JP4853026B2 - Information processing apparatus and program - Google Patents

Description

  The present invention relates to an information processing apparatus and a program, and more particularly, to an information processing apparatus and a program that store a block-encrypted file.

  Conventionally, as a method for encrypting a file, a block encryption method for encrypting a file for each block has been adopted, and a US government standard encryption selected by the National Institute of Standards and Technology (NIST) as a block encryption algorithm here. AES (Advanced Encryption Standard) is known.

  For example, the CBC (Cipher Block Chaining) mode, which is one of the AES modes, is different even when the same plaintext block is consecutive for each block by taking the exclusive OR of the plaintext block and the ciphertext block of the previous block. In this mode, a ciphertext block can be generated. In this case, since the ciphertext block of the immediately preceding block does not exist in the first block of the file, an initial vector (IV) is set separately.

A block encryption method is known in which the initial vector is stored in advance in units of files, and when the data is encrypted, the initial vector is encrypted while being changed for each file and stored in the HDD (patent). Reference 1).
JP2002-42424

  However, in the block encryption method described in Patent Document 1, since the initial vector is stored in units of files and block encryption is performed in units of files, only the data at a specific location in the file stored in the HDD is extracted. There is a problem in that it cannot be read and the access time increases. If only specific location data can be read out, it is necessary to configure a file in that unit in advance, increasing the number of initial vectors for each file and increasing the area for storing the initial vectors. There is a problem that.

  The present invention has been made to solve the above-described problem, and is an information processing apparatus that can extract only data in the middle of an encrypted file at high speed and can suppress an increase in the storage area of the initial vector. And to provide a program.

In order to achieve the above object, an information processing apparatus according to a first invention comprises file storage means for storing a file by dividing the file into predetermined storage units, and block encryption for encrypting the files in predetermined block units. Initial vector storage means for storing a plurality of first initial vectors to be used for each file in the conversion, and changing the first initial vector used for the file based on a predetermined rule, whereby the block cipher of the file Initial vector generating means for generating a second initial vector for each predetermined storage unit for use in each predetermined storage unit, and the predetermined when the input file is divided into the predetermined storage units When the first block in the storage unit is block-encrypted, the second initial value generated by the initial vector generating means is used. Vector, plaintext block of the first block, on the basis of the及beauty encryption key, the first block is block encryption, a block not the head block in the predetermined storage unit in the case of block encryption is just before the block A block ciphertext block obtained by block-encrypting the block, an encryption means for block-encrypting the block based on the plaintext block of the block, and the encryption key, and a file encrypted by the encryption means. Storage control means for storing in the file storage means.

A program according to the second invention uses a computer for each file in a file storage means for storing a file by dividing the file into predetermined storage units, and block encryption for encrypting the file into predetermined block units. Initial vector storage means for storing a plurality of first initial vectors for use in the block encryption of the file by changing the first initial vector used for the file based on a predetermined rule. Initial vector generation means for generating a second initial vector for each predetermined storage unit, and blocks the first block in the predetermined storage unit when the input file is divided into the predetermined storage units When encrypting, the second initial vector generated by the initial vector generating means, Plaintext block of the first block, on the basis of the及beauty encryption key, the first block is block encryption, in the case of block encryption block not the head block in the predetermined storage unit, the immediately preceding block of the block A block-encrypted ciphertext block, a plaintext block of the block, and an encryption means for block-encrypting the block based on the encryption key, and a file block-encrypted by the encryption means as the file storage It is characterized by functioning as storage control means for storing in the means.

  According to the first invention and the second invention, when the first block in a predetermined storage unit when the input file is divided into the predetermined storage unit is block-encrypted, the initial vector generating means By changing the first initial vector used for the file based on a predetermined rule, a second initial vector to be used for each predetermined storage unit in the block encryption of this file is generated, and the encryption means The head block is block-encrypted based on the second initial vector generated by the initial vector generating means, the plaintext block of the head block, and the encryption key.

  When a block that is not the first block in a predetermined storage unit is block-encrypted, the ciphertext block obtained by block-encrypting the block immediately before this block by the encryption means, the plaintext block of this block, and the encryption key This block is block-encrypted based on

  Then, the file that has been block encrypted by the encryption means is stored in the file storage means by the storage control means.

  Therefore, by performing block encryption for each predetermined storage unit using the second initial vector for each predetermined storage unit, only the data in the middle of the encrypted file is retrieved at high speed for each predetermined storage unit. In addition, the second initial vector used for each predetermined storage unit is generated by changing the first initial vector used for each file, thereby suppressing an increase in the storage area of the initial vector. Can do.

