JP5115424B2 - Time certification apparatus, time certification method, and program - Google Patents

Description

  The present invention relates to a time certification device, a time certification method, and a program.

One technique for proving that electronic information existed at a certain time is a time stamp technique. In this time stamp technology, as described in Non-Patent Document 1 below, a server of a time stamp authority generates and generates a digital signature for information obtained by combining a hash value of electronic information and time information. This time stamp ensures that the electronic information was present at the time indicated in the date / time information. The public key cryptography (PKI) technology used for electronic signatures is described in Non-Patent Document 2 below, and is a proof that links a public key with identification information such as a person's name and company name and related information such as an expiration date. Non-Patent Document 3 below describes the verification of the public key certificate, which is a certificate, and the revocation processing of the public key certificate.
X.509 PKI Time-Stamp Protocol X.509 PKI Online Certificate Status Protocol X.509 PKI Certificate and Certificate Revocation List (CRL) Profile

  When giving time certification information (time stamp) to multiple pieces of electronic information, the key information used by the time stamp organization is common, so the time depends on the validity period of the public key certificate attached to this key information. The validity period of the certification information (time stamp) is set to one, and an individual validity period cannot be given for each electronic information.

  It is an object of the present invention to provide a time certification apparatus, a time certification method, and a program that can make a public key certificate used for time certification information (time stamp) have a one-to-one correspondence with electronic information.

In order to achieve the above-mentioned object, the invention of the time certification device according to claim 1 is a receiving means for accepting, from the information terminal, a request for issuing the time certification information and specific information of the electronic information that is the issue target of the time certification information and, said to each accept the issuance request at the time of time certification information Ri by the receiving unit, and send the information of the public key is a pair of secret key used for the electronic signature of the time certification information to the certification authority, the public key a certificate request means for requesting a public key certificate to the certification authority to ensure the validity of the information including the unique information and the time information received by said receiving means, by the certificate issuance request means Time certificate information that has been digitally signed using a private key that is a public key pair of a public key certificate issued by the certificate authority in response to a certificate issuance request and the public key certificate are sent to the information terminal. Send to Characterized in that it comprises a transmitting means.

  According to a second aspect of the present invention, in the time certification apparatus according to the first aspect, the certificate issuance requesting unit is given a valid period corresponding to the time certification information issuance request received by the receiving unit. Requesting the certificate authority to issue a public key certificate.

  Further, the invention described in claim 3 is the time proof device according to claim 1 or 2, wherein the time proof information issued to the electronic information together with a request for revocation of the time proof information is received and specific information specifying the time proof information is accepted. Further comprising request acceptance means, and revocation request means for requesting the certificate authority to revoke the public key certificate corresponding to the time certification information specified by the specific information received by the revocation request acceptance means. And

  According to a fourth aspect of the present invention, in the time certification apparatus according to the third aspect, the specific information includes unique information of the electronic information and user information of the information terminal. .

Further, the invention of the time certification method according to claim 5 includes a reception step of receiving the time certificate information issuance request from the information terminal and the unique information of the electronic information to which the time certification information is issued, and the reception step. every accepts the request for issuing good Ri at the time certification information, and send the information of the public key is a pair of secret key used for the electronic signature of the time certification information to the certification authority, to ensure the validity of the public key a certificate issuance request step of requesting public key certificate to the authentication station, depending on the certificate request by the certificate issuance request step information including the unique information and the time information received by said receiving step The time certification information subjected to the electronic signature using the private key that is the public key pair of the public key certificate issued by the certificate authority and the public key certificate are transmitted to the information terminal. Characterized by comprising signal and step.

The invention of a program according to claim 6, together with the issue request of the time certification information from the information terminal, and receiving means for receiving unique information of the electronic information which is issued subject to the time certification information, Ri by said receiving means during each accepting a request for issuing time certification information, the public key and sending the information of the public key is a pair of secret key used for the electronic signature of the time certification information to the authentication station, to ensure the validity of the public key and certificate issuance requesting means for requesting the certificate to the authentication station, the information including the unique information and the time information received by the receiving means, depending on the certificate request by the certificate issuance request means Compile as a transmission means for transmitting to the information terminal the time certification information that has been digitally signed using a private key that is a public key pair of the public key certificate issued by the certificate authority and the public key certificate. It is a program for the functioning of the over data.

