JP2007028015A - Program, system and method for time stamp verification, and time stamp generation request method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To individually verify time stamps added to digital data even if a time stamp common among a plurality of digital data is acquired. <P>SOLUTION: In requesting to verify the time stamp common among contents C1-C3 which is added to a content C1, a client 1 adds the IDs and digests of the other contents C2, C3 and additional information including time stamps to the content C1, and transmits them. In a content management server 4, a digest generator 62 compares a combined digest of the digest generated from the received content C1 and digests of the other contents C2, C3 included in the additional information and a time stamp generating time with a digest obtained by decoding the time stamp, thereby verifying the time stamp added to the content C1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to time stamp verification, and particularly to handling of a time stamp when a common time stamp is generated for a plurality of digital data.

  When digital data such as an electronic file is created on a computer, the creation time is set as attribute information of the digital data. However, although the creation time is considered to be attribute information that should not be changed, it can be rewritten in the same way as normal data. In other words, since digital data can be freely created as data with a past or future time, it is actually impossible to guarantee when the digital data was actually created with only attribute information. is there.

  Therefore, at present, a time stamp station by a third party is provided to perform time authentication of digital data. That is, when a user transmits a time stamp request including a digest of digital data to a time stamp authority, the time stamp authority adds time information to the sent digest, and then uses the time stamp authority's private key to create a digital signature. After replying, reply with the signed digest. The information to be returned is generally called a “time stamp token”. When the user wants to prove the existence of digital data at a certain time, the digest with the digital data time stamp added has a public key corresponding to the secret key used for the digital signature at the time stamp authority. Request time stamp verification by sending it to a time stamp authority. Upon receiving the request, the time stamp authority or the like verifies the time stamp sent using the digital signature. As a result, the user can prove that the digital data already existed at that time.

  As described above, conventionally, a time-stamped time stamp can be obtained by transmitting a digest generated from digital data to a time stamp station. However, in order to obtain a time stamp from the time stamp station, it is necessary to transmit a digest to the time stamp station. That is, when it is desired to obtain time stamps for a large number of digital data, conventionally, it is troublesome to transmit a digest of all digital data.

  In order to solve such a problem, a technique has been proposed in which a plurality of digital documents are combined to generate a digest, and the combined digest is transmitted to a time stamp station (for example, Patent Document 1). . By using this conventional technique, the user can acquire a common time stamp for a plurality of digital documents. Therefore, managing the correspondence between multiple digital documents and one common time stamp eliminates the hassle of sending digests of all digital documents to the time stamp station, and also issues time stamps. However, if pay-as-you-go is charged, it can also contribute to cost reduction.

JP 2001-142398 A JP 2003-338815 A JP 2001-209308 A

  However, in the prior art, when a common time stamp is added to a digital document, the time stamp of the digital document cannot be individually verified. For example, to obtain a common time stamp for three digital documents A, B, and C, the digital documents A, B, and C are combined to generate a digest, and the combined digest is sent to the time stamp station. For example, in the decoding process at the time of verifying the time stamp of the digital document A, not only the digital document A but also the other digital documents B and C generated with the digital document A and the combined digest are required. Come. That is, the time stamp of the digital document A cannot be verified unless the digital document A and other digital documents B and C are handled.

  The present invention has been made to solve the above-described problems, and even when a time stamp common to a plurality of digital data is acquired, the time stamp added to the digital data can be individually verified. The purpose is to do.

  In order to achieve the above object, the time stamp verification program according to the present invention provides a time stamp using side computer used by a user of a time stamp issued by a time stamp authority for authentication of the generation time of digital data. , For the verification target digital data that is the target of the time stamp verification request, information about other digital data in which a time stamp common to the verification target digital data is generated, and the time including the time stamp and the time stamp generation time information Additional information generating means for generating additional information including the stamp information, time stamp verification requesting means for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer It is to function as.

  Further, the time stamp using computer further sends a digest generated from each of the plurality of digital data to the time stamp verifying computer to request generation of a common time stamp for each of the plurality of digital data. A stamp generation requesting unit, and a time stamp receiving unit that receives time stamp information sent from the time stamp verification computer in response to a generation request by the time stamp generation requesting unit.

  A time stamp verification program according to another invention is a time stamp verification side computer that performs verification of a time stamp added to digital data sent from a time stamp use side computer. Additional information including time stamp information added to the digital data, and information related to other digital data that is used to verify a time stamp of the digital data that is generated in common with the digital data. Receiving means for receiving digital data to which information is added; time stamp decoding means for generating a digest by decoding time stamp information included in additional information added to digital data received by the receiving means; and the receiving means But Digest generation that combines the digest of the other digital data acquired based on the information about the other digital data included in the additional information added to the received digital data and the digest generated from the digital data received by the receiving means And the digest generated by the digest generating means is compared with the digest generated by the time stamp decoding means to function as a time stamp verifying means for verifying the time stamp.

  In addition, the time stamp verification computer further uses a combined digest of a plurality of digital data digests sent from the time stamp using computer at the time of the time stamp generation request request, for authentication of the digital data generation time. A time stamp request means for transmitting a time stamp to the time stamp authority, time stamp information sent from the time stamp authority in response to a request from the time stamp request means, and time stamp information including time stamp generation time information, It serves as a time stamp notifying means for notifying the time stamp generating request request source computer of the time stamp using side computer.

  A time stamp verification program according to another invention is a verification target in which a time stamp using computer used by a user of a time stamp issued by a time stamp authority is used as a time stamp verification request target for authentication of digital data generation time. For the digital data, additional information including information related to other digital data in which a time stamp common to the verification target digital data is generated and time stamp information including the time stamp and time stamp generation time information is generated. The additional information generating means that functions as time stamp verification requesting means for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verifying computer. On the other hand, the time stamp verification side computer for verifying the time stamp added to the digital data sent from the time stamp using side computer is the digital data sent from the time stamp using side computer, The digital data to which additional information including time stamp information added to the digital data and information related to other digital data that is used for time stamp verification of the digital data that is generated in common with the digital data is added. Receiving means for receiving, time stamp decoding means for generating a digest by decoding time stamp information included in the additional information added to the digital data received by the receiving means, added to the digital data received by the receiving means Tatsuki Digest generating means for combining a digest of the other digital data acquired based on information about the other digital data included in the information and a digest generated from the digital data received by the receiving means, and the digest generating means are combined The generated digest and the digest generated by the time stamp decoding means are compared to function as time stamp verification means for performing time stamp verification.

  The additional information generating means includes the digest of the other digital data in the additional information as information on the other digital data, and the digest generating means adds the additional information added to the digital data received by the receiving means. The digest included in the information is combined with the digest generated from the digital data received by the receiving means.

  The additional information generation means includes data identification information for identifying the other digital data in the additional information as information on the other digital data, and further includes the time stamp verification computer. Are made to function as acquisition means for acquiring digital data corresponding to each data identification information included in the additional information added to the received digital data. The digest generating unit combines the digest generated from the digital data acquired by the acquiring unit and the digest generated from the digital data received by the receiving unit.

  The additional information generating means includes each data identification information in the additional information as information related to the other digital data after being encrypted with the public key of the time stamp verification side computer. The computer further decrypts the encrypted data identification information contained in the additional information added to the digital data received by the receiving means with a secret key corresponding to the public key of the time stamp verifying computer. It functions as an extracting means for extracting data identification information of other digital data. Then, the acquisition means acquires digital data corresponding to each data identification information extracted by the extraction means.

