JP7119851B2 - Communication device, certificate revocation list creation method, and program - Google Patents

Description

The present invention relates to a technical field such as a system using a certificate revocation list indicating revoked electronic certificates.

In recent years, the number of IoT (Internet of Things) devices has increased, and it is said that more than 20 billion IoT devices will be connected to the Internet by around 2020. With the increase in the number of IoT devices, they are becoming more and more targeted for attacks, and cyber-attacks using IoT devices as springboards and the spread of viruses through IoT devices are becoming social problems. By the way, in order to protect a computer from attacks such as viruses, there is a mechanism using an electronic signature as a means of checking whether data has been falsified or spoofed. In this mechanism, the data sender uses its own private key to apply an electronic signature, and the data receiver uses the public key of the sender to verify the signature. Electronic certificates (digital certificates) are issued by certificate authorities to certify that such public keys are correct. An expiration date is set for the electronic certificate, but the electronic certificate may be revoked before the expiration date due to reasons such as a decrease in the reliability of the key. Such electronic certificates are managed by a Certificate Revocation List (CRL). In the system disclosed in Patent Document 1, an authentication server transmits a revocation list storing serial numbers of revoked electronic certificates to the information terminal device in response to a request from the information terminal device, and the information terminal device receives the revocation list. Based on the list, it is determined whether or not the electronic certificate has been revoked.

JP 2017-212517 A

By the way, when an IoT device receives data with an electronic signature from a communication partner, it acquires a certificate revocation list as one of the verification procedures to check the validity of the electronic certificate (in other words, the reliability of the electronic certificate decreases. (to check if the same key has been used). Therefore, it is desirable that the IoT device stores the certificate revocation list in its own memory. However, the amount of data in the certificate revocation list is large for inexpensive computers used in IoT devices, and it may not be possible to store the list as it is. On the other hand, there is also a method called OCSP (Online Certificate Status Protocol) as a method for confirming the validity of an electronic certificate on the server side. untargetable.

Therefore, the present invention has been made in view of the above points, and enables an IoT device to easily check the validity of the electronic certificate of the communication partner by using the certificate revocation list, thereby providing a secure IoT environment. It is an object of the present invention to provide a server device, a communication device, a method of creating a certificate revocation list, and a program that can realize the construction of the above.

According to the first aspect of the present invention, there is provided a communication device capable of accessing, via a network, a server device that stores a certificate revocation list describing information on each of a plurality of revoked electronic certificates, and which is another communication device. a receiving means for receiving a request for a certificate revocation list for the other communication device from, a list obtaining means for obtaining the certificate revocation list from the server device in response to the request received by the receiving means ; creating means for creating, based on the certificate revocation list obtained by the list obtaining means, the certificate revocation list for the other communication device having a smaller amount of data than the certificate revocation list; transmitting means for transmitting the created certificate revocation list to the other communication device; and after the certificate revocation list for the other communication device is transmitted to the other communication device, the list acquisition means and deletion means for deleting the acquired certificate revocation list.

The invention according to claim 2 is the communication device according to claim 1 , wherein the creation means selects the information of each of the plurality of electronic certificates in the certificate revocation list acquired by the list acquisition means. The certificate revocation list is created by deleting the information of the electronic certificate other than the electronic certificate specified from the communication partner information of the communication device.

The invention according to claim 3 is the communication device according to claim 1 , wherein the creating means deletes part of the information of each of the plurality of electronic certificates in the certificate revocation list acquired by the list acquiring means. to create the certificate revocation list.

The invention according to claim 4 is the communication device according to claim 1 , wherein the creation means selects the information of each of the plurality of electronic certificates in the certificate revocation list acquired by the list acquisition means. Deletion of electronic certificate information other than the electronic certificate specified from the communication partner information of another communication device, and part of the information of the electronic certificate specified from the communication partner information of the other communication device is deleted to create the certificate revocation list.

