JP4338185B2 - How to encrypt / decrypt files - Google Patents

Description

  The present invention relates to a file encryption / decryption method depending on a logical file configuration in which information reference in a file is kept in a specific logical environment.

In a conventionally known file encryption method, a user who can access an encryption key obtained by encrypting a file can decrypt and view the encrypted file. The encryption key is recorded on an external medium or an internal storage medium, and the encrypted file can be decrypted anywhere in an environment where the encryption key can be accessed (see, for example, Non-Patent Document 1). This is a feature that can be said for general encryption products as well (for example, see Non-Patent Document 2). On the other hand, there is one that generates an encryption key and encrypts a target by a physical device configuration (see, for example, Patent Document 1).
JP 2001-243105 A PGP Corporation, “PGP CORPORATION WHITE PAPERS”, [online], August 2002, PGP Corporation, [searched on January 29, 2003], Internet <URL: http://www.pgp.com/> Information Processing Promotion Association, Security Center, “List of Cryptographic Products Available in Japan”, [online], November 29, 2000, IPAISEC, [Search January 29, 2003], Internet <URL: http: / www.ipa.go.jp/security/enc/product.htm>

However, in the above-described conventional technology, an environment in which an encrypted file can be browsed can be obtained wherever an encrypted file and an encryption key are present. For example, if a mobile personal computer storing an encrypted file is carried around, the encrypted file can be decrypted in the same way in a protection area in a company, on a train, or at a customer site. Therefore, there is a risk that the contents of the encrypted file may leak due to theft of the mobile personal computer or the carelessness or intention of the user.
The technique described in Japanese Patent Laid-Open No. 2001-243105 is a method for encrypting data storage on a physical medium in an environment that depends on a plurality of components. In addition, there is a problem in that the content of the encrypted file cannot be protected against the act of taking out the encrypted file by remotely accessing from the network in an environment where the component configuration is maintained.

  An object of the present invention is to provide a file encryption / decryption method capable of preventing a file content from being referred to in an environment other than an environment that should be referred to or saved even if the user is an authorized user.

In order to achieve the above object, a file encryption / decryption method according to the present invention includes a first step of creating an encrypted file obtained by encrypting a body to be encrypted with a pre-selected encryption algorithm and encryption key, One or more environment information that is a prerequisite for decrypting the body of the encrypted file is designated, a key for encrypting the encryption key is generated based on the position information of the environment information, and the encryption key is used for encryption. A second step of generating key information including the encrypted encryption key and the environment information; a third step of storing an identifier of the encryption algorithm and the key information in the encryption file;
The location information of one or a plurality of environment information is extracted from the encryption file storing the key information, the environment information existing at the logical position indicated by the location information is acquired, and any environment information is successfully acquired. Only when the decryption key information of the encryption key is generated from the position information of the environment information that has been successfully acquired, and the encryption key is decrypted by the decryption key information, the decrypted encryption key and the encryption algorithm And a fifth step of decrypting the text stored in the encrypted file by the encryption algorithm indicated by the identifier.
Further, the environment information is position information of a dependency file having a logical dependency relationship with the encrypted file.
The environment information is information depending on hardware of a computer that permits reference to the encrypted file.

According to the present invention, it is possible to prevent the file contents from being referred to in an environment other than the environment in which the file is originally referred to or stored without incurring the storage cost of the file encryption key or the key exchange cost.
In the unlikely event that an encrypted file is leaked, the dependency of the dependent file cannot be verified by changing the dependency of the dependent file, making it impossible to refer to the encrypted file. It is possible to prevent information leakage due to access to encrypted files, illegal take-out and outflow.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
1 and 2 are block diagrams showing an embodiment of a computer system to which a file encryption method according to the present invention is applied. FIG. 1 shows an example of creating an encrypted file using file dependency on the network, and FIG. 2 shows another file in the viewing computer 201 in addition to the file dependency on the network of FIG. This example shows how to create an encrypted file using the dependency relationship with
In FIG. 1, reference numerals 101, 104, 107, and 109 denote general computers. The computer storing the dependency file 105 is referred to as a server 104, and the other computers are referred to as a client A 101, a client B 107, and a client C 109, respectively.
The server 104 and the client A 101 are connected to the same LAN 100, and the client B 107 is connected to the server 104 by the WAN 106. In the case where the client A 101 creates the encryption file 103 for the client B 107 connected to the network, the encryption file 103 is created using the dependency file 105 and distributed to the client B 107. Since the client B 107 is in an environment where the dependent file 105 of the distributed encrypted file 103 can be referred to by the WAN 106, the contents of the encrypted file 103 can be correctly decrypted and referenced. If the reference is attempted by the client C 109 that was not intended due to the leakage of the encrypted file 103, the client C 109 not connected to the server 104 cannot access the necessary dependent file 105 for the encrypted file 103. For this reason, the contents of the encrypted file 103 cannot be correctly decrypted.

