Key issuance system, key issuance method, and program

Abstract

A key issuing system 1 comprises: a multifunctional communication gateway 10 including a communication unit 101 capable of performing communication via a communication network N1 and a communication network N2 that uses a bandwidth narrower than that of the communication network N1; and at least one communication device 20 capable of performing communication via the communication network N2. The multifunctional communication gateway 10 comprises a first security unit 102 in a secure environment. The first security unit 102 comprises a master key generation unit 1021 that generates a master public key, a user secret key generation unit 1022 that generates a user secret key by using the master public key and an identifier of the communication device 20, and a key distribution unit 1023 that transmits the user secret key to the communication device 20 having the received identifier.

Description

Technical Field

[0001] This disclosure relates to key issuance technology.

Background Art

[0002] With the spread of IoT (Internet of Things) devices, important communications are also being carried out in IoT devices (IoT devices). Therefore, authentication technology for confirming whether each other is a correct device during communication has become important in IoT devices.

[0003] In IoT technology that uses a large number of devices (hereinafter also referred to as "devices"), an IoT gateway device (IoT-GW) that aggregates a large number of IoT devices may be used. In this case, a narrow-band network such as LPWA (Low Power Wide Area) is used between the IoT device and the IoT gateway device from the perspective of price, and a wide-band network such as a mobile network is used between the IoT gateway device and the server device. A configuration that uses is often adopted.

[0004] In a network that uses a narrow band such as LPWA, it is expected to use a mutual authentication method with low communication volume that utilizes ID-based cryptography. The use of ID-based cryptography requires a key issuance authority to issue a secret key corresponding to the ID of each entity such as an IoT device. However, since the key issuance authority of ID-based cryptography issues the secret keys of all entities, it can decrypt ciphertext addressed to any recipient. It is necessary to take strict measures so that not only the reliability of the key issuance authority itself but also the master key and parameters used for secret key generation are not leaked. From the above background, so far, the key issuance authority has been assumed to be operated on a server that can take sufficient measures including physical security.

[0005] However, when using ID-based encryption only on the local network under an IoT gateway device, there are cases where it is desirable to have the key issuing authority located on the local network from the standpoint of load balancing, availability, and latency. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Shinzaki, et al., "IoT Security for Big Data Utilization: Mutual Authentication and Location Data Anonymization Technology," FUJITSU, 2016, Vol. 67, No. 2, pp. 52-59. [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional technologies assume that the key issuing authority is operated on a server, which presents a problem in that there is no way to securely build a key issuing authority on IoT devices participating in the IoT local network (to ensure the security of communication).

[0008] This disclosure aims to solve the above-mentioned problems by providing a technology that enables secure key issuance in devices participating in a local network by equipping IoT devices equipped with a secure environment with the functionality of a key issuing center. [Means for solving the problem]

[0009] To solve the above problems, a key issuance system according to one aspect of the present disclosure comprises a communication gateway equipped with a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line, and at least one communication device capable of communicating with the communication gateway using the second line, wherein the communication gateway has a security unit for a secure environment, and the security unit comprises a master key generation unit that generates a master public key using a selected master private key, a user private key generation unit that generates a user private key using the master public key generated by the master key generation unit and an identifier of the communication device received as input by the communication unit, and a key distribution unit that transmits the user private key generated by the user private key generation unit to the communication device having the identifier received by the communication unit.