According to a fifth aspect of the present invention, there is provided a certificate revocation list executed by a communication device accessible via a network to a server device storing a certificate revocation list describing information of each of a plurality of revoked electronic certificates. A creation method comprising the steps of: receiving a request for a certificate revocation list for another communication device from another communication device; and obtaining the certificate revocation list from the server device in response to the received request. creating, based on the acquired certificate revocation list, the certificate revocation list for the other communication device having a smaller data volume than the certificate revocation list; and the created certificate sending a certificate revocation list to the other communication device; and deleting the obtained certificate revocation list after the certificate revocation list for the other communication device is sent to the other communication device. and .

According to the sixth aspect of the invention, a computer included in a communication device accessible via a network to a server device storing a certificate revocation list describing information of each of a plurality of revoked electronic certificates is Receiving means for receiving a request from a communication device for a certificate revocation list for the other communication device; and list obtaining means for obtaining the certificate revocation list from the server device in response to the request received by the receiving means. and creating means for creating , based on the certificate revocation list obtained by the list obtaining means, the certificate revocation list for the other communication device having a data amount smaller than that of the certificate revocation list; transmitting means for transmitting the certificate revocation list created by means to the other communication device; and acquiring the list after the certificate revocation list for the other communication device is transmitted to the other communication device. It is characterized by functioning as deletion means for deleting the certificate revocation list acquired by the means.

According to the present invention, an IoT device can easily check the validity of a communication partner's electronic certificate using a certificate revocation list, and a secure IoT environment can be constructed.

1 is a diagram showing a schematic configuration example of an IoT system according to an embodiment; FIG. (A) is a flowchart showing processing of the control unit 13 of the IoT device T1, and (B) is a flowchart showing processing of the control unit 3 of the authentication server SA. FIG. 4 is a conceptual diagram showing a method of creating a lightweight CRL; (A) is a flowchart showing processing of the control unit 13 of the IoT device T1, and (B) is a flowchart showing processing of the control unit 3 of the authentication server SA. (A) is a flowchart showing the processing of the control unit 13 of the IoT device T3, (B) is a flowchart showing the processing of the control unit 13 of the IoT device T2, and (C) is a control of the authentication server SA. 10 is a flowchart showing processing of part 3;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are embodiments in which the present invention is applied to an IoT system.

[1. Outline configuration of IoT system]
First, with reference to FIG. 1, a schematic configuration of an IoT system S according to this embodiment will be described. FIG. 1 is a diagram showing a schematic configuration example of an IoT system S according to this embodiment. As shown in FIG. 1, the IoT system S includes an authentication server SA, an application server SAm (m=1, 2, 3 . . . ), and IoT devices Tn (n=1, 2, 3 . composed of The authentication server SA and application server SAm are each connected to a network NW. The network NW is composed of, for example, the Internet, a mobile communication network, a gateway, and the like.

The authentication server SA (an example of the server device of the present invention) is a server operated by a certificate authority that issues electronic certificates and certificate revocation lists (hereinafter referred to as "CRL"). The authentication server SA includes a communication unit 1 for establishing communication with the outside, a storage unit 2 for storing various data and programs, a control unit 3, and the like. The storage unit 2 (an example of a storage unit in the present invention) is configured by a hard disk drive or the like, and includes an electronic certificate issued to each of the application server SAm and the IoT device Tn, and an electronic certificate issued by a certification authority. stores a CRL that indicates an electronic certificate that has been revoked before the expiration date. Here, the electronic certificate includes the serial number of the electronic certificate, the public key, the information of the owner of the private key corresponding to the public key (for example, the application server SAm and the IoT device Tn in which the private key is stored). identification name), signature method (signature algorithm), expiration date, and information about the certificate authority that issued the electronic certificate. Information (for example, the serial number of the electronic certificate) of each of a plurality of electronic certificates revoked before the expiration date is described in the CRL.

