re-encrypt with the new shared key.

  As one of encryption key (shared key) distribution methods, there is a “rekey” operation defined in Non-Patent Document 1. In this distribution method, a user who uses an encryption key (shared key) requests the server to regenerate and distribute the encryption key. However, when this distribution method is applied to distribution of a shared key to users in a group, there are the following problems. For example, when each user requests the server to generate and distribute an encryption key all at once, there is a problem that the load on the server and the network may increase and a delay may occur. Therefore, in order to employ this distribution method, it is necessary to adjust each user's request timing in advance.

  As another method for distributing the encryption key (shared key), there is a “put” operation defined in Non-Patent Document 1. This distribution method is so-called push distribution of an encryption key (shared key) from a server to individual users registered in a group. When this distribution method is applied to the distribution of the shared key to the users in the group, the encryption key distribution interval can be adjusted. That is, the load on the server and the network can be reduced. As a result, the delivery delay can be alleviated to some extent. However, in this distribution method, it is necessary to sequentially repeat one-to-one communication between the server and each user. For this reason, it may take some time to distribute the encryption key to all users.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to apply a P2P communication technique to the distribution of a shared key shared within a group and to enable the simultaneous distribution of a shared key. To do.

  In order to achieve this object, in the present invention, a server that is requested to distribute a shared key from a client terminal has another client terminal or key that already holds the shared key with respect to the client terminal that has requested distribution of the shared key. Provide a mechanism to return the network address of the distribution server.

  According to the present invention, a client terminal that requests distribution of a shared key can request distribution of the shared key not only to the key distribution server but also to other client terminals that already have the shared key. As a result, it is possible to reduce the load concentration on the key distribution server and the surrounding network. In addition, according to the present invention, mutual distribution of a shared key between client terminals becomes possible. That is, it is possible to realize the simultaneous distribution of shared keys that is more than the number of key distribution servers. Thereby, it is possible to shorten the time until the shared key is completely distributed to all the client terminals as compared with the conventional case.

It is a figure explaining the outline | summary of the network structure in embodiment of this invention. It is a figure explaining the outline | summary of the function structure of the key management server program in embodiment of this invention. It is a figure explaining the outline | summary of a function structure of the key distribution server program in embodiment of this invention. It is a figure explaining the outline | summary of a function structure of the key distribution agent program in embodiment of this invention. It is a figure explaining the example of a process sequence at the time of the key generation request in embodiment of this invention. It is a figure explaining the example of a process sequence at the time of the key owner search request at the time of embodiment of this invention, and a key distribution request. It is a figure which shows the 1st example of the content preserve | saved in the connection table of the key distribution server program in embodiment of this invention. It is a figure which shows the 2nd example of the content preserve | saved in the connection table of the key distribution server program in embodiment of this invention. It is a figure which shows the 3rd example of the content preserve | saved of the connection table of the key distribution server program in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the descriptions and drawings in the embodiments of the present invention are exclusively for the purpose of explaining the present invention, and can be combined with or replaced with known techniques.

(1) Configuration of Shared Key Distribution System FIG. 1 shows an outline of the network configuration of the shared key distribution system according to the embodiment of the present invention. The shared key distribution system according to the embodiment includes the Internet 1, a key management server 2, a key distribution server 3, and a plurality of PCs 4 (PCa4, PCb4,...). The PC here corresponds to the “client terminal” in the claims. The key management server 2, the key distribution server 3, and the PC 4 are all connected to the Internet 1 and can communicate with each other. The key management server 2, the key distribution server 3, and the PC 4 are a secondary storage device such as a CPU, a ROM, a RAM, and a hard disk drive, a NIC (network interface card) physically connected to a network, a keyboard, a mouse, and the like. The computer includes an input device, an output device such as a display, and a physical component such as a bus that interconnects these devices to exchange data with each other. The ROM stores basic software for controlling an input / output device called a BIOS program. The secondary storage device stores software called an OS (operating system) and an application program that provides a function having a purpose by using an abstract function provided by the OS. Note that the OS absorbs small differences in computer hardware specifications, functions for input / output device operations, ROM, RAM, secondary storage device management functions, and communication functions using a network interface card. This is software that provides abstraction of The BIOS, the OS read from the secondary storage device and temporarily placed on the RAM, application programs, and the like are executed by the CPU.