  In addition, the information processing apparatus according to the first aspect of the present invention generates an initial vector when block decoding a head block in a predetermined storage unit when a file stored in the file storage unit is divided into predetermined storage units. When the first block is decrypted based on the second initial vector generated by the means, the ciphertext block of the first block, and the encryption key, and the block that is not the first block in a predetermined storage unit is block-decrypted Includes a ciphertext block obtained by block-encrypting the block immediately before this block, a ciphertext block of this block, and a decryption means for block-decrypting this block based on the encryption key, and generating an initial vector The means changes the first initial vector used for the file based on a predetermined rule. Accordingly, it is possible to generate a second initial vector for use in predetermined storage unit in block decoding of the file for each predetermined unit of storage. Thereby, when the block-encrypted and stored file is extracted by block decryption, even if the data to be extracted is data in the middle of the file, the second initial vector generated by the initial vector generating means is used. Only data in the middle of the file can be decoded and extracted for each predetermined storage unit.

  Further, the encryption means according to the first invention, when block encryption of the head block of the input file, the first initial vector stored in the initial vector storage means, the plaintext block of this head block, Based on a predetermined encryption key, the head block can be block-encrypted.

  In addition, when the information processing apparatus performs block decryption on the first block of the file stored in the file storage means, the first initial vector used for the file, the ciphertext block of the first block, and the encryption When block decoding is performed on the head block based on the encryption key and the head block in the predetermined storage unit when the file is divided into the predetermined storage unit is block-decoded, the first block generated by the initial vector generation means is used. Based on the initial vector of 2, the ciphertext block of the head block, and the encryption key, the head block is block-decrypted, and the block that is not the file block and is not the head block in the predetermined storage unit is block-decrypted If this is the case, the ciphertext block in which the block immediately before this block is encrypted And a decryption unit for performing block decryption on the block based on the ciphertext block of the block and the encryption key, and the initial vector generation unit is configured to determine the first initial vector used for the file in advance. Thus, the second initial vector to be used for each predetermined storage unit in the block decoding of this file can be generated for each predetermined storage unit.

  The predetermined storage unit can be a logical address division unit of the file storage means.

  The file storage means is a hard disk, and a predetermined storage unit can be a sector unit of the hard disk.

  As described above, according to the information processing apparatus and program of the present invention, encryption is performed by performing block encryption for each predetermined storage unit using the second initial vector for each predetermined storage unit. Only the data in the middle of the file can be retrieved at high speed for each predetermined storage unit, and the second initial vector used for each predetermined storage unit is generated based on the first initial vector, so that the initial An effect is obtained that an increase in the storage area of the vector can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a copying machine will be described.

  As shown in FIG. 1, the copying machine 10 according to the first embodiment of the present invention includes a ROM 12 that stores various programs, parameters, and the like, a CPU 14 that executes various programs, and a work performed when the CPU 14 executes various programs. A RAM 16 used as an area, a data processing device 18 for encrypting and decrypting image files, and a bus 20 for connecting them to each other are provided.

  The data processing device 18 is connected to an HDD 22 for storing an encrypted image file. The recording area of the HDD 22 is divided in units of sectors (for example, 512 bytes), and the image file is divided into a plurality of sectors and stored. The image file may have a size stored in a single sector or a size stored in a plurality of sectors. The number of sectors may be different for each image file.

  The copying machine 10 further includes a scanner 24 that reads an original to generate an image file, and records an electrostatic latent image on a photoconductor based on the image file, and the electrostatic latent image is printed with monochrome toner or color toner. There are provided a printing unit 26 that develops and develops the image, transfers the developed image to a recording sheet, and outputs, and an operation panel unit 28 including operation buttons and an operation panel for instructing various processes of the copying machine 10. These are also connected to the bus 20.

  Further, as shown in FIG. 2, the data processing device 18 stores a bus interface 30 for controlling input / output with the bus 20 and an initial vector used for encryption and decryption of an image file. Initial vector storage memory 32, initial vector change unit 34 for changing the initial vector stored in initial vector storage memory 32, common key storage memory 36 storing a common key used for encryption and decryption, image An encryption unit 38 for encrypting the file and an HDD interface for controlling input / output with the HDD 22 are provided. The encryption unit 38 also has a function of decrypting the image file read from the HDD 22.

  The functions of each unit of the data processing device 18 are mounted so as to be realized by, for example, a circuit (LSI chip).

  Note that the copying machine 10 only needs to have a general configuration and functions of a conventionally known printer and scanner, and detailed description of other configurations and general functions of the copying machine 10 is omitted.

  Next, encryption and decryption methods performed by the encryption unit 38 of the data processing device 18 will be described with reference to FIG.