  According to the first aspect of the present invention, the public key certificate used for the time certification information (time stamp) can be associated with the electronic information on a one-to-one basis.

  According to the second aspect of the present invention, the validity period of the public key certificate used for the time certification information (time stamp) can be made to correspond one-to-one with the validity period of the requested electronic information.

  According to the invention described in claim 3, the electronic information can be individually revoked.

  According to the invention described in claim 4, the public key certificate of the time certification information (time stamp) for each electronic information can be specified by the unique information of the electronic information and the user information of the information terminal.

  According to the fifth aspect of the present invention, the public key certificate used for the time certification information (time stamp) can be associated with the electronic information on a one-to-one basis.

  According to the invention described in claim 6, it is possible to make the computer function so that the public key certificate used for the time certification information (time stamp) has a one-to-one correspondence with the electronic information.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments (hereinafter referred to as embodiments) for carrying out the invention will be described with reference to the drawings.

  FIG. 1 shows a system configuration diagram of a time certification system 1 according to the present embodiment. As shown in FIG. 1, the time certification system 1 includes a client device 10, a time certification device 20, and a certificate authority device 30. The client device 10 and the time certification device 20, and the time certification device 20 and the certificate authority device 30 perform data communication with each other.

  The client device 10 is an information terminal operated by a user, calculates a hash value as unique information of electronic information to which a time stamp (time certification information) is assigned, and uses the calculated hash value as a time certification device. 20 to issue a time stamp issue request. The time stamp is information that gives accurate time information to the electronic information and proves the existence and non-falsification of the electronic information at the time indicated by the time information. The hash value is information calculated based on electronic information data by a predetermined hash function. In this embodiment, a hash value is used for the unique information of the electronic information. However, other information may be used as long as the information is unique to the electronic information.

  The time certification device 20 is a server installed in a time stamp organization that receives a time stamp issue request from the client device 10 and generates a time stamp. The time certification device 20 requests the certification authority device 30 to issue a public key certificate (hereinafter simply referred to as a certificate) in response to the received time stamp issuing request, and the certification issued by the certification authority device 30. Get a certificate. Then, the time certification device 20 generates a time stamp by applying an electronic signature to the set of the hash value and the time information, and transmits the generated time stamp to the client device 10 together with the acquired certificate. Details of the configuration of the time certification device 20 and the processing executed will be described later.

  The certificate authority device 30 is a server installed in a certificate authority that issues a certificate for the public key of the private key pair used when the time certification device 20 performs the electronic signature of the time stamp, and guarantees the validity of the public key It is. The time stamp information is verified by checking whether the hash value of the electronic information in the time stamp given to the electronic information matches the hash value calculated from the electronic information, and whether the electronic signature of the time stamp is correct. However, it is confirmed based on the certificate issued by the certificate authority device 30 that the public key used at the time of verification is appropriate information.

  In the present embodiment, the client device 10 and the certificate authority device 30 perform processing based on the protocol of the standardized time stamp technology described in Non-Patent Documents 1 to 3, and the time certification device 20 While cooperating with the client apparatus 10 and the certificate authority apparatus 30 that use such a protocol of the existing time stamp technology, an individual validity period is given to the time stamp given to each electronic information. Hereinafter, details of a configuration provided in the time certification device 20 in order to realize the above processing will be described.

  FIG. 2 shows a functional block diagram of the time certification device 20. As shown in FIG. 2, the time certification device 20 includes a time stamp issuance request reception unit 40, a key information management unit 42, a certificate issuance request unit 44, a certificate acquisition unit 46, a time stamp generation unit 48, and a time stamp transmission. Section 50, time stamp information management section 52, time stamp revocation request receiving section 54, and certificate revocation request section 56.

  The time certification device 20 includes hardware that constitutes a computer, such as a control unit configured by a CPU or the like, a storage unit configured by a semiconductor memory element or a magnetic disk device, a communication unit configured by a network interface, and the like. The function of each of the above parts is realized. The function of each unit may be realized by a program stored in a computer-readable information storage medium being read and executed by the time certification device 20 that is a computer system using a medium reader (not shown). . Note that the program may be supplied to the time certification device 20 by an information storage medium, or may be supplied via data communication means such as the Internet. The client device 10 and the certificate authority device 30 may be realized in the same manner as the time certification device 20.