  The time stamp verifying computer further includes a random number generating means for generating a random number, a digital data transmitting means for adding the random number generated by the random number generating means to the digital data transmitted to the time stamp using computer, the time The data identification information of the digital data transmitted to the stamp using computer is made to function as random number information storage means for storing the added random number in association with each other. On the other hand, the time stamp use side computer is further caused to function as a use side receiving means for receiving the digital data sent from the time stamp verification side computer. Then, the additional information generating means combines the random number transmitted from the time stamp verifying computer added to the digital data to each data identification information of the other digital data, and the random number is combined. Each data identification information is encrypted with the public key of the time stamp verifying computer and then included in the additional information as information on the other digital data, and the extracting means is added to the digital data received by the receiving means. The encrypted data identification information and random number included in the additional information are decrypted with a secret key corresponding to the public key of the time stamp verifying computer, and are associated with the data identification information of the digital data received by the receiving means. The random number is taken out from the random number storage means, and the decrypted data is based on the taken random number. And extracts data identification information by separating the random number from the identification information.

  The time stamp using computer according to the present invention is a time stamp verifying target to be verified in a time stamp using computer used by a user of a time stamp issued by a time stamp authority for authenticating the generation time of digital data. For the digital data, additional information including information related to other digital data in which a time stamp common to the verification target digital data is generated and time stamp information including the time stamp and time stamp generation time information is generated. And a time stamp verification requesting unit for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer.

  The time stamp verifying computer according to the present invention is a time stamp verifying computer that verifies a time stamp added to digital data sent from a time stamp using computer, and is sent from the time stamp using computer. Additional information including time stamp information added to the digital data, and information related to other digital data that is used to verify a time stamp of the digital data that is generated in common with the digital data. Receiving means for receiving digital data to which information is added; time stamp decoding means for generating a digest by decoding time stamp information included in additional information added to the digital data received by the receiving means; The digest of the other digital data acquired based on the information related to the other digital data included in the additional information added to the digital data received by the receiving means is combined with the digest generated from the digital data received by the receiving means. And a time stamp verification means for verifying the time stamp by comparing the digest generated by the digest generation means by combining with the digest generated by the time stamp decoding means. To do.

  A time stamp verification system according to the present invention includes the time stamp using computer and the time stamp verifying computer.

  A time stamp generation request method according to the present invention is performed by a time stamp using computer used by a user of a time stamp issued by a time stamp authority for authentication of the generation time of digital data, and is a time stamp verification request target. Additional information including information related to other digital data in which a time stamp common to the verification target digital data is generated and time stamp information including the time stamp and time stamp generation time information with respect to the verification target digital data. And a time stamp verification requesting step for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer. To do.

  The time stamp verification method according to the present invention is implemented by a time stamp verification side computer for verifying a time stamp added to digital data sent from a time stamp use side computer, and is sent from the time stamp use side computer. Digital data that is included, and includes time stamp information added to the digital data, and information related to other digital data in which a time stamp common to the digital data is generated and used for time stamp verification of the digital data. A receiving step for receiving digital data to which additional information is added, and a time stamp decoding for generating a digest by decoding time stamp information included in the additional information added to the digital data received by the receiving step. The digest of the other digital data acquired based on the information related to the other digital data included in the additional information added to the digital data received in the reception step, and the digital data received in the reception step. A digest generation step for combining the generated digest, a time stamp verification step for verifying a time stamp by comparing the digest generated by the digest generation step and the digest generated by the time stamp decoding step; It is characterized by including.

  According to the present invention, when a time stamp using computer acquires a common time stamp for a plurality of digital data, additional information including information related to other digital data necessary for time stamp verification is converted into digital data. Since it is added, the time stamp verifying computer can individually verify the time stamp added to the digital data without using other digital data.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram showing an embodiment of a time stamp verification system according to the present invention. FIG. 1 shows a configuration in which a plurality of clients 1, a content management server 4, and a time stamp server 7 are connected to a public network 9. In this embodiment, a time authentication technique for digital data using a time stamp issued by a time stamp authority is provided. The time stamp server 7 corresponds to a server computer for time stamp issuance installed in the time stamp authority. . In this embodiment, an existing time stamp server can be used as it is. The client 1 corresponds to a time stamp using computer used by a user who acquires and uses a time stamp issued by a time stamp authority for authentication of the generation time of content corresponding to digital data. In this embodiment, two types of time stamp verification methods, simple verification and normal verification, are provided. In the case of simple verification, the client 1 responds to a request from the client 1 that is a computer using the time stamp. Accordingly, it can be a time stamp verifying computer that performs time stamp verification. The content management server 4 is a computer that holds and manages the content handled by each client 1, and corresponds to a time stamp verifying computer that performs time stamp verification in both simple verification and normal verification in the present embodiment.

  FIG. 2 is a block configuration diagram of the time stamp verification system in the present embodiment. FIG. 2 shows a client 1 operating as a time stamp using computer and a content management server 4 operating as a time stamp verifying computer.

  The client 1 includes a content acquisition unit 12, a time stamp generation request processing unit 14, a time stamp verification request processing unit 16, and a display unit 18. The content acquisition unit 12 acquires content to be added with a time stamp from the content management server 4 and stores it in the content storage unit 34. The time stamp generation request processing unit 14 includes a digest generation unit 20, a digest transmission unit 22, and a time stamp acquisition unit 24. The time stamp generation request processing unit 14 transmits a time stamp generation request to the content management server 4 and is common to a plurality of contents. To obtain the timestamp to be added. The digest generation unit 20 generates a digest from the content using a hash function. The digest transmission unit 22 sends a request to generate a time stamp by transmitting the digest generated from each content to the content management server 4. The time stamp acquisition unit 24 acquires time stamp information acquired from the time stamp station by the content management server 4 in response to the generated generation request, and registers the time stamp information in the time stamp holding table 36. The time stamp information includes a time stamp included in the time stamp token and a time stamp generation time, and the time stamp holding table 36 includes a plurality of time stamps to which the time stamp is added to the acquired time stamp information. Information for identifying the content, in the present embodiment, the content ID is set and registered in association with each other.

  The time stamp verification request processing unit 16 includes an additional information generation unit 26, a verification request unit 28, and a verification result acquisition unit 30, and requests the content management server 4 to verify the time stamp added to the content. The additional information generation unit 26 included in the time stamp verification request processing unit 16 generates additional information necessary for time stamp verification in the content management server 4. The other content information generation unit 32 included in the additional information generation unit 26 generates, for each content to which a time stamp is added, information related to the other content in which the time stamp is generated together with the content. The verification request unit 28 transmits the content information formed by adding the additional information generated by the additional information generation unit 26 to the content to which the time stamp to be verified is added to the content management server 4, thereby verifying the time stamp. Request. The verification result acquisition unit 30 acquires the result of time stamp verification in the content management server 4 from the content management server 4. The display unit 18 displays the verification result acquired by the verification result acquisition unit 30. The processing functions of the constituent elements 12 to 18 included in the client 1 are realized by a cooperative operation of a time stamp verification program that exhibits the processing functions and hardware configuring the client 1.

  On the other hand, the content management server 4 includes a content distribution unit 42, a time stamp acquisition processing unit 44, and a time stamp verification processing unit 46. The content distribution unit 42 downloads the content stored in the content database 68 to the client 1 that requested the distribution. The time stamp acquisition processing unit 44 includes a digest acquisition unit 48, a time stamp request unit 50, a time stamp acquisition unit 52, and a time stamp notification unit 54, and responds to a time stamp generation request from the client 1 with a time stamp server. The time stamp is acquired from 7 and returned to the requesting client 1. The digest acquisition unit 48 accepts a time stamp generation request from the client 1. Since the generation request request sent from the client 1 includes digests of a plurality of contents to which time stamps are added, the time stamp request unit 50 uses a single hash function H from each digest. A combined digest is generated, and a time stamp request including the combined digest is transmitted to the time stamp server 7. The time stamp acquisition unit 52 receives the time stamp token generated by the time stamp server 7 in response to the time stamp request, and includes time stamp information included in the time stamp token, that is, time stamp and time stamp generation time information. Identification information of a plurality of contents to which time stamps are added is associated with the generation time and registered in the time stamp management table 70. The time stamp notifying unit 54 transmits time stamp information including the time stamp and the generation time thereof to the generation requesting client 1.

