JP4740649B2 - Public key certificate issuing device, public key certificate issuing system, public key certificate issuing program, and public key certificate issuing method - Google Patents

Description

The present invention relates to a public key certificate issuing device, a public key certificate issuing system, a public key certificate issuing program, and a public key certificate for issuing a public key certificate that proves that the public key belongs to the client about the issue how.

  Content obtained by digitizing music, images, movies, etc. will not deteriorate even after repeated copying and transmission. For this reason, distribution and exchange tend to be performed beyond the permitted scope of the right holder. Therefore, it has been considered to encrypt the content in order to limit the distribution and reproduction of the content.

  One method for encrypting content is a secret key cryptosystem that encrypts and decrypts content data with the same key (secret key), that is, a symmetric key cryptosystem. However, since it is necessary to transport the key by a secure route, it is difficult to manage the key, and there is a problem inferior in security.

  In order to deal with the problem, a public key cryptosystem, that is, an asymmetric key cryptosystem has been considered. In the public key cryptosystem, data is encrypted and decrypted using two pairs of keys. One key is a public key that is widely disclosed to others, and the other key is a secret key that is strictly managed by a legitimate right holder. Data encrypted with the private key can be decrypted only with the corresponding public key, and data encrypted with the public key can be decrypted only with the corresponding private key. Therefore, the public key cryptosystem has an advantage that the management of the key is easy and the security is high because it is not necessary to transport the public key through a secure route as compared with the secret key cryptosystem.

  In this public key cryptosystem, data encryption needs to be performed using a public key paired with a private key possessed by a legitimate recipient. In other words, the sender who wants to send encrypted data needs to verify whether the public key used for encryption is legitimate, is not someone else, and has not been tampered with. There is. A public key certificate is used to prove the authenticity of such a recipient, that is, a public key user. The public key certificate is obtained by digitally signing a public key by a certificate authority (CA), which is an issuer or issuing device that is a third party who can guarantee validity.

  Conventionally, when a host sends a message requesting an anonymous public key certificate digitally signed using a private key, the router authenticates the host using the host's public key, and then sends the message to a CA (Certification Authority; public key). A public key certificate issuance method is known in which the CA confirms the validity of the authentication signature and issues a public key certificate including the digital signature of the CA (for example, patent document). 1).

  In addition, after sharing the same common secret information (CSI) in the AD (Authorized Domain) and authenticating the distribution request source (reproducing device, recording medium) using this common secret information The content key is distributed to the distribution request source and the number of content keys that can be distributed is decremented by 1. When distributing the content key to the playback device, the key information not including the expiration date is distributed, and the recording medium A content server that distributes key information including an expiration date when distributing a content key to the Internet is known (see, for example, Patent Document 2).

JP 2004-32699 A (paragraphs 0090-0102, FIG. 1) Japanese Patent Laying-Open No. 2004-112788 (paragraph 0104-0105, FIG. 16)

  However, in the conventional public key certificate issuance method, this CA examines a certificate authority in the sense of an institution that issues public key certificates and a user (host) of the public key certificate, and makes the identity thereof unique. It plays both roles as a responsible registration authority. For this reason, this CA, as a registration authority, verifies that the applicant (host) of the public key certificate is the same as the person specified in the application form (request message) and that the private key corresponding to the applicant is legitimate. It is necessary to check whether the authentication conditions such as possession are satisfied. Furthermore, when this public key certificate issuance method is implemented, for example, in a home or school, an administrator who operates a registration authority (CA) needs to be arranged in each home or campus. Therefore, there is a problem that the configuration on the issuer (CA) side of the public key certificate is complicated, the management cost is high, and the operation is complicated.

  Further, in the conventional content server, since the same common secret information (CSI) is shared in AD (Authorized Domain), this content is used to register a new device in AD. The server needs to have the same function as a conventional certificate authority. For this reason, the registration operation of the device is complicated, the configuration of both the content server and the device is complicated, and there is a problem that the management cost is increased.

The present invention has been made in view of the above problems, and eliminates the need for installing a certificate authority or an administrator, which was conventionally required for issuing public key certificates, and reduces the management expenses. public key certificate issuing apparatus that strive to reduce can be simplified operation, public key certificate issuing system, and to provide the public key certificate issuing program and a public key certificate issuing process.

The present invention has been developed to achieve the above object, and first, the public key issuing device according to claim 1 issues a public key certificate for proving that the public key belongs to the client. A public key certificate issuing device, a public key certificate generating means, an integrated issue number storage means, an integrated issue number update means, an issue number upper limit value storage means, an issue number determination means, and a public key certificate It is configured to include a writing invalidation means and a cumulative issuance number subtraction means .

  According to this configuration, the public key certificate issuing device generates a public key certificate and issues it to the client in response to a public key certificate issuing request from the client by the public key certificate generating unit. In other words, when receiving a public key certificate issuance request from a client, the public key certificate generating means issues a public key certificate to the client under the conditions described later.

  Further, the public key certificate issuing device stores the cumulative number of issued public key certificates issued by the public key certificate generating means by means of the cumulative issued number storage means. Further, the cumulative issue number is updated according to the public key certificate issued number issued by the cumulative issue number update means. Thus, the cumulative issue number stored in the cumulative issue number storage means is updated according to the number of issued public key certificates. For this reason, the cumulative issue number accurately indicates the number of public key certificates issued by the public key certificate issuing device so far.

  The public key certificate issuing device stores the issued key upper limit value of the public key certificate by the issued number upper limit storage unit. This issuance number upper limit value indicates the maximum value of the number of public key certificates permitted to be issued by the public key certificate issuing device.

  In the public key certificate issuing device, the issued number determination means refers to the accumulated issued number stored in the accumulated issued number storage means and the issued number upper limit value stored in the issued number upper limit storage means. Then, it is determined whether or not the cumulative issue number has reached the issue number upper limit value. The fact that the total number of issued certificates has reached the maximum number of issued cards means that the number of issued public key certificates has reached the allowable upper limit. This means that a key certificate must not be issued. On the other hand, the fact that the cumulative issue number has not reached the issue number upper limit value means that the number of issued public key certificates has not reached the allowable upper limit. It means that further public key certificates may be issued.

  Furthermore, the public key certificate issuing device does not issue the public key certificate by the public key certificate generating means when the cumulative number of issued has reached the upper limit of issued numbers based on the determination result of the issued number determining means. Therefore, when the number of issued public key certificates reaches an allowable upper limit, the public key certificate issuing device does not issue further public key certificates by the public key certificate generating unit. On the other hand, when the total number of issued certificates has not reached the maximum number of issues, that is, when the number of issued public key certificates has not reached the upper limit allowed, the public key certificate issuing device When the certificate issuance request is received, a further public key certificate is issued by the public key certificate generating means. In this way, the public key certificate issuing device issues public key certificates up to an allowable upper limit, but does not issue public key certificates exceeding this limit.

