Key management apparatus, encrypted communication system, key provision apparatus, and method for key management, and program

Abstract

To provide a key management apparatus, an encrypted communication system, a key provision apparatus, a method for key management, and a program which can share an encryption key more flexibly according to a use case of the encryption key.SOLUTION: The key management apparatus according to an embodiment is a key management apparatus connected to a first server apparatus. The key management apparatus of the embodiment includes a processing unit for providing, to the first server apparatus, an unshared encryption key that is not shared with another key management apparatus, together with unshared information indicating that the encryption key is not shared with another key management apparatus.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a key management device, a cryptographic communication system, a key providing device, a key management method, and a program. [Background technology]

[0002] There are several well-known quantum key distribution (QKD) technologies between QKD devices connected via optical fiber links, including a technology that immediately starts sharing encryption keys upon request from an application, and a technology that sets a key reference value for each node and determines which node to share the encryption key with based on the reference value and the current remaining key balance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5634427 [Patent Document 2] Japanese Patent Application Publication No. 2019-195198 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional techniques have not been able to share encryption keys more flexibly depending on the use case of the encryption keys. [Means for solving the problem]

[0005] A key management device according to an embodiment is a key management device connected to a first server device, and includes a processing unit that provides an unshared encryption key, which is not shared with other key management devices, to the first server device together with unshared information indicating that the encryption key is not shared with other key management devices. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of the device configuration of an encrypted communication system according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the functional configuration of a key management device and a server device according to the first embodiment. [Figure 3] FIG. 4 is a diagram showing an example of encryption key management information according to the first embodiment. [Figure 4] FIG. 2 is a diagram showing an example of an encrypted communication method according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing an example of the device configuration of an encrypted communication system according to a second embodiment. [Figure 6] FIG. 10 is a diagram showing an example of the functional configuration of a key providing device according to a second embodiment. [Figure 7] FIG. 2 is a diagram showing an example of the hardware configuration of the QKD device according to the first and second embodiments. [Figure 8] FIG. 2 is a diagram showing an example of the hardware configuration of a key management device and a server device according to the first and second embodiments, and a key providing device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, with reference to the accompanying drawings, embodiments of a key management device, a cryptographic communication system, a key providing device, a key management method, and a program will be described in detail.

[0008] First, examples of use cases for using encryption keys will be described. Note that the following use cases are examples, and the method for using encryption keys is not limited to these use cases.

[0009] (Use Case 1) Use case 1 is when a large amount of local data is stored in a remote location such as the cloud. The data-related characteristics are as follows:

[0010] (1) Local data is stored in a remote location and then deleted (reducing data management costs). (2) The remote data is not accessed frequently (the remote data is rarely referenced). (3) The data is referenced remotely and not locally.

[0011] For example, a biobank that collects genetic information is an example of Use Case 1. In a biobank business, genetic information is collected in a large-scale storage server located in a specific location. Also, considering the seriousness of data leakage, it is quite conceivable to implement access control so that data can only be viewed locally (at a specific location).

[0012] Applications that upload large amounts of data require large numbers of encryption keys to encrypt the data, but the larger the amount of data, the greater the chance that the QKD device will not be able to provide enough encryption keys.

[0013] If the QKD device cannot provide a sufficient number of encryption keys, for example, the application cannot encrypt and transmit data until it receives an encryption key from the QKD device, and the application must repeatedly request the encryption key from the QKD device (encryption key request polling) to receive the encryption key, which requires the device on which the application is running to be kept powered on.

[0014] (Use Case 2) Use case 2 is a storage service provided by a cloud service provider. Users save data in cloud storage and then access the cloud storage when needed.

[0015] Typically, data stored on the cloud can be viewed immediately, but with some services it can take several minutes to several hours from the time you start accessing the data until you can actually view it (for example, AWS (registered trademark)'s S3 Glacier). Although this has the disadvantage that users cannot view the data immediately, it has the advantage that storage fees are cheaper, helping to keep costs down. There are various types of data that users store in the cloud, and this service focuses on the fact that some data does not need to be used immediately.

[0016] A similar service can be considered for quantum cryptography key provisioning. This is a use case where data is stored remotely but not immediately used. In such a use case, local data is immediately encrypted and stored remotely, but the data does not need to be decrypted immediately.

[0017] In other words, from the perspective of the application side (the party that receives the keys), costs can be reduced if there is a service that separates keys that can be decrypted immediately from those that cannot, and varies the usage fee for each (keys that cannot be decrypted immediately are cheaper).