Further, when the client A 101 sets the file in the distribution destination local HDD as the dependency file 204, the encrypted file is also used by using the machine information of the distribution destination machine and the dependency file 204 registered in advance in the reference machine information DB 102. 103 is generated. This is shown below.
In FIG. 2, reference numeral 201 denotes a general computer, and a dependency file 204 that is one of the dependency files of the encrypted file 103 is stored in a directory path in the local HDD 203 in the computer 201. If the computer has the dependency file 204 and can generate the same machine information 205 as the machine information specified when the encrypted file 103 is created, the encrypted file 103 can be referred to correctly.

3 to 6 show information about the encrypted file 103. FIG. 3 shows the encrypted file information 310, FIG. 4 shows the key information 320, FIG. 5 shows the dependent file information 330, and FIG. 6 shows the reference machine of the distribution destination machine. An example of the table 350 of the information DB 102 is shown.
In FIG. 3, an eye catcher 311 represents an identifier indicating that it is the encrypted file 103 of the present invention, and for example, “SFD” is set as a fixed character string.
The algorithm ID 312 represents an identifier of an encryption algorithm used for encryption processing in the encrypted file 103, and is one of identifiers of usable encryption algorithms including “AES” (Advanced Encryption Standard) and “DES” (Data Encryption Standard). Set.
The key length 313 represents the key length of the encryption algorithm set by the algorithm ID 312 in bits.
The number of keys 314 is a value representing how many pieces of key information 320 having the contents shown in FIG. 4 are stored, and the body length 316 represents the length of the encrypted plaintext body contents 317 in bytes.

  In FIG. 4, an encrypted file encryption key 321 represents the result of encrypting the file encryption key used for file encryption by the dependency relationship with the dependency file 105 or the like. The number of dependent files 322 is a value representing how many pieces of dependent file information 330 having the contents shown in FIG. 5 are stored.

In FIG. 5, the dependency file location information 331 represents the storage location of the dependency file 105 or 204. In the case of the dependency file 105 placed on the network, a URL (Uniform resource Locator) format starting with http or ftp or path information indicating a position on the network file system is set. In the case of the dependency file 204 (FIG. 2) placed in the computer 201, path information indicating the position on the file system is set.
The dependency file hash value 332 is a hash value of the contents of the dependency file 105 or 204 indicated by the dependency file position information 331.

  In FIG. 6, the machine information 351 is information of the distribution destination computer 201 registered in advance, and is a value obtained by concatenating the CPU type, the BIOS type, the MAC address of the network card, etc. indicating the hardware characteristics of the distribution destination computer 201. It is a hash value. In the reference machine information DB 102 of FIG. 1, machine information 350 corresponding to the number of registrations is stored.

FIGS. 7 and 8 are flowcharts showing an embodiment of the procedure of the file encryption method according to the present invention, and FIGS. 9 and 10 are flowcharts showing the decryption procedure.
In FIG. 7, when encrypting a file, first, after starting the encryption program according to the present invention, a target file to be encrypted is selected (step 701). Next, an encryption algorithm such as DES used for encryption is selected (step 702). Thereafter, a file encryption key is automatically generated (step 703), and the file contents are encrypted with the selected encryption algorithm and file encryption key (step 704). Up to this point, the procedure is the same as the conventional file encryption procedure using the encryption key.
Next, specify the number of keys. That is, it is specified how many keys are included in the encrypted file 103 in order to construct a dependency relationship with the encrypted file 103 (step 705).
The key set is used to set the dependent file 105 or 204 corresponding to each environment when it is desired to refer to the encrypted file 103 in a plurality of environments.
In steps 706 to 719, one or more dependent files 105 or 204 are designated for each key number, the specified dependent file 105 or 204 is input (step 707), and the input dependent file 105 or 204 is successfully acquired. It is determined whether or not (step 708). If successful, the dependent file position information is input (step 709). The dependency file location information indicates the location where the dependency file 105 or 204 exists, as indicated by the dependency file location information 331 in FIG. 5, and is the absolute path format or URL format of the local HDD that can be referred to in the decryption environment. Specify.
When the absolute path format of the local HDD 203 is specified as the dependency file position information (step 710), machine information 351 of a machine permitted to be browsed is input from the reference machine information DB 102 in order to limit the browsing environment (step 710). 711).
In addition, when a path on the network such as a URL format is specified as the dependency file location information, the MAC of the network card of the server 104 that is the dependency file storage destination machine is used to prevent the storage location of the dependency file 105 from being disguised. An address is acquired (step 712), and the hash value of the MAC address is used as machine information (step 713).

