JP3933999B2 - Digital certificate issuing system and system program thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital certificate issuing system, and more particularly to a system capable of extending the expiration date of a digital certificate.
[0002]
[Prior art]
Currently, in order to guarantee the existence and non-tampering of digital documents at a certain point in time, a format called a digital certificate is generally used. As shown in FIG. 7, a message digest 72 is generated for a digital document 71 using a one-way hash function (MD5, SHA-1, etc.), and additional information such as time information at that time is generated. 73 is added to generate a plaintext of the digital certificate, and this plaintext, that is, the message digest 72 and the additional information 73 is encrypted with the private key of the public key system (RSA system or the like) to form an encrypted part 74, In addition to the document 71, it is filed as a digital certificate. In some cases, the original digital document 71 and the encrypted portion 74 are not used as one file, but only the encrypted portion 74 is used as a separate file, and this is used as a digital certificate as it is.
[0003]
The above method is based on the difficulty of creating the same hash value of a one-way function and the authenticity of the public key method. The encrypted part is decrypted with the target public key, and the decrypted message digest is converted into the original message digest. By collating with the message digest obtained from the digital document, it is possible to assert the existence or non-falsification of the original digital document at a certain point in time.
[0004]
Public key cryptosystems are often based on the difficulty of analyzing a mathematical problem by a computer. For example, the RSA method is based on the difficulty of prime factorization of a large composite number. Therefore, the expiration date of the private key / public key pair is considered to be finite, and the expiration date is also set for the digital certificate generated using this technology. In many cases, the expiration date of a digital certificate is about 1 to 2 years. On the other hand, the storage period of paper documents is required to be longer.
[0005]
For this reason, techniques for extending the expiration date of digital certificates have been attempted. For example, this type includes those disclosed in Japanese Patent Application Laid-Open No. 08-504965. As shown in FIG. 8, the original document (D) is acquired (step 8a), and the original certificate C _{1 is obtained} from the original digital document (D) by the function (F ₁ ) as the first encryption function. (C ₁ = F ₁ (D)) is generated (step 8b), and the original digital document (D) and the original certificate C ₁ are combined within the validity period (D, C ₁ ) (step 8c), The extended certificate C ₂ (C ₂ = F ₂ (D, C ₁ )) is generated by applying the function (F ₂ ) as the second encryption function to this (step 8d).
[0006]
[Problems to be solved by the invention]
However, the original digital document (D) is combined with the certificate C ₁ generated by the function (F ₁ ), and this is further applied to the function (F ₂ ) to generate a certificate C ₂ with an extended period. Then, if a plurality of time limit extension processes, that is, update processes are to be performed, a new certificate is generated by adding the previous certificate to the original digital document (D) each time the update process is performed. In other words, since it is a nested update process that recertifies the previous certificate as a digital document with another encryption function, when decrypting a certificate for notarization, it is decrypted in multiple stages. It is necessary to make the decoding process complicated. Further, since a new certificate is added every time update processing is performed, the amount of data increases each time, and this increment cannot be ignored when handling a large number of certificates. In addition, even if another encryption function is selected within the validity period of the previous encryption function, the reliability of the initially assumed validity period is greatly affected by the improvement of the processing capacity of the computer, and the expiration date management is difficult. It was.
[0007]
Accordingly, an object of the present invention is to enable digital certificate renewal a plurality of times without increasing the amount of data and complicating the decryption process, and to facilitate the management of the expiration date.
[0008]
[Means for Solving the Problems]
The digital certificate issuing system of the present invention generates a key pair that is a pair of a private key and a public key whose expiration date is m times a unit period (m is a positive integer of 2 or more). A digital certificate by encrypting a message digest of a digital document and additional information such as the date and time of existence of the digital document using a key generation means for generating a generation key pair, and the latest key pair generated by the key generation means; A certificate generation means for generating a certificate, and the validity period of the digital certificate generated previously is from the generation of the digital certificate to the unit period, and a new key pair is generated from the key generation means And the certificate generating means encrypts the message digest and the first of the additional information using the latest key pair to generate a new digital certificate and Characterized in that it comprises an update control means for updating the Manual.
For example, the unit period is a time limit that the key pair generated by the key generation unit is estimated to be at least valid, and the key generation unit generates a key pair for each unit period of 1 / m of the expiration date. Update.