[0010] Furthermore, another aspect of the key issuance system of the present disclosure is a key issuance system corresponding to a hierarchical ID-based cryptographic scheme, comprising: a communication gateway equipped with a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line; at least one communication device capable of communicating using the second line; and an intermediate key issuance device comprising k-1 (k is an integer of 2 or more) first devices, ..., the (k-1)th device, capable of communicating using the second line, wherein the communication gateway has a first security unit of a first secure environment, the first security unit comprises a master key generation unit that generates a master public key and a master private key, a root private key generation unit that generates a root private key using the master private key, the master public key, the root private key, and the intermediate key obtained by the communication unit. The intermediate key issuing device has a first secret key generation unit that generates a first secret key using a first identifier of a first device of the intermediate key issuing device, and a key distribution unit that transmits the first secret key to the first device of the intermediate key issuing device, wherein the nth (n=1,2,...,k-1) device of the intermediate key issuing device has a second security unit having a second secure environment, and the second security unit has an (n+1) secret key generation unit that generates an (n+1) secret key using the master public key and the first secret key and an (n+1) identifier obtained from either the (n+1) device of the intermediate key issuing device or a communication device capable of communicating with the (n)th device of the intermediate key issuing device, and a key distribution unit that transmits the (n+1) secret key to the (n+1) device of the intermediate key issuing device or the communication device capable of communicating with the (n)th device of the intermediate key issuing device. [Effects of the Invention]

[0011] According to this disclosure, secure key issuance can be achieved in devices participating in a local network. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a diagram showing an example of the functional configuration of a key issuance system according to the first embodiment of this disclosure. [Figure 2] Figure 2 shows an example of the functional configuration of the multi-functional communication gateway 10 and the communication device 20. [Figure 3] Figure 3 is a sequence diagram showing an example of the processing of the key issuance system 1. [Figure 4] Figure 4 is a diagram showing an example of a modified functional configuration of the key issuance system according to the first embodiment of this disclosure. [Figure 5] Figure 5 is a diagram showing an example of the functional configuration of a key issuance system according to the second embodiment of this disclosure. [Figure 6] Figure 6 shows an example of the functional configuration of the multi-function communication gateway 10B, the intermediate key issuing device 35n, and the communication device 20. [Figure 7] Figure 7 is a sequence diagram showing an example of the processing of the key issuance system 1B. [Figure 8] Figure 8 is a diagram showing an example of a modified functional configuration of the key issuance system according to the second embodiment of this disclosure. [Figure 9] Figure 9 shows a multi-function communication gateway 10C, an intermediate key issuing device 35Cn, and a communication device 20 as an example of a functional configuration of another modified key issuing system according to the second embodiment of this disclosure. [Figure 10] Figure 10 is a sequence diagram showing an example of processing in another modified version of the key issuance system according to the second embodiment. [Figure 11] Figure 11 illustrates the functional configuration of a computer. [Modes for carrying out the invention]

[0013] The embodiments of this disclosure will be described in detail below with reference to the figures. Components having the same function will be numbered the same, and redundant explanations will be omitted.

[0014] <First Embodiment> <<Definition of Symbols>> The symbols used in the first embodiment are defined as follows:

[0015] ID A Identifier of communication device 20A ID B Identifier of communication device 20B D A : Private key of communication device 20A D B : Private key of communication device 20B k: Security parameter p, q: Prime numbers satisfying p ≠ q G1: Finite field F p Let the elliptic curve over it be E1, and the subgroup of the group E(F p ) G2: Finite field F p Let the elliptic curve over its k-th extension field be E2, and the group on the elliptic curve E2

Number

[0016] [Key Issuance System] As shown in FIG. 1, the key issuance system 1 according to the first embodiment of the present disclosure includes a server X, a multifunctional communication gateway 10, and a plurality of communication devices 20 (20A, 20B,...).

[0017] Server X and the multi-function communication gateway 10 are connected via a communication network N1 (first line), such as a mobile network. Server X may be configured as an edge device. Server X and the communication network N1 do not have to be essential components of the key issuance system 1. That is, the key issuance system 1 may be configured without including Server X and the communication network N1.

[0018] The multi-functional communication gateway 10 and each communication device 20 are connected in a way that allows communication via a communication network N2 (second line), such as an LPWA that uses a narrower bandwidth than the communication network N1. The multi-functional communication gateway 10 and each communication device 20 constitute a local network.