Further, the public key certificate issuing device invalidates the public key certificate in response to the public key certificate invalidation request from the client by the public key invalidating means, and discloses the public key certificate issuing means by the cumulative issue number subtracting means. The cumulative issue number stored in the cumulative issue number storage means is decreased according to the number of public key certificates revoked by the key certificate invalidation means. In this way, the cumulative issue number stored in the cumulative issue number storage means is subtracted and updated according to the number of invalid public key certificates. Therefore, not only when the public key certificate is issued, but also when the public key certificate is invalidated, the accumulated issue number stored in the accumulated issue number storage means is the public key certificate that is issued and valid. Indicates the number of

Further, the public key certificate issuing device according to claim 2 is the same as the public key certificate issuing device according to claim 2, but includes a revocation list generating unit.

  According to this configuration, the public key certificate issuing device generates a revocation list including information indicating the revoked public key certificate by the revocation list generation unit and distributes the revocation list to the client. Specifically, the revocation list is obtained by signing data indicating a revoked public key certificate with the private key of the public key certificate issuing device itself. By distributing this revocation list to the client, the client can know an invalid public key certificate.

Further, the public key certificate issuing device according to claim 3 is the public key certificate issuing device according to any one of claims 1 to 3, wherein issuance number setting information receiving means, issuance number upper limit value rewriting Means.

  According to such a configuration, the public key certificate issuing device receives the issue number setting information indicating the new maximum number of issues of the public key certificate issued by the public key certificate issuing device by the issue number setting information receiving unit, and issues The number upper limit value rewriting unit rewrites the issued number upper limit value stored in the issued number upper limit storage unit based on the received number setting information. For this reason, when it is desired to rewrite the upper limit value of the number of issues stored in the public key certificate issuing device to another value, the issue number setting information indicating the new upper limit number of public key certificates issued to the public key certificate issuing device , The public key certificate issuing device receives the issued number setting information by the issued number setting information receiving means, and the issued number upper limit value rewriting means, based on the issued number setting information, Will be rewritten to another new value.

The public key certificate issuing system according to claim 4 includes a public key certificate issuing device that issues a public key certificate that certifies that the public key belongs to a client, and a public key certificate issuing device. A public key certificate issuance system including a client whose public key is proved by the public key certificate to be issued. The client includes a public key certificate issuance request unit, a public key certificate A public key certificate issuing device, an integrated issue number storage unit, an integrated issue number update unit, an issue number upper limit value storage unit, and an issue number determination. Means, public key certificate revocation means, and total issued number subtraction means .

  According to this configuration, the client of the public key certificate issuing system makes a public key certificate issuing request to the public key certificate issuing device by using the public key certificate issuing request unit, and the public key certificate storing unit To receive and store the issued public key certificate. In this way, the client obtains the public key certificate from the public key certificate issuing device.

  The public key certificate issuing device of the public key certificate issuing system generates a public key certificate in response to a public key certificate issuance request from the client by the public key certificate generating means and issues the public key certificate to the client. . In other words, when receiving a public key certificate issuance request from a client, the public key certificate generating means issues a public key certificate to the client under the conditions described later.

  In addition, the public key certificate issuing device of the public key certificate issuing system stores the cumulative number of issued public key certificates issued by the public key certificate generating means by means of the cumulative issued number storage means. Further, the cumulative issue number is updated according to the issued public key certificate issue number by the cumulative issue number update means of the public key certificate issuing device. Thus, the cumulative issue number stored in the cumulative issue number storage means is updated according to the number of issued public key certificates. For this reason, the cumulative issue number accurately indicates the number of public key certificates issued by the public key certificate issuing device so far.

  In addition, the public key certificate issuing device of the public key certificate issuing system stores the issued key upper limit value for the public key certificate by the issued number upper limit value storage unit. This issuance number upper limit value indicates the maximum value of the number of public key certificates permitted to be issued by the public key certificate issuing device.

  Further, the public key certificate issuing system of the public key certificate issuing system uses the issued number determining means to store the accumulated issued number stored in the accumulated issued number storage means and the issued number upper limit value stored in the issued number upper limit storage means. Refer to Then, it is determined whether or not the cumulative issue number has reached the issue number upper limit value.

The public key certificate issuing device of the public key certificate issuing system invalidates the public key certificate in response to the public key certificate invalidation request from the client by the public key invalidating means and The issued number subtracting means decreases the accumulated issued number stored in the accumulated issued number storage means in accordance with the number of public key certificates revoked by the public key certificate revoking means. In this way, the cumulative issue number stored in the cumulative issue number storage means is subtracted and updated according to the number of invalid public key certificates. Therefore, not only when the public key certificate is issued, but also when the public key certificate is invalidated, the accumulated issue number stored in the accumulated issue number storage means is the public key certificate that is issued and valid. Indicates the number of

  Further, in the public key certificate issuing device of the public key certificate issuing system, the total number of issued certificates has reached the upper limit of issued numbers, that is, the number of issued public key certificates has reached an allowable upper limit. In some cases, no further public key certificate is issued by the public key certificate generating means. On the other hand, when the total number of issued certificates has not reached the maximum number of issues, that is, when the number of issued public key certificates has not reached the upper limit allowed, the public key certificate issuing device When the certificate issuance request is received, a further public key certificate is issued by the public key certificate generating means. In this way, the public key certificate issuing system issues public key certificates up to an allowable upper limit, but does not issue public key certificates exceeding this limit.

The public key certificate issuing program according to claim 5 stores an upper limit value of the number of issued public key certificates in order to issue a public key certificate that certifies that the public key belongs to the client. The issued number upper limit value storage means and the accumulated issue number storage means for storing the accumulated issuance number of the public key certificate are referred to, so that the computer issues an accumulated issue number update means, an issue number determination means, and a public key certificate. It functions as a generating means, a public key certificate revoking means, and an integrated issuance number subtracting means .

According to this configuration, in the public key certificate issuance program, the cumulative issuance number is updated according to the issuance number of the public key certificate by the cumulative issuance number updating unit.
Further, the public key certificate issuing program determines whether or not the cumulative number of issued has reached the issued number upper limit value by the issued number determining means.

Further, the public key certificate issuance program invalidates the public key certificate in response to the public key certificate invalidation request from the client by the public key invalidation means, and discloses the public key certificate issuance by the cumulative issue number subtraction means. The cumulative issue number stored in the cumulative issue number storage means is decreased according to the number of public key certificates revoked by the key certificate invalidation means. Then, the public key certificate issuing program does not issue the public key certificate when the cumulative issue number reaches the issue number upper limit value based on the determination result of the issue number determination unit by the public key certificate generation unit.