Next, in order to encrypt the file encryption key generated in step 703, a hash value of a value obtained by concatenating the dependency file position information, the contents of the dependency file 105 or 204, and the machine information is calculated, and a file encryption key encryption key buffer is obtained. Is added to the end of the data (step 714).
Next, the hash value of the contents of the dependent file 105 or 204 is set as the hash value 332, the dependent file position information is generated as the dependent file position information 331, and these are generated and stored as the dependent file information 330 (step 715).
Thereafter, it is determined whether to add the dependent file 105 or 204 (step 716).

If all the dependent files 105 or 204 have been added, a key for encrypting the file encryption key is generated from the file encryption key encryption key buffer (step 717), and the file encryption key is encrypted with the key. The encrypted file encryption key 321 of the information 320 is stored. In this case, the number of dependent files 322 and the dependent file information 323 are also stored in the key information 320 (step 718).
Steps 707 to 718 are repeated a number of times equal to the number of keys.
As a result, key information 320 corresponding to the number of keys input in step 705 is generated.
When all the key information 320 corresponding to the number of keys has been generated, the encryption file information 310 including the eye catcher 311, algorithm ID 312, key length 313, key number 314, key information 315, text length 316, text 317 is generated ( Step 720). Further, after adding the encryption file information 310 to the browsing program (step 721), the file is output as the encryption file 103 (step 722).

When the encrypted file 103 generated as described above is decrypted, it is stored in the encrypted file 103 after starting the browsing program containing the encrypted file 103 as shown in the flowcharts of FIGS. Dependencies of the key information 320 corresponding to the number of the key information 320 are confirmed, and if it matches any environment of the key information 320 stored in the encrypted file 103, the browsing process is permitted.
Therefore, all the dependent file information 330 stored for each key information 320 is examined (step 902). First, an attempt is made to acquire the dependency file 105 or 204 from the dependency file position information 331 of the dependency file information 330 (step 903). At this time, in the environment where the dependency file 105 or 204 does not exist in the specified path or access to the dependency file 105 or 204 is restricted, acquisition of the dependency file 105 or 204 fails. If acquisition fails, the process proceeds to step 918.

When the dependency file 105 or 204 can be acquired (step 904), the hash value of the content of the dependency file 105 or 204 is calculated, and the hash value of the calculation result is compared with the dependency file hash value 332 ( Step 905). If the hash values are the same (step 906), it is determined that they are the same as the dependent file 105 or 204 used when creating the encrypted file 103, and if the hash values are different, it is determined that the dependent file 105 or 204 is not correct. If the hash values are different, the process proceeds to step 918.
If the hash values match, it is determined whether the dependency file position information 331 indicates the dependency file 204 in the local HDD 203 (step 907), and indicates the dependency file 204 in the local HDD 203. In that case, the machine information 205 of the computer 201 of the browsing environment destination is acquired (step 908). The machine information 205 is a feature of a hardware configuration that can identify the computer 201 of the browsing environment destination, and is a hash value of a value obtained by concatenating the CPU type, the BIOS type, and the MAC address of the network card (step 909).

On the other hand, if the dependency file location information 331 indicates the dependency file 105 on the network, the MAC address of the network card of the server 104 storing the dependency file 105 is acquired (step 910), and the MAC address The hash value is used as machine information (step 911).
Thereafter, in order to decrypt the file encryption key itself, a hash value of a value obtained by concatenating the dependency file position information 331, the contents of the dependency file 105 or 204 and the machine information is calculated, and the end of the data in the file encryption key decryption key buffer is calculated. (Step 912).