  The key management server 2, the key distribution server 3, and the PC 4 execute the above-described BIOS program and OS. The key management server 2, the key distribution server 3, and the PC 4 execute application programs called a key management server program, a key distribution server program, and a key distribution agent program, which will be described later.

  The Internet 1 is composed of networks connected to each other by routers, switches, and other network relay devices. A computer connected to the Internet has an IP address assigned in accordance with IP (Internet Protocol). The communication data in which the transmission source and destination computers are specified by the IP address is relayed on the Internet according to the path selected by the network relay device and the computer having the communication path selection function, and transmitted from the transmission source computer to the destination computer.

  Communication data received by the NIC of the destination computer is received by the OS operating on the computer. The OS specifies the destination port number included in the received data in advance, and passes the received data to a program operating on the OS that is in a reception waiting state. The program that processes the received data creates reply data by designating the IP address and port number of the transmission source computer included therein, and requests the OS to transmit. The OS passes this reply data to the NIC, and the NIC sends the reply data to the transmission source computer via the Internet 1.

An IP address is described using only numbers and symbols “.” (Dots), but a computer having an IP address can also have an identifier (called a host name) expressed in characters such as alphabets. The correspondence between the IP address and the host name is managed by a DNS server existing in each network of the Internet 1. If the computer that is about to start communication does not know the IP address of the destination computer, it can also obtain the IP address corresponding to the host name of the destination computer by querying the DNS server. Assume that the IP address of the DNS server to be inquired is set in advance in each computer.
In the following description, the above-described BIOS, OS, and NIC processes are omitted. Note that Windows (registered trademark) or Linux (registered trademark) is used as the OS in the embodiment of the present invention. However, the OS is not limited to these.

(2) Functional Configuration of Computer Program FIG. 2 shows a schematic diagram of a functional configuration of a key management server program that operates on the key management server 2. The arrows in the figure indicate the flow of data processed by each component. The key management server program has a function of generating and returning a shared key in response to a request from the key distribution server 3. When receiving the communication data transmitted to the key management server program, the receiving unit 201 dispatches a message included in the communication data to the constituent elements of the processing unit. The transmission unit 202 transmits communication data transmitted by the key management server program to the destination. The functions of the other components will be described together with the description of the processing procedure shown in FIG.

  FIG. 3 shows a schematic diagram of a functional configuration of a key distribution server program operating on the key distribution server 3. The arrows in the figure indicate the flow of data processed by each component. The key distribution server program requests the key management server 2 to generate a shared key, stores the returned shared key, and already has a shared key in response to a request from the PC 4 that does not have the shared key And the function of returning the IP address of the computer (including not only the key distribution server 3 but also the PC 4). When receiving the communication data transmitted to the key distribution server program, the receiving unit 301 dispatches a message included in the communication data to the constituent elements of the processing unit. The transmission unit 302 transmits the communication data transmitted by the key distribution server program to the destination. The functions of the other components will be described together with the description of the processing procedure shown in FIGS.

  FIG. 4 shows a schematic diagram of a functional configuration of the key distribution agent program operating on the PC 4. The arrows in the figure indicate the flow of data processed by each component. The key distribution agent program inquires of the key distribution server 3 about the IP address of the computer holding the shared key and receives a reply, and the computer having that IP address (including not only the key distribution server 3 but also the PC 4) has a shared key. And a function for requesting and receiving a reply. The receiving unit 401 receives the communication data transmitted to the key distribution agent program, and dispatches a message included in the communication data to the constituent elements of the processing unit. The transmission unit 402 transmits the communication data transmitted by the key distribution agent program to the destination. The functions of the other components will be described together with the description of the processing procedure shown in FIG.