For example, the update control means includes an upper limit means for obtaining an upper limit value of the number of updates of the digital certificate based on a maximum validity period of the digital certificate and the unit period, and a count means for counting the number of updates of the digital certificate. The digital certificate is updated by the certificate generation unit until the number of updates counted by the counting unit reaches the upper limit value obtained by the upper limit unit.
For example, the update control means uses the certificate generation means to convert the digital certificate into a plaintext using a public key that is within the validity period, and encrypts it with the latest private key that is within the validity period, Renew digital certificate.
[0009]
The digital certificate issuance system program of the present invention generates a key pair that is a pair of a private key and a public key whose expiration date is m times the unit period (m is a positive integer equal to or greater than 2). The key generation process for generating a next-generation key pair and the message digest of the digital document and the additional information such as the date and time of the digital document are encrypted using the latest key pair generated by the key generation process. A certificate generation process for issuing a digital certificate, and the validity period of the digital certificate generated previously is from the generation of the digital certificate to the unit period, and a new key pair is created by the key generation process. Once generated, a new digital certificate is created by encrypting the message digest and the first of the additional information by the certificate generation process using the latest key pair. To generate, characterized in that allowed to realized on the computer and an update control process for updating the digital certificate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The outline of the digital certificate issuing system and its system program of the present invention is as follows. As shown in FIG. 1, at a certain point in time X, a key pair that is a private key / public key pair whose expiration date is m times the unit period (m is a positive integer of 2 or more), for example, a unit period N (for example, N 1 is a positive integer greater than or equal to 1), and in FIG. 1, a key pair KP _X having an expiration date of 2N years, which is twice the unit period N, is generated. Thereafter, a new key pair KP _{X +} is generated every unit period N years. ₁ , KP _{X + 2} ,... KP _{X + i} is generated. For example, a digital certificate is issued with a key pair KP _{X + 1} to a digital document at a point A between X + N years and X + 2N years within the expiration date of the first key pair KP _X , and thereafter Each time a new key pair is generated, additional information indicating the date and time of existence of the earliest digital document is encrypted with the newly generated key pair and a new digital certificate is issued. The expiration date of a key pair is estimated from the number of bits, but it is difficult to say that it will be valid over the entire period, which is estimated to be an expiration date in the future, due to the improvement in computer processing power. It is estimated that it is sufficiently effective at least at 1 / m. Therefore, in the present invention, the key pair is updated every 1 / m unit period of the expiration date and a new digital certificate is issued, whereby the certificate can be easily and safely updated. It is possible. In the embodiment described below, the unit period is set to 1 year and the expiration date is set to 2 years. However, the unit period and m are not limited to this, and safety can be ensured by predicting improvement in computer processing capacity. Is set appropriately to the estimated value. In addition, for the message digest used in the certificate and the additional information indicating the existence date and time of the digital document, the latest digital certificate is decrypted and encrypted with the latest key pair. A certificate. For this reason, the problem that the amount of data increases at each update or the decoding process becomes complicated is solved.
[0011]
Next, the configuration of a digital certificate issuing system and its system program according to an embodiment of the present invention will be described. In this example, the present invention is applied to a system for issuing a digital certificate on the Internet. FIG. 2 is a block diagram showing the configuration of this example.
[0012]
The WEB server 1 is connected to the Internet 3 via the intranet 2, and provides a reception page, which is a homepage for a digital certificate issuing service, to the clients 4 to 4 via the Internet 3. The reception page is generated in the WEB process 11 provided in the WEB server 1. For example, as shown in FIG. 3, user information such as the company name, name, and mail address of the user, the file name of the digital document, and the usage period of the digital certificate Input fields 21 to 25 for (maximum expiration date by update), an execution button 26 of a program for calculating a message digest, a transmission button 27, and the like are provided. In addition, on the reception page, necessary items are entered in the input fields 21 to 25 on the client 4, and when the execute button 26 is pressed, the message digest is calculated, and when the send button 27 is pressed, each input is entered. The message digest is sent to the WEB server 1 together with the input items in the columns 21 to 25. The hash function is used for calculating the message digest. However, the present invention is not limited to this, and the message digest calculation program is not included in the reception page and can be variously modified such as being provided separately in the client 4. In addition, the WEB server 1 provides the client 4 with a response page that is a home page for sending the digital certificate to the user. As shown in FIG. 4, the response page is displayed in addition to the display of the user's company name 31, name 32, mail address 33, digital document file name 34, its message digest 35, time stamp 36, and digital certificate usage period 37. A digital certificate download button 38 is provided, and when the download button 38 is pressed, the digital certificate is downloaded to the client 4. When downloading, the public key used to encrypt the digital certificate is also attached.