[0018] However, conventional quantum cryptography communication technology basically provides keys that can be decrypted immediately, and there is no technology to provide keys that take into account use cases such as those described above, such as providing keys that cannot be used immediately but are therefore cheaper.

[0019] (First embodiment) Next, an example of the device configuration of the encrypted communication system 100 of the first embodiment that enables more flexible sharing of encryption keys in accordance with the use cases described above will be described.

[0020] [Example of equipment configuration] 1 is a diagram showing an example of the device configuration of an encrypted communication system 100 according to the first embodiment. The encrypted communication system 100 according to the first embodiment includes QKD devices 1a to 1c, key management devices 2a to 2c, a server device 3a, and a server device 3c.

[0021] QKD devices 1a and 1b-1 share a local key by QKD. QKD device 1a provides the local key shared with counterpart QKD device 1b-1 to key management device 2a. QKD device 1b-1 provides the local key shared with counterpart QKD device 1a to key management device 2b. The operation of QKD devices 1b-2 and 1c is similar to that of QKD devices 1a and 1b-1, so a description thereof will be omitted.

[0022] The key management device 2a encrypts the encryption key used by the server device 3a (the decryption key used by the server device 3c) with a local key shared between the QKD devices 1a and 1b-1, and then transmits the encryption key encrypted with the local key to the key management device 2b.

[0023] When key management device 2b receives the encryption key encrypted with the local key from key management device 2a, it decrypts the encrypted encryption key using the local key shared between QKD devices 1a and 1b-1. Next, key management device 2b encrypts the encryption key using the local key shared between QKD devices 1b-1 and 1c. Then, key management device 2a transmits the encryption key encrypted with the local key to key management device 2c.

[0024] When the key management device 2c receives the encryption key encrypted with the local key from the key management device 2b, it decrypts the encrypted encryption key using the local key shared between the QKD devices 1b-2 and 1c.

[0025] The server device 3a encrypts the data using the encryption key provided by the key management device 2a, and transmits the encrypted data to the server device 3c. The server device 3a is, for example, a local server device.

[0026] The server device 3c receives the encrypted data from the server device 3c and decrypts the data using the decryption key (the same key as the encryption key used for encryption) provided by the key management device 2c. The server device 3c is, for example, a cloud server device.

[0027] [Example of functional configuration] FIG. 2 is a diagram showing an example of the functional configuration of the key management devices 2a to 2c and the server devices 3a and 3c according to the first embodiment.

[0028] The key management device 2a includes a providing unit 21a, a generating unit 22a, a storage unit 23a, a determining unit 24a, a transfer processing unit 25a, and a network IF processing unit 26a.

[0029] The providing unit 21a, the determining unit 24a, the transfer processing unit 25a, and the network IF processing unit 26a are realized by at least one processing unit. This processing unit includes, for example, a control unit and an arithmetic unit, and is realized by analog or digital circuits, etc. The processing unit may be a central processing unit (CPU), a general-purpose processor, a microprocessor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof.

[0030] The providing unit 21a provides the encryption key to the server device 3a in response to a request for the encryption key from the server device 3a.

[0031] The generation unit 22a generates an encryption key used in the server device 3a (a decryption key used in the server device 3c). The generation unit 22a is realized by, for example, a random number generator such as a QRNG (Quantum Random Number Generation) or the like.

[0032] The storage unit 23a stores the encryption key generated by the generation unit 22a and management information for the encryption key. Details of the management information for the encryption key will be described later with reference to FIG.

[0033] The storage unit 23a is realized by a combination of, for example, a main storage device such as a read-only memory (ROM) and a random access memory (RAM), and an auxiliary storage device such as a hard disk drive (HDD) and a memory card.

[0034] The determination unit 24a determines an encryption key to be shared with the key management device 2c based on the encryption key management information.

[0035] The transfer processing unit 25a uses a routing protocol to identify a route to a sharing destination of the encryption key that has been decided to be shared by the determination unit 24a.

[0036] The network IF processing unit 26a identifies the next destination on the path identified by the transfer processing unit 25a (in the example of FIG. 2, the key management device 2b), encrypts the encryption key using the local key, and then transmits the encrypted encryption key to the next destination via a wireless or wired communication IF.

[0037] The key management device 2b includes a providing unit 21b, a generating unit 22b, a storage unit 23b, a determining unit 24b, a transfer processing unit 25b, and network IF processing units 26b-1 and 26b-2. In the example of Fig. 2, the key management device 2b functions as a relay device by the transfer processing unit 25b and the network IF processing units 26b-1 and 26b-2.

[0038] When a new server device 3b is connected to the key management device 2b, the providing unit 21b, the generating unit 22b, the storage unit 23b, and the determining unit 24b perform the same operations as those of the key management device 2a.