  Note that the key management server 2, the key distribution server 3, and the PC 4 adopt a public key encryption method for the purpose of mutually authenticating the encryption of communication performed between them and the communication partner belonging to the group. Assume that a public key / personal key pair is generated and owned in advance. It is assumed that the key management server 2 also owns a public key certificate that has been certified as a valid public key owner in advance. Although omitted in the following description, the communication contents in each communication are encrypted according to the encryption communication protocol SSL (Secure Sokcet Layer), and after mutually authenticating that the communication partner is a valid group member belonging to the group. Each message is exchanged.

(3) Processing procedure (3-1) Processing procedure at the time of key generation request FIG. 5 shows an example of processing procedure at the time of key generation request according to the embodiment of the present invention.
<Step 501>
First, the key generation request message generation unit 308 of the key distribution server program creates a key generation request message, designates the IP address and port number of the key management server 2 as the destination, and sends them from the transmission unit 302. Note that the IP address and port number of the key management server 2 are set in advance in the key distribution server program.

<Step 502>
Next, the key generation request message analysis unit 203 of the key management server program checks whether the key generation request message dispatched by the reception unit 201 conforms to a predetermined format, and sends the source IP address and port number to the shared key generation unit 204. hand over. The predetermined format includes various parameters (type of encryption algorithm, key length, etc.) for generating an encryption key. However, the predetermined format is not limited to these.

  The shared key generation unit 204 generates an encryption key shared by the PC 4 and passes it to the key generation response message generation unit 205 together with the transmission source IP address and port number passed from the key generation request message analysis unit 203. It is assumed that the encryption key uses an AES encryption algorithm of a common key encryption system or an RSA encryption algorithm of a public key encryption system. However, the encryption key is not limited to those using these algorithms.

  Further, the key generation response message generation unit 205 generates a key generation response message for sending back the encryption key generated by the shared key generation unit 204 to the transmission source of the key generation request message, and is passed from the shared key generation unit 204. The specified IP address and port number are designated as the destination and returned from the transmission unit 202.

<Step 503>
Next, the key generation response message analysis unit 303 of the key distribution server program extracts the shared key from the key generation response message dispatched by the reception unit 301, and the shared key provided in the secondary storage device of the key distribution server 3 Save in the storage unit 309.

<Step 504>
Finally, the key generation response message analysis unit 303 of the key distribution server program creates the connection table 310 and registers the host name and IP address of the key distribution server 3. The connection table 310 is provided on the RAM of the key distribution server 3 and is used for recording the host name and IP address of the shared key holder. FIG. 7 shows an example of the contents of the connection table at this point. At this time, the shared key has not been distributed to the PC 4 yet. Therefore, only the IP address of the key distribution server 3 exists in the connection table at this time.

(3-2) Key distribution procedure (part 1)
FIG. 6 shows a processing procedure example at the time of key distribution according to the embodiment of the present invention. First, a procedure for distributing the shared key stored in the key distribution server 3 to the PCa 4 will be described. Note that at the time of starting this procedure, the PCa 4 does not have a shared key, and the connection table 310 of the key distribution server 3 is in the state shown in FIG.

<Step 601>
First, the key distribution agent program operating on the PCa 4 generates a key owner search request message for inquiring the shared key holder in the key owner search request message generation unit 408, and the IP address and port of the key distribution server 3. The number is designated as a destination and sent from the transmission unit 402. It is assumed that the IP address and port number of the key distribution server 3 are set in advance in the key distribution agent program.

<Step 602>
Next, the key owner search request message analysis unit 304 of the key distribution server program extracts the host name, IP address, and port number of the inquiry source from the key owner search request message dispatched by the receiving unit 301, and owns the key. To the user search response message generator 307. The key owner search response message generation unit 307 refers to the connection table 310 and selects the IP address of the key owner. At this time, since the connection table 310 is in the state shown in FIG. 7, the IP address “172.16.2.2” of the host name “key distribution server”, which is the only entry, is selected.