The public key certificate issuing method according to claim 6 is a public key certificate issuing method in a public key certificate issuing apparatus that issues a public key certificate that certifies that the public key belongs to the client. The public key certificate issuing device stores the upper limit value of the number of public key certificates issued and the cumulative number of issued public key certificates issued by the public key certificate issuing device. A step of issuing a public key certificate, and a step of issuing a public key certificate when an invalidation request for the public key certificate is received from the client. an issuing number subtraction step, the characterized by containing Mukoto.

  According to this procedure, in the public key certificate issuance method, the accumulated issue number is updated according to the issued number of issued public key certificates by the accumulated issue number update step. In this way, the cumulative issue number stored in the public key certificate issuing device is updated according to the number of issued public key certificates. For this reason, the cumulative issue number accurately indicates the number of public key certificates issued by the public key certificate issuing device so far.

  In the public key certificate issuance method, the issued number determination step refers to the accumulated issue number and the issued number upper limit value stored in the public key certificate issuing device. Then, it is determined whether or not the cumulative issue number has reached the issue number upper limit value.

  In the public key certificate issuance method, the public key certificate issuance step responds to a public key certificate issuance request from the client when the cumulative issuance number has not reached the issuance upper limit value based on the issuance number determination step. A public key certificate is generated and issued to the client, and the public key certificate is not issued when the cumulative issue number reaches the issue upper limit value based on the issue number determination step.

Further, when the public key certificate revocation request is received from the client, the public key certificate is revoked in response to the public key certificate revocation request from the client. Invalidate the certificate. Then, according to the number of the public key certificates revoked in the public key certificate revocation step, the accumulated issuance number stored in the accumulated issuance number subtraction step is decreased.

According to the invention described in claim 1, claim 4 , claim 5, or claim 6 , it is determined whether or not the cumulative issue number has reached the issue number upper limit value. Based on the determination result, the public key certificate is not issued when the cumulative issue number reaches the issue number upper limit value. In other words, when the number of issued public key certificates has reached the allowable limit, no further public key certificates are issued, but the number of issued public key certificates has reached the allowable limit. If not, upon receiving a public key certificate issuance request from the client, a further public key certificate is issued. With such a configuration, it is possible to reduce the management cost and simplify the operation by eliminating the need for setting up a registration authority and the arrangement of an administrator, which were conventionally necessary for issuing a public key certificate. .

Further , according to the present invention, the stored cumulative issuance number is subtracted and updated according to the number of public key certificates that have become invalid. Accordingly, not only when the public key certificate is issued, but also when the public key certificate is invalidated, the accumulated issue number stored in the accumulated issue number storage means is issued and valid. Can be matched with the number of

According to the second aspect of the present invention, the revocation list including information indicating the revoked public key certificate is generated and distributed to the client, so that the client can know the invalid public key certificate. it can.

According to the third aspect of the present invention, when the issuance number upper limit value stored in the public key certificate issuing apparatus is to be rewritten to another value, a new issuance upper limit of the public key certificate is issued to the public key certificate issuing apparatus. If the issued number setting information indicating the number is transmitted, the public key certificate issuing device receives the issued number setting information, and rewrites the issued number upper limit value to another new value based on the issued number setting information. . For this reason, it is possible to rewrite the number of public key certificates (issue number upper limit value) that is permitted to be issued by the public key certificate to a desired value .

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
First, an outline of the configuration and operation of the public key certificate issuing system 1 according to the present invention will be described.
FIG. 1 is a block diagram showing a configuration example of a public key certificate issuing system 1 according to the present invention.

  The public key certificate issuing system 1 is constructed using a closed network having a relatively small number of nodes, for example, a network laid in a home or school, and issues a public key certificate in this network. And includes a public key certificate issuing device 10, clients 20a, 20c, and 20d connected to the public key certificate issuing device 10, and a client 20b cascaded to the client 20a. Any of the clients 20a to 20d may be reduced, or a client having the same configuration as that of the clients 20a to 20d may be further added to the public key certificate issuing device 10 directly or by cascade connection.

  The public key certificate issuing device 10 is for issuing a public key certificate to the clients 20a to 20d, and replaces a conventional certificate authority (CA). As will be described later, the public key certificate issuing device 10 is set with an upper limit value for the number of public key certificates issued, and the number of public key certificates valid in the public key certificate issuing system 1 is as follows. Controlled below the maximum number of issues. The public key certificate issuing device 10 is further connected to the management device 4 through the external network 2 so as to be communicable.

  The management device 4 sends the issuance number setting information from outside the public key certificate issuing system 1 to the public key certificate issuing device 10 via the external network 2, and issuance set in the public key certificate issuing device 10 It has a function of rewriting the number upper limit value.

  The public key certificate issuing device 10 manages the cumulative number of public key certificates issued, that is, the number of valid public key certificates issued within the public key certificate issuing system 1. The public key certificate issuing device 10 issues a public key certificate in response to a request from the clients 20a to 20d when the cumulative issue number has not reached the issue number upper limit value, and this cumulative issue number is the issue number upper limit value. If it has reached, it will be rejected. In this way, the number of valid public key certificates issued in the public key certificate issuing system 1 is controlled to be equal to or less than the upper limit of the number of issues.

  As described above, in the public key certificate issuing system 1, complicated authentication procedures are not imposed on the clients 20a to 20d connected directly or indirectly to the public key certificate issuing device 10. A public key certificate is issued. For this reason, the complicated procedure which the conventional certificate authority has performed every time the public key certificate is issued becomes unnecessary, and the configuration can be simplified and the management cost can be reduced. In addition, in the public key certificate issuing system 1, it is easy to add or withdraw clients (20a to 20d), and the public key certificate can be issued flexibly within the range of the maximum number of issue. It is suitable for giving a plurality of licenses for content use without specifying the clients 20a to 20d for each range such as in a classroom.

  The clients 20a to 20d are devices for decrypting and using the encrypted content, and have a configuration to be described later, specifically, a television receiver having a communication function and the like. The clients 20 a to 20 d have a function of receiving content from the content supply device 5 via the external network 3. Furthermore, the clients 20a to 20d have a function of receiving content encrypted and distributed wirelessly from the broadcasting station 6.

  The content supply device 5 is a content server that distributes encrypted content in accordance with a request from the clients 20a to 20d or unilaterally. The broadcasting station 6 broadcasts encrypted content wirelessly.

  The external networks 2 and 3 are communication networks that mediate transmission of data between the public key certificate issuing device 10 and the clients 20a to 20d and the outside of the public key certificate issuing system 1, and specifically, the Internet or WAN. (Wide Area Network). Although the external networks 2 and 3 are shown as separate, they may be the same network.

