JPH10268764A - Computerized information assurance method, assurance server, and recording medium storing assurance server program - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an electronic information assurance method for ensuring that the contents of electronic information created in the past have not been changed. SOLUTION: A user deposits digitized information digitally signed to a guarantee server. The assurance server adds assurance information such as a time stamp to the digitized information digitally signed by the user, performs an electronic signature, encrypts the information, and stores it in a database. The encryption method is appropriately changed. At a later date, the user requests the guarantee server to issue the digitized information. The warranty server
Reads, decodes, and delivers digitized information from the database. [Effect] With the double signature of the user's own digital signature and the digital signature of the guarantee server, it is possible to guarantee that the contents have not been changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic information assurance method, an assurance server, and a recording medium on which an assurance server program is recorded. More specifically, the present invention relates to a method for ensuring that contents of electronic information created in the past have not been changed. Computerized information assurance method for assurance, an assurance server for assuring a user that the contents of the deposited electronic information have not been changed, and a record of an assurance server program for realizing the functions of the assurance server on a computer Regarding the medium.

[0002]

2. Description of the Related Art Conventionally, a certification authority (Certification
rities) to distribute the certificate issued electronically, and to verify the identity of the digitized information by adding an electronic signature (digital signature) to the digitized information created. Proof message authentication techniques are known. However, there is no known computerized information assurance technology that guarantees that the contents of computerized information created in the past have not been changed.

[0003]

Therefore, the first aspect of the present invention
It is an object of the present invention to provide an electronic information assurance method for ensuring that the contents of electronic information created in the past have not been changed. A second object of the present invention is to provide a guarantee server that guarantees to a user that the contents of the deposited electronic information have not been changed. Further, a third object of the present invention is to provide a recording medium recording a guarantee server program for causing a computer to realize the functions of the guarantee server.

[0004]

According to a first aspect of the present invention, a user deposits digitized information with a third party that is recognized as having a fair position, and the third party deposits the digitized information. A method of assuring digitized information, characterized by storing the digitized information and providing the stored digitized information to a user while ensuring that the content is not changed. In the electronic information assurance method according to the first aspect, since a third-party organization that is deemed to be in a fair position stores the electronic information, it is assured that the contents have not been changed, and the stored electronic information is stored. Information can be provided to users. Therefore, for example, if the contract is digitized and deposited, it is possible to confirm at any time that the contents of the contract held by the parties have not been tampered with after the contract, and to ensure the security of the transaction. become.

[0005] In a second aspect, the present invention provides a method in which a user deposits digitized information with a third party that is recognized as having a fair position,
When the third party stores the digest of the digitized information and generates the digest of the digitized information requested by the user for assurance, matches it with the stored digest, and the content is not changed when it matches. Is provided to the user. In the above configuration, the digest is a value that has a smaller amount of information than the digitized information but expresses a characteristic pattern of the digitized information, and is also called a message digest. For example, it is a hash value created from the digitized information by a one-way hash function. In the method for assuring digitized information according to the second aspect, the contents of the digitized information requested by the user for guarantee are deposited in order to store a digest of the digitized information by a third party recognized as fair. It can be verified whether the information matches the digitized information. That is, it is possible to guarantee that the contents are not changed. Therefore, for example, if the contract is digitized and deposited, it is possible to confirm at any time that the contents of the contract held by the parties have not been tampered with after the contract, and to ensure the security of the transaction. become. Furthermore, since the third party stores the digest without storing the digitized information as it is, the burden of storage can be reduced.

[0006] In a third aspect, the present invention provides a storage means for storing digitized information deposited by a user, a digitized assurance that the stored digitized information and its contents have not been changed. And a computerized certificate issuing means for issuing a computerized certificate. If the assurance server according to the third aspect is used, the computerized information assurance method according to the first aspect can be suitably implemented. Therefore, for example, if the contract is digitized and deposited, it is possible to confirm at any time that the contents of the contract held by the parties have not been tampered with after the contract, and to ensure the security of the transaction. become.

In a fourth aspect, the present invention provides a storage means for generating and storing a digest of digitized information deposited by a user, and generating and storing a digest of digitized information requested by a user for guarantee. And an electronic guarantee issuing means for issuing an electronic guarantee that assures that the content has not been changed when the digest has been checked and matched. If the assurance server according to the fourth aspect is used, the electronic information assurance method according to the second aspect can be suitably implemented. Therefore, for example, if the contract is digitized and deposited, it is possible to confirm at any time that the contents of the contract held by the parties have not been tampered with after the contract, and to ensure the security of the transaction. become.