[0013]
The time server 5 generates compensated high-precision time information, and supplies the compensated time information to the WEB server 1 via the intranet 2. The WEB server 1 maintains the accuracy of the time information by synchronizing the time information measured by the built-in clock with the time information periodically compensated.
[0014]
The WEB server 1 includes a time stamp process 6 that gives a time stamp based on compensated time information to a message digest or the like of a received digital document and executes a digital certificate issuance process.
[0015]
Next, details of the time stamp process 6 will be described with reference to FIG. The time stamp process 6 includes a key generation process 61, an encryption / decryption process 62, a digital certificate database 63, a time interface 64, a WEB interface 65, and a main process 66.
[0016]
The key generation process 61 starts from a common key generation process set in advance, for example, a key generation process using an RSA public key encryption algorithm every unit period N years, here an expiration date of 2 years. Key pairs KP _{X + 1} , KP _{X + 2} ,... KP _{X + i} are generated. That is, the key generation process 61 generates a next-generation key pair by using a key generation algorithm common to generations and changing parameters for key generation every year. For example, in the case of the RSA method, a public index e is determined every year, prime numbers p and q are determined by a key generation algorithm common among generations, a modulus n is determined by multiplying p and q, and e and p And a secret index d based on q and n and e are public keys and n and d are secret keys. In addition, a key parameter, for example, a public index e is randomly generated for each generation. In this way, digital certificates can be renewed at specific intervals by setting the expiration date estimated between generations of key pairs using a common key generation algorithm between generations. Therefore, digital certificate renewal management becomes easier.
[0017]
The encryption / decryption process 62 encrypts the plaintext of the digital certificate received from the main process 66 by using the key pair generated by the key generation process 61 to generate a digital certificate. Also, under the control of the main process 66, the digital certificate read from the digital certificate database 63 is decrypted into plain text, encrypted using the next-generation key pair generated by the key generation process 61, and a new digital Generate a certificate.
[0018]
The digital certificate database 63 generates an issued digital certificate by generating user information such as a user's e-mail address, user-specified expiration date, key pair used at the time of encryption, and at least the digital certificate. It is stored in association with update history information including the used key pair. These data are read from the digital certificate database 63 when the digital certificate is updated, and are stored again after updating the data. The digital certificate database 63 is used when notifying a digital document based on the stored digital certificate in accordance with a request from a user later.
[0019]
The time interface 64 is used to pass time information necessary for giving a time stamp to the information received via the reception page shown in FIG. 3 from the clock built in the WEB server 1 to the main process 66. Also, time information is extracted from the clock when the key pair and the digital certificate are updated.
[0020]
The WEB interface 65 passes the information received via the reception page shown in FIG. 3 to the main process 66, and also sends the information and digital certificate necessary for generating the response page shown in FIG. 4 from the main process 66 to the WEB process. 11 to hand over.
[0021]
The main process 66 receives the user's company name, name, email address, digital document file name, digital certificate usage period, and message digest via the WEB interface 65, and sends necessary information from the time interface 64. The plain time of the digital certificate is generated by adding the received time information. The main process 66 causes the encryption / decryption process 62 to encrypt the plaintext using the latest key pair generated by the key generation process 61 to generate a digital certificate, and the generated digital certificate is sent to the WEB interface 65. To the WEB process 11 and issued to the user. The main process 66 sets the number of digital certificate updates based on the usage period received from the user, and stores it in the digital certificate database 63 together with the digital certificate, user information, and update history information. In this example, for example, the digital certificate is updated once, six times, and 19 times for the short-term, medium-term, and long-term usage periods selected by the user on the reception page shown in FIG. Are stored in the digital certificate database 63. In addition, the main process 66 causes the key generation process 61 to generate a new key pair with an expiration date of 2 years for each unit period, here, every year, and the digital certificate with the update count set to 1 or more is used as the user information. The digital certificate is read from the digital certificate database 63 together with the update history information, etc., and the digital certificate is decrypted by the encryption / decryption process 62 based on the key pair included in the history information. The digital certificate is re-encrypted to generate a new digital certificate, and the new digital certificate is issued by sending the new digital certificate to the user by e-mail or the like according to the user information. The new digital certificate is stored in the digital certificate database 63 together with the update history including the updated key pair. At this time, the update count is decremented by one, and the update for the update count of 0 is not performed next time.
