JP2000267939A - Method for generating and reading ciphered file by using common key - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ciphered file generating and reading method capable of easily managing a ciphered document and a key necessary for ciphering the document. SOLUTION: This data file generating method to be utilized for plural readers A to C having respectively different deciphering keys KDA to KDC is provided with a procedure for ciphering a document P by a prescribed common ciphering key KX, a procedure for ciphering a common deciphering key KY corresponding to the common ciphering key KX by respective ciphering keys KEA to KEC and a procedure for storing the ciphered document and the ciphered common deciphering keys KYA' to KYC' as a data file. The data file reading method is provided with a procedure for deciphering plural ciphered common deciphering keys KYA' to KYC' by a deciphering key owned by a reader, a procedure for successively judging the deciphered common deciphering keys are correctly deciphered or not, a procedure for deciphering the ciphered document by the common deciphering key KY, and a procedure for displaying the deciphered document to the reader.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating and browsing a data file using a common key used by a plurality of viewers having different decryption keys.

[0002]

2. Description of the Related Art In recent years, an information sharing environment using a computer network has rapidly spread. By storing shared documents and other information on a network server and accessing it from a large number of clients, the management and use efficiency of the information is greatly improved. In such an environment, there is a demand to limit users who can view specific information. For example, in an internal network environment, only certain officers, only certain departments,
Alternatively, it is necessary to make a configuration such that only a specific employee can view a target document.

[0003] In order to meet this kind of request, there is a method of encrypting target information by using information encryption technology and permitting only a person having a decryption key corresponding to this encryption to view it.

[0004] One of the conventional methods using encryption technology is:
A security level for limiting the viewer is set, target information is encrypted with a different key for each security level, and only a person having a decryption key corresponding to the security level can view the target information.

However, in this method of setting a key for each security level, in order for a specific user to be able to view information of a plurality of security levels,
A plurality of keys must be managed, and key management becomes complicated on the user side and the administrator side. For example, in an in-house network, it is necessary to distribute keys corresponding to the officer level and the level of each business unit to be supervised to officers and the like, and to use these keys as needed. In addition, it is difficult to provide information to a group of users who do not comply with a preset security level, and there is a problem that the degree of freedom in selecting a viewing target is low.

Another conventional method using an encryption technique is to set an individual decryption key for each user and encrypt information for each target user of the information with an encryption key corresponding to the decryption key. . 7 and 8 show a conventional encrypted file creation and browsing system according to the above method. At first,
With reference to FIG. 7, a description will be given of a method of providing a document P having the same content to users A to C in an encrypted manner in a conventional method of creating an encrypted file. As shown in the figure, a unique encryption key KEA, KEB and K
The EC is determined in advance, and the document P is written using each encryption key KE.
Is encrypted, and ciphertexts CA to CC are generated. That is, the system encrypts the document P for the user A using the encryption key KEA in the encryption unit 70, and generates the document CA on the main memory. The writing unit 71 stores the document CA on the main memory as one data file on the hard disk of the server. Similarly, a ciphertext CB for the user B is generated using the encryption key KEB, and a ciphertext CC for the user C is generated using the encryption key KEC, and stored as a data file on the server.

As shown in FIG. 8, these ciphertexts CA to CC are transmitted to clients operated by users A to C.
Decryption is performed using the respective decryption keys KDA to KDC. That is, the user A reads the ciphertext CA on the main memory of the client A, and in the decoding unit 81, performs decoding using the decoding key KDA corresponding to the encryption key KEA to obtain the original document P. . Similarly, in the clients of user B and user C, ciphertexts CB and CC are decrypted using decryption keys KDB and KDC, respectively.

[0008]

However, according to the above-mentioned conventional method, although the management of keys on the user side and the administrator side becomes easy, it is possible to browse documents of the same contents as in the above-mentioned example. When there are a plurality of users, the number of data files is created by the number of users, so that the number of files stored on the server may be enormous, which is a management problem.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an encrypted file generating method and a browsing method in which management of an encrypted document and management of a key required for the encryption are easy.