[0039] The key management device 2c includes a providing unit 21c, a generating unit 22c, a storage unit 23c, a determining unit 24c, a transfer processing unit 25c, and a network IF processing unit 26c. In the example of Fig. 2, the key management device 2c is used to provide a decryption key (the same key as the encryption key used for encryption).

[0040] When the key management device 2c generates and transmits an encryption key, the provision unit 21c, generation unit 22c, memory unit 23c, judgment unit 24c, transfer processing unit 25c and network IF processing unit 26c perform the same operations as those of the key management device 2a.

[0041] The server device 3a includes an application unit 31a, a communication unit 32a, an encryption processing unit 33a, and an acquisition unit 34a.

[0042] At least one application runs in the application unit 31a. Before transmitting encrypted data, the application requests an encryption key from the key management device 2a via the acquisition unit 34a. The communication unit 32a transmits the encrypted data to the server device 3c. The encryption processing unit 33a encrypts the data to be transmitted by the application using the encryption key. The acquisition unit 34a acquires the encryption key used to encrypt the data from the key management device 2a via a wireless or wired communication IF.

[0043] The server device 3c includes an application unit 31c, a communication unit 32c, an acquisition unit 34c, and a decryption processing unit 35c.

[0044] At least one application runs in the application unit 31c. The communication unit 32c receives encrypted data from the server device 3a. The acquisition unit 34c acquires a decryption key used to decrypt the data from the key management device 2c via a wireless or wired communication IF. The decryption processing unit 35c decrypts the encrypted data using the decryption key.

[0045] Hereinafter, when there is no need to distinguish between the QKD devices 1a to 1c, they will simply be referred to as the QKD device 1. Similarly, when there is no need to distinguish between the key management devices 2a to 2c, they will simply be referred to as the key management device 2. Similarly, when there is no need to distinguish between the server devices 3a and 3c, they will simply be referred to as the server device 3.

[0046] 1 and 2, the communication destination of server device 3a is server device 3c, but any number of communication destination server devices 3 may be included in the encryption communication system 100. That is, any number of combinations of QKD device 1, key management device 2, and server device 3 may be included in the encryption communication system 100, each of which has a configuration similar to the combination of QKD device 1c, key management device 2c, and server device 3c in FIG.

[0047] In addition, in the example of Figure 2, a functional configuration has been described in which server device 3a transmits data encrypted with an encryption key and server device 3c decrypts the encrypted data, but server device 3a may further have a decryption function as decryption processing unit 35a, and server device 3c may further have a decryption function as encryption processing unit 33c.

[0048] [Example of management information] Fig. 3 is a diagram showing an example of management information for encryption keys according to the first embodiment. In the example of Fig. 3, the management information includes, for each encryption key-k (k=1,...,N), a shared flag, a provided flag, and the time (minutes) elapsed since the key was provided.

[0049] The shared flag indicates whether or not the encryption key-k has been shared with the receiving-side key management device 2. In the example of Fig. 3, shared is indicated by a circle, and not shared is indicated by an x.

[0050] The provided flag indicates whether or not the encryption key-k has been provided to the server device 3. In the example of Fig. 3, provided status is indicated by a circle, and not provided status is indicated by an x.

[0051] The time elapsed since provision (minutes) indicates the time elapsed since the encryption key-k was provided. The elapsed time is calculated, for example, from the difference between the time when the encryption key-k was provided and the current time.

[0052] [Example of encrypted communication method] Fig. 4 is a diagram showing an example of the encrypted communication method of the first embodiment. In the example of Fig. 4, an operation example will be described in which the server device 3c on the receiving side does not need to immediately decrypt the encrypted data.

[0053] First, the acquisition unit 34a transmits an encryption key request to the key management device 2a (step S1), the encryption key request including a flag indicating that an unshared key is permitted, a requested amount of the encryption key, and destination (shared party) information of the data to be encrypted. In the example of Fig. 4, the destination (shared party) information includes destination information such as an IP address that identifies the server device 3c.

[0054] Next, the generation unit 22a generates an encryption key and stores the encryption key in the storage unit 23a (step S2). At this time, the generation unit 22a also stores management information of the encryption key in the storage unit 23a, and sets the shared flag of the management information of the encryption key to unshared.

[0055] The generating unit 22a may generate an encryption key before receiving a request for the encryption key and store the encryption key in an unshared state in the storage unit 23a in advance.

