JP2003242036A - Data decoding method, and data decoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data decoding method which can minimize leaks of decoded data to be protected, and a data decoder using the method. <P>SOLUTION: A decoding key to decode the decoding data is saved in a key saving means until the decoding key is read. In the decoding, the decoded key is read from this key saving means, the decoding data of the predetermined quantity are decoded by using the read decoding key, and the decoding key used in the decoding is disposed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decrypting encrypted data and an apparatus for decrypting encrypted data using the method.

In particular, a decryption method for decrypting and reading the protected data from a database that stores encrypted data of the protected data such as personal information and confidential information of a company, and decryption of the encrypted data using the decryption method. Regarding the device.

[0003]

2. Description of the Related Art Generally, a database that stores and manages data to be protected such as company confidential information and personal information such as a customer list is susceptible to theft by an end operator. When managing customers with WWW services, the database is encrypted and SSL (Secure
Even if cryptographic communication such as Socket Layer) is used, the server decrypts and uses the data, so there is always a risk that all confidential information and personal information will be stolen once it is hacked.

As a measure for preventing the leakage of the data to be protected such as confidential information and personal information in advance, other than storing and encrypting the data to be protected,
There was no particularly effective measure.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention aims to minimize the amount of information leaked out by unauthorized access to a database that stores protected data such as confidential information and personal information. An object of the present invention is to provide a possible data decoding method and a data decoding device using the same.

[0006]

According to the present invention, a decryption key for decrypting encrypted data is stored in a key storage means until the decryption key is read out, and at the time of decryption, The decryption key is read from the key storage means, a predetermined fixed amount of the encrypted data is decrypted using the read decryption key, and then the decryption key used for the decryption is discarded. Thus, the amount of encrypted data that can be decrypted and read can be limited depending on the maximum number of decryption keys stored in the key storage means, and therefore, even if unauthorized attempts are made to read the encrypted data, Since only the encrypted data having the data amount corresponding to the number of the decryption keys stored in the key storage means can be decrypted, the amount of leaked information can be minimized.

Further, the decryption that has been erased so far is performed such that the number of the decryption keys stored in the key storage means becomes a predetermined maximum number at predetermined predetermined time intervals. By writing the key in the key storage means, the maximum number of decryption keys can be stored in the key storage means within a predetermined time (for example, one day, one week, etc.). The amount of encrypted data that can be decrypted and read can be limited. That is, the maximum amount of encrypted data that can be read and decrypted within a predetermined time such as one day can be determined. Therefore, even if the encrypted data is read out illegally, for example, only the maximum amount of the encrypted data can be decrypted within one day, so that the amount of leaked information can be minimized.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration example of a database management system according to an embodiment of the present invention.

The database management system shown in FIG.
It is roughly divided into an encryption device 1, an encrypted data storage device 2, an information protection device 3, and a decryption key writing device 4.

Here, the protection target data accumulated and managed by the database management system shown in FIG. 1 may be personal information such as customer information or confidential information such as a company.

The encryption device 1 is composed of an encryption key storage unit 11 for storing an encryption key and an encryption unit 12, and the encryption unit 12 has a predetermined encryption algorithm and an encryption key storage unit. Using the encryption key stored in 11, the protection target data stored in the database is encrypted.

The encrypted data storage device 2 includes a writing unit 2
1, a reading unit 22, and a storage unit 23. When the writing unit 21 receives the protection target data (encrypted data) encrypted by the encryption device 1, the writing unit 21 writes it in the storage unit 23. The storage unit 23 is
It is an encrypted database. The reading unit 22
In response to the read request from the information protection device 3, the storage unit 2
Encrypted data is read out from No. 3.

The information protection device 3 corresponding to the data decryption device of the present invention for decrypting encrypted data comprises a decryption key storage part 31, a reading part 32, a decryption part 33 and a decryption control part 34. Composed.

In the database management system, a device external to the database management system (for example, a terminal device 10 for operation by an end operator).
From 1), when an application program (CGI program or the like) for accessing the database is executed and a read request for information from the database is transmitted, the read request is sent to the decryption control unit 34 of the information protection device 3. input. Upon receiving the read request, the decryption control unit 34 reads out the encrypted data from the encrypted data storage unit device 2 and also reads out one decryption key from the decryption key storage unit 31 via the readout unit 32. Then, using the read decryption key, the read encrypted data is decrypted and output. In this way, the information protection device 3 uses the encrypted data storage device 2
It is for reading the encrypted data from and decrypting it, but at that time, for a predetermined time (for example, one day,
The amount of encrypted data that can be decrypted within a week is limited. That is, the maximum data amount of encrypted data that can be decrypted within a predetermined time such as one day is predetermined.