[0010]

According to the present invention, there is provided a method for generating a data file used by a plurality of viewers having different decryption keys, wherein at least one information to be viewed is stored in a predetermined format. A procedure of encrypting with a common encryption key, a procedure of respectively encrypting a common decryption key corresponding to the predetermined common encryption key with an encryption key corresponding to the different decryption key, Storing the plurality of encrypted common decryption keys as at least one data file.

[0011] Further, the method of generating the encrypted file is as follows.
A procedure of encrypting a predetermined determination code with an encryption key corresponding to the different decryption key, and associating the determination code encrypted with the same key with each of the encrypted common decryption keys. And storing the encrypted browsed information and the plurality of encrypted common decryption keys together with the determination code in the storage step.
It is preferable to save the data as one data file.

[0012] The method of generating the encrypted file is as follows.
A step of generating at least position information for identifying a position of the encrypted viewed information in the data file, wherein the storing step includes storing the encrypted viewed information together with the position information in one form. Preferably, it is saved as a data file.

The present invention also relates to a method of browsing an encrypted file generated by the above method, comprising: a step of loading the data file on a main storage; and a step of loading a plurality of encrypted common files in the data file. A procedure for sequentially decrypting the decryption key with a decryption key possessed by the viewer, and a procedure for sequentially determining whether or not the decrypted common decryption key has been correctly decrypted into a common decryption key before encryption. A procedure for decrypting the encrypted viewed information with the correctly decrypted common decryption key, and a step of displaying the decrypted viewed information to a viewer. .

[0014] Further, the method of browsing the encrypted file is as follows.
The method further comprises the step of sequentially decrypting the plurality of encrypted determination codes with a decryption key possessed by the viewer, wherein the determining step includes converting the decrypted determination codes to the above-described encrypted code. It is preferable to determine whether or not the decrypted common decryption key has been correctly decrypted to the common decryption key before encryption by sequentially comparing with the determination code.

[0015] Further, the method of browsing the encrypted file is as follows.
Preferably, the step of decoding the viewed information further comprises a step of extracting the viewed information from the data file based on the position information.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on one embodiment shown in the drawings. FIG. 1 is a system configuration diagram for realizing an encrypted file creation method according to an embodiment of the present invention. Basically, according to this creation method, one document to be provided is encrypted using a predetermined common encryption key. At the same time, the common decryption key corresponding to the common encryption key is encrypted using the encryption key set for each user. The encrypted document and each common decryption key are collected and stored in one data file.

In FIG. 1, an encrypted file generation device 1
0 can be realized by a computer operated by a file manager and a program operated on the computer. As its functional configuration, a key encryption unit 11, a key setting unit 12,
Key / key data writing unit 13, block size calculation unit 1
4, a document encryption unit 15, a document writing unit 16, and a data storage unit 17.

The key encryption unit 11 encrypts input data using a predetermined algorithm using the encryption key KE set by the key setting unit 12. The data input to the key encryption unit 11 is a confirmation code M and a common decryption key KY. The key encryption unit 11 encrypts the confirmation code M to generate an encryption confirmation code M ′, and outputs the common decryption key KY To generate an encrypted common decryption key KY '. Here, the confirmation code M
Is for determining whether or not the user who intends to view the document P has the authority to use the common decryption key KY. The confirmation code M may be any character string, symbol, or other identifier, but a hash value generated based on the document P or another message digest may be used as the confirmation code M. A method for determining the viewing authority using the confirmation code M will be described later. The common decryption key KY is
It corresponds to the common encryption key KX used for encrypting the document P to be browsed, and is a key for correctly decrypting the document P encrypted with the common encryption key KX.