  In this description, the network and the connection may be realized by any of wired, wireless, or a mixture of wired and wireless.

  Each node in the public key certificate issuing system 1, that is, the public key certificate issuing device 10 and the clients 20a to 20d are assigned a private key and a public key paired with the private key. When using each public key to encrypt data distributed to the clients 20a to 20d, it is necessary to verify whether it is legitimate, is not someone else, and has not been tampered with. There is. Therefore, in the public key certificate issuing system 1, it is assumed that the identity of each node is authenticated by the public key certificate issued by the public key certificate issuing device 10. The public key certificate corresponding to each node is obtained by signing the public key assigned to each node by the public key certificate issuing device 10 using the private key of the public key certificate issuing device 10 itself. is there.

  In this description, the secret key assigned to each node, the public key paired with the secret key, and the sign of the public key certificate that proves the identity of the public key are summarized as follows.

  The public key certificate is, for example, ITU-T (International Telecommunication Union Telecommunication Standardization Sector) 1996 Recommendation X. 509. The public key certificate includes a version number of the public key, a serial number of the public key certificate, public key information, information related to the public key certificate issuing device 10 that has issued the public key certificate, a validity period of the public key certificate, It may have items such as information of the subject to be certified, that is, the clients 20a to 20d and an extended area, and the extended area may include information such as an e-mail address and an IP address. The public key certificate is generated according to an encryption method such as DH (Diffie-Hellman) method, RSA (R. Rivest, A. Shamir, L. Adelman) method, or DSA (Digital Signature Algorithm).

  The public key certificate K13 that proves the identity of the public key certificate issuing device 10 is assigned to the public key certificate issuing device 10 by a certificate authority (not shown) that manages the public key certificate issuing device 10. The private key K11 is a private key corresponding to the public key certificate K13. The public key certificate K23a for proving the identity of the client 20a is obtained by signing the public key K22a assigned to the client 20a with the private key K11 assigned to the public key certificate issuing device 10. It is. Similarly, public key certificates K23b, K23c, and K23d that prove the identity of the clients 20b, 20c, and 20d are transferred to the public keys K22b, K22c, and K22d assigned to the clients 20b, 20c, and 20d, respectively. The signature is applied using the secret key K11 assigned to the issuing device 10.

  The public key certificate issuing device 10 has a function of storing the private key K11 assigned to itself and the corresponding public key certificate K13. Furthermore, the public key certificate issuing device 10 generates and stores a pair of the public keys K22a to K22d corresponding to the secret keys K21a to K21d assigned to the clients 20a to 20d and stores the generated secret keys K21a to K21d. It has a function of writing to the storage medium 30. In this case, the secret keys K21a to K21d are stored in the storage medium 30 and manually transported, and any of the corresponding secret keys K21a to K21d is read and stored by each of the clients 20a to 20d.

  Alternatively, each of the clients 20a to 20d has a function of generating and storing a pair of the public key K22a to K22d corresponding to the secret key K21a to K21d assigned to each client and writing the secret key K21a to K21d to the storage medium 30. May be.

  Thus, if the secret keys K21a to K21d are distributed in the storage medium 30 and distributed, there is no danger of leakage during transmission or destination error that may occur when distributing online. The storage medium 30 can write or rewrite data. Specifically, the storage medium 30 is a flexible disk, a nonvolatile semiconductor memory, a magneto-optical disk, or the like.

  The public key certificate issuance system 1 preferably has a firewall function that blocks or restricts communication from paths and nodes other than predetermined in order to prevent unauthorized access to the outside or outside. Alternatively, the public key certificate issuing system 1 may be constructed as a completely independent network. In this case, the issuance number upper limit value set in the public key certificate issuing device 10 is rewritten by directly operating the public key certificate issuing device 10 itself, instead of being performed from the management device 4. Further, instead of receiving content supply online from the content supply device 5, each of the clients 20a, 20b, 20c, 20d uses a portable medium storing the content, for example, an optical disk, a magneto-optical disk, or a magnetic tape. You may make it receive supply of content by reading.

Next, the internal configuration and functions of the public key issuing device 10 will be described in detail with reference to FIG.
FIG. 2 is a block diagram showing the public key certificate issuing device 10 in detail.
The public key certificate issuing device 10 connects an arithmetic processing device, a main storage device, an auxiliary storage device, an interface device, an input device and an output device via a bus, and installs a required program on a computer server device equipped with the auxiliary device. However, this can be realized by loading and executing this program.

  The public key certificate issuing device 10 includes a receiving unit 101, an issued number upper limit storage unit 102, an issued number determining unit 103, a request receiving unit 105, an invalidating unit 106, a revocation list generating unit 107, and a revocation list. List storage unit 117, key storage unit 108, storage medium drive unit 109, key generation unit 110, public key certificate generation unit 111, issue number management unit 112, issue number storage unit 113, secure communication A unit 120, a control unit 130, and an operation unit 131 are included.

  Note that the connection between the public key certificate issuing device 10 and the client 20a will be described, but the connection between the public key certificate issuing device 10 and the client 20c or 20d is the same as that in the case of the client 20a.

First, elements relating to the entire public key certificate issuing apparatus 10 will be described.
The control unit 130 has a function of controlling the entire public key certificate issuing device 10 and is realized including, for example, a microprocessor (not shown).

  The operation unit 131 has a function of giving instructions and information to each unit in the public key certificate issuing apparatus 10 via the control unit 130, and is realized by including a key and a pointing device, for example.

Next, each element related to key generation and storage will be described.
The key storage unit 108 has a function of storing the private key K11 of the public key certificate issuing device 10 and the public key certificate K13 paired with the private key K11. The key storage unit 108 further includes the secret keys K21a to K21d of the clients 20a to 20d, the public keys K22a to K22d paired with the secret keys K21a to K21d, and the public key certificate K23a corresponding to the public keys K22a to K22d. Has a function of storing ~ K23d. The stored secret keys K11 and K21a to K21d are strictly stored so that they are not easily read or rewritten from the outside.

  The storage medium drive unit 109 has a function of reading and writing the storage medium 30 and includes, for example, a flexible disk drive device, a non-volatile semiconductor memory reader / writer, or a magneto-optical disk drive device.

  The key generation unit 110 reads out the private key K11 of the public key certificate issuing device 10 from the storage medium 30 by the storage medium driving unit 109 and stores the private key K11 in the key storage unit 108. Alternatively, the key generation unit 110 itself may have a function of generating the secret key K11.