Even if there is a bug in a program that accesses the database (for example, a CGI program) or an unauthorized access to the database, encrypted data that stores encrypted data to be protected as in this embodiment By adopting a configuration in which the storage device 2 is accessed via the information protection device 3, the amount of encrypted data to be decrypted is limited, so that the amount of leaked information can be minimized. .

Note that it is necessary to perform protection such as data encryption with respect to the transmission of the read request from the terminal device 101 and the decrypted data which is a response thereto, but regarding this point and other communication protection, Since it can be realized by an easy combination of known cryptographic techniques, the description thereof will be omitted in the present embodiment.

An outline of a method for limiting the amount of encrypted data that can be decrypted within a predetermined time (for example, one day here) by the information protection device 3 is shown in FIG. It will be described with reference to FIG.

In this embodiment, the length (amount) of encrypted data that can be decrypted at one time is determined in advance.

In the encryption device 1, when the data to be protected is encrypted, it is encrypted in a predetermined data amount unit. Then, for the sake of simplicity of explanation, the encrypted data obtained as a result of encrypting the protection target data of a predetermined data amount is stored in the storage unit 23 as one unit (as one block). The reading unit of the reading unit 22 is also the block unit.

In the present embodiment, the storage unit 23 stores in FIG.
As shown in (a), a plurality of blocks (B-1, B-
2, ...) And the encrypted data is stored.
In this case, each block is encrypted data encrypted with one encryption key. The data amount of each block is almost the same, but here, for example, about 1
Let's say it is K bytes.

When the reading unit 22 receives a reading request from (the decoding control unit 34 of) the information protection device 3,
For example, one block is read from the storage unit 23 and returned to the decoding control unit 34.

Since the encryption is performed in block units, decryption is also in block units. In the decryption unit 33,
For example, the data amount of encrypted data that can be decrypted with one decryption key is the data amount of one block, that is, (about) 1 Kbyte here. Then, only one decryption key is used for one read request (read request from the terminal device 101 or the like). Therefore,
The amount of encrypted data that can be decrypted with respect to one read request is one block data amount, that is, (about) 1 Kbyte.

The reading unit 22 is used by the information protection device 3
When a read request is received from (the decoding control unit 34), a plurality of blocks may be read from the storage unit 23 and returned to the decoding control unit 34. Even in this case, the amount of encrypted data that is decrypted for one read request is only the amount of data that can be decrypted with one decryption key.

In the present embodiment, the data amount of the encrypted data read by the reading unit 22 at one time and the data amount of the encrypted data decrypted by the decrypting unit 33 at the same time are both the data amount of one block. However, the present invention is not limited to this case, and the reading unit 22 may read a predetermined number of blocks.
The decryption unit 33 may decrypt all of the read predetermined number of blocks with one decryption key.

It is assumed that the decryption key is stored in advance in the decryption key storage unit 31 in the information protection device 3. However, once the decryption key is read from here, the decryption key is erased from the storage location. And The decryption key storage unit 31 is composed of, for example, a hard disk or a semiconductor memory. For example, here, when the reading unit 32 reads one decryption key from the decryption key storage unit 31, the decryption key may be deleted from the storage location. This control can be realized, for example, by using a memory operation instruction that is provided in advance as one of the instruction sets of the CPU. For example, write the data specified using the above command to the memory area corresponding to the storage location of the read decryption key (overwrite with the specified data) and delete the decryption key. May be.

In order to ensure higher security, when the decryption key is read, the decryption key storage unit 31 itself does not depend on the control of the decryption key storage unit 31 from the outside.
It is desirable to erase the decryption key that has been read. Preferably, the decryption key storage unit 31 is configured by using a special semiconductor whose reading is limited to one time. The decryption key storage unit 31 is configured by using such a special semiconductor, and when the decryption key is erased, the decryption key storage unit 31 and the reading unit 32 operate integrally to provide the decryption key. It is possible to save and retrieve the data more safely.

A predetermined time (for example, here,
If the maximum amount of encrypted data that can be decrypted within one day is defined as, for example, 3 blocks (that is, approximately 3 Kbytes), one decryption key can decrypt the encrypted data. If only one block (approximately 1 Kbyte) of encrypted data can be decrypted at one time, the number of decryption keys required per day is 3
It becomes one. That is, in the present embodiment, as shown in FIG. 1, the decryption key storage unit 31 stores up to three decryption keys per day.