The key setting section 12 is for setting an encryption key KE used in the key encryption section 11. In the example shown in the figure, the key setting unit 12 generates the encryption keys KE corresponding to the decryption keys KDA, KDB, and KDC distributed in advance to users A, B, and C who have the authority to view the document P to be encrypted.
A, KEB, and KEC are sequentially set as keys used in the key encryption unit 11. As a result, the key encryption unit 11
As the data for use, an encryption confirmation code MA ′ encrypted with the encryption key KEA and an encryption common decryption key KYA ′ are generated,
As data for the user B, an encryption confirmation code MB ′ and an encryption common decryption key KYB ′ encrypted with the encryption key KEB are generated, and as the data for the user C, the encryption encrypted with the encryption key KEC is performed. A confirmation code MC 'and an encrypted common decryption key KYC' are generated.

The key data writing unit 13 arranges the encryption confirmation code M ′, the encryption common decryption key KY ′ and the block size data S described later, which are generated by the key encryption unit 11, on the main memory 18. Things. As shown in the figure, the above data are grouped for each user and are sequentially mapped on the main memory (hereinafter, these data are referred to as key data as necessary). That is, on the main memory 18, as the key data for the user A, the block size data SA, the encryption confirmation code MA ', and the encryption common decryption key KYA' are successively arranged. As data, block size data SB, encryption confirmation code MB 'and encryption common decryption key KYB' are successively arranged, and subsequently, as key data for user C, block size data SC, encryption confirmation code MC ' And the encryption common decryption key KYC 'are arranged continuously.

The block size calculator 14 calculates each encryption key K
For each output of the key encryption unit 11 using EA to KEC, the total number of bytes of the encryption confirmation code M ′ and the encryption common decryption key KY ′ input to the key data writing unit 13 is calculated, and the number of bytes is calculated. The stored block size data S is output to the key data writing unit 13. In this embodiment, each user A, B
And C, three block size data SA and SB
And SC are generated. The block size data SA to SC generated as described above are converted by the key data writing unit 13 into the encryption confirmation code M ′ and the encryption common decryption key K.
It is arranged on the main memory 18 together with Y '. The block size calculation unit 14 also calculates the total number of bytes of an encrypted document code N ′ and a ciphertext C described later, and stores the block size data SP storing the number of bytes in the key data writing unit 1
Output to 3. Generated block size data SP
Is stored in the main memory 18 together with the encrypted document code N ′ and the ciphertext C by the document writing unit 16 described later.
It is arranged in an area following the data written by the key data writing unit 13.

The document encryption section 15 encrypts input data by a predetermined algorithm using a common encryption key KX.
The data input to the document encryption unit 15 is a document code N and a document P to be viewed. The document encryption unit 15 encrypts the document code N to generate an encrypted document code N ′.
The document P is also encrypted to generate a ciphertext C. here,
The document code N indicates that the user who wants to view the document P
This is for determining whether or not the user has the reading authority for the document. The document code N, like the confirmation code M, can be composed of an arbitrary character string, symbol, or other identifier.

The document writing unit 16 includes the document encryption unit 1
The encrypted document code N ', ciphertext C, and their block size data SP (hereinafter referred to as "document data as necessary") generated in step 5 are arranged in the main memory 18. The document data is sequentially mapped on the main memory following the key data written by the key data writing unit 13. That is, as shown in the figure, following the encryption common decryption key KYC 'for the user C, the block size data SP,
The encrypted document code N ′ and the ciphertext C are arranged. The block size data SP is generated by the block size calculation unit 14 described above.

The data storage section 17 stores the above-mentioned data arranged on the main memory 18, that is, the block size data SA to SC written by the key data writing section 13, the encryption confirmation codes MA 'to MC', and the encryption common code. Decryption key KY
A ′ to KYC ′ and the block size data SP, the encrypted document code N ′ and the ciphertext C written by the document writing unit 16 are stored on the hard disk of the server as one data file F in the order of the arrangement. . Note that the key data written by the key writing unit 13 and the document data written by the document writing unit 16 may be stored in different files. In this case, the data file storing the key data includes link information to the data file storing the corresponding document data.