According to a fifth aspect of the present invention, in the assurance server according to the third or fourth aspect, the storage means encrypts and stores the digitized information or the digest and re-encrypts it using a different encryption method. A guarantee server characterized in that it can be stored again. In the assurance server according to the fifth aspect, since the digitized information or the digest is encrypted and stored, it is possible to prevent the contents from being tampered with during storage (it is impossible to know where to falsify). In addition, there is a possibility that the decryption method of the currently used encryption method may be discovered.However, since it is possible to re-encrypt and store it again using an encryption method for which no decryption method has been found, security is reduced. Can be secured.

[0009] In a sixth aspect, the present invention provides a storage means for storing digitized information deposited by a user, a digitized assurance that the stored digitized information and its contents have not been changed. And a computer-readable recording medium which records a guarantee server program for causing a computer to implement a computerized certificate issuing means for issuing a computerized certificate including the following. If the computer reads the guarantee server program recorded on the recording medium according to the sixth aspect, the guarantee server according to the third aspect can be realized.

[0010] In a seventh aspect, the present invention provides a storage means for generating and storing a digest of digitized information deposited by a user, and generating and storing a digest of the digitized information requested by a user for guarantee. A computer-readable record that records an assurance server program that causes a computer to implement an electronic assurance issuing means that issues an electronic assurance certificate that assures that the contents have not been changed when the digest is compared with the digest that has been performed. Provide media.
If the computer reads the guarantee server program recorded on the recording medium according to the seventh aspect,
A guarantee server from the viewpoint of can be realized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below with reference to the embodiments of the present invention shown in the drawings. Note that the present invention is not limited by this.

First Embodiment FIG. 1 is an explanatory diagram of an operation in which a proof server H100 receives a proof server certificate HC and a proof server public key CK from a proof server C100 trusted by society. . The assurance server H100 passes necessary documents (such as a corporate registry), assurance server information (such as the name of the assurance server) HI, and the assurance server public key HK to the certification server C100.
Apply for issuance of the guarantee server certificate HC. Certification server C
100 is the assurance server information HI and the assurance server public key HK
Are combined to create combined information Ghc (C1). Next, a hash value is calculated from the composite information Ghc using a hash function, and the hash value is encrypted by public key encryption using a certification server private key to create a certification server signature CSh (C2). Next, the combining information Ghc and the certification server signature CSh are combined (C3), a proof server certificate HC is created, and passed to the proof server H100. At the same time, the certification server public key CK is also passed to the guarantee server H100.

FIG. 2 shows that the user device U100 sends a user certificate UC and a certification server public key CK from the certification server C100.
FIG. User device U100
Passes the necessary documents, user information (user name, etc.) UI and user public key UK to the certification server C100, and applies for issuance of the user certificate UC. The certification server C100 combines the user information UI and the user public key UK to create combined information Guc (C11). Next, a hash value is calculated from the composite information Guc using a hash function, and the hash value is encrypted by public key encryption using a certification server private key to create a certification server signature CSu (C12). Next, the combining information Guc and the certification server signature CSu are combined (C13), a user certificate UC is created, and passed to the user device U100. At the same time, the certification server public key CK is also passed to the user device U100.

FIG. 3 is an explanatory diagram of the operation of connecting the user apparatus U100 to the guarantee server H100. User device U
100 and the assurance server H100 constitute an electronic information assurance system 100. The function of the guarantee server H100 is realized by a computer reading a recording medium on which the guarantee server program is recorded. Similarly, the user device U100 is also a computer, and the user device U100 and the guarantee server H100 are connected by a communication line. The user device U100 sends a connection request Rc to the guarantee server H100, and receives the guarantee server certificate HC returned as a response from the guarantee server H100. Next, the assurance server certificate HC is decomposed into composite information Ghc and a certification server signature CSh (U1), a hash value is obtained from the composite information Ghc by a hash function (U2), and the certification server signature CSh is converted to a certification server public key CK. The hash value is decrypted by using the public key encryption used (U3), and the signature of the certification server C100 is confirmed by comparing the two hash values (U4). When the signature of the certification server C100 is confirmed,
The combined information Ghc is decomposed into assurance server information HI and assurance server public key HK (U5). If the signature of the certification server C100 cannot be confirmed, the processing is terminated (the same applies hereinafter). Next, the assurance server information HI is confirmed (U6), and if there is no error, the user certificate UC is sent to the assurance server H100. If there is an error, the processing is terminated (the same applies hereinafter).