[0019] (Multifunctional communication gateway 10) The multi-functional communication gateway 10 is a device that includes a computer or computer system that functions as a KGC (Key Generation Center) in addition to a device that functions as a communication gateway. The multi-functional communication gateway 10 generates a master public key in advance using a master private key and then makes the master public key public. Furthermore, when the multi-functional communication gateway 10 receives an identifier of a communication device 20 as a key issuance request, as described later, it generates a user private key from this identifier and then distributes (transmits) the user private key to the communication device 20 corresponding to that identifier.

[0020] As shown in Figure 2, the multi-functional communication gateway 10 in this embodiment includes a communication unit 101 that communicates with external devices and a first security unit 102 that is connected to the communication unit 101.

[0021] The communication unit 101 communicates with external devices, such as a server X, via the communication network N1. The communication unit 101 also performs various types of communication with the communication device 20 via the communication network N2.

[0022] The first security unit 102 includes a master key generation unit 1021, a user private key generation unit 1022, a key distribution unit 1023, and a storage unit 1024 that stores various data (for example, various data such as master public key and master private key).

[0023] The first security unit 102 has the function of a secure environment. The first security unit 102 may consist of secure elements such as an eSIM (An Embedded SIM), as well as secure components such as a TEE (Trusted Execution Environment).

[0024] (Communication device 20) The communication device 20 uses the user's secret key distributed from the multi-function communication gateway 10 to perform encrypted communication and authentication (i.e., verification of legitimacy) with other communication devices 20 using ID-based encryption.

[0025] Any identifier can be used as the identifier for the communication device 20 used in this embodiment. Examples of identifiers include the manufacturing number, IP (Internet Protocol) address, physical address, user ID of the user of the communication device 20, name of the user of the communication device 20, email address of the user of the communication device 20, etc.

[0026] An example of a communication device 20 is an IoT device. Examples include various sensor devices, embedded devices, wearable devices, digital home appliances, surveillance cameras, lighting equipment, medical equipment, industrial equipment, etc. When the communication device 20 is an IoT device, its computing resources are often limited. For example, the processing performance of the processor and the memory capacity are often inferior compared to general computers. However, the communication device 20 in this disclosure may also be a device that does not fall under the category of IoT devices, such as a PC (personal computer), server equipment, smartphone, or tablet terminal.

[0027] As shown in Figure 2, the communication device 20 in this embodiment includes a communication unit 201 and a storage unit 202 for storing various data (for example, a user's private key).

[0028] The communication unit 201 performs various communications with other communication devices 20 and the multi-function communication gateway 10, etc.

[0029] Hereafter, when referring to each of the multiple communication devices 20 separately, they may be referred to as, for example, "communication device 20A," "communication device 20B," etc.

[0030] [How to issue a key] The processing method of the key issuance system according to this embodiment is realized when the multifunctional communication gateway 10, which is equipped with a first security unit 102 that has the function of a secure environment, performs the processing shown in Figure 3. As an example, two communication devices 20, communication device 20A and communication device 20B, make a key issuance request to the multifunctional communication gateway 10, and the multifunctional communication gateway 10 issues the user secret key D A and user private key D B The process will be explained using the case where it is issued.

[0031] The master key generation unit 1021 generates a master public key and a master private key. That is, the master key generation unit 1021 selects the master private key z, calculates the master public key Z, and stores it in the storage unit 1024 (step S1021). Note that during generation, the master public key Z may be configured to be made public to each communication device 20.

[0032] The communication unit 101 receives an identifier as input from the communication device 20 as a request for the issuance of a user private key (hereinafter also simply referred to as a "key issuance request"). That is, the communication unit 101 receives the identifier ID of the communication device 20A at any time. A and the identifier ID of communication device 20B BThe and are accepted as input (step S101). The identifier of the communication device 20 may be configured to be transmitted by the communication device 20 itself, for example, or by other terminals connected to the multifunction communication gateway 10 via the communication network N1 or the communication network N2. If the multifunction communication gateway 10 has an input device, it may be configured to allow the identifier of the communication device 20 to be input from that input device.