  The encryption and decryption in the present embodiment employs a block encryption method and a block decryption method in which a file is divided into block units. First, with respect to the first block of the file, the plaintext block P1 of the first block and For the initial vector IV, an exclusive OR (XOR) is calculated for each bit, and the operation result is encrypted with the common key K (E) to generate a ciphertext block C1. Then, for the next block, an exclusive OR (XOR) operation is performed on the plaintext block P2 and the ciphertext block C1 of the immediately preceding block, and the operation result is encrypted with the common key K (E) to obtain a ciphertext. Block C2 is generated, and encryption is similarly performed for the subsequent blocks.

  In the case of decryption, for the first block of the file, the ciphertext block C1 is decrypted with the common key K, the exclusive OR (XOR) of the decryption result and the initial vector IV is calculated, and the plaintext A block P1 is generated. For the next block, the ciphertext block C2 is decrypted with the common key K, and an exclusive OR (XOR) between the decryption result and the ciphertext block C1 of the immediately preceding block is calculated to generate a plaintext block P2. The decoding is performed in the same manner for the subsequent blocks.

  Next, the operation of the first embodiment will be described. An example in which an image file is block-encrypted and stored in the HDD 22 will be described as an example.

  First, when a user sets a document at a document reading position of the scanner 24 of the copying machine 10 and the user operates the operation panel unit 28 to instruct a document reading process, the document is read by the scanner 24. An image file indicating the document is generated.

  Then, the data processing device 18 executes the encryption processing routine shown in FIG.

  First, in step 100, it is determined whether an image file has been input. When the image file generated by the scanner 24 is input via the bus 20, the process proceeds from step 100 to step 102, where the head of the image file is entered. Set the block to be encrypted.

  In step 104, it is determined whether or not the encryption target block is the first block in the sector unit, and it is the first block of the image file (first block in the first sector), or the image file is converted into the sector unit. If it is the first block of any sector when divided, it is determined in step 106 whether or not the encryption target block is the first block of the image file. In step 108, the initial vector is read from the initial vector storage memory 32, and the process proceeds to step 112. On the other hand, if the block to be encrypted is the first block of a sector in the middle of the image file in step 106, the initial vector read in step 108 by the initial vector changing unit 34 is determined based on a predetermined rule in step 110. Change to generate a new initial vector and proceed to step 112.

  As a method for generating a new initial vector, for example, a method of increasing the initial vector in the previous sector by a predetermined amount may be used (or a method of increasing the read initial vector by a predetermined number of sectors). Or other known methods may be used. This generation method is secretly defined.

  In step 112, the read initial vector or the generated initial vector is set as the ciphertext block of the immediately preceding block in the encryption, and in step 114, the block encryption processing described in FIG. 3 is performed. The generated ciphertext block is stored in the HDD 22 by the interface 40.

  If the encryption target block is not the first block in the image file in step 104 and is not the first block of any sector when the image file is divided into sectors, the process proceeds to step 114. In step 114, as described in FIG. 3, block encryption processing is performed using the ciphertext block of the immediately preceding block.

  In step 118, it is determined whether the encryption target block is the last block of the image file. If there is a block that has not been subjected to block encryption processing in the image file, in step 120, the image file is checked. The next block in is set as an encryption target block, and the process returns to step 104, and the above steps 104 to 118 are performed on the next block. On the other hand, when the block encryption process is performed for all the blocks of the image file and the ciphertext block is stored in the HDD 22, the encryption process routine is terminated.

  When the block encryption processing is performed as described above, as shown in FIG. 5, the initial sector A read out from the initial vector storage memory 32 is used as the head sector in which the image file A in the HDD 22 is stored. The encrypted ciphertext block is stored, and for each of the second sector and the third sector, the ciphertext block-encrypted using the initial vectors A2 and A3 generated by changing the initial vector A The block is stored. For the other image file B, a ciphertext block that is block-encrypted using the initial vector B read from the initial vector storage memory 32 is stored in the first sector, and the initial vector B is stored in the subsequent sector. A ciphertext block that is block-encrypted using the initial vectors B2 and B3 generated by the change is stored.

  When the head sector of the image file A is extracted from the HDD 22, block decoding is performed using the initial vector A of the initial vector storage memory 32, and the decrypted plaintext block is extracted.

  When only the second sector or the third sector of the image file A is extracted from the HDD 22, the initial vector A2 or A3 obtained by changing the initial vector A of the initial vector storage memory 32 is generated and generated. Block decryption is performed using the initial vector A2 or A3, and a decrypted plaintext block is extracted. Note that the initial vector A used in block encryption performed when the image file A is stored in the head sector is the same as the initial vector A used in block decryption performed when the image file A is extracted from the head sector. The initial vectors A2 and A3 used in block encryption performed when the image file A is stored in each of the second sector and the third sector, and the second sector and the third sector The initial vectors A2 and A3 used in block decoding performed when the image file A is extracted from each are the same.