FIG. 4 is an explanatory diagram of an operation in which the guarantee server H100 accepts the connection of the user device U100. The guarantee server H100 transmits a connection request R from the user device U100.
Upon receipt of c, a guarantee server certificate HC is returned as a response. Next, a user certificate UC sent from the user device U100 is received. Next, the user certificate UC is decomposed into the composite information Guc and the certification server signature CSu (H1),
A hash value is obtained from the composite information Guc by a hash function (H2), and the certification server signature CSu is decrypted by public key encryption using the certification server public key CK and returned to a hash value (H3), and the two hash values are collated. To confirm the signature of the certification server C100 (H4). Certification server C10
When the signature of 0 is confirmed, the composite information Guc is decomposed into the user information UI and the user public key UK (H5). next,
The user information UI is confirmed (H6), and if there is no error, the connection of the user device U100 is accepted.

FIG. 5 is an explanatory diagram of a work in which the user device U100 deposits digitized information (hereinafter referred to as deposited data) to the guarantee server H100. The user device U100 calculates a hash value from the deposited data DD using a hash function, encrypts the hash value using public key encryption using a user secret key, and creates a user signature USd (U1).
2). Next, the deposited data DD and the user signature USd are combined (U13), the deposited signature data SDU is created, and sent to the guarantee server H100. Next, the trust signature data SDH returned as a response from the guarantee server H100 is received. Next, the trust signature data SDH is decomposed into composite data Ghd and trust signature HSd (U21), and the composite data Ghd
A hash value is obtained by a hash function from (U22),
The trust signature HSd is decrypted by public key encryption using the assurance server public key HK and returned to a hash value (U23), 2
The signature of the guarantee server H100 is confirmed by comparing the two hash values (U24). When the signature of the guarantee server H100 is confirmed, the combined data Ghd is decomposed into guarantee information (such as a time stamp at the time of acceptance) CI and deposited signature data SDU (U25). If the signature of the guarantee server H100 cannot be confirmed, the processing is terminated (the same applies hereinafter). Next, the assurance information CI is confirmed (U26). Also, it checks whether the deposited signature data SDU obtained by disassembly matches the sent one (U27). Further, the trust signature HSd is stored (U28).

FIG. 6 is an explanatory diagram of an operation in which the guarantee server H100 stores the deposit data DD from the user device U100. The guarantee server H100 receives the deposited signature data SDU sent from the user device U100. Next, the deposited signature data SDU is decomposed into the deposited data DD and the user signature USd (H11), a hash value is obtained from the deposited data DD by a hash function (H12), and the user signature USd is used for the user public key UK. Decrypted by the public key encryption and returned to the hash value (H13), the two hash values are collated to confirm the signature of the user (H14). If the user's signature cannot be confirmed, the processing is terminated (the same applies hereinafter). When the signature of the user is confirmed, the deposited signature data SDU and the guarantee information CI are combined, and the combined data Gh
d is created (H21). Next, a hash value is calculated from the combined data Ghd using a hash function, and the hash value is encrypted by public key cryptography using a guarantee server private key to create a trust signature HSd (H22). Next, the synthetic data Ghd and the trust signature HSd are synthesized to create the trust signature data SDH (H23). Then, the contracted signature data SDH is sent to the user device U100, and is encrypted by an internally used encryption method and stored in the storage DB in association with the contracted signature HSd. In addition, it re-encrypts regularly or irregularly using the latest encryption method in which the decryption method is not found at that time, and stores it again.