<Step 603>
Next, the key owner search response message generation unit 307 registers the inquiry source host name and IP address passed from the key owner search request message analysis unit 304 in the connection table 310. If the inquiry source IP address is “192.168.100.10”, the connection table 310 changes to the state shown in FIG. That is, the host name and IP address of PCa4 are newly added to the connection table 310.

<Step 604>
Next, the key owner search response message generation unit 307 generates a key owner search response message including the key holder's IP address, and the inquiry source IP address passed from the key owner search request message analysis unit 304. The port number is designated as the destination and sent from the transmission unit 302.

<Step 605>
Next, the key owner search response message analysis unit 404 of the key distribution agent program operating on the PCa 4 uses the key owner's IP address (here, the key distribution server 3) from the key owner search response message dispatched by the reception unit 401. IP address “172.16.2.2”) is extracted and passed to the key distribution request message generation unit 407. At this time, the key distribution request message generation unit 407 generates a key distribution request message, and the IP address of the key owner (the IP address of the key distribution server 3 “ 172.16.2.2 ") and a port number set in advance in the key distribution agent program are designated and transmitted from the transmission unit 402.

<Step 606>
Next, the key distribution request message analysis unit 305 of the key distribution server program extracts the IP address and port number of the request source from the key distribution request message dispatched by the reception unit 301 and passes it to the key distribution response message generation unit 306. . Here, the key distribution response message generation unit 306 reads the shared key from the shared key storage unit 309, generates a key distribution response message including this shared key, and receives the request passed from the key distribution request message analysis unit 305 to the destination. The original IP address and port number are designated and sent from the transmission unit 302.

<Step 607>
Finally, the key distribution response message analysis unit 403 of the key distribution agent program operating on the PCa 4 extracts the shared key from the key distribution response message dispatched by the reception unit 401 and shares the shared key provided in the secondary storage device of the PCa 4 Save to the key storage unit 409.

(3-3) Key distribution procedure (part 2)
Next, a shared key distribution procedure in the case where the key distribution server 3 that has received an inquiry about the key holder from the PCb 4 returns the PCa 4 as the shared key holder will be described with reference to FIG. That is, a case where the PCb 4 receives a shared key from the PCa 4 will be described. At the time of starting this procedure, it is assumed that PCa4 has a shared key but does not have PCb4. That is, the connection table 310 of the key distribution server 3 is in the state shown in FIG.

<Step 601>
First, the key distribution agent program operating on the PCb 4 generates a key owner search request message for inquiring the shared key holder in the key owner search request message generation unit 408, and the IP address and port of the key distribution server 3. The number is designated as a destination and sent from the transmission unit 402. It is assumed that the IP address and port number of the key distribution server 3 are set in advance in the key distribution agent program.

<Step 602>
Next, the key owner search request message analysis unit 304 of the key distribution server program extracts the host name, IP address, and port number of the inquiry source from the key owner search request message dispatched by the receiving unit 301, and owns the key. To the user search response message generator 307. The key owner search response message generation unit 307 refers to the connection table 310 and selects the IP address of the key owner. At this time, a plurality of entries are registered in the connection table 310 as shown in FIG. Therefore, the key owner search response message generation unit 307 selects one entry from a plurality of entries. As a method for selecting one entry, there are a method for selecting one entry at random, a method for selecting an IP address existing in the vicinity of the IP address of the inquiry source in terms of network topology, and the like. However, it is not limited to these selection methods. In this procedure, it is assumed that the IP address “192.168.100.10” of the host name “PCa” in FIG. 8 is selected.

<Step 603>
Next, the key owner search response message generation unit 307 registers the inquiry source host name and IP address passed from the key owner search request message analysis unit 304 in the connection table 310. If the inquiry source IP address is “192.168.200.20”, the connection table 310 changes to the state shown in FIG. In other words, the PCab host name and IP address are newly added to the connection table 310.