[0056] Next, the providing unit 21a provides the encryption key to the server device 3a (step S3). At this time, when providing the encryption key to the server device 3a, the providing unit 21a provides the encryption key together with a flag (an example of unshared information) indicating that this encryption key has not yet been shared. This enables the server device 3a to determine that this encryption key has not yet been shared with the server device 3c and cannot be immediately decrypted by the server device 3c, but can still be used to encrypt data.

[0057] Next, the providing unit 21a records the management information of the encryption key provided in step S3 (step S4). Specifically, the providing unit 21a sets the provided flag to "provided" and records the provided time used to calculate the elapsed time since the encryption key was provided in the management information.

[0058] Next, the communication unit 32a transmits the data encrypted with the encryption key provided in the process of step S3 to the server device 3c (step S5).

[0059] On the other hand, the determination unit 24a determines an encryption key to be shared with the key management device 2c based on the encryption key management information (step S6). Specifically, the key management device 2a determines to share an encryption key with the key management device 2c starting from the encryption key having the highest priority for sharing.

[0060] Next, the acquisition unit 34c requests the decryption key from the key management device 2c at an arbitrary timing (for example, several hours or several days after receiving the encrypted data) (step S7). Next, the provision unit 21c provides the decryption key to the server device 3c (step S8).

[0061] As described above, the key management device 2a connected to the server device 3a provides the server device 3a with an unshared encryption key that has not been shared with other key management devices 2, along with unshared information indicating that the encryption key has not been shared with other key management devices 2.

[0062] As a result, the key management device 2a of the first embodiment allows for more flexible sharing of encryption keys depending on the use case of the encryption keys. For example, since it is permitted to provide unshared encryption keys, it is possible to more flexibly create an encryption key sharing schedule, such as by allowing encryption keys with a relatively low priority to be shared later.

[0063] For example, suppose that applications A and B are running in the application unit 31a, and application A, which allows unshared keys, requests an encryption key, and then application B, which does not allow unshared keys, requests an encryption key. In this case, if the amount of encryption key shared with the destination for the encryption key requested by application B is insufficient, priority can be given to sharing the encryption key requested later by application B.

[0064] That is, although the encryption key request from application A was made earlier, the data encrypted by application A is not immediately decrypted, so the encryption key required by application B can be shared with other key management devices 2 before the encryption key required by application A. For example, the encryption key required by application A is shared with other key management devices 2 after the encryption key required by application B has been shared.

[0065] Furthermore, by allowing an application to use an unshared encryption key, for example, even if there are not enough shared encryption keys, the application can receive an encryption key more quickly.

[0066] When an encryption key that allows unshared encryption keys is requested, the key management device 2a may provide a shared encryption key if there are enough encryption keys shared with the destination. Furthermore, when an application requests an encryption key, it may explicitly request an unshared encryption key instead of using a flag indicating whether or not unshared keys are allowed. For example, if the fee for providing unshared encryption keys is set lower than the fee for providing shared encryption keys, the cost of encryption processing can be reduced by explicitly requesting an unshared encryption key.

[0067] (Modification 1 of the first embodiment) Next, a first modification of the first embodiment will be described. In the description of the first modification, the same description as in the first embodiment will be omitted, and only differences from the first embodiment will be described. The device configuration and functional configuration of the encrypted communication system 100 of the first modification are the same as those in FIGS. 1 and 2.

[0068] In the first modification, when the acquisition unit 34a requests the key management device 2a for an encryption key that can be in an unshared state, the acquisition unit 34a transmits an encryption key request that further includes the sharing expiration date of the unshared encryption key to the key management device 2a. This allows the key management device 2a to identify the deadline by which the unshared encryption key should be shared with the destination, and therefore allows the order of encryption key sharing processing to be flexibly determined according to the sharing expiration date even in a complicated situation where there are multiple unshared encryption keys or multiple destinations to share with.

[0069] For example, when the key management device 2a receives an encryption key request from the application unit 31a in which an unshared encryption key is permitted and the expiration date of the encryption key is set to one day later, the providing unit 21 first provides the unshared encryption key to the server device 3a.

[0070] Thereafter, the key management device 2a needs to share the unshared encryption key, but the expiration date for sharing is one day later. Therefore, if there is sufficient time before the expiration date, the determination unit 24a can prioritize sharing of the encryption key with another key management device 2 other than the key management device 2c connected to the communication destination requested by the application unit 31a. For example, the determination unit 24a can prioritize sharing of the encryption key with another key management device 2 that has a smaller remaining amount of shared encryption key.

[0071] (Modification 2 of the first embodiment) Next, a second modification of the first embodiment will be described. In the description of the second modification, the same description as in the first embodiment will be omitted, and only differences from the first embodiment will be described. The device configuration and functional configuration of the encrypted communication system 100 of the second modification are the same as those in FIGS. 1 and 2.