[0022]
Next, the digital certificate issuance and renewal procedure of this example will be described with reference to the flowchart of FIG. The reception page shown in FIG. 3 receives data such as a message digest of a digital document and a desired usage period from the user's client 4 (step a). The received data from the client is transferred to the main process 66 via the WEB interface 65. The main process 66 gives time information and the like from the time interface 64 to the received data, and generates a plaintext of a digital certificate as shown in FIG. 7, that is, a plaintext composed of a message digest 72 and an additional information portion 73 such as time. (Step b). Next, the main process 66 causes the encryption / decryption process 62 to encrypt the plaintext of the digital certificate using the secret key of the latest key pair generated by the key generation process 61, and uses the encrypted portion 74 as a digital certificate. Generate (step c). Next, the main process 66 returns the encrypted digital certificate to the client via the WEB interface 65 (step d). That is, the WEB server 1 provides the digital certificate response page shown in FIG. 4 on the client 4 and downloads the digital certificate to the client 4 with the public key in response to pressing of the download button. Next, the main process 66 stores the generated digital certificate in the digital certificate database 63 together with user information and update history information. The update history information includes the key pair used for encryption. Further, the main process 66 associates the digital certificate with the number of updates corresponding to the usage period selected by the user and stores it in the digital certificate database 63 (step e).
[0023]
The main process 66 monitors the passage of time (step f) and causes the key generation process 61 to generate a new key pair with an expiration date of 2 years every year (step g). Next, the main process 66 reads out the digital certificate whose update count is set to 1 or more from the digital certificate database 63 together with the update history information and the like, and based on the public key of the key pair included in the history information. The encryption / decryption process 62 is made to decrypt (step h). Next, the main process 66 encrypts the decrypted plaintext with the private key of the new key pair by the encryption / decryption process 62, and updates the digital certificate (step i). Next, the main process 66 passes the new digital certificate together with the new public key to the WEB process 11 via the WEB interface 65, and does not describe the configuration for realizing it in detail, but sends it to the user by e-mail or the like, and A digital certificate is issued (step j). Next, the main process 66 stores the new digital certificate in the digital certificate database 63 along with the update history including the updated key pair (step k). At this time, the update count is decremented by 1, and the update count of 0 is not read from the digital certificate database 63 and the next update is not performed. In this example, digital certificates are issued and updated by repeating the operations of steps a to k.
[0024]
As described above, in this example, a key pair is generated in which the expiration date estimated using a key generation algorithm that is common among generations every unit period, for example, every year is m times the unit period, for example, two years. Each time a digital certificate already generated needs to be updated, it is updated and issued to the user. Therefore, it becomes easy to manage the expiration date of each digital certificate, and it is possible to easily update the digital certificate while ensuring sufficient security. In addition, the digital certificate is always the plaintext decrypted with the predecessor key pair and encrypted with the next generation key pair, and the message digest and time information of the earliest digital certificate are used as they are. Because the previous digital certificate is not directly encrypted with the next-generation key pair as in the conventional method, decryption is easy and the amount of data in the digital certificate increases with each update. Nor.
[0025]
In this example, the authenticity of digital certificate renewal cannot be verified from a digital certificate as in the past, but if the digital certificate issuing organization is highly reliable, there is a practical problem. Absent. The issuing authority of the digital certificate in this example is the issuing authority side if another digital certificate issuing authority is used so as to prove the existence of the digital certificate by using a conventional nested digital certificate renewal method. Can be assured of reliability of renewal, and digital certificates handled by users can be easily decrypted without increasing the amount of data, and time is required for decryption when notarizing. The renewal can improve the practicality of a digital certificate whose expiration date can be extended.
[0026]
In the above embodiment, for convenience of explanation, whether a common key pair is used in each generation for an arbitrary digital document is not limited to this. For example, if the key pairs used for a plurality of digital documents in each generation are of the above-mentioned RSA method, the number of bits of each of the key pairs e and n is determined in common, and other values are set for each digital document. It is preferable to produce. In this case, the number of bits of the key pair e and n is increased in accordance with a predetermined algorithm every time an update is made in anticipation of the improvement of the processing capacity of the computer, It is also preferable to realize. When actually operating the system of the above-described embodiment, it is desirable from the viewpoint of safety that the system should always be constructed such that the friendship period of the latest key pair is always a predetermined multiple of the unit period. In addition, various changes can be made to the key pair update method.