  The time stamp verification processing unit 46 includes a verification request receiving unit 58, a content reading unit 60, a digest generation unit 62, a time stamp verification unit 64, and a verification result notification unit 66, and is added to the content in response to a request from the client 1. Verify the time stamp. The verification request receiving unit 58 receives a time stamp verification request sent from the client 1. This request includes content to which additional information including a time stamp to be verified is added. The content reading unit 60 reads content necessary for normal verification from the content database 68. The digest generation unit 62 generates a digest from the content using a hash function. The hash function used by the digest generation unit 62 is the same as the hash function used by each client 1. The time stamp verification unit 64 verifies the time stamp by comparing the digests generated by the two types of methods from the content sent from the client 1 and the additional information. The verification result notification unit 66 notifies the content transmission source client 1 of the verification result in the time stamp verification unit 64. The processing functions of the constituent elements 42 to 46 included in the content management server 4 are realized by a cooperative operation of a time stamp verification program that exhibits the processing functions and the hardware that configures the content management server 4.

  Next, the operation in the present embodiment will be described. Before that, various symbols, variables, and the like used for the description of the operation will be defined.

  First, a content used as message data to which a time stamp is added is defined as Cx (x = 1, 2,... N). The time stamp generation target area of each content Cx is Sx, and the time stamp information area for storing information other than Sx such as additional information including time stamp information is Ex. The time stamp generation target area Sx is an area including data used for generating a digest necessary for generating a time stamp among data constituting the content. The time stamp information area Ex is a storage area for information to be added to the digest, and corresponds to an area for storing additional information including time stamp information in the present embodiment. The client 1 sends, for each content Cx, a signature target area Sx including data used for generating a digest and a signature information area Ex including information necessary for signature verification to the content management server 4 as a set. become. The hash function used by the client 1 and the content management server 4 to generate a digest of content is f, the hash function used by the content management server 4 when acquiring a time stamp is H, and information for identifying each content is used. The content ID is IDx, the signature function is Enc (signkey, data), the verification function is Dec (verifykey, data), the public key of the content management server 4 is Es, the secret key of the content management server 4 is Ds, and the time stamp server 7 The public key is defined as Et, the secret key of the time stamp server 7 as Dt, the time stamp generation time as Tt, and the time stamp token as TST (time, SigValue). Note that the key used for encryption / decryption is set in the signkey and verifykey specified for the signature function and the verification function, and the data to be encrypted / decrypted is set in the data. In addition, a time stamp generation time is set in time specified in the time stamp token, and a time stamp is set in SigValue.

  The time stamp verification in this embodiment will be described using the data and functions defined as described above. Time stamp verification can be broadly divided into time stamp generation processing and time stamp verification processing. First, the time stamp generation processing will be described with reference to FIG. 3 showing processing in the client 1 and FIG. 4 showing processing in the content management server 4.

  When the content acquisition unit 12 of the client 1 issues a content download request to the content management server 4, the content distribution unit 42 of the content management server 4 responds to the request from the client 1 with N pieces of content to be time stamped. Cx (x = 1 to N) is transmitted to the client 1 (step 211). When the content acquisition unit 12 acquires N pieces of content Cx in this manner, the content acquisition unit 12 stores them in the content storage unit 34 (step 111). It is considered that the content Cx is stored once because the content Cx is necessary at the time of verifying the time stamp, and the time stamp is verified after a time has passed since the time stamp was acquired. Because. The time stamp information is held in a time stamp holding table 36 described later for the same reason. The IDs of the acquired contents Cx (x = 1 to N) are IDx (x = 1 to N), respectively.

  The digest generation unit 20 in the time stamp generation request processing unit 14 generates N digests f (Sx) from the data included in the signature target area Sx of each acquired content IDx using the hash function f (step 112). ). Subsequently, the digest transmission unit 22 sends a request for generating a time stamp by transmitting the digest f (Sx) generated from the content Cx to the content management server 4 (step 113).

In the content management server 4, when the digest acquisition unit 48 receives a request for generating a time stamp from the client 1 (step 212), the time stamp requesting unit 50 combines a plurality of digests included in the generation request. . This combined digest F can be expressed as follows.

  Then, the time stamp requesting unit 50 generates a single digest H (F) from the combined digest F using the hash function H (step 213), and the time stamp request including the digest H (F) is time stamped. This is transmitted to the server 7 (step 214).

The time stamp server 7 adds the current time acquired from a reliable time source to the digest sent from the content management server 4 as a time stamp generation time, and signs it using its own private key Dt, Generate a time stamp token. Then, a time stamp token is returned to the requesting content management server 4. It should be noted that the signature TSValue and the time stamp token TSToken can be expressed as follows:
TSValue = Enc (Dt, Tt + H (F))
TSToken = TST (Tt, TSValue)

  In the content management server 4, the time stamp acquisition unit 52 receives the time stamp token generated by the time stamp server 7 in response to the time stamp request (step 215), and the time stamp information included in the time stamp token, that is, The identification information IDx of a plurality of contents to which time stamps are added is associated with the time stamp TSValue and the time stamp generation time Tt and registered in the time stamp management table 70 (step 216). It should be noted that since the time stamp information may be added with information that can identify the time stamp for which content, it may not necessarily be the identification information IDx. In the present embodiment, it is not necessary to use the time stamp management table 70, but the time stamp is held and managed as one function of the management server. The time stamp notification unit 54 notifies the client 1 of the generation request request source of the time stamp information including the time stamp and the generation time (step 217).

  In the client 1, when receiving the time stamp information sent from the content management server 4 in response to the generation request request, the time stamp acquisition unit 24 sets the time stamp information, that is, the time stamp TSValue and the time stamp generation time Tt to the time stamp information. The identification information IDx of a plurality of contents to which stamps are added are associated with each other and registered in the time stamp holding table 36 (step 114). It should be noted that since the time stamp information may be added with information that can identify the time stamp for which content, it may not necessarily be the identification information IDx.

  In the present embodiment, a common time stamp can be generated for a plurality of contents as described above. As a result, it is not necessary to request time stamp generation for each content, which is convenient and can reduce the cost.

  Next, the time stamp verification process will be described. In the present embodiment, as described above, two types of time stamp verification methods, namely simple verification and normal verification, are provided. First, simple verification will be described with reference to FIG. 5 showing processing in the client 1 that makes a time stamp verification request and FIG. 6 showing processing in the content management server 4 that performs time stamp verification in response to a request from the client 1. To do.

I would like to request verification of the time stamp of any of the N content Cx (x = 1 to N) whose IDs are IDx (x = 1 to N), respectively. And Note that the processing described below is the same for all the contents Cx, and therefore, the contents C ₁ with ID ₁ will be described as a representative here.

At this time, the time stamp verification request processing unit 16 reads all the content Cx from the content storage unit 34 and generates additional information to be added to the content C ₁ to be transmitted to the content management server 4 for the verification request. It is made to produce | generate to the part 26 (step 115).

That is, the other content information generation unit 32 in the additional information generation unit 26 identifies the other content Cx (x = 2 to N) in which the time stamp is generated together with C ₁ as information related to content other than C _1. {ID ₂ , ID ₃ , ID ₄ ,..., ID _N } and the digest of the other content {f (S ₂ ), f (S ₃ ), f (S ₄ ),. S _N )}. The digest f (Sx) (x = 2 to N) of other content is generated from the data included in the signature target area Sx of each content IDx using the hash function f. In the case of content C ₂ with ID ₂ , identification information {ID ₁ , ID ₃ , ID ₄ ,..., ID _N } of other content for which a collective signature is generated together with C ₂ and the other content Digests {f (S ₁ ), f (S ₃ ), f (S ₄ ),..., F (S _N )} are generated. Further, the additional information generation unit 26 extracts time stamp information common to the contents Cx (x = 1 to N) from the time stamp holding table 36 and includes it in the additional information. The additional information generated as described above can be expressed as follows.