  The key generation unit 110 further causes the key storage unit 108 to store the secret keys K21a to K21d of the clients 20a to 20d read by the storage medium driving unit 109 and the public keys K22a to K22d to be paired. Alternatively, the key generation unit 110 itself generates the secret keys K21a to K21d of the clients 20a to 20d and the public keys K22a to K22d to be paired, and stores them in the key storage unit 108 and stores the secret keys K21a to K21d. The medium driving unit 109 may have a function of writing to the storage medium 30.

Next, elements related to communication with the client 20a, particularly reception from the client 20a will be described.
The secure communication unit 120 has a function of setting an encrypted communication path with the client 20a under the control of the control unit 130. For this reason, the secure communication unit 120 stores a secret key and a public key certificate for setting an encrypted communication path, which are different from the secret key K11 and the public key certificate K13. Also, the secure communication unit 120 can perform communication without setting an encrypted communication path under the control of the control unit 130.

The request receiving unit 105 has the following two functions.
(1) When a request for issuing the public key certificate K23a of the client 20a is received from the request transmission unit 205 (to be described later) of the client 20a, the public key certificate generating unit 111 is notified of the request with the issue request. To do. This issuance request includes the public key K22a of the client 20a.

  (2) When a request to delete the public key certificate K23a of the client 20a is received from the request transmission unit 205 (described later) of the client 20a, the deletion request is notified to the invalidation unit 106 together with the deletion request. The deletion request includes the public key certificate K23a of the client 20a or information that can specify the public key certificate K23a. As this information, for example, a serial number may be allocated to each of the public key certificates K23a to K23d, and this serial number may be used.

Next, elements related to the issue number management of the public key certificates K23a to K23d will be described.
The issuance number upper limit storage unit 102 rewritably stores an issuance number upper limit value that represents the upper limit of the issuance numbers of the public key certificates K23a to K23d allowed in the public key certificate issuance system 1. The upper limit of the number of issues is, for example, the number of clients 20a to 20d, but may be a number corresponding to this in advance when there is a plan to connect a client (not shown).

When the receiving unit 101 receives the issuance number setting information indicating the new issuance upper limit number of the public key certificates K23a to K23d from the management apparatus 4, the issuance number upper limit value stored in the issuance number upper limit value storage unit 102 is issued. Rewrite the number based on the number setting information.
The issue number upper limit value stored in the issue number upper limit storage unit 102 can be rewritten by operating the operation unit 131.

  The issued number storage unit 113 stores the issued number of public key certificates K23a to K23d generated and issued by the public key certificate generating unit 111, that is, the accumulated issued number. For example, in the initial state (when the public key certificate issuance system 1 is established), the cumulative number of issuances is zero.

The issuance number management unit 112 has the following two functions.
(1) Every time one public key certificate (any one of K23a to K23d) is issued by the public key certificate generating unit 111, 1 is added to the cumulative number of issued issues stored in the issued number storage unit 113. And update it.
(2) Each time the public key certificate (any one of K23a to K23d) is revoked by the revocation unit 106, 1 is subtracted from the accumulated number of issued issues stored in the issued number storage unit 113. Update memorize.

  In this way, whenever the public key certificate (any one of K23a to K23d) is issued or invalidated, the issue number storage unit 113 is rewritten by the issue number management unit 112, so that the accumulated issue number is This means the number of public key certificates K23a to K23d valid in the public key certificate issuing system 1.

The issue number determination unit 103 compares the cumulative issue number stored in the issue number storage unit 113 with the issue number upper limit value stored in the issue number upper limit storage unit 102. And
(1) If the cumulative number of issues has not reached the maximum number of issues, issue a permission decision,
(2) If the cumulative number of issues has reached the maximum number of issues, make an issue rejection decision,
In either case, the public key certificate generation unit 111 is notified of this.

Next, elements relating to the issuance and invalidation of public key certificates (any of K23a to K23d) will be described.
When the public key certificate generating unit 111 receives a notification from the request receiving unit 105 that there is a request for issuing the public key certificate K23a of the client 20a, the public key certificate generating unit 111 refers to the determination result of the issued number determining unit 103.

  (1) Therefore, when the issuance permission determination is made, the public key certificate generation unit 111 passes the key generation unit 110 through the key generation unit 110 to store the private key of the public key certificate issuing device 10. Read K11. Then, the public key K22a of the client 20a is signed using the secret key K11 to generate a public key certificate K23a related to the client 20a. The generated public key certificate K23a is issued to the key management unit 212 (described later) of the client 20a through the secure communication unit 120. The issue number management unit 112 is also notified that the issue has been made.

The public key certificates K13 and K23a to K23d are generated in advance by the key generation unit 110 and stored in the key storage unit 108, and the public key certificate generation unit 111 receives the key from the notification from the request reception unit 105. The public key certificate K13 or K23a to K23d related to the notification may be read from the storage unit 108 and used for issuance.
(2) Therefore, when the issue refusal determination is made, a message indicating that the accumulated issue number has reached the issue number upper limit value is generated, and the key management unit 212 (to be described later) of the client 20a is generated through the secure communication unit 120. ). The issue number management unit 112 is also notified that this message has been transmitted.

  When the revocation unit 106 receives a message indicating a request for deleting the public key certificate K23a of the client 20a from the request reception unit 105, the revocation unit 106 invalidates the public key certificate K23a, and notifies the issue number management unit 112 and the revocation list. Notify the generation unit 107.

  The revocation list storage unit 117 includes a revocation list, that is, a list indicating public key certificates (including any of K23a to K23d) revoked by the revocation unit 106, and the private key K11 of the public key certificate issuing device 10. Remember what you signed with. For example, in the initial state, none of the public key certificates (K23a to K23d) is listed in this list.

  When the revocation list generation unit 107 receives notification from the revocation unit 106 that the public key certificate K23a has been revoked, the revocation list generation unit 107 reads the revocation list stored in the revocation list storage unit 117, and has already been revoked. A list indicating the key certificate (any one of K23b to K23d) is extracted, and the public key certificate K23a is added to this list to update the list. Then, the private key K11 of the public key certificate issuing device 10 is read from the key storage unit 108 through the key generation unit 110, and the updated list is signed using the private key K11 to generate a new revocation list. The revocation list generation unit 107 updates and stores this new generation list in the revocation list storage unit 117 and distributes it to the clients 20a to 20d via the secure communication unit 120.

Next, the internal configuration and functions of the client 20a will be described in detail.
FIG. 3 is a block diagram showing the client 20a in detail.
The client 20a can be realized by adding a computer system to an apparatus for using content, such as a television receiver with a decoder. In this computer system, an arithmetic processing unit, a main storage unit, an auxiliary storage unit, an interface unit, an input unit and an output unit are connected by a bus, a required program is installed in a computer equipped with the auxiliary unit, and this program is loaded To make it executable.