[0027]
In the above embodiment, the user is prompted to set the digital certificate usage period in advance, the number of updates is set accordingly, and the digital certificate stored in the database is updated accordingly. However, the present invention is not limited to this, and a message prompting the user to renew the digital certificate is sent when the key pair is renewed. The digital certificate may be renewed only when there is. In this case, the user may be requested to send a certificate and a public key, and the public key may be sent from the user without being stored in the database.
[0028]
【The invention's effect】
According to the present invention, a key pair having an expiration date that is m times the unit period (m is a positive integer of 2 or more) is generated for each unit period, and the message digest and existence date of the original digital certificate are generated for each unit period. Since the additional information is encrypted and the digital certificate is updated, the digital certificate is not newly encrypted in a nested manner as in the conventional update method, so that the amount of data does not increase, There is no complication of the decoding process. In addition, since the key pair expiration date is uniformly set to a predetermined multiple of the unit period and the key pair is updated every unit period, the expiration date management becomes easy. In addition, the key pair is updated every unit period in which the key pair is recognized to be sufficiently valid, and the digital certificate is updated based on the unit period. Therefore, the digital certificate can be easily and securely updated a plurality of times.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining the concept of a digital certificate issuing system and a system program thereof according to the present invention.
FIG. 2 is a block diagram showing a configuration of a digital certificate issuing system according to an embodiment of the present invention.
3 is an explanatory diagram showing a digital certificate acceptance page of the digital certificate issuing system of FIG. 2. FIG.
FIG. 4 is an explanatory diagram showing a digital certificate response page of the digital certificate issuing system of FIG. 2;
FIG. 5 is a block diagram illustrating details of a time stamp process of the digital certificate issuing system in FIG. 2;
6 is a flowchart for explaining the operation of the digital certificate issuing system in FIG. 2;
FIG. 7 is an explanatory diagram for explaining the configuration of a digital certificate.
FIG. 8 is a flowchart for explaining the configuration of a conventional digital certificate issuing system.
[Explanation of symbols]
61 Key generation means, key generation processing (key generation process)
62 Certificate generation means, certificate generation processing (encryption / decryption process)
66 Update control means, update control processing (main process)

Claims (5)

Key generation means for generating a key pair that is a pair of a secret key and a public key whose expiration date is m times the unit period (m is a positive integer of 2 or more), and for generating a next-generation key pair for each unit period When,
Certificate generating means for generating a digital certificate by encrypting a message digest of the digital document and additional information such as the date and time of existence of the digital document using the latest key pair generated by the key generating means;
The expiration date of the digital certificate generated previously is from the generation of the digital certificate to the unit period, and when a new key pair is generated from the key generation unit, the certificate generation unit Update control means for encrypting the message digest and the first of the additional information using a key pair to generate a new digital certificate and updating the digital certificate Certificate issuing system.   The unit period is a time limit estimated that the key pair generated by the key generation means is at least valid,
  The key generation means updates the key pair every unit period of 1 / m of the expiration date.
The digital certificate issuing system according to claim 1.   The update control means includes
  Based on the maximum validity period of the digital certificate and the unit period, an upper limit means for obtaining the upper limit value of the digital certificate update count, and a count means for counting the digital certificate update count,
  The digital certificate is updated by the certificate generation unit until the number of updates counted by the counting unit reaches the upper limit value obtained by the upper limit unit.
The digital certificate issuing system according to claim 1 or 2, characterized in that   The update control means uses the certificate generation means to convert the digital certificate into a plain text using a public key that is within the validity period, and encrypts the digital certificate with the latest private key that is within the validity period. The digital certificate issuing system according to claim 1, 2, or 3, wherein the certificate is updated. Key generation processing for generating a key pair that is a pair of a secret key and a public key whose expiration date is m times the unit period (m is a positive integer of 2 or more), and generating a next-generation key pair for each unit period When,
A certificate generation process for issuing a digital certificate by encrypting a message digest of the digital document and additional information such as the date and time of existence of the digital document using the latest key pair generated by the key generation process;
The expiration date of the digital certificate generated earlier is from the generation of the digital certificate to the unit period, and when a new key pair is generated by the key generation process, the latest key pair is used. An update control process for encrypting the message digest and the first of the additional information by the certificate generation process to generate a new digital certificate and updating the digital certificate is realized on a computer. A featured digital certificate issuing system program.

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