E ₁ = ({ID ₂ , ID ₃ , ID ₄ ,..., ID _N }, {f (S ₂ ), f (S ₃ ), f (S ₄ ),..., F (S _N ) }, Tt, TSValue)

The verification request unit 28 requests time stamp verification by adding the additional information to the content C ₁ to be verified and transmitting it to the content management server 4 (step 116).

  In the present embodiment, since it is necessary to include the digest f (Sx) (x = 2 to N) of other contents in the additional information, when performing a time stamp verification request, the time stamp verification request processing unit 16, the corresponding digest is generated at the time of the time stamp generation request. Therefore, the digest generated at this time is stored in the time stamp holding table 36. You may make it reuse at the time of a time stamp verification request.

In the content management server 4, when the verification request receiving unit 58 in the time stamp verification processing unit 46 receives a time stamp generation request request issued from the client 1 (step 221), the time stamp verification unit 64 receives the received content C _1. A digest is generated by decrypting the time stamp TSValue included in the additional information using the public key Et of the time stamp server 7 (step 222). Since the generation of this digest uses a verification function, it can be expressed as Dec (Et, TSValue), but the decoded TSValue can be expressed as Tt + H (F).

On the other hand, the digest generating unit 62 generates a digest from the content C ₁ sent from the client 1 (step 224). Strictly speaking, the digest generation unit 62 generates the digest f (S ₁ ) from the data included in the signature target area S ₁ of the content C ₁ using the hash function f. Here, the digest of the content _{C 1} than the content Cx (x = 2~N) f ( Sx) (x = 2~N) is because it is included in the additional information of the content _{C 1,} the digest generation unit 62 , F (S ₁ ) and f (Sx) (x = 2 to N), that is, a digest of all contents Cx (x = 1 to N) for which a common time stamp is generated is combined to generate a combined digest F (Step 224).

  The time stamp verification unit 64 generates a digest H (F) from the combined digest F using the hash function H in order to complete the digest for time stamp verification, and the time stamp included in the additional information received thereby. The generation time Tt is added to obtain Tt + H (F).

When the digests to be compared are generated as described above, the two digests, that is, the digest Dec (Et, TSValue) obtained by decoding the time stamp, that is, Tt + H (F), and the content management server 4 By comparing the generated digest Tt + H (F), the time stamp added to the content C ₁ is verified (step 225). As described above, the digests to be compared are both expressed as Tt + H (F), and if they have not been tampered with, the verification should succeed.

  In the flowchart, the process of decoding the received time stamp and generating the digest has been described so that the digest generating unit 62 performs the process before generating the combined digest, but the order of the processes may be reversed, You may make it carry out simultaneously.

The verification result notifying unit 66 notifies the verification request source client 1 of the verification result of the time stamp added to the content C ₁ as described above (step 226).

  In the client 1, when the verification result acquisition unit 30 acquires the verification result notified from the content management server 4 (step 117), the display unit 18 displays the result on the display of the client 1 (step 118), so that the user is notified. Notify the result of time stamp verification.

Although the simple verification of the time stamp in the present embodiment is performed as described above, in the present embodiment, the digest of other content necessary for the time stamp verification of each content is added to the additional information of the content. To be included. That is, in the case of verifying a digest of another content used when generating a time stamp, for example, a time stamp added to the content C ₁ , the digest f (Sx of the content Cx (x = 2 to N)) ) and (x = 2 to N) since to include the additional information of the content _{C 1,} the content management server 4 to perform time stamp verification is necessary to generate a digest from another content Cx (x = 2 to N) There is no. That is, the content management server 4 can individually verify the time stamp added to the content C ₁ even without other content Cx (x = 2 to N).

  Next, normal verification will be described, but the processing in the client 1 on the time stamp document request side is the same as the simple verification, and thus description thereof is omitted. Here, the time stamp verification process in the content management server 4 will be described with reference to the flowchart shown in FIG. Note that the same processing as that in the simple verification is assigned the same step number, and description thereof is omitted or simplified as appropriate.

In the content management server 4 is a time stamp verification side, the verification request receiving unit 58 receives a time stamp generation request request (step 221), the time stamp verifying unit 64, included in the received additional information of the content C ₁ The current time stamp is decoded to generate a digest Tt + H (F) (step 222).

On the other hand, the digest generation unit 62 takes out identification information {ID ₂ , ID ₃ , ID ₄ ,..., ID _N } of other contents included in the additional information of the content C ₁ . Then, the digest generation unit 62 passes the extracted content ID to the content reading unit 60. The content reading unit 60 reads the content from the content database 68 using the content ID as a key. If the content management server 4 does not have the content database 68, the content reading unit 60 obtains it from outside via the network. As a result, the digest generation unit 62 generates the digest f (S ₁ ) from the content C ₁ sent from the client 1 using the hash function f in the same manner as the simple verification, and the other read out from the content database 68. A digest f (Sx) (x = 2 to N) is generated from the content Cx (x = 2 to N) (step 227). In this way, since it is possible to obtain the digests of all the contents for which a common time stamp is generated, these digests are combined to generate a combined digest F (step 228). This combined digest has the same contents as the simple verification.

  The subsequent processing is the same as the simple verification, and the time stamp verification unit 64 generates a digest H (F) from the combined digest F in order to complete the digest for performing the time stamp verification, and receives the additional information received thereto. Is added to the time stamp generation time Tt to obtain Tt + H (F).

When the digest to be compared is generated as described above, the time stamp verification unit 64 uses the digest Tt + H (F) obtained by decoding the time stamp and the digest Tt + H (F) generated by the content management server 4. by comparing the bets, it verifies the time stamp added to the content C ₁ (step 225). Then, the verification result notification unit 66 notifies the verification request source client 1 of the verification result of the time stamp added to the content C ₁ (step 226). Note that the verification result notification and display processing is the same as the simple verification, and is therefore omitted.

  The normal verification of the time stamp in the present embodiment is performed as described above, but the normal verification is also performed in the same manner as the simple verification even when a common time stamp is generated for a plurality of contents. Can be verified for each content.

  In the above description, the content management server 4 transmits content to the client 1 and processes so as to receive the digest generated by the client 1. Therefore, it is also possible to receive information that can identify content that generates a common time stamp, for example, a content ID, and generate a digest of each content on the content management server 4 side.

  In addition, the content management server 4 receives the digest to be combined from the client 1 and generates the combined digest F in the content management server 4, but generates the combined digest F on the client 1 side. You may make it receive.

In the present embodiment, the content management server 4 generates a digest of a plurality of contents in the process of generating a digest to be compared with the digest generated by decoding the time stamp included in the additional information. In simple verification and normal verification, content Cx (x = 2 to N) other than content to which additional information including a time stamp is added (hereinafter also referred to as “added content”, which is content C ₁ in the above example). ) Digest acquisition method is different. That is, in simple verification, a digest of content other than the content to be added is acquired from the additional information of the content to be added, whereas in normal verification, the ID of other content acquired from the additional information of the content to be added is acquired. The key is used to acquire content, and a digest of other content is generated by itself. Due to differences in other content digest acquisition methods, each verification method performed in the content management server 4 has the following characteristics.

  First, in the case of normal verification, the content itself is required to generate a digest. Therefore, for the content management server 4 that holds and manages the content itself, normal verification is performed without acquiring content from the outside. Can do. That is, in the case of normal verification, the content ID may be included in the additional information, so there is no possibility that the digest itself is falsified. Thereby, the accuracy of time stamp verification can be improved.

  On the other hand, the simple verification directly receives the content digest and does not require the content itself. Accordingly, not only the content management server 4 but also the client 1 that does not hold and manage the content itself can perform time stamp verification with simple verification. That is, when the client 1 performs simple verification, the client 1 also has the time stamp verification processing unit 46 from the content management server 4 shown in FIG. 2, so that the client 1 also operates as a computer on the time stamp verification side. Can be made.