When the decryption control unit 34 of the information protection device 3 receives a read request from the terminal device 101 or the like, the decryption unit 33 issues a predetermined read request to the encrypted data storage device 2 and then, as shown in FIG. ), A predetermined amount (here, for example, one block) of encrypted data is obtained. Further, in response to the instruction from the decryption control unit 34, the reading unit 32 reads one decryption key from the decryption key storage unit 31. At that time, as shown in FIG. 2B, the read decryption key is erased from the decryption key storage unit 31.

When the decryption unit 33 receives one read request, and if at least one decryption key is stored in the decryption key storage unit 31 at that time, the decryption unit 33 stores the encrypted data in the encrypted data storage device 2. The read one block of encrypted data can be decrypted and output. After decrypting one block of encrypted data, the decryption unit 33 discards the decryption key used at that time. For example, when the decryption unit 33 completes the decryption process for a predetermined amount (here, one block) of encrypted data, the contents of a predetermined register of the CPU that has executed the process are initialized using an instruction of the CPU. (Or write specified data).

In the decryption unit 33, the decryption key used for decryption is discarded (disposable) so that it will not be used again.
Therefore, another encrypted data cannot be decrypted again using the decryption key.

In the above database management system as described above, the maximum amount of encrypted data that can be decrypted and read within a predetermined time (for example, one day) is stored in the decryption key storage unit 31. It can be limited by the maximum number of decryption keys. That is, the maximum amount of encrypted data that can be decrypted within one day is, for example, 3
When the block is defined (that is, approximately 3 Kbytes), the decryption key storage unit 31 stores up to three decryption keys per day.

What is indispensable in the framework of limiting the maximum amount of encrypted data that can be decrypted per day by the number of decryption keys is that the decryption key stored in the decryption key storage unit 31 is The control is such that it is always erased from the decryption key storage unit 31 every time it is read from. Alternatively, the decryption key storage unit 31 itself has a mechanism of erasing the decryption key once read.

In order to limit the amount of encrypted data that can be decrypted within a predetermined time (for example, one day in this case) by the number of decryption keys stored in the decryption key storage unit 31, this embodiment is used. In the mode, the erased decryption key is rewritten (refreshed) in the decryption key storage unit 31 every predetermined time (here, every day, that is, at a fixed time every day) (supplementing the decryption key). ).

The operation of supplementing the information protection device 3 with the decryption key is performed by using the decryption key writing device 4 of FIG. 1, for example.

The decryption key writing device 4 stores the decryption key storage unit 41 for storing the decryption key and the decryption key stored in the decryption key storage unit 41 at every predetermined time. It is composed of a scheduler that gives an instruction for writing to (the decryption key storage unit 31 of) the protection device 3. The decryption key writing device 4 connects to the information protection device 3 only when writing the decryption key to the information protection device 3.

In the decryption key storage unit 41 of the decryption key writing device 4, when the encryption key stored in the encryption key storage unit 11 of the encryption device 1 is updated, the decryption corresponding to the encryption key concerned is updated. The activation key is written. This operation can be performed only by a specific user who is authorized in advance.

The information protection device 3 is connected by a predetermined network and a predetermined cable so as to be able to communicate with an external device of the database management system such as the terminal device 101. Normally (except when writing the decryption key), since the decryption key writing device 4 is not connected, it cannot be accessed at all from a device outside the database management system.
Further, the encryption device 1 is not connected to a network or a cable as shown in FIG. 1, so that it cannot be accessed at all from a device outside the database management system. Therefore, the decryption key is not refreshed by the information protection device 3 illegally.

Since the encrypted data storage device 2 is configured as a device separate from the information protection device 3, even if the encrypted data storage device 2 is stolen, the encrypted data stored therein is decrypted. If there is no information protection device 3 that can
The protected data cannot be read.

Next, the processing operation of the database management system shown in FIG. 1 will be described with reference to the flow charts shown in FIGS.

First, the processing operation at the time of writing will be described with reference to the flowchart shown in FIG.

It is assumed that the data to be protected can be encrypted and written only by a user who is given such authority beforehand.

When the data to be protected is input to the encryption device 1, the encryption unit 12 reads out the encryption key stored in advance in the encryption key storage unit 11 and performs encryption for each predetermined amount (step). S1). The encrypted data obtained as a result of encrypting a predetermined amount of data to be protected is treated as one block of encrypted data thereafter. The encrypted data for each block is sent to the encrypted data storage device 2, and is written in the storage unit 23 by the writing unit 21 in the block unit (step S2).