The control unit 3 (an example of a computer) is composed of a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like. Executes various types of processing such as certificate issuance processing and electronic certificate revocation processing. Revocation processing of an electronic certificate is performed when, for example, the owner of the electronic certificate leaks the private key and notifies the certificate authority. The CRL with the added information will be published. Further, the control unit 3 functions as receiving means, creating means, and transmitting means in the present invention, and receives a CRL (hereinafter referred to as a "lightweight (miniaturized) CRL") having a smaller data amount than the CRL (that is, the regular CRL). ) may be created and provided.

The application server SAm is a server that collects information acquired by the IoT device Tn or remotely controls the IoT device Tn. Each application server SAm has a key pair of its own public key and private key, its own electronic certificate (electronic certificate issued by a certificate authority), its own electronic certificate, and a CRL. etc., and it is possible to perform secure communication with any IoT device Tn. Note that the CRL is acquired from the authentication server SA via the network NW at a predetermined timing (for example, periodically by a timer or immediately before performing secure communication with the IoT device Tn).

The IoT device Tn (an example of the communication device of the present invention) includes a communication unit 11 for establishing communication (wired or wireless communication) with the outside, a storage unit 12 for storing various data and programs, and a control unit 13. etc. The IoT device Tn may be equipped with a sensor that detects surrounding conditions (for example, temperature, humidity, atmospheric pressure, illuminance, water level, noise, etc.). In the example of FIG. 1, the IoT device T1, the IoT device T2, and the IoT device T4 are each connectable to the network NW, but the IoT device T2 (an example of another communication device) is connected to the network NW. Cannot connect. Therefore, when the IoT device T2 communicates with the authentication server SA, the application server SAm, etc. connected to the network NW, the communication needs to be mediated by the IoT device T2 or the IoT device T4.

The storage unit 12 is composed of a non-volatile memory or the like, and stores a key pair of the public key and the private key of the IoT device Tn itself (that is, the storage unit 12 of the IoT device T1 stores the public key and the private key of the IoT device T1 itself. key pair), the electronic certificate of the IoT device Tn itself, the electronic certificate of the certificate authority, and the like. Further, the storage unit 12 stores a lightweight CRL having a data amount smaller than that of the regular CRL. Note that when the IoT device Tn is provided with a sensor, the storage unit 12 stores state information indicating the state detected by the sensor. Also, if the IoT device Tn includes an SE (secure element) that communicates with the control unit 13, the lightweight CRL may be stored in the SE.

The control unit 13 (an example of a computer) is composed of a CPU, a RAM, a ROM, etc., and performs secure communication with the application server SAm and other IoT devices Tn according to a program stored in the storage unit 12. It is possible to do In addition, the control unit 13 executes one or more of a lightweight CRL acquisition process, a lightweight CRL creation process, and a lightweight CRL creation and provision process. The lightweight CRL acquisition process is a process of acquiring and storing a lightweight CRL created by the authentication server SA or another IoT device Tn. The lightened CRL creation process is a process in which the control unit 13 functions as list acquisition means, creation means, and deletion means in the present invention, and creates and stores a lightened CRL. In the process of creating and providing a lightweight CRL, the control unit 13 functions as receiving means, list acquiring means, creating means, deleting means, and transmitting means in the present invention, and creates a lightweight CRL for other IoT devices Tn. It is a process that provides When receiving data with an electronic signature from a communication partner (application server SAm, other IoT device Tn, etc.), the control unit 13 first refers to the lightweight CRL and invalidates the electronic certificate of the communication partner. (that is, confirm the validity of the electronic certificate), and if the electronic certificate has not been revoked, verify the electronic signature using the public key of the communication partner It's like

[2. Operation when creating a lightweight CRL]
Next, the operation when creating a lightweight CRL will be described separately for the first to third embodiments.

(Example 1)
First, with reference to FIG. 2, etc., the operation of creating a lightweight CRL in the first embodiment will be described. FIG. 2A is a flow chart showing processing of the control unit 13 of the IoT device T1, and FIG. 2B is a flow chart showing processing of the control unit 3 of the authentication server SA.