  Note that the content additional information includes IDs of other contents and digests of other contents as information related to other contents. As is clear from the explanation of each process of the simple verification and the normal verification, as the information related to other contents, the digest of the other contents is used in the simple verification, the ID of the other contents is used in the normal verification, and the other information is Not used. Therefore, if it is clear that the client 1 performs the simple verification, it is not necessary to include the ID of another content in the additional information. On the other hand, if it is clear that the normal verification is performed, it is not necessary to include the digest of other contents in the additional information. However, in the present embodiment, the time stamp verification computer uses both IDs and digests of other content as information related to other content so that any verification method can be used as appropriate according to its configuration or the like. Included.

  Next, the above-described time stamp generation processing and verification processing will be described using a specific example. The contents of the process are the same as described above, and will be described in a simplified manner as appropriate. Here, a case will be described as an example in which three contents C1, C2, and C3 whose IDs are ID1, ID2, and ID3 are generated. In addition, the signature target areas of the contents C1 to C3 are S1, S2, and S3, and the signature information areas are E1, E2, and E3. First, although processing from the time stamp generation will be described, the processing content in the client 1 is the same in the simple verification and the normal verification.

  When the client 1 obtains the above three contents by downloading them from the content management server 4 (step 111), it generates digests f (S1), f (S2), and f (S3) using the hash function f, respectively. (Step 112), a request to generate a time stamp is issued by transmitting to the content management server 4 (Step 113).

  When the content management server 4 receives the time stamp generation request request from the client 1 (step 212), the time stamp requesting unit 50 receives a plurality of digests F (= f (S1 + S2 + S3) included in the generation request. Combined, generates a digest H (F) using the hash function H (step 213), and transmits it to the time stamp server 7 (step 214), and receives the time stamp token sent from the time stamp server 7. The time stamp information, that is, Tt and H (F) are notified to the client 1 (step 217).

  In this way, the client 1 can obtain a time stamp common to the contents C1 to C3. Subsequently, simple verification will be described in the processing at the time of time stamp verification. Here, a case where the time stamp added to the content C1 is verified will be described as an example.

The additional information generation unit 26 of the time stamp verification request processing unit 16 generates the digests f (S2) and f (S3) of the other contents C2 and C3 using the hash function f, and the other contents C2 and C3. Identification information {ID2, ID3} and digest {f (S2), f (S3)} are generated. Further, the time stamp information is extracted from the time stamp holding table 36 to generate additional information. The additional information is as follows.
E1 = ({ID2, ID3}), {f (S2), f (S3)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}

For reference, the additional information of the contents C2 and C3 is as follows.
E2 = ({ID3, ID1}), {f (S3), f (S1)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}
E3 = ({ID1, ID2}), {f (S1), f (S2)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}

  The additional information E1 generated in this way is added to the area S1 in which the content C1 is stored, and is transmitted to the content management server 4 as a time stamp generation request (step 116). Here, the content management server 4 is taken as an example of the time stamp verification side computer in the case of simple verification, but the client 1 may be used as described above.

  When the content management server 4 receives a time stamp generation request request issued from the client 1 (step 221), the time stamp verification unit 64 includes a time stamp Enc (Dt, Dt, included in the additional information of the received content C1. By decrypting Tt + H (f (S1) + f (S2) + f (S3)) using the public key Et of the time stamp server 7, a digest Tt + H (f (S1) + f (S2) + f (S3)) is generated. (Step 222).

  On the other hand, the digest generation unit 62 generates a digest f (S1) from the content C1 sent from the client 1 using the hash function f (step 224), and f (S2) and f (S3) extracted from the additional information. ) To generate a combined digest F (= f (S1) + f (S2) + f (S3)) (step 224). The time stamp verification unit 64 generates a digest H (f (S1) + f (S2) + f (S3)) from the combined digest F using the hash function H, and generates a time stamp generation time extracted from the additional information received thereby. Tt is added to obtain Tt + H (f (S1) + f (S2) + f (S3)).

  When the digests to be compared are generated as described above, two digests, that is, the digest Tt + H (f (S1) + f (S2) + f (S3)) obtained by decoding the time stamp, and the content management server The time stamp added to the content C1 is verified by comparing the digest Tt + H (f (S1) + f (S2) + f (S3)) generated in 4 (step 225). As described above, simple verification can be performed.

  Next, the case of normal verification will be described, but the processing on the time stamp verification request side is the same as the simple verification, and therefore the description thereof will be omitted, and the processing on the time stamp verification side will be described.

  When the content management server 4 receives a time stamp generation request request issued from the client 1 (step 221), the time stamp verification unit 64 includes a time stamp Enc (Dt, Dt, included in the additional information of the received content C1. By decrypting Tt + H (f (S1) + f (S2) + f (S3)) using the public key Et of the time stamp server 7, a digest Tt + H (f (S1) + f (S2) + f (S3)) is generated. (Step 222) The processing so far is the same as the simple verification.

  On the other hand, the digest generation unit 62 reads the contents C2 and C3 from the contents database 68 using the IDs (= ID2 and ID3) of other contents extracted from the additional information as keys. Thus, since the contents C1 to C3 can be obtained, the digest generation unit 62 uses the hash function f to obtain the digests f (S1), f (S2), and f (S3) from the contents C1 to C3. And a combined digest F (= f (S1) + f (S2) + f (S3)) is generated (step 228).

  The subsequent processing is the same as the simple verification, and the time stamp verification unit 64 generates a digest H (f (S1) + f (S2) + f (S3)) from the combined digest F using the hash function H, The time stamp generation time Tt extracted from the received additional information is added to this to obtain Tt + H (f (S1) + f (S2) + f (S3)).

  When the digests to be compared are generated as described above, two digests, that is, the digest Tt + H (f (S1) + f (S2) + f (S3)) obtained by decoding the time stamp, and the content management server The time stamp added to the content C1 is verified by comparing the digest Tt + H (f (S1) + f (S2) + f (S3)) generated in 4 (step 225). As described above, normal verification can be performed.

  In this way, in the case of normal verification, the content management server 4 acquires content from the content database 68 held internally using the ID of the other content as a key, and generates a digest of the other content by itself and compares the digests. I was able to do it. Thus, since the digest included in the additional information is not used, the accuracy of time stamp verification can be improved.

  According to the present embodiment, as described above, even when time stamps are acquired in common for a plurality of contents, the time stamp verification can be individually verified on the time stamp verification side. . As a result, the side using the time stamp does not need to acquire the time stamp for each content, so that the troublesomeness of acquiring the time stamp for each content is eliminated. On the other hand, the time stamp verification side can perform time stamp verification even if no content other than the content to be subjected to time stamp verification is sent. That is, in the case of simple verification, from the digest of other content included in the additional information, in the case of normal verification, the ID of the other content included in the additional information is used for the content with the time stamp added in common. Since each digest can be acquired, a digest necessary for time stamp verification can be generated on the time stamp verification side.

Embodiment 2. FIG.
FIG. 8 shows a flowchart of processing in the client 1 at time stamp verification in this embodiment, and FIG. 9 shows a flowchart of processing in the content management server 4 in normal verification at time stamp verification. 8 and FIG. 9 are diagrams corresponding to FIG. 5 and FIG. 7 in the first embodiment. As is clear from comparison with the flowcharts shown in FIG. 5 and FIG. 1 is characterized in that other content IDs included in the additional information are encrypted before being sent to the content management server 4.