  The time stamp issue request receiving unit 40 receives a time stamp issue request signal transmitted from the client device 10. The time stamp issuance request signal transmitted from the client device 10 includes the user ID of the user who instructed the issuance request and the hash value of the electronic information for which the time stamp is issued. The electronic information for which the time stamp is issued may be various types of information such as an electronic document and image information.

  The key information management unit 42 includes a key information generation unit 42A, and manages a key pair of a public key and a secret key generated by the key information generation unit 42A. In this embodiment, every time a time stamp issuance request is received from the client device 10 by the time stamp issuance request acceptance unit 40, a key pair of a public key and a private key is generated, and a unique key corresponding to the time stamp issuance request is generated. Key information is generated. When generating the public key and the secret key, various methods such as RSA and elliptic curve cryptography may be used. In addition, instead of generating a key pair every time a request for issuing a time stamp is received, a plurality of different key pairs are generated at a predetermined timing and used, and different public key certificates are used for each issue request. As long as is used for the time stamp, it may be anything. The key pair is preferably held in a tamper-resistant holding means, for example, in order to reduce the risk of the secret key leaking to the outside.

  When the certificate issuance request unit 44 receives the time stamp issuance request by the time stamp issuance request acceptance unit 40, the certificate authority device issues a certificate for the public key generated by the key information generation unit 42A for the issuance request. Request to 30. The certificate issuance request unit 44 transmits the public key together with the certificate issuance request to the certificate authority device 30. The certificate authority device 30 transmits the transmitted public key and the information of the time certification device 20 that has the public key. And the certificate authority device 30 that issued the certificate and the digital signature of the certificate authority device 30 are generated.

  The certificate acquisition unit 46 receives and acquires the certificate generated by the certificate authority device 30 in response to the certificate issue request from the certificate issue request unit 44. The certificate acquisition unit 46 stores the certificate acquired from the certificate authority device 30 in a storage unit such as a memory.

  The time stamp generation unit 48 uses the private key corresponding to the certificate acquired by the certificate acquisition unit 46 to digitally sign information that is a combination of the hash value and time information received from the client device 10 and performs time Generate a stamp. The time information used for the time stamp may be a time obtained from a time source based on the international standard time, and the specific time may be the time when the time stamp is generated, or the hash value of the electronic document may be used. Another time related to the processing according to the time stamp issue request such as the received time may be used.

  The time stamp transmission unit 50 transmits the time stamp generated by the time stamp generation unit 48 to the client device 10 together with the certificate acquired by the certificate acquisition unit 46.

  The time stamp information management unit 52 manages information related to the time stamp generated by the time stamp generation unit 48. In the present embodiment, the time stamp information management unit 52 stores a time stamp management table that stores the hash value received from the client device 10, the generated key information, and the certificate information acquired from the certificate authority device 30 in association with each other. Generate and manage time stamp related information. By referring to the time stamp management table, a certificate corresponding to each electronic information (hash value) is specified.

  FIG. 3 shows an example of the time stamp management table. In the example shown in FIG. 3, the time stamp management table includes a user ID for identifying a user who has requested a time stamp, and a hash value, key information, and certificate information transmitted at the time of the time stamp request. Stored and configured. The key information is information on the private key used for generating the time stamp and the public key of the pair, and the certificate information is information on the certificate issued by the certificate authority for the public key. For example, a serial number for identifying a certificate may be used.

  The time stamp revocation request receiving unit 54 receives a time stamp revocation request given to the electronic information from the client device 10 together with information on the user ID and the hash value of the electronic information. The time stamp revocation request reception unit 54 performs user authentication based on the received user ID, and outputs the received user ID and hash value information to the certificate revocation request unit 56 when the user authentication is passed.

  The certificate revocation request unit 56 specifies a certificate corresponding to the time stamp for which revocation is requested based on the user ID and the hash value information input from the time stamp revocation request reception unit 54. In other words, the certificate revocation request unit 56 specifies a certificate including the public key of the private key pair used when the time stamp for which revocation is requested is digitally signed. Then, the certificate revocation request unit 56 makes a revocation request for the specified certificate to the certificate authority device 30. When the certificate revocation process is completed by the certificate authority, the corresponding time stamp is also revoked.