The process (lightening CRL acquisition process) shown in FIG. immediately before doing). When the process shown in FIG. 2A is started, the control unit 13 of the IoT device T1 accesses the authentication server SA via the communication unit 11 and the network NW, and transmits a request for a lightweight CRL to the authentication server SA. (step S1). The request for a lightweight CRL contains information indicating that it is a lightweight CRL rather than a regular CRL.

When the authentication server SA receives the request for the lightweight CRL from the IoT device T1, it starts the process (process for creating and providing the lightweight CRL) shown in FIG. 2(B). When the process shown in FIG. 2A is started, the control unit 3 of the authentication server SA, based on the CRL (authorized CRL) stored in the storage unit 2, responds to the received request. A lightweight CRL having a data amount smaller than that of the CRL is created (step S11).

Here, a method for creating a lightweight CRL will be described with reference to FIG. FIG. 3 is a conceptual diagram showing a method of creating a lightweight CRL. The example of FIG. 3 shows three methods of creating a lightweight CRL (A) to (C). In the case of FIG. 3A, the control unit 3 of the authentication server SA acquires communication partner information of the IoT device T1 (for example, the identification name of the application server SA1 and the identification names of the IoT devices T2 and T4) from the IoT device T1. do. For example, the control unit 13 of the IoT device T1 may include the information of the communication partner in the request for the lightweight CRL and transmit the request to the authentication server SA. The control unit 3 of the authentication server SA selects the information (for example, the serial number of the electronic certificate) of each of the plurality of electronic certificates in the CRL stored in the storage unit 2, and selects the “IoT A lightweight CRL is created by deleting the electronic certificate information other than the electronic certificate specified from the communication partner information of the device T1. In other words, the lightweight CRL is created by removing the electronic certificate information of devices that do not communicate with the IoT device T1 from the normal CRL. Information about the communication partner of the IoT device T1 is stored in the storage unit 12 in advance. Further, the communication partner information of the IoT device T1 may be stored in advance in the authentication server SA.

On the other hand, in the case of FIG. 3B, the control unit 3 of the authentication server SA creates a lightweight CRL by deleting part of the information of each of the plurality of electronic certificates in the CRL stored in the storage unit 2. . Here, the part of the information of the electronic certificate may be, for example, a predetermined low-order byte of the serial number, a predetermined high-order byte of the serial number, or other bytes. good too. In other words, a limited range (for example, several bytes to several tens of bytes) in the byte string that constitutes the serial number is sufficient. On the other hand, in the case of FIG. 3(C) (the combination of FIGS. 3(A) and 3(B)), the control unit 3 of the authentication server SA stores a plurality of electronic Among the information of each certificate, delete the information of the electronic certificate other than the electronic certificate specified from the "communication partner information of the IoT device T1" included in the request for the lightweight CRL, and include it in the request. A lightened CRL is created by deleting part of the information of the electronic certificate specified from the "communication partner information of the IoT device T1".

Then, the control unit 3 of the authentication server SA transmits the lightweight CRL created in step S11 to the IoT device T1 that transmitted the request (step S12). When the control unit 13 of the IoT device T1 receives the lightweight CRL from the authentication server SA (step S2), it stores (saves) the received lightweight CRL in the storage unit 12 (step S3). In this way, when the control unit 13 of the IoT device T1 that stores the lightweight CRL receives data with an electronic signature from its own communication partner, it refers to the lightweight CRL to determine whether the electronic certificate of the communication partner has been revoked. It will be checked to see if it is not.

Here, when using the lightweight CRL shown in FIG. 3A, the control unit 13 of the IoT device T1, for example, receives the serial number of the electronic certificate described in the lightweight CRL and the data with the electronic signature. Determine whether or not the serial number of the transmitted communication partner's electronic certificate (which is acquired from the communication partner) matches If there is, match each serial number of the electronic certificate). Then, when the control unit 13 of the IoT device T1 determines that the serial number of any electronic certificate described in the lightweight CRL matches the serial number of the electronic certificate of the communication partner, It is determined that the electronic certificate of the communication partner has been revoked.