  The time stamp verification process in the present embodiment will be described below. Here, as in the first embodiment, time stamps are generated in common for the three contents C1, C2, and C3 whose content IDs are ID1, ID2, and ID3, respectively, and among these, the time stamp added to the content C1 An example of performing the verification will be described. In addition, the signature target areas of the contents C1 to C3 are S1, S2, and S3, and the signature information areas are E1, E2, and E3. 8 and 9, the same processing steps as those in FIGS. In addition, the simple verification that does not use the content ID as information related to other content is the same as that in the first embodiment, and thus the description thereof is omitted. Further, the system configuration in the present embodiment is the same as that in the first embodiment, and thus the description thereof is omitted.

In the client 1, the other content information generation unit 32 included in the additional information generation unit 26 generates digests f (S2) and f (S3) of the other contents C2 and C3 using the hash function f. Further, as information related to other contents, identification information {ID2, ID3} of other contents C2 and C3 is also collected. At this time, the ID of the other contents is disclosed to the content management server 4 that performs time stamp verification. After being encrypted with the key Es, it is included in the additional information (steps 121 and 122). Each additional information generated in this way is as follows.
E1 = (Enc (Es, ID2 + ID3), {f (S2), f (S3)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}

For reference, the additional information of the contents C2 and C3 is as follows.
E2 = (Enc (Es, ID3 + ID1), {f (S3), f (S1)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}
E3 = (Enc (Es, ID1 + ID2), {f (S1), f (S2)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3))}

  The additional information E1 generated in this way is added to the area S1 in which the content C1 is stored, and is transmitted to the content management server 4 as a time stamp generation request (step 116).

  When the content management server 4 receives a time stamp generation request request issued from the client 1 (step 221), the time stamp verification unit 64 includes a time stamp Enc (Dt, Dt, included in the additional information of the received content C1. Tt + H (f (S1) + f (S2) + f (S3)) is decoded to generate a digest Tt + H (f (S1) + f (S2) + f (S3)) (step 222).

On the other hand, the digest generation unit 62 extracts IDs of other contents, that is, ID2 and ID3, from the additional information of the content C1, but in this embodiment, the other content IDs are encrypted with their own public key. Therefore, the digest generation unit 62 extracts the content ID by decrypting with its own private key corresponding to this public key (step 229). The extracted content ID can be expressed as follows.
IDx = Dec (Ds, Enc (Es, ID2 + ID3)) (x = 2, 3)

  Thus, the processing after obtaining the ID of another content by decryption is the same as that of the first embodiment. That is, when the digest generation unit 62 reads the contents C2 and C3 from the content database 68 using the ID (= ID2, ID3) of the other content obtained by decryption as a key, the digest f ( S1), f (S2), and f (S3) are generated (step 227), and a combined digest F (= f (S1) + f (S2) + f (S3)) is generated (step 228). Subsequently, the time stamp verification unit 64 generates a digest H (f (S1) + f (S2) + f (S3)) from the combined digest F using the hash function H, and extracts the time taken from the additional information received therein The stamp generation time Tt is added to obtain Tt + H (f (S1) + f (S2) + f (S3)).

  When the digest to be compared is generated as described above, the time stamp verification unit 64 uses the digest Tt + H (f (S1) + f (S2) + f (S3)) obtained by decoding the time stamp and the content management. The time stamp added to the content C1 is verified by comparing the digest Tt + H (f (S1) + f (S2) + f (S3)) generated by the server 4 (step 225). As described above, normal verification can be performed.

  According to the present embodiment, since the content ID is encrypted and then sent from the client 1 to the content management server 4, the accuracy of time stamp verification can be improved by preventing falsification of the content ID.

Embodiment 3 FIG.
FIG. 10 is a block diagram of the time stamp verification system in the present embodiment. In FIG. 10, the same components as those in FIG. In the present embodiment, the content management server 4 has a configuration in which a random number generation unit 72 and a random number holding unit 74 are added. The random number generator 72 is means for generating a random number. The random number generated by the random number generation unit 72 is added to the content together with the random number generation time information and downloaded to the client 1. When the content is downloaded, it is combined with the ID of the downloaded content and the random number generation time information. And registered in the random number holding unit 74. An example of the data structure registered in the random number holding unit 74 is shown in FIG. Note that the processing function of the random number generation unit 72 is realized by a cooperative operation of a time stamp verification program that exhibits the processing function and hardware configuring the content management server 4.

  Next, time stamp generation processing and verification processing according to the present embodiment will be described using a specific example. Here, as in the first and second embodiments, a time stamp is generated in common for the three contents C1, C2, and C3 whose content IDs are ID1, ID2, and ID3, respectively, and among these, the time stamp is added to the content C1. A case where time stamp verification is performed will be described as an example. In addition, the signature target areas of the contents C1 to C3 are S1, S2, and S3, and the signature information areas are E1, E2, and E3. Note that in each flowchart used to describe the present embodiment, the same processing steps included in the flowcharts of the above-described embodiments are denoted by the same reference numerals, and description thereof will be omitted as appropriate. As will be apparent from the following description, in the present embodiment, only the other content IDs included in the additional information are encrypted in the second embodiment, whereas in this embodiment, random numbers are assigned to the other content IDs. And encryption after adding random number generation time information. First, processing at the time of generating a time stamp in the present embodiment will be described using the flowcharts shown in FIGS.

  In the content management server 4, when a content download request is sent from the client 1, the random number generation unit 72 generates a random number for each requested content (step 231). Then, the content distribution unit 42 extracts the requested content C1 to C3 to be signed from the content database 68, adds the random numbers r1 to r3 and the random number generation time information T1 to the content C1 to C3, and sends the content C1 to C3 to the client 1. Transmit (step 232). The generation time of each random number is the same T1 for each content. Then, as illustrated in FIG. 11, the content distribution unit 42 registers each ID of the transmitted content C1 to C3, the random number, and the random number generation time information as a set in the random number holding unit 74 (step 233).

  When the client 1 acquires the contents C1 to C3 and the random number from the contents management server 4 (step 131), the digest generation unit 20 uses the hash function f to digests f (S1), f (S2), and f (S3). Are generated (step 112) and transmitted to the content management server 4 to issue a request for generating a time stamp (step 113).

  When the content management server 4 receives the time stamp generation request request from the client 1 (step 212), the time stamp requesting unit 50 receives a plurality of digests F (= f (S1 + S2 + S3) included in the generation request. Combined, generates a digest H (F) using the hash function H (step 213), and transmits it to the time stamp server 7 (step 214), and receives the time stamp token sent from the time stamp server 7. The time stamp information, that is, Tt and H (F) are notified to the client 1 (step 217).

  In this way, the client 1 can obtain a time stamp that is common to the contents C1 to C3. However, the time stamp generation request processing unit 14 performs content ID, random number generation time information, random number, and time stamp for each content. The information is associated and stored in the time stamp holding table 36 (step 133). An example of the data structure set and registered in the time stamp holding table 36 is shown in FIG.

  Next, normal verification among the processes at the time of time stamp verification will be described with reference to the flowcharts shown in FIGS. 15 and 16. Note that the simple verification that does not use the content ID included in the additional information is the same as that in the second embodiment, and a description thereof will be omitted. Here, the case where the time stamp added to the content C1 is verified will be described as an example.

In the client 1, the other content information generation unit 32 included in the additional information generation unit 26 generates digests f (S2) and f (S3) of the other contents C2 and C3 using the hash function f. Further, the identification information {ID2, ID3} of the other contents C2 and C3 is further collected as information related to the other contents. At this time, the other contents information generating unit 32 uses the random numbers that are used together with the contents C2 and C3 when acquiring the contents. The r2 and r3 and the random time information T1 are read from the time stamp holding table 36, and the random numbers are combined with the IDs of other contents and then encrypted with the public key Es of the content management server 4 (step 134). The time information T1 is encrypted with the public key Es of the content management server 4 and included in the additional information of the content C1 (step 122). Each additional information generated by the above processing is as follows.
E1 = (Enc (Es, r1 + ID2 + ID3), Enc (Es, T1), {f (S2), f (S3)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3)) }

For reference, the additional information of the contents C2 and C3 is as follows.
E2 = (Enc (Es, r2 + ID3 + ID1), Enc (Es, T1), {f (S3), f (S1)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3)) }
E3 = (Enc (Es, r3 + ID1 + ID2), Enc (Es, T1), {f (S1), f (S2)}, Tt, Enc (Dt, Tt + H (f (S1) + f (S2) + f (S3)) }

  The additional information E1 generated in this way is added to the area S1 in which the content C1 is stored, and is transmitted to the content management server 4 as a time stamp generation request (step 116).