[0072] In the second modification, an example of the determination process by the determination unit 24a will be described in more detail.

[0073] In variant example 2, the judgment unit 24a sets a predetermined amount (for example, an amount greater than a first threshold) of remaining capacity of a shared encryption key, and if there is a remaining capacity greater than the predetermined amount and a certain time (0 hours or more) has passed since the provision of an unshared encryption key, the judgment unit 24a prioritizes sharing of the unshared encryption key.

[0074] That is, when the amount of encryption keys shared with other key management devices 2 is greater than a predetermined amount, the determination unit 24a of Modification 2 determines to prioritize sharing of unshared encryption keys that have been provided and have an elapsed time since provision that is greater than a predetermined first time, among the unshared encryption keys that have been provided. Specifically, when the amount of encryption keys shared with other key management devices 2 is greater than a predetermined amount, the determination unit 24a of Modification 2 determines to share more unshared encryption keys that have been provided and have an elapsed time since provision that is greater than the predetermined first time than unshared encryption keys that have an elapsed time within the predetermined first time. This makes it possible to share encryption keys with other key management devices 2 in order to maintain the remaining amount of encryption keys, while sharing unshared keys with other key management devices 2 in the free time.

[0075] (Modification 3 of the first embodiment) Next, a third modification of the first embodiment will be described. In the description of the third modification, the same description as in the first embodiment will be omitted, and only differences from the first embodiment will be described. The device configuration and functional configuration of the encrypted communication system 100 of the third modification are the same as those in FIGS. 1 and 2.

[0076] In the third modification, an example of the determination process by the determination unit 24a will be described in more detail.

[0077] In variant example 3, if there is an encryption key among the provided unshared encryption keys that has been provided for a predetermined second time (e.g., one hour), the judgment unit 24a preferentially shares the unshared key regardless of the remaining amount of shared encryption keys.

[0078] That is, when there is an unshared encryption key that has been provided for a time longer than the predetermined second time, the determination unit 24a of Modification 3 determines to prioritize sharing of the unshared encryption key that has been provided for a time longer than the predetermined second time. Specifically, the determination unit 24a of Modification 3 determines to share more unshared encryption keys that have been provided for a time longer than the predetermined second time than unshared encryption keys that have been provided for a time shorter than the predetermined second time. This makes it possible to control so that too much time does not pass since the provision of an unshared encryption key.

[0079] (Fourth modification of the first embodiment) Next, a fourth modification of the first embodiment will be described. In the description of the fourth modification, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described. The device configuration and functional configuration of the encrypted communication system 100 of the fourth modification are the same as those in FIGS. 1 and 2.

[0080] In the fourth modification, a case will be described in which the timing for starting the encryption key sharing process is controlled based on whether or not there is data access in the server device 3c.

[0081] In the fourth modification, when an acquisition unit 34c of the server device 3c detects access to data encrypted with an unshared encryption key, the acquisition unit 34c transmits a decryption key request to the key management device 2c to decrypt the encrypted data. When the key management device 2c receives the decryption key request from the server device 3c, the key management device 2c requests the key management device 2a to share the unshared encryption key. The determination unit 24a of the key management device 2a then determines that sharing the encryption key requested by the key management device 2c is to be prioritized. This allows the encrypted data to be decrypted relatively quickly when the user needs to refer to the encrypted data.

[0082] (Fifth Modification of the First Embodiment) Next, a fifth modification of the first embodiment will be described. In the description of the fifth modification, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described. The device configuration and functional configuration of the encrypted communication system 100 of the fourth modification are the same as those in FIGS. 1 and 2.

[0083] In the fifth modification, a case will be described in which an application running on the server device 3a controls the timing for starting the encryption key sharing process.

[0084] In the fifth modification, the communication unit 32a of the server device 3a transmits a request to decrypt data encrypted with an unshared encryption key to the server device 3c. When the request to decrypt the encrypted data is received, the acquisition unit 34c of the server device 3c transmits a decryption key request to the key management device 2c for decrypting the encrypted data. When the key management device 2c receives the decryption key request from the server device 3c, it requests the key management device 2a to share the unshared encryption key. Then, the determination unit 24a of the key management device 2a determines that sharing the encryption key requested by the key management device 2c is to be prioritized.

[0085] Specifically, variant example 5 is a control in which, for example, when server device 3a is a local server device and server device 3c is a cloud server device, an application on the local server device instructs an application running on the cloud server device that received the encrypted data to decrypt the encrypted data.

[0086] According to the control of the fifth modification, for example, it is possible to decrypt the encrypted data relatively quickly before the encrypted data is referenced by a user.