On the other hand, when using the lightweight CRL shown in FIGS. 3B and 3C, the control unit 13 of the IoT device T1, for example, controls the lower predetermined bytes of the serial number of the electronic certificate described in the lightweight CRL, Determining whether the lower predetermined bytes of the serial number of the electronic certificate of the communication partner to which the data with the electronic signature was sent If it is written, it is determined whether it matches for each lower predetermined byte. Then, the control unit 13 of the IoT device T1 makes sure that the predetermined low-order bytes of the serial number of any electronic certificate described in the lightweight CRL match the predetermined low-order bytes of the serial number of the electronic certificate of the communication partner. If it is determined that they match, a regular CRL is acquired from the authentication server SA, and the serial number of the electronic certificate described in the CRL and the serial number of the electronic certificate of the communication partner match. If determined, it is determined that the electronic certificate of the communication partner has been revoked. As another example, the control unit 13 of the IoT device T1 can transfer the predetermined low-order bytes of the serial number of any electronic certificate described in the lightweight CRL and the predetermined low-order bytes of the serial number of the electronic certificate of the communication partner. are matched, the serial number of the electronic certificate of the communication partner is transmitted to the OCSP server, thereby causing the OCSP server to check the validity of the electronic certificate of the communication partner. Then, the control unit 13 of the IoT device T1 checks whether or not the electronic certificate of the communication partner has expired by receiving the validity check result from the OCSP server.

As described above, according to the first embodiment, the IoT device T1 can easily check the validity of the electronic certificate of the communication partner by using the lightweight CRL. (For example, the possibility that the IoT device is hacked and the server or the like is attacked by the IoT device) is reduced, and a secure IoT environment can be constructed. In addition, according to the first embodiment, the weighted CRL created from the authorized CRL is sent instead of the authorized CRL from the authentication server SA to the IoT device T1. It is possible to reduce the amount of data transmitted (that is, reduce traffic).

(Example 2)
Next, with reference to FIG. 4, etc., the operation of creating a lightweight CRL in the second embodiment will be described. FIG. 4A is a flow chart showing processing of the control unit 13 of the IoT device T1, and FIG. 4B is a flow chart showing processing of the control unit 3 of the authentication server SA.

The process shown in FIG. 4A (lightweight CRL creation process) is performed at a predetermined timing (for example, periodically by a timer, or by performing secure communication with the application server SAm or another IoT device Tn). immediately before doing). When the process shown in FIG. 4A is started, the control unit 13 of the IoT device T1 accesses the authentication server SA via the communication unit 11 and the network NW, and transmits a request for a valid CRL to the authentication server SA. (step S21).

When the authentication server SA receives the request for the authorized CRL from the IoT device T1, it starts the process shown in FIG. 4(B). When the process shown in FIG. 4B is started, the control unit 3 of the authentication server SA acquires the CRL (authorized CRL) stored in the storage unit 2 according to the received request (step S31), the acquired CRL is transmitted to the IoT device T1 that transmitted the request (step S32). Here, the authentication server SA may send the CRL all at once or in segments according to the amount of data in the CRL.

When the control unit 13 of the IoT device T1 receives the CRL transmitted collectively or in segments from the authentication server SA (step S22), it stores the received CRL in the buffer memory and creates a lightweight CRL (step S23). ). Creation of a lightweight CRL is executed as shown in FIG. 3, as in the first embodiment. That is, in the case of FIG. 3A, the control unit 13 of the IoT device T1 acquires the communication partner information stored in advance in the storage unit 12, A lightweight CRL is created by deleting, from among the information of each certificate, the information of the electronic certificate other than the electronic certificate specified from the information of the communication partner of the IoT device T1.