FIG. 7 is an explanatory diagram of an operation in which the user device U100 requests the guarantee server H100 to issue a warranty IC. The user device U100 uses the stored trust signature H
A hash value is calculated from Sd using a hash function, and the hash value is encrypted by public key encryption using a user secret key to create a user signature USi (U32). next,
The trust signature HSd and the user signature USi are combined (U3
3), create a grant request Ri and send it to the guarantee server H100. Next, a guarantee IC returned as a response from the guarantee server H100 is received. Next, the guarantee IC is decomposed into the combined data Ghi and the guarantee signature HSi (U41), a hash value is obtained from the combined data Ghi by a hash function (U42), and the guarantee signature HSi is converted into a public key cryptosystem using the guarantee server public key HK. And returns to the hash value (U43), the two hash values are collated and the guarantee server H
The signature of 100 is confirmed (U44). Warranty server H10
If the signature of 0 is confirmed, the combined data Ghi is decomposed into delivery information (time stamp at the time of delivery, etc.) II and the commissioned signature data SDH (U45). Next, the trust signature data SDH is decomposed into the composite data Ghd and the trust signature HSd (U46). Next, the combined data Ghd is decomposed into guarantee information CI and deposited signature data SDU (U47). next,
Deposited signature data SDU is replaced with deposited data DD and user signature U
Decomposes into Sd (U48). Thus, the user can obtain the deposit data DD in which the guarantee server H100 guarantees that there is no change in the contents. Since the user has his / her own user signature USd, the user cannot deny the assurance of the assurance server H100 that the content is not changed.

FIG. 8 is an explanatory diagram of an operation in which the guarantee server H100 issues a warranty IC to the user device U100.
The guarantee server H100 receives the grant request Ri sent from the user device U100. Next, the grant request Ri is disassembled into the trust signature HSd and the user signature USi (H3
1), a hash value is obtained from the trust signature HSd by a hash function (H32), the user signature USi is decrypted by public key encryption using the user public key UK and returned to a hash value (H33), and two hash values are obtained. Is checked to confirm the signature of the user (H44). When the signature of the user is confirmed, the storage DB is searched using the trust signature HSd as a key, the corresponding data is extracted, and the data is decrypted by an internally used encryption method to obtain the trust signature data SDH (H35).
Next, the combined signature data SDH and the grant information II are combined to create combined data Ghi (H41). Next, a hash value is calculated from the composite data Ghi using a hash function, and the hash value is encrypted by public key encryption using a guarantee server private key to create a guarantee signature HSi (H4).
2). Next, the combined data Ghi and the guarantee signature HSi are combined to create a guarantee IC (H43). Then, the warranty IC is sent to the user device U100.

According to the computerized information assurance system 100 of the first embodiment, the assurance server H100 confirms that the contents of the computerized information (deposited data DD) created in the past have not been changed by the user (U100). ) Can be guaranteed.

In the first embodiment, the connection work and the deposit work from the user device U100 to the guarantee server H100 are performed in order, but they are performed simultaneously as described in the following second embodiment. Is also good.

Second Embodiment A computerized information assurance system 200 is composed of a user device U200 and an assurance server H200. The functions of the guarantee server H200 are realized by a computer reading a recording medium on which the guarantee server program is recorded. Similarly, the user device U200 is also a computer, and the user device U200 and the guarantee server H200 are connected by a communication line. FIG. 9 is an explanatory diagram of a work in which the user device U200 connects to the guarantee server H200 and deposits digitized information (hereinafter, referred to as deposit data) at the same time. U12 ~
U13 is the same as U12 to U13 in FIG. 5, calculates a hash value from the deposited data DD using a hash function, encrypts the hash value using public key cryptography using a user secret key, and converts the hash value into a user signature USd. (U12), and combines the deposited data DD with the user signature USd (U13).
Create the deposit signature data SDU. Next, the deposited signature data SDU and the user certificate UC are combined (U51), and the proof deposited signature data XD is created and sent to the guarantee server H200. Next, it receives the certification acceptance signature data YD returned as a response from the assurance server H200. Next, the certification acceptance signature data YD is decomposed into the acceptance signature data SDH and the guarantee server certificate HC (U61). U1 to U5 are the same as U1 to U6 in FIG. 3, and decompose the assurance server certificate HC into the combined information Ghc and the certification server signature CSh (U
1) A hash value is obtained from the synthetic information Ghc by a hash function (U2), the certification server signature CSh is decrypted by public key encryption using the certification server public key CK, and the hash value is returned (U3). To verify the signature of the certification server C100 (U4),
c is divided into assurance server information HI and assurance server public key HK (U5), and the contents of the assurance server information HI are confirmed (H6). U21 to U28 are the same as U21 to U28 in FIG.
(U21) and the combined data Gh
A hash value is calculated from d by a hash function (U2
2), the trust signature HSd is decrypted by public key encryption using the assurance server public key HK and returned to a hash value (U2
3) Check the two hash values and verify the guarantee server H200
(U24), the combined data Ghd is decomposed into assurance information (such as a time stamp at the time of acceptance) CI and the deposited signature data SDU (U25), and the assurance information CI is confirmed (U26) and decomposed. The obtained deposited signature data SDU is checked to see if it matches the one sent (U27), and the deposited signature HSd
Is stored (U28). Further, the composite data Ghd
Is stored (U68).