[0033] When the user secret key generation unit 1022 receives an identifier from the communication device 20, it generates a user secret key from this identifier. That is, the user secret key generation unit 1022 generates the user secret key D according to the following formula. A and D B Generate (step S1022).

number

number

[0034] i A and iB The generation is performed by the communication device 20A i A It generates and the communication device 20B i B It is conceivable to configure it to generate i. However, if the computing resources of the communication device 20 are limited and a lot of computing resources are needed for the calculation of H1, or if certain conditions are met, the multi-function communication gateway 10 may perform i A and i B It may be configured to generate one or both of the above.

[0035] The key distribution unit 1023 distributes (transmits) the user's private key to the communication device 20 corresponding to the identifier. That is, the key distribution unit 1023 distributes (transmits) the user's private key D A The user's private key D is distributed to the communication device 20A. B The keys are distributed to the communication device 20B (step S1023). As for the method of distributing user secret keys by the key distribution unit 1023, for example, the key distribution unit 1023 may be configured to send the user secret key to the corresponding communication device 20 as a trigger when the user secret key is generated. Alternatively, the key distribution unit 1023 may be configured to distribute the user secret key from the communication unit 101 to the communication device 20 in response to a request for distribution of the user secret key from the communication device 20.

[0036] Furthermore, in order to securely distribute keys, the system may be configured to share a distribution encryption key in advance with the communication device by some means, for example, by using an initial key written at the time of device shipment, or a key exchanged based on the initial key, as the encryption key for key distribution (hereinafter, these are collectively referred to as the "distribution encryption key"), and then encrypt and distribute the user's private key using the distribution encryption key stored in the memory. Alternatively, the user's private key may be recorded on a recording medium or the like and then distributed to the communication device 20.

[0037] By implementing the processing method described above, the communication device 20 can obtain a user secret key to be used when performing authenticated key exchange with other communication devices 20. In other words, by using the key issuance system 1 according to this embodiment, secure key issuance can be achieved in devices participating in the local network.

[0038] <Modified form of the first embodiment> The first embodiment of this disclosure may be configured as the key issuance system 1A shown in Figure 4. That is, it may be configured as a device equipped with a communication unit capable of communicating with a communication network N2, and having a key issuance device 30 having key issuance station functions equivalent to those of the multifunctional communication gateway 10. In this case, the multifunctional communication gateway 10 may be configured as a communication gateway 10A that does not include key issuance station functions.

[0039] <Second Embodiment> The second embodiment of this disclosure is configured to place a key issuing station function and an intermediate key issuing station function, which are compatible with a hierarchical ID-based encryption scheme, in a secure environment within each device. The key issuing system 1B shown in Figure 5 differs from the key issuing system 1 shown in Figure 1 in that the multi-function communication gateway 10 has been changed to a multi-function communication gateway 10B that is compatible with a hierarchical ID encryption scheme, and the intermediate key issuing device 35, which was not included in the key issuing system 1. n The point is that it has (n=1,2,...,k-1 (k is an integer greater than or equal to 2)). Here, the intermediate key issuing device 35 n It is configured to communicate via the communication network N2, just like the communication device 20. Intermediate key issuing device 35 n It may be composed of multiple layers to support a hierarchical ID encryption scheme. For the sake of explanation, the intermediate key issuing device 35 n This is sometimes referred to as "intermediate key issuing device 35".

[0040] (Multifunctional communication gateway 10B) The differences between the multi-functional communication gateway 10B in Figure 6 and the multi-functional communication gateway 10 according to the first embodiment shown in Figure 2 are that a root secret key generation unit 1021-1, which was not included in the first security unit 102, has been newly added, and the user secret key generation unit 1022 has been changed to the first secret key generation unit 1022B. Along with these changes, the name of the first security unit 102 has been changed to the first security unit 102B.

[0041] The first security unit 102B, like the first security unit 102, has the function of a secure environment (first secure environment). Also, because the processing content is different, the communication unit 101 has been renamed to communication unit 101B.