FIG. 2 is a flowchart showing a procedure for generating an encrypted file in the above system. Hereinafter, the procedure for generating the encrypted file will be described with reference to FIG. 1 and FIG. When the encryption file generation program is started on the computer operated by the file manager, the encryption key KEA for the user A who provides the document P is set in the key encryption unit 11 by the key setting unit 12 (201). Using the encryption key KEA, the key encryption unit 11 encrypts a predetermined confirmation code M to generate an encrypted confirmation code MA '(202). Subsequently, the key encryption unit 11 encrypts the common decryption key KY using the same encryption key KEA to generate an encrypted common decryption key KYA '(203).

Next, the block size calculation section 14 calculates the total number of bytes of the generated encryption confirmation code MA 'and the encrypted common decryption key KYA', and generates block size data SA storing the number of bytes. (20
4). Then, the block size data SA, the encryption confirmation code MA 'and the encryption common decryption key KYA' are written by the key data writing unit 13 into a predetermined area on the main memory 18 (205).

The processing of steps 201 to 205 is as follows:
This is repeated for the number of target users (206). In the above example, the target users are the users A to C, and the above processing is repeated for the users B and C. In this case, the key setting unit 12 sends the encryption key KEB to the key encryption unit 11 to generate data for user B,
The encryption key KEC is set in order to generate data for use, and the above processing is executed.

After the key data has been generated by the above processing, the document encryption unit 15 is started. Document encryption unit 1
5 encrypts the document code N using the set common encryption key KX to generate an encrypted document code N '(20)
7). Subsequently, the document encryption unit 15 encrypts the document P using the same common encryption key KX to generate a ciphertext C (208).

The block size calculation unit 14 calculates the total number of bytes of the generated encrypted document code N 'and ciphertext C, and generates block size data SP storing the number of bytes (209). Then, the document writing unit 16 writes the block size data SP, the encrypted document code N ′, and the ciphertext C after the key data on the main memory 18 (210).

After these processes, the main memory 18
The generated data is arranged as shown in FIG. Then, the data on the main memory 18 is stored on the server as one data file F by the data storage unit 17 (211). Thus, an encrypted file is generated.

FIG. 3 is a block diagram of a system for browsing the document P encrypted by the system of FIG. The encrypted file browsing device 30 can be realized by a client computer operated by a user and a program operated on the client computer. The functional configuration thereof includes a file reading unit 31, a key block reading unit 32, and a key decrypting unit 33. , A confirmation code determination unit 34, a document block reading unit 35, a document decryption unit 36, a key setting unit 37, a document code determination unit 38, and a document display unit 39.

The file reading section 31 is a function for reading a file specified by the user onto the main memory 40 of the client, whereby the data file F stored on the server is stored in the main memory 40 by an arbitrary user. Expanded above. The key block reading unit 32
The block size data SA at the head of the data file F is first read out from the data file F expanded on the main memory 40, and its value, that is, the following encryption confirmation is performed. The total number of bytes of the code MA 'and the encryption common decryption key KYA' is stored in the block size register 41. The key block reading unit 32 sequentially reads the blocks of the encryption confirmation code M ′ and the encryption common decryption key KY ′,
Give to.

The key decryption unit 33 decrypts the encrypted confirmation code M 'to generate the confirmation code M, and decrypts the encrypted common decryption key KY' to generate the common decryption key KY. Here, as the decryption key KD used in the key decryption unit 33, one assigned to each user (in this example, KDA, KDB, KDC for users A, B, C) is used. Therefore, for example, the decryption key KDA used by the user A
When the above confirmation code and cipher text are decrypted by using, only the encryption confirmation code MA 'and the encryption common decryption key KYA' encrypted by the corresponding encryption key KEA are normally decrypted. .