FIG. 10 is an explanatory diagram of an operation in which the guarantee server H200 permits the connection of the user device U200 and encrypts and stores the hash value of the deposit data DD. The assurance server H200 decomposes the proof deposited signature data XD sent from the user device U200 into the deposited signature data SDU and the user certificate UC (H51). H1-H6
Is the same as H1 to H6 in FIG.
Is decomposed into composite information Guc and certification server signature CSu (H
1) A hash value is obtained from the synthetic information Guc by a hash function (H2), and the certification server signature CSu is decrypted by public key encryption using the certification server public key CK and returned to a hash value (H3). To verify the signature of the certification server C100 (H4),
c is decomposed into user information UI and user public key UK (H
5), the user information UI is confirmed (H6), and if there is no error, the connection of the user device U200 is permitted. H11-H1
4 is the same as H11 to H14 in FIG. 6, decomposes the deposited signature data SDU into the deposited data DD and the user signature USd (H11), obtains a hash value from the deposited data DD by a hash function (H12), and uses The user signature USd is decrypted by public key encryption using the user public key UK and returned to a hash value (H13), and the two hash values are collated to confirm the user's signature (H14). H21-H23
Is the same as H21 to H23 in FIG. 6, and combines the deposited signature data SDU with the assurance information CI to obtain the combined data Ghd.
(H21), a hash value is calculated from the combined data Ghd using a hash function, and the hash value is encrypted by public key cryptography using a secure server private key to create a trustee signature HSd (H22). The data Ghd and the trust signature HSd are combined to create the trust signature data SDH (H23). Next, a hash value is calculated from the combined data Ghd using a hash function (H57), encrypted by an internally used encryption method (H58), and the trust signature HSd
And store it in the storage DB in association with. In addition, it re-encrypts regularly or irregularly using the latest encryption method in which the decryption method is not found at that time, and stores it again. Further, the trust signature data SDH and the guarantee server certificate HC are combined (H59), and the proof trust signature data YD is created and sent to the user device U200.

FIG. 11 is an explanatory diagram of an operation in which the user device U200 requests the guarantee server H200 to guarantee that the contents of the deposited data DD have not been changed. The user device U200 combines the stored trust signature HSd with the combined data Ghd (U71), and creates guarantee request data Gvd. Next, a hash value is calculated from the guarantee request data Gvd by using a hash function, and the hash value is encrypted by public key encryption using a user secret key, and the user signature U is obtained.
Sv is created (U72). Next, the warranty request data Gv
d and the user signature USv are combined (U73), and the guarantee request V
D is created and sent to the guarantee server H200. Next, the guarantee result VR returned as a response from the guarantee server H200
Receive. Next, the assurance result VR is decomposed into the combined information Ghv and the assurance signature HSv (U81), a hash value is obtained from the combined information Ghv by a hash function (U82), and the assurance signature HSv is converted into a public key using the assurance server public key HK. The hash value is decrypted and returned to the hash value (U83), and the two hash values are collated to confirm the signature of the guarantee server H200 (U84). When the signature of the guarantee server H200 is confirmed, the composite information Ghv is decomposed into the grant information II and the collation result R (U85). In this way, the user can check the collation result R obtained by the assurance server H200 that the contents have not been changed.
Can be obtained.

FIG. 12 is an explanatory diagram of an operation in which the guarantee server H200 issues a guarantee result VR to the user device U200. The guarantee server H200 receives the guarantee request VD sent from the user device U200. Next, warranty request V
D is divided into assurance request data Gvd and user signature USv (H81), a hash value is obtained from the assurance request data Gvd by a hash function (H82), and the user signature USv is used as public key encryption using the user public key UK. To return to the hash value (H83), and collate the two hash values to confirm the signature of the user (H84). Once the user's signature is confirmed, the guarantee request data Gvd is
hd and the trust signature HSd (H85). Next, a hash value is obtained from the combined data Ghd by a hash function (H86). Further, the storage DB is searched using the trust signature HSd as a key, the corresponding data is extracted, and the data is decrypted by an internally used encryption method to obtain a hash value (H
87). Next, the hash value obtained from the composite data Ghd and the decrypted hash value are collated (H88), and the collation result R
Create Next, the matching result R and the grant information II are combined to create combined information Ghv (H91). Next, a hash value is calculated from the synthetic information Ghv by using a hash function, and the hash value is encrypted by public key encryption using a guarantee server secret key to create a guarantee signature HSv (H9).
2). Next, the combining information Ghv and the guarantee signature HSv are combined to create a guarantee result VR (H93). Then, the guarantee result VR is sent to the user device U200.