When the above steps 902 to 913 are repeated for the number of dependent files, and all of the dependent files 105 or 204 are confirmed normally, a decryption key for the file encryption key is generated from the decryption key buffer for the file encryption key ( Step 914), the file encryption key is decrypted with the key (Step 915). Thereafter, the body 317 is decrypted with the decrypted file encryption key (step 916), and the display process of the decrypted content is performed with the browsing program (step 917).
At this time, if the browsing environment of the encrypted file 103 is different from the environment having the machine information 205 specified when the encrypted file 103 is generated, or the server 104 storing the dependent file 105 is different, it is necessary to decrypt the file encryption key. A correct key cannot be generated, and the encrypted file 103 cannot be viewed in an unauthorized environment.
If confirmation of the dependency file 105 or 204 fails, it is determined that the environment is not browseable as indicated by the key information 320, and the next key information 320 is processed. If the processing of all the key information 320 has failed, the display processing by the browsing program is not performed and the program is terminated.

As described above, according to the present embodiment, the user does not input a password or saves the data encryption key in another secure location, and other files that are logically dependent on the encrypted file Ciphertext reference is permitted when the dependency relationship can be confirmed (verified), and reference can be prohibited when the dependency relationship cannot be confirmed (verified). Therefore, an encrypted file can be shared with other users in the intended environment without incurring key storage costs or key exchange costs.
Also, depending on the storage location and number of dependent files, for example, an encrypted file that cannot be decrypted outside the company, or an encrypted file that can be decrypted only by a specific user can be generated by controlling access to the dependent file. .
Furthermore, by storing a plurality of key information, even if one environment cannot be used, it can be referred to in another environment.
As a result, if an encrypted file leaks, if the access environment to the dependent file is changed, even if the key that encrypted the body text is known, the relationship with the dependent file cannot be confirmed, and decryption is not possible. It is possible to prevent access to encrypted information in an unintended environment and information leakage due to illegal take-out, such as preventing the encrypted file that has failed and leaked from being decrypted.

The block diagram which shows schematic structure of one embodiment of this invention, The block diagram which shows schematic structure of one embodiment of this invention, It is a figure which shows the structure of encryption file information. It is a figure which shows the structure of key information. It is a figure which shows the structure of the dependence file information in a network environment and a local environment. It is a figure which shows the structure of the machine information DB of the distribution destination environment of an encryption file. It is a flowchart which shows the encryption processing procedure of the file which concerns on this invention. It is a flowchart which shows the continuation of FIG. It is a flowchart which shows the decoding process procedure of the file which concerns on this invention. 10 is a flowchart showing a continuation of FIG. 9.

Explanation of symbols

100 LAN
101 Client A
102 Reference machine DB
103 Encryption file 104 Server 105 Dependent file 107 Client B
109 Client C

Claims (1)

A file encryption / decryption method for encrypting a file to be encrypted with an encryption key by a computer and decrypting the encrypted file,
The computer is
A first step of creating an encrypted file obtained by encrypting a body of the file to be encrypted with an encryption key;
Information indicating the contents of the dependent file having a logical dependency with the encrypted file, the location information of the storage means storing the dependent file, and the characteristics of the client computer that permits browsing of the encrypted file stored in the database For environment information consisting of the contents of a dependency file having a logical dependency with the encryption file, location information on the network where the dependency file is stored, and the MAC address of the network card. A key that is stored in a key buffer, generates a key for encrypting the encryption key based on the contents of the stored dependency file and environment information, and includes the encryption key and the environment information encrypted by the generated key A second step of generating information;
A third step of storing the key information in the encrypted file;
The environment information is extracted from the encrypted file storing the key information, the dependency file existing at the logical position indicated by the environment information is acquired, and only when the acquisition is successful , the contents of the dependency file successfully acquired Storing the environment information in a decryption key buffer, generating decryption key information of the encryption key based on the contents of the stored dependency file and the environment information , and decrypting the encryption key based on the decryption key information Steps,
A file encryption / decryption method comprising: a fifth step of decrypting a body text stored in the encrypted file with the decrypted encryption key.

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