  Next, referring to FIG. 4 to FIG. 7, each of the time stamp issue processing, time stamp verification processing (when using CRL and when using OCSP), certificate revocation processing performed by the time certification system 1 is performed. A processing sequence will be described.

  FIG. 4 shows a sequence diagram of the time stamp issuing process. As shown in FIG. 4, the client device 10 transmits a request for issuing a time stamp to the electronic document together with the hash value of the electronic information to the time certification device 20 (S101). The time certification device 20 generates a key pair of a secret key and a public key in response to the time stamp issuance request (S102). Then, the time certification device 20 transmits a certificate issuance request for the public key to the certificate authority device 30 together with the generated public key (S103).

  The certificate authority device 30 issues a certificate to the public key transmitted from the time certification device 20 (S104), and transmits the issued certificate to the time certification device 20 (S105). The time certification device 20 receives the certificate from the certificate authority device 30, and uses the private key generated in S102 to digitally sign information that is a combination of the hash value and time information to generate a time stamp (S106). ). The time certification device 20 transmits the generated time stamp to the client device 10 together with the certificate received from the certificate authority device 30 (S107). Then, the time certification device 20 stores the user ID, hash value, key information, and certificate information in the time stamp management table (S108).

  Hereinafter, two examples of the time stamp verification processing of the electronic document performed in the client device 10 will be described, using CRL and using OSCP, either of which may be used.

  First, a case where the client device 10 verifies a time stamp using a CRL (Certificate Revocation List) will be described. The CRL is list information that stores a list of digital certificates revoked within the valid period.

  FIG. 5 shows a sequence diagram of verification processing for verifying a time stamp issued for an electronic document by CRL.

  As illustrated in FIG. 5, the client apparatus 10 calculates a hash value of electronic information (electronic document) to be verified (S201). The client apparatus 10 checks whether or not the hash value of the electronic information in the time stamp matches the hash value calculated from the electronic information (S202). If the client device 10 confirms that the hash values match, the client device 10 verifies the electronic signature of the time stamp (S203).

  When verifying that the electronic signature of the time stamp is correct, the client device 10 acquires and holds information on the certificate revocation list (CRL) generated by the certificate authority device 30 (S204). (S205) and download and acquire the CRL (S206).

  Next, the client device 10 confirms whether or not the CRL is appropriate based on the downloaded digital signature information of the CRL (S207). When the client device 10 confirms that the CRL is proper, the client device 10 searches the CRL list to determine whether or not the certificate of the time stamp given to the electronic information (electronic document) to be verified is included, and the time It is confirmed whether the stamp certificate has expired (S208). If all the verifications are successful through the above processing, the client device 10 determines that the electronic data to be verified exists at the time of the time stamp and that the electronic data has not been tampered with, and the hash value If they are different, it is determined that the electronic data has been tampered with. In the above processing, certificate verification may be performed first.

  FIG. 6 shows a sequence diagram of a verification process for verifying a time stamp issued for an electronic document by OCSP (Online Certificate Status Protocol).

  As shown in FIG. 6, the client device 10 calculates a hash value of electronic information (electronic document) to be verified (S301). The client apparatus 10 checks whether or not the hash value of the electronic information in the time stamp matches the hash value calculated from the electronic information (S302). When the client device 10 confirms that the hash values match, the client device 10 verifies the electronic signature of the time stamp (S303).

  When it is verified that the electronic signature of the time stamp is correct, the client device 10 holds certificate revocation information (CRL or the like) held by the certificate authority (S304). The information (serial number etc.) of the certificate of the time stamp given to the electronic document) is transmitted (S305). The OCSP server refers to revocation list information such as CRL to check whether the certificate received from the client device 10 has been revoked (S306), and transmits the check result to the client device 10 (S306). S307). The client device 10 confirms whether the certificate has been revoked based on the confirmation result transmitted from the OCSP server (S308). If all the verifications are successful through the above processing, the client device 10 determines that the electronic data to be verified exists at the time of the time stamp and that the electronic data has not been tampered with, and the hash value If they are different, it is determined that the electronic data has been tampered with.

  FIG. 7 shows a sequence diagram of time stamp revocation processing for revoking a time stamp issued for an electronic document. As shown in FIG. 7, the client device 10 sends a time stamp revocation request to the time stamp together with the hash value obtained from the electronic information to which the time stamp that is the target of the revocation request is attached and the user information (user ID). It transmits to the certification | authentication apparatus 20 (S401).