  When the content management server 4 receives the time stamp generation request request issued from the client 1 (step 221), the time stamp verification processing unit 46 includes the time stamp Enc (Dt included in the received additional information of the content C1. , Tt + H (f (S1) + f (S2) + f (S3)) is decoded to generate a digest Tt + H (f (S1) + f (S2) + f (S3)) (step 222).

On the other hand, the digest generation unit 62 extracts IDs of other contents, that is, ID2 and ID3, from the additional information of the content C1, but in this embodiment, the other content IDs are encrypted with their own public key. Therefore, the digest generation unit 62 extracts the content ID by decrypting with its own private key corresponding to this public key (step 234). However, in this embodiment, the random number r1 and the random number generation time information T1 are to be decrypted together with the content ID. The contents of this decoding can be expressed as follows.
IDx, r1 = Dec (Ds, Enc (Es, r1 + ID2 + ID3))
However, x = 2, 3
T1 = Dec (Ds, Enc (T1))

  As shown in the above equation, since the random number r1 is combined with the IDs (ID2, ID3) of the other decrypted contents C2 and C3, the time stamp verification processing unit 46 determines the contents to be verified. The random number holding unit 74 is searched using the set of the content ID (= ID1) of C1 and the decrypted random number generation time information T1 as a key, and the random number r1 is extracted (step 235). Since the content C1 may be downloaded a plurality of times by one or a plurality of clients 1, in this embodiment, a random number can be uniquely specified by a set of a content ID and random number generation time information. Then, IDx (x = 2, 3) is extracted by subtracting the extracted random number r1 from the decrypted result (IDx, r1). Subsequent processing is the same as in the second embodiment. That is, the digest generation unit 62 takes out the contents C2 and C3 by instructing the content reading unit 60, and uses the hash function f to obtain the digests f (S1), f (S2), and f (S3) of each content. These are combined (step 227) and combined to generate a combined digest F (= f (S1) + f (S2) + f (S3)) (step 228). Subsequently, the time stamp verification unit 64 generates a digest H (f (S1) + f (S2) + f (S3)) from the combined digest F using the hash function H, and extracts the time taken from the additional information received therein The stamp generation time Tt is added to obtain Tt + H (f (S1) + f (S2) + f (S3)).

  When the digest to be compared is generated as described above, the time stamp verification unit 64 uses the digest Tt + H (f (S1) + f (S2) + f (S3)) obtained by decoding the time stamp and the content management. The time stamp added to the content C1 is verified by comparing the digest Tt + H (f (S1) + f (S2) + f (S3)) generated by the server 4 (step 225). As described above, normal verification can be performed.

  According to the present embodiment, since the content ID is encrypted and then sent from the client 1 to the content management server 4, the accuracy of time stamp verification can be achieved by preventing falsification of the content ID as in the second embodiment. Can be improved. Further, by combining a random number with the content ID when encrypting, the following effects can be obtained. Here, the case where the time stamp added to the content C1 is verified will be described as an example.

  For example, it is assumed that the content ID (= ID2, ID3) in the additional information stored in the time stamp information area E1 has been altered to be changed to a different content ID, for example, ID1, ID2, due to an illegal act by an unauthorized accessor. Such tampering can be achieved by overwriting the additional information of the content C1 with the additional information of the content C3, for example. When the random number is not combined with the content ID, the content management server 4 can acquire the altered content IDs, that is, ID1 and ID2, from the additional information of the content C1, and normally acquire the content C1 and C2 from the content database 68. can do. In this way, digest comparison processing is performed after the content has been successfully acquired. The digest compared with the digest generated by decoding the time stamp is a combined digest originally generated from the contents C1, C2, and C3. Since the power is generated from the contents C1, C2, and C1 by falsification, the digests do not completely match. That is, time stamp verification fails. In this case, the content management server 4 has successfully extracted the content ID (= ID1, ID2) from the additional information and has successfully extracted the content C1, C2 from the content database 68. Will erroneously recognize that the content C1 stored in the signature target area S1 has been tampered with.

On the other hand, when the random number is combined with the content ID, the content management server 4 takes out the random number r3 instead of the random number r1 of the content C3 overwriting the content C1 as described above. As a result, the formula described above,
IDx, r1 = Dec (Ds, Enc (Es, r1 + ID2 + ID3))
However, x = 2, 3
Even if the random number r3 is subtracted from the IDx, r1 (x = 2, 3) extracted in step 1, ID2 and ID3 cannot be correctly extracted. For this reason, since the content management server 4 cannot normally retrieve the content from the content database 68, it is correct that the additional information stored in the signature information area E1 is altered, not the content data stored in the signature target area S1. Can be recognized.

  In the present embodiment, the reason why the random number generation time information is associated with the content ID and registered in the random number holding unit 74 is to uniquely identify the random number added to the content. Therefore, the information need not be limited to the random number generation time information as long as it can be uniquely specified. For example, it may be content transmission time information or event identification information of download.

1 is an overall configuration diagram showing an embodiment of a time stamp verification system according to the present invention. 1 is a block configuration diagram of a time stamp verification system in Embodiment 1. FIG. 3 is a flowchart illustrating processing on the client side when generating a time stamp in the first embodiment. 3 is a flowchart showing processing on the content management server side when generating a time stamp in the first embodiment. 4 is a flowchart illustrating processing on the client side that requests time stamp verification in the first embodiment. 4 is a flowchart showing processing on the client side for performing time stamp verification in simple verification in the first embodiment. 6 is a flowchart illustrating processing on the client side for performing time stamp verification in normal verification in the first embodiment. 10 is a flowchart illustrating processing on the client side that requests time stamp verification in the second embodiment. 10 is a flowchart illustrating processing on the client side for performing time stamp verification in normal verification in the second embodiment. FIG. 10 is a block configuration diagram of a time stamp verification system in a third embodiment. FIG. 10 is a diagram illustrating a data configuration example registered in a random number holding unit in the third embodiment. 14 is a flowchart illustrating processing on the content management server side when generating a time stamp in the third embodiment. 14 is a flowchart illustrating processing on the content management server side when generating a time stamp in the third embodiment. FIG. 10 is a diagram showing a data configuration example set and registered in a time stamp holding table in the third embodiment. 14 is a flowchart illustrating processing on the client side that requests time stamp verification in the third embodiment. 10 is a flowchart illustrating processing on the client side that performs time stamp verification in normal verification in the third embodiment.

Explanation of symbols

  1 client 4 content management server 7 time stamp server 9 public network 12 content acquisition unit 14 time stamp generation request processing unit 16 time stamp verification request processing unit 18 display unit 20 digest generation unit 22 digest transmission Unit, 24 time stamp acquisition unit, 26 additional information generation unit, 28 verification request unit, 30 verification result acquisition unit, 32 other content information generation unit, 34 content storage unit, 36 time stamp holding table, 42 content distribution unit, 44 time Stamp acquisition processing unit, 46 Time stamp verification processing unit, 48 Digest acquisition unit, 50 Time stamp request unit, 52 Time stamp acquisition unit, 54 Time stamp notification unit, 58 Verification request reception unit, 60 Content reading unit, 62 Digest Generating unit, 64 a time stamp verifying unit, 66 a verification result notifying unit, 68 content database 70 timestamp management table, 72 random number generating unit, 74 a random number holding unit.