[0042] (Intermediate key issuing device 35) n ) Newly added intermediate key issuing device 35 n It has a communication unit 351 and a second security unit 352 connected to the communication unit 351. The second security unit 352 has a (n+1) secret key generation unit 3521, a key distribution unit 3522, and a storage unit 3523. The second security unit 352 has the same function as the first security unit 102B, providing a secure environment (second secure environment).

[0043] Furthermore, the key issuing authorities placed in the secure environment (for example, the elements constituting the first security unit 102B and the second security unit 352) may be configured to be implemented in all devices in the hierarchical structure, or they may be configured to be implemented in only some of them. An example of partial implementation is the intermediate key issuing device 35. n Among these, one example is implementing it only in the terminal intermediate key issuing device.

[0044] [Key Issuance Method for Key Issuance System 1B] Each of the following devices has the functionality of a secure environment: a multi-functional communication gateway 10B and an intermediate key issuing device 35. n However, by performing the process shown in Figure 7, the processing method of the key issuance system 1B according to this embodiment is realized.

[0045] In the following explanation, b is a random number selected according to a uniform distribution between 0 and 1. Also, let x = 1, 2, ..., k, and id (x) =(I1, I2, ..., I x ) and b.id (x) =(b||I1, I2, ..., I x This shall indicate ).

[0046] As shown in Figure 7, the master key generation unit 1021 generates security parameter 1 κ Get (mpk',msk')←SetUp'(1 κ ) is executed to generate the master public key mpk' and the master private key msk' (step S1021). In this case, the generated master public key mpk' is used for encryption when distributing user private keys, and is distributed to each intermediate key issuing device 35 n Alternatively, it may be shared (made public) with the communication device 20.

[0047] The root secret key generation unit 1021-1 generates a root secret key using the master secret key. That is, the root secret key generation unit 1021-1 generates the root secret key sk[id (0) ]=(msk',msk') is generated (step S1021-1).

[0048] The first secret key generation unit 1022B, via the communication unit 101B, sends an ID, which is the identifier of the first (k=2) intermediate key issuing device 351 (or a communication device 20 capable of communicating with the multi-function communication gateway 10B), as a key issuance request. (1) If obtained, mpk=mpk' will be set to sk[id (0) ]=(sk'[0.id (0) ],sk'[1.id (0) ]) to parse (step S1022B-1).

[0049] The first secret key generation unit 1022B generates a first secret key using the master public key, the root secret key, and the first identifier of the first intermediate key issuing device obtained by the communication unit. That is, for each b ∈ {0, 1}, the first secret key generation unit 1022B generates sk'[b.id(1) ]←KG'(mpk',sk'[b.id (0) ],b.id (1) ) execute and the first private key sk[id (1) ]=(sk'[0.id (1) ],sk'[1.id (1) Generate ] (step S1022B-2).

[0050] The key distribution unit 1023 receives the first secret key sk[id] generated by the first secret key generation unit 1022B. (1) The ] is distributed (transmitted) to the first intermediate key issuing device 351 or to a communication device 20 that can communicate with the multi-function communication gateway 10B (step S1023).

[0051] The n+1th secret key generation unit 3521 of the first intermediate key issuing device 351, upon receiving an n+1 identifier as a key issuance request via the communication unit 351, generates the master public key mpk' and the first secret key sk[id] received in step S1023. (1) ]=(sk'[0.id (1) ],sk'[1.id (1) ] to mpk=mpk', sk[id (n) ]=(sk'[0.id (n) ],sk'[1.id (n) ]) is parsed (step S3521-1). For example, if n=1, the communication unit 351 of the first (k=2) intermediate key issuing device 351 receives the identifier id of n+1, which is the ID, from the second (k=3) intermediate key issuing device 352 or the communication device 20 that can communicate with the first intermediate key issuing device 351 as a key issuance request. (n+1) (If n=1, id (2) The (n+1) secret key generation unit 3521 obtains the identifier. If it obtains the (n+1) identifier, it performs the parsing process described above.