According to the electronic information assurance system 200 of the second embodiment described above, the previously created deposit data DD
Can be assured to the user device U200 by the assurance server H200 that the content has not been changed. further,
The assurance server H200 stores the hash value of the deposited data DD without storing the deposited data DD as it is, so that the burden of storage can be reduced.

In the second embodiment, the connection work from the user device U200 to the guarantee server H200 and the depositing work are performed at the same time. However, the connection work is sequentially performed as described in the first embodiment. Is also good.

[0028]

According to the electronic information assurance method of the present invention,
Since a fair third party guarantees that the contents of the digitized information created in the past have not been changed, transaction security can be ensured. Further, according to the assurance server of the present invention, it is possible to assure the user that the contents of the deposited digitized information have not been changed. Further, according to the recording medium storing the guarantee server program of the present invention, the function of the guarantee server can be realized by a computer.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an operation in which a proof server receives a proof server certificate and a proof server public key from a proof server.

FIG. 2 is an explanatory diagram of an operation in which a user device receives a user certificate and a certification server public key from a certification server.

FIG. 3 is an explanatory diagram of a work in which a user device connects to a guarantee server.

FIG. 4 is an explanatory diagram of an operation in which a guarantee server accepts a connection of a user device.

FIG. 5 is an explanatory diagram of a work in which a user device deposits digitized information with a guarantee server.

FIG. 6 is an explanatory diagram of an operation in which a guarantee server stores deposited data from a user device.

FIG. 7 is an explanatory diagram of an operation in which a user device requests a guarantee server to issue a guarantee.

FIG. 8 is an explanatory diagram of an operation in which a guarantee server issues a guarantee to a user device.

FIG. 9 is an explanatory diagram of a work in which the user device connects to the guarantee server and deposits digitized information at the same time.

FIG. 10 is an explanatory diagram of an operation in which a guarantee server permits connection of a user device and encrypts and stores a hash value of deposited data.

FIG. 11 is an explanatory diagram of a work in which a user device requests a guarantee to a guarantee server that contents of deposited data have not been changed.

FIG. 12 is an explanatory diagram of an operation in which a guarantee server issues a guarantee result to a user device.

Claims (7)

[Claims] Claims 1. A user deposits digitized information with a third party that is deemed to be in a fair position, and the third party stores the digitized information and guarantees that the contents have not been changed. A method for assuring digitized information, wherein the stored digitized information is provided to a user. 2. The user deposits the digitized information with a third party that is deemed to be in a fair position, and the third party keeps a digest of the digitized information and the digitized information requested by the user for assurance. A computerized information assurance method comprising: generating a digest of information; collating the digest with the stored digest; and assuring to the user that the content has not been changed when the digest matches. A means for storing the digitized information deposited by a user, and a digitized guarantee including a digitized guarantee that the stored digitized information and its contents have not been changed are issued. An assurance server comprising electronic guarantee issuing means. 4. A storage means for generating and storing a digest of the digitized information deposited by a user, and generating a digest of the digitized information requested by the user for verification and matching with the stored digest. And an electronic guarantee issuing means for issuing an electronic guarantee that assures that the contents have not been changed. 5. The assurance server according to claim 3, wherein the storage unit encrypts and stores the digitized information or the digest and re-encrypts and stores the encrypted information or the digest using a different encryption method. Assurance server characterized in that it is possible. 6. A means for storing the digitized information deposited by a user, and a digitized guarantee including a digitized guarantee that the stored digitized information and its contents have not been changed are issued. A computer-readable recording medium that records a guarantee server program that causes a computer to realize the electronic guarantee issuing means. 7. A storage means for generating and storing a digest of the digitized information deposited by the user, and generating a digest of the digitized information requested by the user for collation and matching with the stored digest. A computer-readable recording medium that stores a guarantee server program that causes a computer to implement an electronic guarantee issuing unit that issues an electronic guarantee that assures that the contents have not been changed.