Claims (14)

A time stamp user computer used by a user of a time stamp issued by a time stamp authority to authenticate the generation time of digital data,
A time stamp including information related to other digital data in which a time stamp common to the verification target digital data is generated, and the time stamp and time stamp generation time information for the verification target digital data to be a time stamp verification request target Additional information generating means for generating additional information including information,
A time stamp verification request means for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer;
Time stamp verification program to function as. The time stamp verification program according to claim 1, further comprising:
Time stamp generation requesting means for requesting generation of a common time stamp for each of the plurality of digital data by transmitting a digest generated from each of the plurality of digital data to the time stamp verification side computer;
Time stamp receiving means for receiving time stamp information sent from the time stamp verifying computer in response to a generation request by the time stamp generation requesting means;
Time stamp verification program to function as. A time stamp verifying computer for verifying a time stamp added to digital data sent from a time stamp using computer,
Other than the digital data sent from the computer using the time stamp, the time stamp information added to the digital data and the time stamp common to the digital data are generated and used for time stamp verification of the digital data Receiving means for receiving digital data to which additional information including information on the digital data is added,
Time stamp decoding means for generating a digest by decoding time stamp information included in additional information added to digital data received by the receiving means;
A digest of the other digital data acquired based on information about other digital data included in the additional information added to the digital data received by the receiving means, and a digest generated from the digital data received by the receiving means Digest generation means to be combined,
Time stamp verification means for verifying a time stamp by comparing the digest generated by the digest generation means with the digest generated by the time stamp decoding means;
Time stamp verification program to function as. The time stamp verification program according to claim 3, wherein the time stamp verification side computer further comprises:
A combined digest of a plurality of digital data digests sent from the time stamp using computer at the time of a time stamp generation request is transmitted to a time stamp authority that issues a time stamp for authenticating the generation time of the digital data Timestamp request means to
Time stamp information including a time stamp and time stamp generation time information sent from a time stamp authority in response to a request from the time stamp requesting unit is notified to the time stamp generation request computer that is the time stamp generation request request source. Time stamp notification means,
Time stamp verification program to function as. The time stamp user computer used by users of time stamps issued by the time stamp authority to authenticate the generation time of digital data,
A time stamp including information related to other digital data in which a time stamp common to the verification target digital data is generated, and the time stamp and time stamp generation time information for the verification target digital data to be a time stamp verification request target Additional information generating means for generating additional information including information,
A time stamp verification request means for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer;
Function as
A time stamp verifying computer for verifying a time stamp added to digital data sent from the time stamp using computer;
Other than the digital data sent from the computer using the time stamp, the time stamp information added to the digital data and the time stamp common to the digital data are generated and used for time stamp verification of the digital data Receiving means for receiving digital data to which additional information including information on the digital data is added,
Time stamp decoding means for generating a digest by decoding time stamp information included in additional information added to digital data received by the receiving means;
A digest of the other digital data acquired based on information about other digital data included in the additional information added to the digital data received by the receiving means, and a digest generated from the digital data received by the receiving means Digest generation means to be combined,
Time stamp verification means for verifying a time stamp by comparing the digest generated by the digest generation means with the digest generated by the time stamp decoding means;
Time stamp verification program to function as. In the time stamp verification program according to claim 5,
The additional information generating means includes the digest of the other digital data in the additional information as information on the other digital data,
The digest generating means is a digital signature program for combining a digest included in additional information added to digital data received by the receiving means and a digest generated from the digital data received by the receiving means. In the time stamp verification program according to claim 5,
The additional information generating means includes data identification information for identifying each of the other digital data in the additional information as information on the other digital data,
The time stamp verification computer further functions as an acquisition unit for acquiring digital data corresponding to each data identification information included in additional information added to the digital data received by the reception unit;
The digest generation unit is a time stamp verification program for combining a digest generated from the digital data acquired by the acquisition unit and a digest generated from the digital data received by the reception unit. In the time stamp verification program according to claim 5,
The additional information generating means includes the data identification information in the additional information as information related to the other digital data after being encrypted with the public key of the time stamp verifying computer,
The time stamp verifying computer further includes the encrypted data identification information included in the additional information added to the digital data received by the receiving means with a secret key corresponding to the public key of the time stamp verifying computer. By functioning as an extraction means for extracting data identification information of the other digital data by decoding,
The acquisition unit is a time stamp verification program for acquiring digital data corresponding to each data identification information extracted by the extraction unit. The time stamp verification program according to claim 8,
The time stamp verifying computer is further
Random number generation means for generating a random number;
Digital data transmission means for adding the random number generated by the random number generation means to the digital data to be transmitted to the computer using the time stamp;
Random number information storage means for storing the added random number in association with the data identification information of the digital data transmitted to the computer using the time stamp;
Function as
The time stamp using computer further functions as a user receiving means for receiving digital data sent from the time stamp verifying computer,
The additional information generating means combines each data identification information of the other digital data with a random number transmitted from the time stamp verification side computer added to the digital data, and each data obtained by combining the random numbers. The identification information is included in the additional information as information on the other digital data after being encrypted with the public key of the time stamp verifying computer,
The extraction unit decrypts the encrypted data identification information and the random number included in the additional information added to the digital data received by the receiving unit, with a secret key corresponding to the public key of the time stamp verifying computer. The random number associated with the data identification information of the digital data received by the receiving unit is extracted from the random number storage unit, and the random number is separated from the decrypted data identification information based on the extracted random number. Time stamp verification program that extracts. In the time stamp using computer used by the user of the time stamp issued by the time stamp authority for the authentication of the generation time of the digital data,
A time stamp including information related to other digital data in which a time stamp common to the verification target digital data is generated, and the time stamp and time stamp generation time information for the verification target digital data to be a time stamp verification request target Additional information generating means for generating additional information including information;
Time stamp verification requesting means for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer;
A computer using a time stamp. In the time stamp verifying computer for verifying the time stamp added to the digital data sent from the time stamp using computer,
Other than the digital data sent from the time stamp using computer, the time stamp information added to the digital data and the time stamp common to the digital data are generated and used for time stamp verification of the digital data Receiving means for receiving digital data to which additional information including:
Time stamp decoding means for generating a digest by decoding time stamp information included in additional information added to digital data received by the receiving means;
A digest of the other digital data acquired based on information about other digital data included in the additional information added to the digital data received by the receiving means, and a digest generated from the digital data received by the receiving means A digest generating means to be combined;
A time stamp verification means for verifying a time stamp by comparing the digest generated by the digest generation means with the digest generated by the time stamp decoding means;
A time stamp verifying computer comprising:   A time stamp verification system comprising the time stamp using computer according to claim 10 and the time stamp verifying computer according to claim 11. Implemented by the time stamp consumer computer used by time stamp users issued by the time stamp authority for authentication of digital data generation time,
A time stamp including information related to other digital data in which a time stamp common to the verification target digital data is generated, and the time stamp and time stamp generation time information for the verification target digital data to be a time stamp verification request target An additional information generating step for generating additional information including information;
A time stamp verification requesting step for requesting time stamp verification by adding the additional information to the verification target digital data and transmitting it to the time stamp verification side computer;
Including a time stamp generation request method. Implemented by a time stamp verifying computer that verifies a time stamp added to digital data sent from a time stamp using computer,
Other than the digital data sent from the time stamp using computer, the time stamp information added to the digital data and the time stamp common to the digital data are generated and used for time stamp verification of the digital data Receiving the digital data to which the additional information including the information related to the digital data is added, and
A time stamp decoding step of generating a digest by decoding time stamp information included in the additional information added to the digital data received by the receiving step;
The digest of the other digital data acquired based on the information about the other digital data included in the additional information added to the digital data received by the receiving step, and the digest generated from the digital data received by the receiving step A digest generation step for combining
A time stamp verification step for performing time stamp verification by comparing the digest generated by the digest generation step with the digest generated by the time stamp decoding step;
A time stamp verification method comprising:

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