[0052] The (n+1)th private key generation unit 3521 generates the (n+1)th private key using the master public key, the nth private key, and the (n+1)th identifier. That is, for each b ∈ {0, 1}, the (n+1)th private key generation unit 3521 generates sk'[b.id (n+1) ]←KG'(mpk',sk'[b.id (n)],b.id (n+1) ) execute and the n+1th private key sk[id (n+1) ]=(sk'[0.id (n+1) ],sk'[1.id (n+1) The (step S3521-2) generates the (n+1) secret key generation unit 3521 of the first intermediate key issuing device 351 generates the second secret key.

[0053] The key distribution unit 3522 receives the (n+1)th secret key sk[id (n+1) The key is distributed to a lower intermediate key issuing device 35 (the (n+1)th intermediate key issuing device) or a communication device 20 (the communication device capable of communicating with the nth intermediate key issuing device) (step S3522). For example, if n=1, the key distribution unit 3522 of the first intermediate key issuing device 351 distributes the second (k=3) intermediate key issuing device 352 or a communication device 20 capable of communicating with the first intermediate key issuing device 351.

[0054] If an intermediate key issuing device 35, which is at a lower level, or a communication device 20 capable of communicating with it, is provided, the above steps (steps S3521-1, S3521-2, and S3522) are repeated.

[0055] By implementing the processing method described above, the communication device 20 can obtain a user secret key to be used when performing authenticated key exchange with other communication devices 20. In other words, by using the key issuance system 1B according to this embodiment, secure key issuance can be achieved in devices participating in the local network.

[0056] <Modified form of the second embodiment> A second embodiment of this disclosure may be configured as shown in Figure 8, as in the key issuance system 1C. In the key issuance system 1C, the key issuance station function that the multifunction communication gateway 10B had is provided as a key issuance device 30 with that function, which can communicate on the communication network N1. Accordingly, the multifunction communication gateway 10B is replaced by a communication gateway 10C that does not have an intermediate key issuance station function. Here, the intermediate key issuance device 35 corresponds to a lower layer of the key issuance device 30.

[0057] Furthermore, since it is sufficient for any of the devices communicating with the communication network N2 to have the intermediate key issuing station function, even in the case of the key issuing system 1C, the communication gateway 10C may also have the intermediate key issuing station function. In addition, in the key issuing system 1C, the intermediate key issuing device 35 provided in the key issuing system 1B shown in Figure 5 n As shown, the intermediate key issuing device 35 n It may be composed of multiple layers.

[0058] <Other variations of the second embodiment> The second embodiment described above may also have the configuration shown in Figure 9. The difference between the configuration shown in Figure 9 and the configuration shown in Figure 6 is that the multi-function communication gateway 10B has been replaced with a communication gateway 10C, and the intermediate key issuing device 35 n Intermediate key issuing device 35C n The point of change is this:

[0059] The multi-function communication gateway 10C now includes a new device authentication unit 1025 within the first security unit, and its name has been changed from the first security unit 102B to the first security unit 102C. Intermediate key issuing device 35C n Within the second security section, a device authentication section 3524 is provided, and its name has been changed from the second security section 352 to the second security section 352C.

[0060] A multi-functional communication gateway 10C equipped with a device authentication unit 1025, and an intermediate key issuing device 35C equipped with a device authentication unit 3524.n However, this modified processing method can be realized by performing the process shown in Figure 10. The differences between the processing method in Figure 10 and the processing method in Figure 7 are that steps S1025 and S3524 for device authentication processing are added, step S1022B-2 is changed to step S1022C, and step S3521-2 is changed to step S3521C.

[0061] In this modified example, the multi-function communication gateway 10C pre-stores a list of information on one or more terminals (devices) capable of issuing keys in the storage unit 1024, for example, as data in a table format. Intermediate key issuing device 35C n When an identifier is received from the intermediate key issuing device 35C, the identifier is sent along with the identifier. n Configure the system to also receive device information.