The confirmation code determination section 34 determines whether or not the confirmation code M decrypted by the key decryption section 33 has been normally decrypted. The confirmation code determination unit 34 compares the decrypted confirmation code M with a preset confirmation code, and controls the read block of the key block reading unit 32 according to the result. If the key KE for encrypting the confirmation code and the key KD for decrypting the key do not correspond to each other, normal decryption is not performed, and the confirmation code determination unit 34 outputs a mismatch. Thus, it is determined that the ciphertext C following the confirmation code is provided to a user other than the user who is trying to view it. When the confirmation code determination unit 34 determines that the decrypted confirmation code M has been normally decrypted, the confirmation code determination unit 34 continues to the key block reading unit 32 according to the value of the block size register 41. It instructs to read out the encryption common decryption key KY ′ and to give it to the key decryption unit 33. In response to this, the key decryption unit 33
Decrypts the encrypted common decryption key KY 'to generate the original common decryption key KY. The generated common decryption key KY is set in a key setting unit 37 described later. Confirmation code judgment unit 3
In 4, when it is determined that the decrypted confirmation code M has not been decrypted normally, the confirmation code determination unit 34
Gives the key block reading unit 32 the following encrypted common decryption key K in accordance with the value of the block size register 41.
Skip Y 'and read the next block, that is, block size data SB.

The document block reading section 35, upon receiving an instruction from the confirmation code determining section 34, enables reading of each block of document data in the data file F expanded on the main memory 40. When the confirmation code determination unit 34 outputs a coincidence signal of the confirmation code, the document block reading unit 35 reads the block size data SP, and reads the value, that is, the following encrypted document code N ′.
And the total number of bytes of the ciphertext C in the block size register 42
To hold. The document block reading unit 35 sequentially reads the blocks of the encrypted document code N ′ and the ciphertext C, and supplies the blocks to the document decrypting unit 36.

The document decrypting section 36 has an encrypted document code N '.
Is decrypted to generate a document code N, and the ciphertext C
Is decrypted to generate a document P. Here, the decryption key used in the document decryption unit 36 is the key setting unit 3
7 is a common decryption key KY set to 7. Common decryption key KY
Is normally decrypted by the key decryption unit 33 and set in the key setting unit 37 when the confirmation code is matched by the confirmation code determination unit 34.

The document code judging section 38 includes a document decoding section 36
It is determined whether or not the document code N decrypted by the above is normally decrypted. The document code determination unit 38 compares the decrypted document code N with a preset document code N, and controls the read block of the document block read unit 35 according to the result.
Key KX which encrypted document code and key KY which decrypts it
If does not correspond, the normal decryption will not be performed,
The document code determination unit 38 outputs a mismatch. Thus, it is determined that the ciphertext C following the document code is provided to a user other than the user who is trying to view the ciphertext. When the document code determination unit 38 determines that the decrypted document code N has been normally decrypted, the document code determination unit 38 continues to the document block reading unit 35 in accordance with the value of the block size register 42. Reads the ciphertext C and decrypts the document
To give to In response, the document decryption unit 36
Decrypts the ciphertext C to generate the original document P.

The document display section 39 has a function of displaying the decrypted document P so that the user can view it. When the user who performs the above operation has viewing authority for the provided document P, the document display unit 39 displays the target document on the display of the client.

FIGS. 4 and 5 are flowcharts showing the procedure for browsing the encrypted file in the above system. Hereinafter, a procedure in which an arbitrary user B having the decryption key KDB browses the encrypted file will be described with reference to FIGS. When the browsing program for the encrypted file is started on the client computer operated by the user B and the data file F on the server is designated, the data reading unit 31 expands the data file F in a predetermined area of the main memory 40 of the client. (401). By the key block reading unit 32, the data file F
Is read out (402) and stored in the block size register 41 (403). Next, the encryption confirmation code MA ′ in the next block is read and sent to the key decryption unit 33. The key decryption unit 33 decrypts the encrypted confirmation code MA 'using the decryption key KDB assigned to the user B (404).

Next, whether the encoded confirmation code is correct is determined by the confirmation code determination unit 34 (405). However, this encryption confirmation code MA '
Since the data is encrypted with the encryption key KEA for the user A, the data cannot be correctly decrypted with the decryption key KDB. Therefore, the process proceeds to step 406, where the confirmation code determination unit 34 moves the pointer indicating the block to be read next to the start address of the next block size data SB according to the value in the block size register 41.