On the other hand, in the case of FIG. 3B, the control unit 13 of the IoT device T1 creates a lightweight CRL by deleting part of the information of each of the plurality of electronic certificates in the CRL stored in the buffer memory. On the other hand, in the case of FIG. 3C, the control unit 13 of the IoT device T1 identifies from the information of the communication partner of the IoT device T1 among the information of each of the plurality of electronic certificates in the CRL stored in the buffer memory. A lightweight CRL is created by deleting the information of the electronic certificate other than the electronic certificate that is the electronic certificate that is used and part of the information of the electronic certificate that is specified from the information of the communication partner of the IoT device T1.

Then, the control unit 13 of the IoT device T1 stores (saves) the lightweight CRL created in step S23 in the storage unit 12 (step S24), and deletes the CRL (regular CRL) stored in the buffer memory. (step S25). In this way, when the control unit 13 of the IoT device T1 that stores the lightweight CRL receives data with an electronic signature from its own communication partner, it refers to the lightweight CRL to determine whether the electronic certificate of the communication partner has been revoked. It will be checked to see if it is not.

As described above, according to the second embodiment, the IoT device T1 can easily check the validity of the electronic certificate of the communication partner by using the lightweight CRL. It reduces the possibility of being lost, and can realize the construction of a secure IoT environment. In addition, according to the second embodiment, since the authorized CRL is transmitted from the authentication server SA to the IoT device T1 and the lightweight CRL is created by the IoT device T1, the creation load of the authentication server SA can be reduced. .

(Example 3)
Next, with reference to FIG. 5, etc., the operation of creating a lightweight CRL in the third embodiment will be described. FIG. 5A is a flowchart showing processing of the control unit 13 of the IoT device T3, FIG. 5B is a flowchart showing processing of the control unit 13 of the IoT device T2, and FIG. 3 is a flow chart showing processing of the control unit 3 of the authentication server SA. Note that, in the third embodiment, the IoT device T2 has a function of creating a lightweight CRL for the IoT device T3 (an example of another communication device) that cannot be connected to the network NW (and therefore cannot directly access the authentication server SA). .

The process shown in FIG. 5A (lightweight CRL acquisition process) is performed at a predetermined timing (for example, periodically by a timer, or immediately before performing secure communication with another IoT device Tn). be started. When the process shown in FIG. 5A is started, the control unit 13 of the IoT device T3 transmits a request for the weight reduction CRL to the IoT device T2 via the communication unit 11 (step S41).

When the IoT device T2 receives the request for the lightweight CRL from the IoT device T3, the IoT device T2 starts the process (process for creating and providing the lightweight CRL) shown in FIG. 5(B). When the process shown in FIG. 5B is started, the control unit 13 of the IoT device T2 accesses the authentication server SA via the communication unit 11 and the network NW in response to the received request, and to the authentication server SA (step S51).

When the authentication server SA receives the request for the authorized CRL from the IoT device T2, it starts the processing shown in FIG. 5(C). When the process shown in FIG. 5C is started, the control unit 3 of the authentication server SA acquires the CRL (authorized CRL) stored in the storage unit 2 according to the received request (step S61), the acquired CRL is transmitted to the IoT device T2 that transmitted the request (step S62). Here, the authentication server SA may send the CRL all at once or in segments according to the amount of data in the CRL.

When the control unit 13 of the IoT device T2 receives the CRL transmitted collectively or in segments from the authentication server SA (step S52), it stores the received CRL in the buffer memory and creates a lightweight CRL (step S53). ). Creation of a lightweight CRL is executed as shown in FIG. 3, as in the second embodiment.

Then, the control unit 13 of the IoT device T2 attaches its own electronic signature to the lightweight CRL created in step S53, and transmits the lightweight CRL to the IoT device T3 that transmitted the request (step S54). , the CRL (regular CRL) stored in the buffer memory is deleted (step S55).

When the control unit 13 of the IoT device T3 receives the weighted CRL from the IoT device T2 (step S42), the electronic signature attached to the weighted CRL is verified using the public key of the IoT device T2. If the verification is successful, the received lightweight CRL is stored (saved) in the storage unit 12 (step S43). In this way, when the control unit 13 of the IoT device T3 that has stored the lightweight CRL receives data with an electronic signature from its own communication partner, it refers to the lightweight CRL to determine whether the electronic certificate of the communication partner has been revoked. It will be checked to see if it is not.