Although the client 20a will be described, the clients 20b to 20d may have the same configuration.
The client 20 a includes a receiving unit 201, a content using device 233, a control unit 230, an operation unit 231, a display unit 232, secure communication units 220 and 221, a storage medium driving unit 209, and a key generation unit 210. , A key storage unit 208, a key management unit 212, an issue / deletion command unit 211, and a request transmission unit 205.

First, elements related to control of the entire client 20a and elements related to use of content will be described.
Specifically, the receiving unit 201 is an interface device with the external network 3 and a reception facility for a transmission wave of the broadcast station 6 (see FIG. 1), and receives a signal from the content supply device 5 or the broadcast station 6. The content use device 233 has a function of converting it into a format that can be used and sending it.

  The content using device 233 has a video playback function, an audio playback function, and the like, and is a device for playing back content using a signal received from the receiving unit 201. The content use device 233 also includes a decryption unit 234 that decrypts the encrypted content data using a content key obtained using the public key certificate K23a.

  The control unit 230 has a function of controlling the entire client 20a, and is implemented including, for example, a microprocessor (not shown).

  The operation unit 231 has a function of giving instructions and information to each unit in the client 20a via the control unit 230, and is realized including, for example, a key and a pointing device (both not shown).

  The display unit 232 includes, for example, a liquid crystal display device, and displays information such as instruction contents input from the operation unit 231 and the state of the client 20a.

Next, elements related to external communication and key management will be described.
The secure communication unit 220 has a function of setting an encrypted communication path with the public key certificate issuing device 10 under the control of the control unit 230. Therefore, the secure communication unit 220 stores a secret key and a public key certificate for setting an encrypted communication path, which are different from the secret key K21a and the public key certificate K23a. Also, the secure communication unit 220 can perform communication without setting an encrypted communication path under the control of the control unit 230.

  Under the control of the control unit 230, the secure communication unit 221 sets an encrypted communication path with the client 20b using a secret key and a public key certificate different from the secret key K21a and the public key certificate K23a. In addition, communication can be performed without setting an encrypted communication path under the control of the control unit 230.

  As described above, since the clients 20a to 20d include the secure communication units 220 and 221, if a further client (not shown) is connected in cascade, the public key certificate is transmitted via the key management unit 212. The encrypted communication path with the issuing device 10 can be extended.

  The storage medium drive unit 209 has a function of reading and writing the storage medium 30 (see FIG. 1), and includes, for example, a flexible disk drive device, a non-volatile semiconductor memory reader / writer, or a magneto-optical disk drive device.

  The key generation unit 210 generates a pair of the secret key K21a and the public key K22a and stores the pair in the key storage unit 208. The key generation unit 210 may be configured to store the generated secret key K21a in the storage medium 30 by the storage medium driving unit 209.

  The key storage unit 208 stores a secret key K21a, a public key K22a, and a public key certificate K23a. In particular, the secret key K21a is strictly stored so that it is not easily read or rewritten from the outside.

  The key management unit 212 controls communication between the public key certificate issuing device 10 and the client 20b, and also generates a private key, public key, and public key generated in the client 20a or received from the public key certificate issuing device 10. It has a function of temporarily storing a certificate or the like and storing it in the key storage unit 208 as necessary. In addition, the revocation list distributed from the public key certificate issuing device 10 is held.

  The issuance / deletion instruction unit 211 generates an issuance request or deletion request for the public key certificate K23a in response to an operation of the operation unit 231 or a request from the content use device 233. This issuance request includes the public key K22a, and the deletion request includes the public key certificate K23a.

  When the deletion request is generated, the key management unit 212 deletes the corresponding public key certificate K23a and private key K21a from the key management unit 212 itself and the key storage unit 208.

  The request sending unit 205 sends the issue request or the delete request generated by the issue / delete command unit 211 to the public key certificate issuing device 10 via the secure communication unit 220.

(First operation example)
Next, with reference to FIG. 4 (refer to FIGS. 1 to 3 as appropriate), a first operation example relating to the issuance permission / issuance of the public key certificate K23a in the public key certificate issuance system 1 will be described. To do.
FIG. 4 is a flowchart showing a first operation example related to issuance permission / issuance of issuance of the public key certificate K23a in the public key certificate issuance system 1.
Here, a case where the client 20a issues an issuance request to the public key certificate issuing device 10 will be described, but the client 20a may be read as the client 20b, 20c, or 20d. This operation example shows a case where the public key certificate K23a is issued or rejected without setting an encrypted communication path between the public key certificate issuing apparatus 10 and the client 20a.

  When the operator operates the operation unit 231 of the client 20a, or the content utilization device 233 makes a request through the control unit 230, the public key certificate K23a issuance request operation is performed (step S101). Thus, the key generation unit 210 generates a pair of secret key K21a and public key K22a (step S102). The secret key K21a and the public key K22a are stored in the key storage unit 208 by the key management unit 212.

  When the private key K21a and the public key K22a are generated, the issuance / deletion instruction unit 211 generates an issuance request for the public key certificate K23a including the public key K22a, and the request transmission unit 205 outputs the issuance request to the public key. This is transmitted to the certificate issuing device 10 (step S103).

  The request receiving unit 105 in the public key certificate issuing device 10 receives the request for issuing the public key certificate K23a transmitted from the client 20a (step S104). The request receiving unit 105 sends a notification indicating an issuance request to the public key certificate generating unit 111.

  The issue number determination unit 103 determines whether or not the cumulative issue number stored in the issue number storage unit 113 has reached the issue number upper limit value stored in the issue number upper limit storage unit 102 (step S105).

  The issuance number determination unit 103 makes an issuance refusal determination if the accumulated issuance number has reached the issuance number upper limit (No in step S105). Therefore, the public key certificate generation unit 111 determines that the accumulated issuance number is the number of issuances. A message indicating that the upper limit has been reached is generated and transmitted to the client 20a (step S111).

The key management unit 212 of the client 20a receives a message indicating that the cumulative number of issues has reached the maximum number of issues (step S112).
A message to the effect that the cumulative issue number has reached the issue number upper limit value is sent from the key management unit 212 to the display unit 232 via the control unit 230. Then, the display unit 232 displays that the cumulative issue number has reached the issue number upper limit (step S113).

  The issuance number determination unit 103 makes an issuance permission determination if the cumulative issuance number has not reached the issuance number upper limit value (Yes in step S105), so the public key certificate generation unit 111 obtains the public key certificate K23a. It is generated and transmitted to the client 20a (step S121). Then, the issuance number management unit 112 adds 1 to the accumulated issuance number stored in the issuance number storage unit 113 (step S122), and updates and stores it.