[0062] The device authentication unit 1025 receives a key issuance request from the intermediate key issuing device 35C. n The system performs an authentication check to see if the device information exists in the list of key-issuing terminals stored in the storage unit 1024. If there is a match, it determines "permission"; if there is no match, it determines "denial" (step S1025).

[0063] If the decision in step S1025 is "permission", the first secret key generation unit 1022B performs the first secret key generation process. At this time, a key is generated using a predetermined flag so that permission can be identified (step S1022C).

[0064] Similarly, the intermediate key issuing device 35C n The system stores a list of information on one or more terminals (devices) capable of issuing keys in the storage unit 3523 beforehand, for example, as data in a table format. When an identifier is received from the (n+1)th intermediate key issuing device, the system is configured to receive the device information of the (n+1)th intermediate key issuing device along with the identifier.

[0065] The device authentication unit 3524 performs an authentication check to determine whether the device information of the (n+1)th intermediate key issuing device that requested the key issuance exists in the list of key issuing terminals stored in the storage unit 3523. If there is a match, it determines "permission"; otherwise, it determines "denial" (step S3524).

[0066] If the determination in step S3524 is "permission", the (n+1)th secret key generation unit 3521 performs the process of generating the (n+1)th secret key. At this time, a key is generated using a predetermined flag so that it can be identified that permission has been granted (step S3521C).

[0067] Furthermore, the device authentication unit 3524 controls all intermediate key issuing devices 35C n It may also be configured to be implemented in this way. If device authentication is not required, the key issuance system may be configured using intermediate key issuance devices that do not have a device authentication unit 3524, or some or all of the intermediate key issuance devices.

[0068] [Programs, recording media] The various processes described above can be carried out by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in Figure 11, and then causing the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc. to operate.

[0069] The program describing this process can be recorded on a computer-readable recording medium. Any computer-readable recording medium can be used, such as a magnetic recording device, optical disc, magneto-optical recording medium, or semiconductor memory.

[0070] Furthermore, this program may be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs or CD-ROMs on which the program is recorded. Alternatively, the program may be stored in the storage device of a server computer and distributed by transferring the program from the server computer to other computers via a network.

[0071] A computer executing such a program may, for example, first store the program recorded on a portable storage medium or a program transferred from a server computer in its own storage device. Then, when processing is to be executed, the computer reads the program stored on its own storage medium and executes the processing according to the read program. Alternatively, the computer may directly read the program from the portable storage medium and execute the processing according to that program, or it may sequentially execute the processing according to the received program each time a program is transferred to it from a server computer. Furthermore, the above processing may be executed by a so-called ASP (Application Service Provider) type service, where the server computer does not transfer programs to this computer, but the processing function is realized only by execution instructions and result acquisition. In this form, the program includes information used for processing by an electronic computer that is equivalent to a program (data that is not a direct instruction to the computer but has the property of defining the processing of the computer, etc.).

[0072] Furthermore, in this configuration, the device is configured by executing a predetermined program on a computer, but at least a part of these processes may be implemented in hardware.

[0073] Although various forms of programs are conceivable, for example, in addition to a program for a device that can be controlled as an entire key issuance system, programs used by various devices shown in the present disclosure (for example, multifunctional communication gateways 1, 1B, intermediate key issuance device 35 n , communication device 20, key issuance device 30, and their modified examples), or programs that collectively execute the processing of two or more devices can be cited.