<Step 604>
Next, the key owner search response message generation unit 307 generates a key owner search response message including the key holder's IP address, and the inquiry source IP address passed from the key owner search request message analysis unit 304. The port number is designated as the destination and sent from the transmission unit 302.

<Step 605>
Next, the key owner search response message analysis unit 404 of the key distribution agent program operating on the PCb 4 uses the key owner IP address (here, the IP address of the PCa 4) from the key owner search response message dispatched by the reception unit 401. “192.168.100.10”) is extracted and passed to the key distribution request message generation unit 407. At this time, the key distribution request message generation unit 407 generates a key distribution request message, and the IP address (“192.168.100.10”) of the key owner passed from the key owner search response message analysis unit 404 to the destination. The port number set in advance in the key distribution agent program is designated and sent from the transmission unit 402. That is, the key distribution request message generation unit 407 sends a key distribution request message to the PCa4.

<Step 606>
Next, the key distribution request message analysis unit 405 of the key distribution agent program operating on the PCa 4 extracts the request source IP address and the port number from the key distribution request message dispatched by the reception unit 401 to generate a key distribution response message. Pass to section 406. Here, the key distribution response message generation unit 406 reads the shared key from the shared key storage unit 409, generates a key distribution response message including the shared key, and requests the request source IP passed from the key distribution request message analysis unit 405 to the destination. An address and a port number are designated and sent from the transmission unit 302.

<Step 607>
Finally, the key distribution response message analysis unit 403 of the key distribution agent program operating on the PCb 4 extracts the shared key from the key distribution response message dispatched by the reception unit 401, and the shared key provided in the secondary storage device of the PCb 4 Save to the key storage unit 409.

(4) Effects in the Embodiments By executing each procedure described above, the common key can be distributed not only from the key distribution server 3 but also from the PC 4 that has already been distributed. Thereby, it is possible to reduce a situation in which an excessive load is applied to the key distribution server 3 and its peripheral network when distributing the shared key. At this time, the distribution of the shared key to the PC that does not have the shared key can be performed from the PC or the key distribution server 3 located in the vicinity in the network topology. Here, the neighborhood in terms of network topology means belonging to the same network domain, for example. Thereby, it is possible to further reduce communication congestion in the entire network. In the case of this embodiment, a plurality of distribution sources can exist simultaneously. Therefore, it becomes possible to distribute the shared key simultaneously. As a result, the time until distribution of the shared key to all PCs can be shortened as compared with the conventional case.

(5) Other Embodiments In the above-described embodiment, the case where there is one key distribution server 3 has been described. However, a plurality of key distribution servers 3 can be provided. In this case, it becomes possible to appropriately allocate the inquiry destination of the key holder by the PC to each key distribution server 3. As a result, it is possible to alleviate a situation where inquiries of key holders are concentrated on one key distribution server 3, and it is possible to reduce the possibility of delay due to high load.

  In the embodiment described above, in step 602, the key distribution server 3 selects the IP address of the key owner from the connection table 310 and returns it to the inquiry source. Alternatively, a part of the entry is returned, and the PC receiving the message sends a key distribution request message to a key owner that is randomly selected from those entries or that exists in the network topology in the vicinity. A program may be configured. Even when such a method is employed, it is possible to obtain the same effects as those described above. At this time, it is desirable to set a certain upper limit on the number of key owner entries returned from the key distribution server 3 and to prevent the key owner search response message from becoming too long.

  In the above-described embodiment, the case where the key management server 2 and the key distribution server 3 exist independently has been described. However, the key management server 2 and the key distribution server 3 may be virtually configured in one server.