As described above, according to the third embodiment, even the IoT device T3, which cannot directly access the authentication server SA, can easily acquire the lightweight CRL from the IoT device T2, and the electronic certification of the communication partner can be obtained by the lightweight CRL. This makes it possible to easily confirm the validity of the document, thereby reducing the possibility that the IoT device T3 will be used as a stepping stone and realizing the construction of a secure IoT environment. In addition, according to the third embodiment, since the authentic CRL is transmitted from the authentication server SA to the IoT device T2 and the lightweight CRL is created by the IoT device T2, the creation load of the authentication server SA can be reduced. . Also in the third embodiment, as in the first embodiment, the authentication server SA may create a lightweight CRL and transmit it to the IoT device T2.

In the embodiments described above, the present invention is applied to the IoT system, but it is also applicable to communication systems other than the IoT system.

1 communication unit 2 storage unit 3 control unit 11 communication unit 12 storage unit 13 control unit SA authentication server SAm application server Tn IoT device

Claims (6)

A communication device accessible via a network to a server device storing a certificate revocation list describing information about each of a plurality of revoked electronic certificates,
receiving means for receiving a request for a certificate revocation list for another communication device from another communication device;
list obtaining means for obtaining the certificate revocation list from the server device in response to the request received by the receiving means ;
creation means for creating, based on the certificate revocation list acquired by the list acquisition means, the certificate revocation list for the other communication device, the data amount of which is smaller than that of the certificate revocation list;
a transmitting means for transmitting the certificate revocation list created by the creating means to the other communication device;
a deletion means for deleting the certificate revocation list acquired by the list acquisition means after the certificate revocation list for the other communication device is transmitted to the other communication device;
A communication device comprising: The creation means obtains, among the information of each of the plurality of electronic certificates in the certificate revocation list obtained by the list obtaining means, an electronic certificate other than the electronic certificate specified from the communication partner information of the other communication device. 2. The communication device according to claim 1 , wherein the certificate revocation list is created by deleting certificate information. 2. The creating means creates the certificate revocation list by deleting part of the information of each of the plurality of electronic certificates in the certificate revocation list acquired by the list acquiring means. The communication device according to . The creation means obtains, among the information of each of the plurality of electronic certificates in the certificate revocation list obtained by the list obtaining means, an electronic certificate other than the electronic certificate specified from the communication partner information of the other communication device. A claim characterized in that the certificate revocation list is created by deleting certificate information and deleting part of the electronic certificate information specified from information of the communication partner of the other communication device. Item 1. The communication device according to item 1. A certificate revocation list creation method executed by a communication device accessible via a network to a server device storing a certificate revocation list describing information of each of a plurality of revoked electronic certificates,
receiving a request from another communication device for a certificate revocation list for that other communication device;
obtaining the certificate revocation list from the server device in response to the received request ;
creating, based on the obtained certificate revocation list, the certificate revocation list for the other communication device having a smaller amount of data than the certificate revocation list;
transmitting the created certificate revocation list to the other communication device;
deleting the obtained certificate revocation list after the certificate revocation list for the other communication device has been sent to the other communication device;
A method for creating a certificate revocation list, comprising: a computer included in a communication device that is accessible via a network to a server device that stores a certificate revocation list that describes information on each of a plurality of revoked electronic certificates;
receiving means for receiving a request for a certificate revocation list for another communication device from another communication device;
list obtaining means for obtaining the certificate revocation list from the server device in response to the request received by the receiving means ;
creation means for creating, based on the certificate revocation list acquired by the list acquisition means, the certificate revocation list for the other communication device, the data amount of which is smaller than that of the certificate revocation list;
a transmitting means for transmitting the certificate revocation list created by the creating means to the other communication device;
A program that functions as deletion means for deleting the certificate revocation list acquired by the list acquisition means after the certificate revocation list for the other communication device is transmitted to the other communication device. .

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