The encryption method of the data to be protected is not particularly limited because it is not the gist of the present invention. The encryption key and the decryption key may be the same, or the encryption key and the decryption key may be different.

Next, the processing operation at the time of reading will be described with reference to the flowchart shown in FIG.

In the database management system, a device external to the database management system (for example, a terminal device 10 for operating an end operator) is provided.
When the application program (CGI program or the like) for accessing the database is executed from 1) and the information read request is transmitted, the read request is input to the decryption control unit 34 of the information protection device 3. . Upon receiving this read request (step S11), the decryption control unit 34 transmits a predetermined read request to the encrypted data storage device 2 (step S12).

Read-out unit 22 of encrypted data storage device 2
In response to the read request from the information protection device 3, reads out one block of encrypted data from the storage unit 23 and sends it to the information protection device 3 (step S13).

On the other hand, in the information protection device 32, the decryption control unit 34 sends a decryption key read request to the read unit 32. In response to this request, the reading unit 32 reads one decryption key from the decryption key storage unit 31.

As described above, the decryption key storage unit 31 stores a maximum of three decryption keys. In this case, the decryption key storage unit 31, for example, as shown in FIG.
It has three decryption key storage areas, each of which has a first area R1 for storing a flag indicating the presence or absence of a decryption key, and
It is composed of a second area R2 for storing a decryption key. When this flag is "1", it indicates that a valid decryption key is stored in the decryption key storage area, and when it is "0", as shown in FIG. It is assumed that the decryption key has been read from the decryption key storage area and has already been erased. In addition,
In this embodiment, a flag is used for the sake of simplicity of description, but a check routine corresponding to the flag may be used in practice. For example, the hash value for the data block is added to the encryption block to check the validity of the decryption key before use.

The reading section 32 checks the first areas R1 one by one, and reads the decryption key from the storage area in which "1" is set. When read, the data in the storage area is erased as described above. In this case, for example, as shown in FIG. 5B, the first region R1
Overwrites the decryption key storage area with specified data so that "0" indicating that the decryption key does not exist in the storage area is set.

By the way, as described above, the database management system of this embodiment can decrypt up to three blocks of encrypted data per day, for example. Therefore, the decryption key storage unit 31 rewrites the decryption keys erased up to that time at a fixed time every day (for example, 7:00 am), and stores a maximum of three decryption keys. Has been done. However, if the read request from the terminal device 101 has already been received three times at the time of reading the decryption key from the decryption key storage unit 31 after 7:00 am (that is, the decryption unit 33 encrypts the three blocks). (When three decryption keys have been read from the decryption key storage unit 31 in order to decrypt the encrypted data), the decryption key storage unit 3
No decryption key already exists in 1. In this case, in this embodiment, “0” is set in the first area R1 of each decryption key storage area of the decryption key storage unit 31. Therefore, the reading unit 32 cannot read the decryption key, and the reading operation is stopped at this point (step S14).

When a valid decryption key exists in the decryption key storage unit 31 (step S14) and the reading unit 32 can read one decryption key (step S15), the step Proceeding to S16, the reading unit 32
The data in the read decryption key storage area of the decryption key storage unit 31 is erased (for example, overwritten with the designated data). The decryption key read by the reading unit 32 is passed to the decryption control unit 34.

The decryption control unit 34 receives, for example, one block of the encrypted data sent from the encrypted data storage device 2 and the decryption key passed from the reading unit 32.
3 to execute decryption processing (step S1)
7). Then, when the decryption of the encrypted data of one block is completed, the decryption key used in the process is discarded as described above (step S18), and the decrypted protected data is the request source, for example, the terminal device 101. (Step S19).

As described above, in the information protection apparatus 3 of the above embodiment, (1) the decryption key storage unit 31 stores the decryption key for decrypting the encrypted data, and the read unit 32 causes the decryption key to be stored. When the decryption key is read therefrom, the read decryption key is erased from the decryption key storage unit 31. (2) The decryption unit 33 decrypts a predetermined fixed amount (for example, one block here) of encrypted data using one decryption key read from the decryption key storage unit 31. To do. That is, one decryption key can only decrypt a predetermined fixed amount (for example, one block here) of encrypted data. (3) After decrypting one block of encrypted data, the decryption key used for the decryption is discarded.

According to the information protection device having such a configuration,
Depending on how many decryption keys are stored in the decryption key storage unit 31 at the maximum, the amount of decrypted encrypted data can be limited. Since only the encrypted data having the data amount corresponding to the number of the decryption keys stored in the decryption key key holding unit 31 can be decrypted, the leaked information amount can be minimized.