With the movement of the pointer, the key block reading section 32 reads the block size data SB next (402) and stores it in the block size register 41 (403). Next, the encryption confirmation code MB ′ in the next block is read and sent to the key decryption unit 33. The key decryption unit 33 decrypts the encryption confirmation code MB 'using the decryption key KDB assigned to the user B (404). Similarly to the above processing, the decrypted confirmation code is determined by the confirmation code determination unit 34 as to be correct (405), but this time, the encrypted confirmation code MB ′ is determined by the encryption key KEB for the user B. Since it is encrypted, it is correctly decrypted with the decryption key KDB. Thus, the process proceeds to Step 407.

In step 407, the size of the encryption common decryption key KYB 'is confirmed according to the value of the block size register 41. The key block reading unit 32 reads the encrypted common decryption key KYB ′ according to the confirmed size, and sends it to the key decryption unit 33. The key decryption unit 33 transmits the encrypted common decryption key KYB ′ to the decryption key K assigned to the user B.
The data is decrypted by the DB (408). Thus, the common decryption key KY is normally decrypted. The decrypted common decryption key KY
Is set in the key setting unit 37 of the document decrypting unit 36 (4
09).

Next, the document block reading section 35 reads the block size data SP in the first block of the document data (501 in FIG. 5) and stores the value in the block size register 42 (502). Next, the encrypted document code N ′ in the next block is read and sent to the document decryption unit 36. The document decrypting section 36 decrypts the encrypted document code N 'using the set common decryption key KY (503).

Next, the encoded document code is judged by the document code judging section 38 as to be correct (504). If the decryption key set in the key setting unit 37 is incorrect, the encrypted document code N ′ cannot be decrypted correctly. In this case, the process ends without decrypting the document P. The key set in the key setting unit 37 is the decryption key K
If Y, the encrypted document code N 'is
, And can be correctly decrypted with the decryption key KY. As a result, the process proceeds to step 505.

In step 505, the size of the ciphertext C is confirmed according to the value of the block size register 42. The document block reading unit 35 reads the cipher text C according to the confirmed size, and
Send to The document decryption unit 36 decrypts the ciphertext C with the set common decryption key KY (506). As a result, the ciphertext C is normally decrypted, and the original document P is obtained. The decrypted document P is displayed on the display by the document display unit 39 and can be viewed by the user B.

Similarly, the users A and C execute the above program on their own clients and access the same data file F, so that the target document P can be browsed. On the other hand, if a user who does not have the authority to read the document P (for example, the user D having the decryption key KDD for the encryption key KED) accesses the data file F, the confirmation code determination unit 34 determines that the confirmation code is correct. It is determined that it will not be decrypted. As a result, any ciphertext cannot be browsed. In such a case, a message for a user who does not have viewing authority, such as "no viewing authority", may be stored in the last block of the data file F and displayed.

Next, another embodiment of the present invention will be described. In the present embodiment, basically, the encrypted file generation device 10 and the encrypted file browsing device 30 used in the previous embodiment are used. In the generation and viewing of the encrypted file in the present embodiment, different security levels (for example, officers, company-specific departments, and general employees)
Different common keys KX and KY are used for each case. Thus, a single data file includes a plurality of documents having the same theme but different contents (adapted to each security level), and only a user at a corresponding security level can view the target document. .

FIG. 6 shows a data file F generated by the encrypted file generation device according to the present embodiment. The data file F includes, at its lower part, three ciphertexts C1 to C3 having different contents, which are encrypted with different common encryption keys KX1 to KX3.
That is, the ciphertext C1 is obtained by encrypting the document P1 provided to the users A and B belonging to the first security level (for example, officer level; hereinafter, level 1) with the common encryption key KX1 assigned to the level. The ciphertext C2 is obtained by assigning the documents P2 provided to the users C and D belonging to the second security level (for example, a specific department level; hereinafter, level 2) to the level. A document encrypted with a common encryption key KX2 and provided to users E, F and G belonging to a third security level (for example, a general employee level; hereinafter, level 3). P3 is encrypted with the common encryption key KX3 assigned to the level. The document code N encrypted with the corresponding common encryption key, that is, the encrypted document codes N1 ′ to N3 ′ and the block size data SP1 to
SP3 is stored.