  The issued public key certificate K23a is received by the key management unit 212 of the client 20a, and is stored by the key storage unit 208 together with the corresponding private key K21a (step S123). Then, the key management unit 212 notifies the fact via the control unit 230, and the display unit 232 displays that the public key certificate K23a has been acquired (step S124).

(Second operation example)
Subsequently, with reference to FIG. 5 (refer to FIGS. 1 to 3 as appropriate), a second operation example relating to the issuance permission / issuance of issuance of the public key certificate K23a in the public key certificate issuance system 1 will be described. To do.
FIG. 5 is a flowchart illustrating a second operation example relating to the issuance permission / issuance of issuance of the public key certificate K23a in the public key certificate issuance system 1.
Here, a case where the client 20a issues an issuance request to the public key certificate issuing device 10 will be described, but the client 20a may be read as the client 20b, 20c, or 20d. This operation example shows a case where an encryption communication path is set between the public key certificate issuing device 10 and the client 20a, and the public key certificate K23a is issued or rejected.

  When the operator operates the operation unit 231 of the client 20a or the content utilization device 233 makes a request through the control unit 230, and the public key certificate K23a issuance request operation is performed (step S201), issuance / deletion is performed. The command unit 211 generates an issuance request for the public key certificate K23a including the public key K22a, and the request transmission unit 205 transmits the issuance request to the public key certificate issuing device 10 (step S202).

  The request for issuing the public key certificate K23a transmitted from the client 20a is received by the request receiving unit 105 in the public key certificate issuing device 10 (step S203). The request receiving unit 105 sends a notification indicating an issuance request to the public key certificate generating unit 111.

  The issue number determination unit 103 determines whether or not the cumulative issue number stored in the issue number storage unit 113 has reached the issue number upper limit value stored in the issue number upper limit storage unit 102 (step S204).

  The issuance number determination unit 103 makes an issuance refusal determination if the accumulated issuance number reaches the issuance number upper limit (No in step S204), so the public key certificate generation unit 111 determines that the accumulated issuance number is the number of issuances. A message indicating that the upper limit has been reached is generated and transmitted to the client 20a (step S211).

The key management unit 212 of the client 20a receives a message indicating that the cumulative issue number has reached the issue number upper limit (step S212).
A message to the effect that the cumulative issue number has reached the issue number upper limit value is sent from the key management unit 212 to the display unit 232 via the control unit 230. Then, the display unit 232 displays that the cumulative issue number has reached the issue number upper limit value (step S213).

  The issue number determination unit 103 makes an issue permission determination if the cumulative issue number has not reached the issue number upper limit value (Yes in step S204), so the key generation unit 110 generates the secret key K21a and the public key K22a. The public key certificate generation unit 111 generates a public key certificate K23a (step S221).

  Then, the secure communication unit 120 of the public key certificate issuing device 10 and the secure communication unit 220 of the client 20a perform mutual device authentication and set an encrypted communication path (step S222). Here, the encryption communication path setting private key and public key certificate stored in the secure communication unit 120 and the secure communication unit 220 are used. The private key and public key certificate are different from the private keys K11 and K21a and public key certificates K13 and K23a.

  The public key certificate generation unit 111 distributes the public key certificate K23a and the private key K21a through the encrypted communication path thus set (step S223) and notifies the issued number management unit 112 of it.

  Then, the issuance number management unit 112 adds 1 to the accumulated issuance number stored in the issuance number storage unit 113 (step S222), and updates and stores it.

  The distributed public key certificate K23a and the secret key K21a are received by the key management unit 212 of the client 20a, and stored together with the corresponding secret key K21a by the key storage unit 208 (step S225). Then, the fact is notified from the key management unit 212 via the control unit 230, and the display unit 232 displays that the public key certificate K23a has been acquired (step S226).

(Example of deletion operation)
Next, an example of the operation of deleting the public key certificate K23a in the public key certificate issuing system 1 will be described with reference to FIG. 6 (refer to FIGS. 1 to 3 as appropriate).
FIG. 6 is a flowchart showing an example of the deletion operation of the public key certificate K23a in the public key certificate issuing system 1.
Here, a case where the client 20a makes a deletion request to the public key certificate issuing device 10 will be described, but the client 20a may be read as the client 20b, 20c, or 20d.

  When the operator operates the operation unit 231 of the client 20a or the content utilization device 233 makes a request through the control unit 230 to perform a deletion request operation for the public key certificate K23a (step S301), the client 20a includes The public key certificate K23a is deleted from the (key storage unit 208 and key management unit 212) (step S302). The public key certificate K23a related to the deletion is held in the issue / deletion command unit 211 until a deletion request is transmitted as will be described later, but is deleted thereafter.

  Then, the issuance / deletion instruction unit 211 generates a deletion request for the deleted public key certificate K23a, and the request transmission unit 205 transmits this deletion request to the public key certificate issuing device 10 (step S303).

  The request reception unit 105 receives this public key certificate K23a deletion request (step S304) and notifies the revocation unit 106 of the request. Then, the revocation list generation unit 107 creates a new revocation list to which the public key certificate K23a is added and distributes the revocation list to the clients 20a to 20d (step S306).

  In the client 20a, the key management unit 212 receives and holds a new revocation list. Then, the fact is notified from the key management unit 212 via the control unit 230, and the display unit 232 displays that the public key certificate K23a has been deleted (step S308).

  Thus, according to the present embodiment, the following effects can be obtained. That is, the issuance number management unit 112 and the issuance number storage unit 113 grasp the cumulative number of public key certificates that are valid in the public key certificate issuance system 1, and whether the cumulative number of issues has reached the maximum number of issues. Depending on whether or not, the public key certificate is issued or rejected, the number of valid public key certificates in the public key certificate issuing system 1 is maintained below the upper limit value of the issued number. This eliminates the need for complicated registration authorities and expensive administrators.

It is a block diagram which shows the example of 1 structure of the public key certificate issuing system by this invention. It is a block diagram which shows a public key certificate issuing apparatus in detail. It is a block diagram which shows a client in detail. It is a flowchart which shows the 1st operation example which concerns on issue permission / issue rejection of a public key certificate in a public key certificate issuing system. It is a flowchart which shows the 2nd operation example which concerns on issuance permission / issuance of issuance of a public key certificate in a public key certificate issuing system. It is a flowchart which shows the example of deletion operation | movement of a public key certificate in a public key certificate issuing system.