DESCRIPTION OF SYMBOLS 1 ... Internet 2 ... Key management server 3 ... Key distribution server 4 ... PC (PCa, PCb, ...)
DESCRIPTION OF SYMBOLS 201 ... Reception part of key management server program 202 ... Transmission part of key management server program 203 ... Key generation request message analysis part of key management server program 204 ... Shared key generation part of key management server program 205 ... Key of key management server program Generation response message generation unit 301 ... Reception unit of key distribution server program 302 ... Transmission unit of key distribution server program 303 ... Key generation response message analysis unit of key distribution server program 304 ... Key owner search request message analysis of key distribution server program 305: Key distribution request message analysis unit of the key distribution server program 306: Key distribution response message generation unit of the key distribution server program 307: Key owner search response message generation unit of the key distribution server program 308: Key distribution server Program key generation request message generation unit 309 ... Shared key storage unit of key distribution server program 310 ... Connection table of key distribution server program 401 ... Reception unit of key distribution agent program 402 ... Transmitter of key distribution agent program 403 ... Key distribution Key distribution response message analysis unit 404 of the agent program Key owner search response message analysis unit 405 of the key distribution agent program Key distribution request message analysis unit 406 of the key distribution agent program Key distribution response message generation unit of the key distribution agent program 407: Key distribution request message generation unit of key distribution agent program 408: Key owner search request message generation unit of key distribution agent program 409: Shared key of key distribution agent program Preservation part

Claims (7)

A shared key distribution management method shared between a plurality of client terminals,
A server that manages the distribution of the shared key;
Receiving from the client terminal an inquiry about the network address of the client terminal or key distribution server that already holds the shared key;
Selecting one network address with reference to a connection table in which network addresses of terminals having the shared key are registered;
Transmitting the selected one network address to a client terminal that is a network address inquiry source;
A shared key distribution management method comprising: registering a network address of a client terminal inquiring about the network address in the connection table. A shared key distribution management method shared between a plurality of client terminals,
A server that manages the distribution of the shared key;
Receiving from the client terminal an inquiry about the network address of the client terminal or key distribution server that already holds the shared key;
Selecting a plurality of network addresses with reference to a connection table in which network addresses of terminals having the shared key are registered;
Transmitting the selected plurality of network addresses to a client terminal that is a network address inquiry source;
A shared key distribution management method comprising: registering a network address of a client terminal inquiring about the network address in the connection table. In the selection of the one or more network addresses, the network address of the client terminal that is the inquiry source of the network address and the network address of the client terminal or key distribution server that already holds the shared key are close to the network topology. The shared key distribution management method according to claim 1 or 2, characterized in that: A client terminal or key distribution server having the one or more network addresses selected by the server that manages the distribution of the shared key;
The method further comprises the step of receiving a shared key distribution request from the client terminal that is the inquiry source of the network address and distributing the held shared key to the client terminal that is the inquiry source of the network address. The shared key distribution management method according to any one of 1 to 3. A server that manages the distribution of shared keys shared among multiple client terminals,
A processing unit that receives an inquiry about the network address of a client terminal or key distribution server that already holds the shared key from a client terminal;
A processing unit that selects one network address with reference to a connection table in which network addresses of terminals having the shared key are registered;
A processing unit that transmits the selected one network address to a client terminal that is an inquiry source of the network address;
A shared key distribution server comprising: a processing unit that registers a network address of a client terminal that is an inquiry source of the network address in the connection table. A server that manages the distribution of shared keys shared among multiple client terminals,
A processing unit that receives an inquiry about the network address of a client terminal or key distribution server that already holds the shared key from a client terminal;
A processing unit that selects a plurality of network addresses with reference to a connection table in which network addresses of terminals having the shared key are registered;
A processor that transmits the selected plurality of network addresses to a client terminal that is an inquiry source of the network address;
A shared key distribution management server comprising: a processing unit that registers a network address of a client terminal that is an inquiry source of the network address in the connection table. In the selection of the one or more network addresses, the network address of the client terminal that is the inquiry source of the network address and the network address of the client terminal or key distribution server that already holds the shared key are close to the network topology. 7. The shared key distribution management server according to claim 5, wherein priority is given to the one.

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