  The time certification device 20 performs an authentication process based on the received user ID (S402), and when the user is authenticated, searches the time stamp management table using the received hash value and the user ID as a key. The certificate information associated with the hash value and the user ID is specified (S403).

  The time certification device 20 transmits a revocation request for revoking the specified certificate to the certificate authority device 30 (S404). The certificate authority device 30 registers the certificate in the revocation list based on the revocation request received from the time certification device 20 (S405).

  In the time proof device 20 described above, a time stamp certificate is generated for each electronic information, and therefore the time stamp validity period is individually set. Further, since a time stamp certificate is assigned to each electronic document, the time stamp of one electronic information is not revoked even if the time stamp of one electronic information is revoked. In the time certification system 1 according to the present embodiment, the client device 10 and the certificate authority device 30 that use the existing protocol of the time stamp technology are provided for each electronic information without changing specifications. A separate validity period is given to the time stamp.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, a public key / private key pair is generated every time a time stamp is generated, but a new public key / private key pair does not necessarily have to be generated. Hereinafter, an example in which an individual validity period is given to a time stamp for each electronic document using key information held in advance by the time certification device 20 will be described as a second embodiment.

  In the second embodiment, the same public key for issuing a certificate is used. That is, in the second embodiment, every time a time stamp issuance request is received from the client device 10, a certificate issuance request for a public key held in advance is made to the certificate authority device 30, and for each certificate, Issuing request identification information for identifying a certificate issuance request is assigned and managed.

  FIG. 8 shows an example of a time stamp management table managed by the time stamp information management unit 52 when issuing a time stamp using the same public key. As shown in FIG. 8, the time stamp management table may further store issuance request identification information for identifying a certificate issuance request in association with a user ID, a hash value, and a certificate.

  FIG. 9 shows an example of a sequence diagram of a time stamp issuing process performed in the time certification system 1 according to the second embodiment.

  As shown in FIG. 9, the client device 10 transmits a request for issuing a time stamp to the electronic document together with the hash value of the electronic information to the time certification device 20 (S501).

  The time certification device 20 transmits a certificate issuance request for the public key to the certificate authority device 30 together with the public key held in advance by the time certification device 20 in response to the time stamp issuance request (S502). At this time, the time certification device 20 generates and stores issuance request identification information for identifying the certificate issuance request (S503).

  The certificate authority device 30 issues a certificate to the public key transmitted from the time certification device 20 (S504), and transmits the certificate to the time certification device 20 (S505). The time certification device 20 receives the certificate from the certificate authority device 30, and uses the private key paired with the public key to digitally sign information that is a set of the hash value and time information, and to obtain a time stamp. Generate (S506).

  The time certification device 20 transmits the generated time stamp to the client device 10 together with the certificate received from the certificate authority device 30 (S507). The time certification device 20 stores the user ID, hash value, issue request identification information, and certificate in association with each other in the time stamp management table (S508).

  In the second embodiment, since the public key and private key pair is not generated every time the time stamp is generated, the number of generated key information is small, and the key management burden is reduced.

  In the above embodiment, a certificate is generated by the certificate authority device 30 every time a time stamp issuance request is made for each electronic information, and a time stamp validity period is set. The certificate authority device 30 may specify. That is, the time certification device 20 transmits a certificate issuance request including information on the validity period set in the certificate to the certificate authority device 30, and the certificate authority device 30 certifies the validity period included in the issued issuance request. After the certificate is generated, the generated certificate may be transmitted to the time certification device 20. The validity period of the certificate may be specified in, for example, a time stamp issuance request transmitted from the client device 10 to the time certification device 20. The time certification device 20 may manage the validity period of each certificate using a time stamp management table. For example, the time stamp management table associates a user ID, a hash value, key information, a certificate, and a validity period of a certificate with each other. It is good also as comprising so that it may memorize.

It is a system configuration diagram of a time certification system. It is a functional block diagram of a time certification device. It is an example of a time stamp management table. It is an example of the sequence diagram of a time stamp issue process. It is an example of the sequence diagram of a time stamp verification process. It is an example of the sequence diagram of a time stamp verification process. It is an example of a sequence diagram of a time stamp expiration process. It is an example of a time stamp management table. It is an example of the sequence diagram of a time stamp issue process.