DESCRIPTION OF SYMBOLS 1 Public key certificate issuing system 10 Public key certificate issuing apparatus 20a-20d Client 30 Storage medium 101, 201 Receiving part (issue number setting information receiving means, issue number upper limit value rewriting means)
102 Issued number upper limit storage unit (issued number upper limit storage means)
103 Issued number determination unit (issued number determination means)
105 Request receiver (public key certificate generation means, public key certificate invalidation means)
106 Revocation unit (public key certificate revocation means)
107 Revocation List Generation Unit (Revocation List Generation Unit)
108, 208 Key storage unit 109, 209 Storage medium drive unit 110, 210 Key generation unit 111 Public key certificate generation unit (public key certificate generation means)
112 issuance number management unit (cumulative issuance number update means, accumulated issuance number subtraction means)
113 issuance number storage unit (cumulative issuance number storage means)
117 Revocation List Storage Units 120, 220, 221 Secure Communication Units 130, 230 Control Units 131, 231 Operation Unit 205 Request Transmission Unit 211 Issue / Delete Command Unit (Public Key Certificate Issuing Request Unit, Key Deletion Unit, Invalidation Request Unit )
212 Key management unit 232 Display unit 233 Content usage device 234 Decryption unit K11, K21a to K21d Private key K22a to K22d Public key K13, K23a to K23d Public key certificate

Claims (6)

A public key certificate issuing device that issues a public key certificate that proves that the public key belongs to the client,
Public key certificate generation means for generating the public key certificate in response to a request for issuing the public key certificate from the client and issuing the public key certificate to the client;
An accumulated issue number storage means for storing an accumulated issue number of the public key certificate issued by the public key certificate generating means;
An accumulated issue number updating unit that updates the accumulated issue number stored in the accumulated issue number storage unit according to the issued number of the public key certificate issued by the public key certificate generating unit;
Issuance number upper limit storage means for storing the issuance number upper limit value of the public key certificate;
Whether or not the cumulative issue number reaches the issue number upper limit value with reference to the cumulative issue number stored in the cumulative issue number storage unit and the issue number upper limit value stored in the issue number upper limit storage unit Issuing number determination means for determining whether or not
Public key certificate revocation means for revoking the public key certificate in response to a request for revocation of the public key certificate from the client;
A cumulative issue number subtracting unit that decreases the cumulative issue number stored in the cumulative issue number storage unit in accordance with the number of the public key certificates invalidated by the public key certificate invalidation unit; ,
The public key certificate generation means further does not issue the public key certificate when the cumulative issue number reaches the issue number upper limit value based on the issue number determination means. apparatus. 2. The public key certificate issuing device according to claim 1 , further comprising: a revocation list generating unit that generates a revocation list including information indicating the revoked public key certificate and distributes the revocation list to the client. Issuance number setting information receiving means for receiving issuance number setting information indicating the new issuance upper limit number of the public key certificate by the public key certificate issuing device;
An issued number upper limit value rewriting unit for rewriting the issued number upper limit value stored in the issued number upper limit value storing unit based on the received issued number setting information;
The public key certificate issuing device according to claim 1 or 2 , further comprising: A public key certificate issuing device that issues a public key certificate that certifies that the public key belongs to the client, and the public key is owned by the public key certificate issued by the public key certificate issuing device. A public key certificate issuing system including a client proved to be,
The client
Public key certificate issuance request means for making a request for issuance of the public key certificate to the public key certificate issuing device;
Public key certificate storage means for receiving and storing the issued public key certificate;
Key deletion means for deleting the public key certificate from the public key certificate storage means;
Revocation request means for making a revocation request for the public key certificate deleted by the key deletion means to the public key certificate issuing device ,
The public key certificate issuing device
Public key certificate generation means for generating the public key certificate in response to a request for issuing the public key certificate from the client and issuing the public key certificate to the client;
An accumulated issue number storage means for storing an accumulated issue number of the public key certificate issued by the public key certificate generating means;
An accumulated issue number updating unit that updates the accumulated issue number stored in the accumulated issue number storage unit according to the issued number of the public key certificate issued by the public key certificate generating unit;
Issuance number upper limit storage means for storing the issuance number upper limit value of the public key certificate;
Whether or not the cumulative issue number reaches the issue number upper limit value with reference to the cumulative issue number stored in the cumulative issue number storage unit and the issue number upper limit value stored in the issue number upper limit storage unit Issuing number determination means for determining whether or not
Public key certificate revocation means for revoking the public key certificate in response to a request for revocation of the public key certificate from the client;
A cumulative issue number subtracting unit that decreases the cumulative issue number stored in the cumulative issue number storage unit in accordance with the number of the public key certificates invalidated by the public key certificate invalidation unit; ,
The public key certificate generation means further does not issue the public key certificate when the cumulative issue number reaches the issue number upper limit value based on the issue number determination means. system. An issuance number upper limit storage means for storing an upper limit value for the number of issued public key certificates and an issuance of the public key certificate for issuing a public key certificate that proves that the public key belongs to the client By referring to the cumulative issuance number storage means that stores the number,
An accumulated issuance number updating means for updating the accumulated issuance number in accordance with the issuance number of the public key certificate;
Issuance number determination means for determining whether or not the cumulative issue number has reached the issue number upper limit;
Public key certificate invalidating means for invalidating the public key certificate in response to the public key certificate invalidation request from the client;
An accumulated issue number subtracting unit that reduces the accumulated issue number stored in the accumulated issue number storage unit in accordance with the number of the public key certificates revoked by the public key certificate invalidation unit;
When the cumulative issue number has not reached the issue number upper limit value, the public key certificate is generated and issued to the client in response to the public key certificate issue request from the client. Public key certificate generation means for not issuing the public key certificate when the upper limit of the number of issue is reached,
Public key certificate issuance program characterized by functioning as A public key certificate issuing method in a public key certificate issuing device that issues a public key certificate that proves that a public key belongs to a client,
The public key certificate issuing device stores an upper limit value of the number of public key certificates issued and an accumulated number of public key certificates issued by the public key certificate issuing device,
An accumulated issue number update step of updating the accumulated issue number according to the issued number of the public key certificate issued by the public key certificate issuing device;
Whether the cumulative issue number reaches the issue number upper limit value with reference to the cumulative issue number updated in the cumulative issue number update step and the issue number upper limit value stored in the public key certificate issuing device Issuing number determination step for determining whether or not,
Based on the issuance number determination step, the public key certificate is generated and issued to the client in response to a public key certificate issuance request from the client when the cumulative issuance number has not reached the issuance upper limit value. A public key certificate issuance step that does not issue the public key certificate when the cumulative issuance number reaches the issuance upper limit value based on the issuance number determination step,
Further, when a revocation request for the public key certificate is received from the client,
A public key certificate invalidation step of invalidating the public key certificate in response to the public key certificate invalidation request from the client;
A cumulative issue number subtracting step of reducing the cumulative issue number of the stored public key certificate in accordance with the number of the public key certificate invalidated by the public key certificate invalidation step. A public key certificate issuing method characterized by:

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