At the top of the data file F, each user A
There are seven blocks each accessed by ~ G
Each block stores the common decryption keys KY1 to KY3 assigned to the level to which each user belongs, encrypted with the encryption keys KEA to KEG assigned to the user. For example, since the user A belongs to the level 1, the common decryption key KY1 of the corresponding level is encrypted with the encryption key KEA, that is, the encrypted common key KY1A 'is stored for the user A. . Further, since the user C belongs to level 2, the common decryption key KY2 of the corresponding level
Is encrypted with the encryption key KEC, that is, the encrypted common decryption key KY2C ′ is stored for the user C. The confirmation code M encrypted with the corresponding common encryption key, that is, the encryption confirmation codes M1 ′ to M3 ′ and the block size data SA
To SG are stored.

The generated data file F can be browsed by the encrypted file browsing device 30 shown in the previous embodiment. That is, according to the procedures of FIGS. 4 and 5, each of the users A to G can correctly decrypt the common decryption keys KY1 to KY3 corresponding to the security level by using their own decryption keys KDA to KDG, respectively. Using the decrypted common decryption keys KY1 to KY3, the provided documents P1 to P3 can be correctly decrypted and browsed. On the other hand, when the user is provided with a document provided to a user of another security level (for example, level 3).
Cannot correctly decrypt the document C1) for the user E in the above, and its security is guaranteed.

The embodiment of the present invention has been described with reference to the drawings. However, it is apparent that the present invention is not limited to the matters described in the above embodiments, and that changes, improvements, and the like can be made based on the description in the claims. There is no particular limitation on the encryption algorithm that can be used in the present invention, and various encryption methods (whether it is a symmetric key encryption method, an asymmetric key encryption method, a stream encryption method, or a block encryption method). And the like) can be used.

Although the method of the present invention is suitably used in a computer network environment, the network may be local (for example, a company LAN) or wide area (for example, the Internet). The information to be encrypted is not limited to a document, but may be an image, a sound, or a mixture of these and a document.
It may be saved as one data file. In addition, the method can be used for distribution of a product catalog to a specific user, in which case the product key and other confidential information are distributed together with the distribution of the product catalog using a different encryption key for each specific user. be able to.

Although the method of the present invention can be basically realized by a computer and a program operated on the computer, a program serving as a display interface of information transmitted and received between networks (for example, WWW of the Internet) (A browser) may be realized by adding a predetermined function (so-called plug-in).

In the above embodiment, an example has been shown in which key data is arranged at the top of a data file to be created and document data is arranged at the bottom. However, when the document data is short or the like, this may be recorded in the key data for each user. Furthermore, for a specific user, a block obtained by encrypting document data using an encryption key (for example, KEA) assigned to the user is arranged in a block in which the above-mentioned encryption common decryption key is arranged. You may. In this case, in order to identify whether the data stored in the block is an encryption common decryption key or document data, two types of confirmation codes are prepared, and the confirmation code determination unit identifies them. Good.

[0055]

As described above, according to the present invention, files of the same or related information to be provided to a plurality of users can be combined into one in an encrypted state, and the management of the stored information is easy. There is an advantage. Further, in this case, it is easy for the user and the administrator to manage keys for encryption and decryption.

Further, one document encrypted with the common encryption key may be stored in the data file.
File size can be minimized.