[0087] (Second embodiment) Next, a second embodiment will be described. In the description of the second embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described.

[0088] In the second embodiment, a case where a key providing device is further added will be described.

[0089] [Example of equipment configuration] 5 is a diagram showing an example of the device configuration of an encrypted communication system 200 according to the second embodiment. The encrypted communication system 200 according to the second embodiment includes QKD devices 1a to 1c, key management devices 2a to 2c, server devices 3a and 3c, and key providing devices 4a and 4c.

[0090] The key providing device 4a receives the encryption key from the key management device 2a and provides the encryption key to the server device 3a. The key providing device 4c receives the decryption key (the same key as the encryption key used for encryption) from the key management device 2c and provides the decryption key to the server device 3c.

[0091] Hereinafter, when there is no need to distinguish between the key providing devices 4a and 4c, they will simply be referred to as the key providing device 4.

[0092] [Example of functional configuration] 6 is a diagram showing an example of the functional configuration of the key providing device 4 according to the second embodiment. The key providing device 4 according to the second embodiment includes a providing unit 41, a storage unit 42, and an acquiring unit 43.

[0093] The providing unit 41 and the acquiring unit 43 are realized by at least one processing unit. This processing unit includes, for example, a control unit and an arithmetic unit, and is realized by analog or digital circuits, etc. The processing unit may be a central processing unit (CPU), a general-purpose processor, a microprocessor, a digital signal processor (DSP), an ASIC, an FPGA (or a combination thereof).

[0094] The providing unit 41 provides, for example, an unshared encryption key together with unshared information indicating that the encryption key is not shared with other key management devices to the server device 3 via a wireless or wired communication IF. The providing unit 41 also provides a decryption key to the server device 3 via a wireless or wired communication IF.

[0095] The storage unit 42 stores the encryption key (decryption key) acquired from the key management device 2. The storage unit 42 is realized by, for example, a combination of a main storage device such as a ROM and a RAM, and an auxiliary storage device such as an HDD and a memory card.

[0096] The acquisition unit 43, for example, requests the key management device 2 for an unshared encryption key that is not shared with other key management devices 2, and receives the encryption key from the key management device 2 via a wireless or wired communication IF. The acquisition unit 43 also requests the key management device 2 for a decryption key, and receives the decryption key from the key management device 2 via a wireless or wired communication IF.

[0097] As in the encrypted communication system 200 of the second embodiment described above, the system may have a configuration in which a key providing device 4 is further added between the key management device 2 and the server device 3.

[0098] Finally, examples of the hardware configurations of the QKD device 1, the key management device 2, and the server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment will be described.

[0099] [Example of hardware configuration] 7 is a diagram showing an example of the hardware configuration of the QKD device 1 of the first and second embodiments. The QKD device 1 of the first and second embodiments includes a control device 301, a main memory device 302, an auxiliary memory device 303, a display device 304, an input device 305, a quantum communication IF 306, and a classical communication IF 307.

[0100] The control device 301 , the main memory device 302 , the auxiliary memory device 303 , the display device 304 , the input device 305 , the quantum communication IF 306 and the classical communication IF 307 are connected via a bus 310 .

[0101] The control device 301 executes a program read from the auxiliary storage device 303 to the main storage device 302. The main storage device 302 is a memory such as a ROM (Read Only Memory) and a RAM. The auxiliary storage device 303 is a HDD, a memory card, or the like.

[0102] The display device 304 displays the status of the QKD device 1, etc. The input device 305 accepts input from the user. The display device 304 and the input device 305 may be realized by a touch panel or the like having a display function and an input function. The display device 304 and the input device 305 may not be provided in the QKD device 1. In this case, for example, the display function and input function of an external terminal connected to the QKD device 1 are used.

[0103] The quantum communication IF 306 is an interface for connecting to a QKD link through which photons are transmitted. The classical communication IF 307 is an interface for connecting to a transmission path through which control signals are transmitted between the opposing QKD device 1 and a transmission path for communication with the key management device 2.

[0104] 8 is a diagram showing an example of the hardware configuration of the key management device 2 and server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment. The key management device 2, server device 3, and key providing device 4 each include a control device 401, a main storage device 402, an auxiliary storage device 403, a display device 404, an input device 405, and a communication IF 406.

[0105] The control device 401 , the main memory device 402 , the auxiliary memory device 403 , the display device 404 , the input device 405 and the communication IF 406 are connected via a bus 410 .