Claims

1. A key issuance system corresponding to a hierarchical ID-based cryptography scheme, comprising: a communication gateway equipped with a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line; at least one communication device capable of communicating using the second line; and an intermediate key issuance device consisting of k-1 (k is an integer of 2 or more) first devices, ..., (k-1) devices capable of communicating using the second line, The aforementioned communication gateway has a first security unit of the first secure environment, The aforementioned first security unit is, A master key generation unit that generates a master public key and a master private key, A root secret key generation unit that generates a root secret key using the master secret key, A first secret key generation unit generates a first secret key using the master public key, the root secret key, and the first identifier of the first device of the intermediate key issuing device acquired by the communication unit, The system includes a key distribution unit that transmits the first secret key to the first device of the intermediate key issuing device, The nth (n=1, 2, ..., k-1) intermediate key issuing device has a second security unit having a second secure environment, The aforementioned second security unit is, A secret key generation unit generates an (n+1) secret key using the master public key and the first secret key, and an (n+1) identifier obtained from either the (n+1)th device of the intermediate key issuing device or a communication device capable of communicating with the nth device of the intermediate key issuing device, A key distribution unit that transmits the n+1 secret key to the n+1th device of the intermediate key issuing device, or to the communication device capable of communicating with the nth device of the intermediate key issuing device, A key issuance system having the following features.

2. The first security unit further includes a device authentication unit, The key issuance system according to claim 1, wherein when the communication gateway receives device information along with a first identifier from the first device of the intermediate key issuance device, the device authentication unit causes the first secret key generation unit to generate a first secret key if the device information matches any of a plurality of device information stored in advance by the communication gateway.

3. A key issuance method using a key issuance system corresponding to a hierarchical ID-based cryptographic scheme, comprising: a communication gateway having a first security unit and a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line; at least one communication device capable of communicating using the second line; and an intermediate key issuance device comprising k-1 (k is an integer of 2 or more) first devices, ..., (k-1) devices capable of communicating using the second line, wherein the n (n=1, 2, ..., k-1) devices are intermediate key issuance devices having a second security unit; The aforementioned first security unit is, Select a master secret key, and use this master secret key to generate a master public key. A root secret key is generated using the aforementioned master secret key. A first secret key is generated using the master public key, the root secret key, and the first identifier of the first device of the intermediate key issuing device acquired by the communication unit. The first secret key is transmitted to the first device of the intermediate key issuing device, The aforementioned second security unit is, Using the master public key and the first private key, and the (n+1) identifier obtained from either the (n+1)th device of the intermediate key issuing device, or a communication device capable of communicating with the (n)th device of the intermediate key issuing device, the (n+1)th private key is generated. The (n+1) secret key is transmitted to the (n+1)th intermediate key issuing device, or to a communication device capable of communicating with the (n)th intermediate key issuing device. How to issue a key.

4. A program to be executed by a computer in a key issuance system corresponding to a hierarchical ID-based encryption scheme, The aforementioned key issuance system is: A communication gateway equipped with a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line, At least one communication device capable of communicating using the aforementioned second line, The system includes an intermediate key issuing device consisting of k-1 (where k is an integer of 2 or more) first devices, ..., and an (k-1)th device, all capable of communicating using the second line, In the first security section of the first secure environment of the aforementioned communication gateway, Generate a master public key and a master private key. Using the aforementioned master private key, generate a root private key. A first secret key is generated using the master public key, the root secret key, and the first identifier of the first device of the intermediate key issuing device acquired by the communication unit. The first secret key is transmitted to the first device of the intermediate key issuing device. program.

5. A program to be executed by a computer in a key issuance system corresponding to a hierarchical ID-based encryption scheme, The aforementioned key issuance system is: A communication gateway equipped with a communication unit capable of communicating via a first line and a second line using a narrower bandwidth than the first line, At least one communication device capable of communicating using the aforementioned second line, The system includes an intermediate key issuing device consisting of k-1 (where k is an integer of 2 or more) first devices, ..., and an (k-1)th device, all capable of communicating using the second line, The nth (n=1, 2, ..., k-1) device of the intermediate key issuing device has, in the second security section of the second secure environment, Using the master public key and the first private key obtained from the communication gateway, and the n+1 identifier obtained from either the (n+1)th device of the intermediate key issuing device, or a communication device capable of communicating with the nth device of the intermediate key issuing device, the (n+1)th private key is generated. The (n+1) secret key is transmitted to the (n+1)th device of the intermediate key issuing device, or to the communication device capable of communicating with the (n)th device of the intermediate key issuing device. program.

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