Further, by judging whether or not decoding is correctly performed using the judging code prior to decoding of the information to be viewed, it is possible to easily and quickly determine whether or not the user has the authority to view the information. Can be determined.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram for implementing an encrypted file creation method according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for generating an encrypted file in the system of FIG. 1;

FIG. 3 is a system configuration diagram for browsing a document encrypted by the system of FIG. 1;

FIG. 4 is a flowchart showing a procedure for browsing an encrypted file in the system of FIG. 3;

FIG. 5 is a flowchart showing a procedure for browsing an encrypted file in the system of FIG. 3;

FIG. 6 is a diagram illustrating a data file generated by an encrypted file generation device according to another embodiment of the present invention.

FIG. 7 is a system configuration diagram for realizing a conventional method for creating an encrypted file.

FIG. 8 is a system configuration diagram for implementing a conventional method of browsing an encrypted file.

[Explanation of symbols]

 KX Common encryption key KYA 'to KYC' Encryption common decryption key KDA to KDC decryption key KEA to KEC Encryption key P Document C Ciphertext M Confirmation code MA 'to MC' Encryption confirmation code N Document code N 'Encrypted document code SA to SC block size data SP block size data F data file 10 encryption file generation device 11 key encryption unit 12 key setting unit 13 key data writing unit 14 block size calculation unit 15 document encryption unit 16 document writing unit 17 data storage unit 18 Main memory 30 Encrypted file browsing device 31 File readout unit 32 Key block readout unit 33 Key decryption unit 34 Confirmation code determination unit 35 Document block readout unit 36 Document decryption unit 37 Key setting unit 38 Document code determination unit 39 Document display unit 40 Main memory 41, 42 Block size register

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[Procedure amendment]

[Submission date] May 12, 1999 (1999.5.1
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B017 AA03 AA08 BA07 BB02 CA01 CA07 CA16 5J104 AA16 EA02 EA04 JA03 NA02 NA27 NA37 PA14 9A001 CC03 DD09 EE03 EE04 EE06 JJ27 LL03

Claims (6)

[Claims] 1. A method for generating a data file used by a plurality of viewers having different decryption keys, comprising: a step of encrypting at least one piece of viewed information with a predetermined common encryption key; A procedure of encrypting a common decryption key corresponding to the encryption key with an encryption key corresponding to the different decryption key; and transmitting the encrypted browsed information and the plurality of encrypted common decryption keys to at least one Storing an encrypted file as one data file. 2. A procedure for encrypting a predetermined determination code with an encryption key corresponding to the different decryption key, and for the encrypted common decryption key, the determination encrypted with the same key. Further comprising a step of associating a plurality of common codes with each other, wherein the storing step stores the encrypted viewed information and the plurality of encrypted common decryption keys together with the determination code as one data file. 2. The method for generating an encrypted file according to claim 1, wherein 3. The method according to claim 1, further comprising a step of generating position information for specifying at least a position of the encrypted information to be viewed in the data file, wherein the storing step includes the step of storing the encrypted information to be viewed. 3. The method according to claim 1, wherein the data is stored as one data file together with the position information. 4. A method for browsing an encrypted file generated by the method according to claim 1, further comprising: a step of loading the data file on a main storage; and a step of loading a plurality of encrypted files in the data file. A procedure for sequentially decrypting the common decryption key with a decryption key possessed by the viewer, and a procedure for sequentially determining whether or not the decrypted common decryption key has been correctly decrypted into a common decryption key before encryption. And a step of decrypting the encrypted viewed information with the correctly decrypted common decryption key, and a step of displaying the decrypted viewed information to a viewer. A method for viewing encrypted files, characterized by the following. 5. A method for browsing an encrypted file generated by the method according to claim 2, wherein the encrypted plurality of determination codes are sequentially decrypted with a decryption key possessed by the viewer. The method further comprises a step of sequentially comparing the decrypted determination code with the determination code before encryption, so that the decrypted common decryption key is 5. The method for browsing an encrypted file according to claim 4, wherein the method determines whether or not the file has been correctly decrypted into a common decryption key. 6. A method for browsing an encrypted file generated by the method according to claim 3, wherein the step of decrypting the information to be browsed is performed from the data file based on the position information. 6. The method according to claim 4, further comprising a step of extracting perused information.
How to view the described encrypted file.