[0106] The control device 401 executes a program read from the auxiliary storage device 403 to the main storage device 402. The main storage device 402 is a memory such as a ROM and a RAM. The auxiliary storage device 403 is a HDD, a memory card, or the like.

[0107] The display device 404 displays the status of the key management device 2 (server device 3, key providing device 4), etc. The input device 405 accepts input from a user. The display device 404 and the input device 405 may be realized by a touch panel or the like having a display function and an input function. Furthermore, the display device 404 and the input device 405 do not have to be provided in the key management device 2 (server device 3, key providing device 4). In this case, for example, the display function and input function of an external terminal connected to the key management device 2 (server device 3, key providing device 4) are used.

[0108] The communication IF 406 is an interface for connecting to a transmission line.

[0109] The programs executed by the QKD device 1, key management device 2 and server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment are stored in installable or executable format files on computer-readable storage media such as CD-ROMs, memory cards, CD-Rs, and DVDs (Digital Versatile Discs) and provided as computer program products.

[0110] In addition, the programs executed by the QKD device 1, key management device 2 and server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network.

[0111] In addition, the programs executed by the QKD device 1, key management device 2 and server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment may be configured to be provided via a network such as the Internet without being downloaded.

[0112] Furthermore, the programs executed by the QKD device 1, key management device 2 and server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment may be configured to be provided by being pre-installed in a ROM or the like.

[0113] The programs executed by the key management device 2 and the server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment, have a modular configuration including functions that can be realized by the programs among the functional configurations of the key management device 2 and the server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment. The functions realized by the programs are loaded into the main storage device 402 by the control device 401 reading and executing the programs from a storage medium such as the auxiliary storage device 403. In other words, the functions realized by the programs are generated on the main storage device 402.

[0114] Note that some or all of the functions of the key management device 2 and the server device 3 of the first and second embodiments, and the key providing device 4 of the second embodiment may be realized by hardware such as an IC (Integrated Circuit). The IC is, for example, a processor that executes dedicated processing.

[0115] Furthermore, when each function is realized using a plurality of processors, each processor may realize one of the functions, or may realize two or more of the functions.

[0116] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0117] (Addendum) The above-described embodiments can be summarized as the following technical proposals.

[0118] Technical proposal 1 A key management device connected to a first server device, a processing unit that provides the first server device with an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; A key management device comprising: Technical proposal 2 the processing unit receives an encryption key request from the first server device, the encryption key request including information indicating whether the unshared encryption key is acceptable, and if the unshared encryption key is acceptable, provides the unshared encryption key together with the unshared information to the first server device. A key management device as described in Technical Proposal 1. Technical proposal 3 the encryption key request further includes a requested encryption key amount and destination information for the data to be encrypted; When the unshared encryption key is permitted, the processing unit provides the first server device with the unshared encryption key amount that is not shared with other key management devices connected to the destination device identified by the destination information, together with the unshared information. A key management device described in Technical Proposal 2. Technical proposal 4 the encryption key request further includes a sharing expiration date of the unshared encryption key; the processing unit determines to share the unshared encryption key with the other key management device by the sharing deadline. A key management device according to technical proposal 2 or 3. Technical proposal 5 when the amount of encryption keys shared with the other key management devices is greater than a predetermined amount, the processing unit determines to share more unshared encryption keys whose elapsed time since provision is greater than a predetermined first time than unshared encryption keys whose elapsed time is within the predetermined first time; A key management device according to any one of technical proposals 1 to 4. Technical plan 6 the processing unit determines to share an unshared encryption key whose elapsed time since provision is greater than a predetermined second time more than an unshared encryption key whose elapsed time is within the predetermined second time. A key management device described in any one of technical proposals 1 to 5. Technical proposal 7 A key management device according to any one of technical proposals 1 to 6; the first server device; a second server device that receives data encrypted with the unshared encryption key; A cryptographic communication system comprising: Technical proposal 8 A first QKD device for performing QKD (Quantum Key Distribution), the key management device receives a key shared by the QKD from the first QKD device; the key management device shares the unshared encryption key by transmitting the unshared encryption key encrypted with the key shared by the QKD; The cryptographic communication system described in Technical Proposal 7. Technical proposal 9 a second QKD device for performing the QKD; another key management device that receives a key shared by the QKD from the second QKD device; the other key management device shares the unshared encryption key by receiving the unshared encryption key encrypted with the key shared by the QKD; The cryptographic communication system described in Technical Proposal 8. Technical proposal 10 when the second server device detects access to data encrypted with the unshared encryption key, it transmits a decryption key request to the other key management device to decrypt the encrypted data; When the other key management device receives the decryption key request from the second server device, the other key management device requests the key management device to share the unshared encryption key. The cryptographic communication system described in Technical Proposal 9. Technical proposal 11 the first server device transmits a decryption request for data encrypted with the unshared encryption key to the second server device; when the second server device receives a decryption request for the encrypted data, it transmits a decryption key request for decrypting the encrypted data to the other key management device; When the other key management device receives the decryption key request from the second server device, the other key management device requests the key management device to share the unshared encryption key. A cryptographic communication system according to Technical Proposal 9 or 10. Technical proposal 12 A key providing device connected between a key management device and a server device, a processing unit that receives an unshared encryption key that has not been shared with other key management devices from the key management device, and provides the unshared encryption key to the server device together with unshared information indicating that the encryption key has not been shared with the other key management devices; A key providing device comprising: Technical proposal 13 A key management method for a key management device connected to a server device, comprising: the key management device provides the server device with an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; Key management method. Technical proposal 14 A key management device connected to the server device causing the server device to provide an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; program. [Explanation of symbols]