Further, as described above, the amount of encrypted data that can be decrypted with one decryption key is predetermined,
Moreover, each time the decryption key stored in the decryption key storage unit 31 is read, the read decryption key is erased from the decryption key storage unit 31, and the decryption key is further stored for a predetermined period of time. For each time, the number of decryption keys stored in the decryption key storage unit 31 reaches a predetermined maximum number, and the decryption keys erased up to that point are decrypted key storage unit 3
By writing to 1, the decryption key storage unit 31 decrypts within the predetermined time depending on the maximum number of decryption keys stored within the predetermined time (for example, one day, one week, etc.). It is possible to limit the amount of encrypted data that can be processed. That is, the maximum data amount of encrypted data that can be decrypted within a predetermined time such as one day can be determined. Therefore, even if the encrypted data stored in the encrypted data storage device 2 is illegally read,
Since only the maximum amount of encrypted data can be decrypted during the day, the amount of leaked information can be minimized.

In the decryption key storage unit 31, it is possible to rewrite the erased decryption key (using the decryption key writing device 4) every time a predetermined time such as one day elapses. For example, the information protection device 3 can be used semipermanently. However, the configuration of supplementing the erased decryption key is not indispensable, and even if it is a disposable type in which the information protection device 3 itself is destroyed after a predetermined time such as one day elapses. Good. In this case, it is necessary to replace with a new information protection device 31 (that is, a predetermined number of decryption keys are written in the decryption key storage unit 31) every time the above time elapses.

In the information protection apparatus described in the embodiments of the present invention, a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), which is a program that can be executed by a computer, other than the decryption key storage unit 31, It can also be stored in a recording medium such as an optical disk (CD-ROM, DVD, etc.), a semiconductor memory or the like and distributed.

The present invention is not limited to the above embodiment, and can be variously modified at the stage of implementation without departing from the spirit of the invention. Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent requirements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the problem (at least one) described in the section of the problem to be solved by the invention can be solved, and the column of the effect of the invention. When the effect (or at least one) described in 1) is obtained, a configuration in which this constituent element is deleted can be extracted as an invention.

[0060]

As described above, according to the present invention,
Leakage of protected data can be minimized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the overall configuration of a database management system according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a method for limiting the amount of encrypted data that can be decrypted within a predetermined time (for example, one day here) in the information protection device.

FIG. 3 is a flowchart for explaining the processing operation of the database management system of FIG. 1, showing the processing operation when writing encrypted data.

4 is a flowchart for explaining the processing operation of the database management system of FIG. 1, showing the processing operation at the time of reading / decrypting encrypted data.

FIG. 5 is a diagram for explaining a storage form of a decryption key in a decryption key storage unit.

[Explanation of symbols]

1 ... Encryption device 11 ... Encryption key storage unit 12 ... Encryption unit 2 ... Encrypted data storage device 21 ... Writing unit 22 ... Read-out section 23 ... Storage unit 3 ... Information protection device 31 ... Decryption key storage unit 32 ... Read-out section 33 ... Decoding unit 34 ... Decoding control unit 4 Decryption key writing device 41 ... Decryption key storage unit 42 ... Scheduler 101 ... Terminal device

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5B017 AA03 BA08 CA05 CA07 CA11                       CA16                 5D044 AB02 BC08 CC09 GK12 GK17                       HL02                 5J104 AA16 AA34 AA46 EA04 EA09                       NA02

Claims (5)

[Claims] 1. A decryption key for decrypting encrypted data is stored in a key storage means until the decryption key is read, and at the time of decryption, the decryption key is stored in the key storage means. And decrypting a predetermined fixed amount of the encrypted data using the read decryption key, and then discarding the decryption key used for the decryption. . 2. The decryption that has been erased so far so that the number of the decryption keys stored in the key storage means becomes a predetermined maximum number at predetermined predetermined time intervals. 2. The data decryption method according to claim 1, wherein the key is written in the key storage means. 3. A key storage means for storing a decryption key for decrypting encrypted data, the key storage means storing the decryption key until the decryption key is read out, and the key storage. Decoding means for reading the decryption key stored in the means, and decrypting a predetermined fixed amount of the encrypted data by using the read decryption key; And a key discarding unit that discards the read decryption key when the encrypted data is decrypted. 4. The key storage means is arranged so that the number of the decryption keys stored in the key storage means reaches a predetermined maximum number every predetermined time. 4. The data decryption device according to claim 3, wherein the decryption key erased is written in the. 5. The key storage means comprises erasing means for erasing the decryption key from the storage area for storing the decryption key when the decryption key is read out. The described data decoding device.