Explanation of symbols

  1 time certification system, 10 client device, 20 time certification device, 30 certificate authority device, 40 time stamp issuance request reception unit, 42 key information management unit, 42A key information generation unit, 44 certificate issuance request unit, 46 certificate acquisition , 48 time stamp generation unit, 50 time stamp transmission unit, 52 time stamp information management unit, 54 time stamp revocation request reception unit, 56 certificate revocation request unit.

Claims (8)

A receiving means for receiving the unique information of the electronic information that is the issue target of the time certification information together with the issue request of the time certification information from the information terminal;
Each time a request for issuing time certification information is accepted by the accepting means, information on the public key, which is a pair of private keys used for the electronic signature of the time certification information, is transmitted to the certificate authority to guarantee the validity of the public key. a certificate request means for requesting the certificate authority to issue issue request every different public key certificate of the public key certificate is a by time certification information,
The information including the unique information and time information received by the receiving unit is a public key pair of the public key certificate issued by the certificate authority in response to the certificate issuance request by the certificate issuance request unit. A time certification apparatus, comprising: transmission means for transmitting time certification information subjected to an electronic signature using a secret key and the public key certificate to the information terminal. The certificate issuing request unit requests the certificate authority to issue a public key certificate to which a valid period corresponding to a request for issuing time certification information received by the receiving unit is given. The time certification device described in 1. A revocation request accepting unit that accepts specific information for identifying the time certification information together with a revocation request for the time certification information issued to the electronic information,
The revocation requesting means for requesting the revocation of the public key certificate corresponding to the time certification information specified by the specific information received by the revocation request receiving means to the certificate authority. Or the time certification apparatus according to 2; The time certification apparatus according to claim 3, wherein the specific information includes unique information of the electronic information and user information of the information terminal.   Each time a request for issuing time certificate information is received by the receiving unit, the method further includes a generating unit that generates a unique private key and a public key used for an electronic signature of the time certificate information,
  The certificate issuance requesting unit requests the certificate authority for a public key certificate that guarantees the validity of the public key generated by the generating unit every time the receiving unit receives a request for issuing time certification information.
  The time certification apparatus according to any one of claims 1 to 4, wherein the time certification apparatus is provided.   The certificate issuance request means requests the certificate authority to issue a public key certificate for a public key held in advance every time a request for issuing time certification information is received by the receiving means.
  The time certification device further includes:
  The issuance request identification information for identifying the issuance request for the time certification information accepted by the accepting unit is associated with the public key certificate issued by the certification authority in response to the issuance request for the certificate by the certificate issuance requesting unit. Management means to manage
  The time certification apparatus according to any one of claims 1 to 4, wherein the time certification apparatus is provided. A reception step for receiving the unique information of the electronic information that is the issue target of the time certification information together with the issue request of the time certification information from the information terminal;
Each time a request for issuance of time certification information is accepted in the acceptance step, the public key information that is a pair of private keys used for the electronic signature of the time certification information is transmitted to the certificate authority, thereby guaranteeing the validity of the public key. the issuance of the issuance request for each different public key certificate of the public key certificate is a by time certification information and certificate issuance request step of requesting to the authentication station,
A secret that is a public key pair of a public key certificate issued by the certificate authority in response to a certificate issuance request in the certificate issuance request step in information including the unique information and time information accepted in the acceptance step A time certification method comprising: a step of transmitting time certification information to which an electronic signature using a key is applied and the public key certificate to the information terminal. A receiving means for receiving the unique information of the electronic information that is the issue target of the time certification information together with the issue request of the time certification information from the information terminal;
Each time a request for issuing time certification information is accepted by the accepting means, information on the public key, which is a pair of private keys used for the electronic signature of the time certification information, is transmitted to the certificate authority to guarantee the validity of the public key. a certificate request means for requesting the certificate authority to issue issue request every different public key certificate of the public key certificate is a by time certification information,
The information including the unique information and time information received by the receiving unit is a public key pair of the public key certificate issued by the certificate authority in response to the certificate issuance request by the certificate issuance request unit. A program for causing a computer to function as transmission means for transmitting time certification information subjected to an electronic signature using a secret key and the public key certificate to the information terminal.

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