[0119] 1 QKD device 2 Key management device 3. Server equipment 4 Key providing device 100,200 Encrypted Communication System 301 Control device 302 Main storage 303 Auxiliary storage device 304 Display device 305 Input Device 306 Quantum Communication Interface 307 Classical Communication IF 310 Bus 401 Control device 402 Main storage 403 Auxiliary storage 404 Display device 405 Input Device 406 Communication Interface 410 Bus

Claims

1. a key management device connected to a first server device, a processing unit that provides the first server device with an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; A key management device comprising:

2. the processing unit receives an encryption key request from the first server device, the encryption key request including information indicating whether the unshared encryption key is acceptable, and if the unshared encryption key is acceptable, provides the unshared encryption key together with the unshared information to the first server device. The key management device according to claim 1 .

3. the encryption key request further includes a requested encryption key amount and destination information for the data to be encrypted; If the unshared encryption key is permitted, the processing unit provides the first server device with the unshared encryption key amount that is not shared with other key management devices connected to the destination device identified by the destination information, together with the unshared information. The key management device according to claim 2 .

4. the encryption key request further includes a sharing expiration date of the unshared encryption key; the processing unit determines to share the unshared encryption key with the other key management device by the sharing deadline. The key management device according to claim 2 or 3.

5. when the amount of encryption keys shared with the other key management devices is greater than a predetermined amount, the processing unit determines to share more unshared encryption keys whose elapsed time since provision is greater than a predetermined first time than unshared encryption keys whose elapsed time is within the predetermined first time; The key management device according to claim 2 or 3.

6. the processing unit determines to share an unshared encryption key whose elapsed time since provision is greater than a predetermined second time more than an unshared encryption key whose elapsed time is within the predetermined second time. The key management device according to claim 2 or 3.

7. A key management device according to any one of claims 1 to 3; the first server device; a second server device that receives data encrypted with the unshared encryption key; A cryptographic communication system comprising:

8. A first QKD device that performs QKD (Quantum Key Distribution), The key management device receives a key shared by the QKD from the first QKD device; the key management device shares the unshared encryption key by transmitting the unshared encryption key encrypted with the key shared by the QKD; The cryptographic communication system according to claim 7.

9. a second QKD device for performing the QKD; and another key management device that receives the key shared by the QKD from the second QKD device; the other key management device shares the unshared encryption key by receiving the unshared encryption key encrypted with the key shared by the QKD; The cryptographic communication system according to claim 8.

10. when the second server device detects access to data encrypted with the unshared encryption key, it transmits a decryption key request to the other key management device to decrypt the encrypted data; When the other key management device receives the decryption key request from the second server device, the other key management device requests the key management device to share the unshared encryption key. The cryptographic communication system according to claim 9.

11. the first server device transmits a decryption request for data encrypted with the unshared encryption key to the second server device; When the second server device receives a decryption request for the encrypted data, the second server device transmits a decryption key request for decrypting the encrypted data to the other key management device; When the other key management device receives the decryption key request from the second server device, the other key management device requests the key management device to share the unshared encryption key. The cryptographic communication system according to claim 9.

12. A key providing device connected between a key management device and a server device, a processing unit that receives an unshared encryption key that has not been shared with other key management devices from the key management device, and provides the unshared encryption key to the server device together with unshared information indicating that the encryption key has not been shared with the other key management devices; A key providing device comprising:

13. A key management method for a key management device connected to a server device, comprising: the key management device provides the server device with an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; Key management method.

14. A key management device connected to the server device causing the server device to provide an unshared encryption key that has not been shared with other key management devices, together with unshared information indicating that the encryption key has not been shared with other key management devices; program.

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