  As described above, according to the copying machine according to the first embodiment, by performing block encryption for each sector unit using the initial vector for each sector unit, only the data in the middle of the encrypted file is stored. Can be extracted at high speed in units of sectors, and the initial vector used for each sector is generated by changing the initial vector used for each file, thereby suppressing an increase in the storage area of the initial vector. Can do.

  In addition, when a block-encrypted and stored file is extracted by block decryption, even if the data to be extracted is data in the middle of the file, only the data in the middle of the file is obtained for each sector using the generated initial vector. Can be decrypted and extracted.

  In addition, since block encryption is performed using the ciphertext block of the immediately preceding block, even if the encryption key and plaintext block are the same for each block, the same ciphertext block is not generated for each block. Can be improved.

  In addition, since the initial vector can be changed for each sector, even if the contents stored in a plurality of sectors are the same, the ciphertext blocks are different, so that it is difficult to decipher.

  Further, the size of the image file can be freely changed in units of sectors, and file management becomes easy.

  Further, since only the data in the middle of the file can be taken out in units of sectors, for example, continuous reading from discontinuous addresses is possible.

  In this embodiment, the case where functions for performing encryption and decryption are mounted on an LSI chip has been described as an example. However, the present invention is not limited to this, and functions for performing encryption and decryption are realized. The program may be stored in advance and executed by the CPU to perform the above-described encryption and decryption.

  Also, when block encryption is performed on the first block of the file, the stored initial vector is used as an example. However, the stored initial vector is also changed for the first block of the file as with other sectors. Then, block encryption may be performed using the newly generated initial vector. In that case, when performing block decoding on the first block of the file, block decoding may be performed using the initial vector generated by changing the stored initial vector.

  Further, although the case where the image file is stored in the HDD has been described as an example, the image file may be stored in another storage medium. In this case, the image file may be divided and stored in logical address division units of the storage medium, and an initial vector may be generated for each logical address division unit.

  Next, an image processing apparatus according to the second embodiment of the present invention will be described. In addition, about the structure and effect | action same as 1st Embodiment, the same code | symbol as 1st Embodiment is attached | subjected and the description is abbreviate | omitted.

  In the second embodiment, an initial vector is generated based on a common initial vector and an address of a sector that stores a block-encrypted ciphertext block, and block encryption is performed for each sector using the generated initial vector. The difference from the first embodiment is that processing is performed.

  As shown in FIG. 6, the data processing device 128 of the copier according to the second embodiment stores a common initial vector that is a basis for generating an initial vector used for each sector in block encryption of an image file. Based on the common initial vector storage memory 130, the address storage memory 132 for storing the sector address of the HDD 22, the common initial vector stored in the common initial vector storage memory 130, and the sector address stored in the address storage memory 132. In block encryption of an image file, an initial vector generation unit 134 that generates an initial vector used for each sector, a bus interface 30, a common key storage memory 36, an encryption unit 38, and an HDD interface 40 are provided. ing. The functions of these units are implemented as LSI chip functions, for example.

  Since the other configuration of the copying machine according to the second embodiment is the same as that of the first embodiment, description thereof is omitted.

  An encryption processing routine according to the second embodiment will be described with reference to FIG.

  First, in step 100, it is determined whether an image file has been input. When the image file generated by the scanner 24 is input via the bus 20, the process proceeds from step 100 to step 102, where the head of the image file is entered. Set the block to be encrypted.

  In step 200, the common initial vector stored in the common initial vector storage memory 130 is read. In step 104, whether the encryption target block is the head block of the sector when the file is divided into sectors. If it is the first block of any sector when the image file is divided into sectors, in step 202, the sector address of the HDD 22 in which the sector of the block to be encrypted is stored is stored in the address storage memory 132. The initial vector is generated based on the common initial vector and the sector address.

  As an initial vector generation method, for example, as shown in FIG. 8, the bitwise exclusive OR (XOR) of the common initial vector and the sector address is calculated, and the calculation result is generated as the initial vector. It should be the method to do. Alternatively, a method of generating an initial vector by rearranging predetermined bits may be used, or another known method may be used.

  In step 204, the initial vector generated in step 202 is set as the ciphertext block of the immediately preceding block in the encryption. In step 114, the block encryption process described with reference to FIG. 3 is performed. The ciphertext block is stored in the HDD 22 by 40.

  On the other hand, if the block to be encrypted is not the first block of any sector when the image file is divided into sectors in step 104, the process proceeds to step 114, and in step 114, as described in FIG. In addition, block encryption processing is performed using the ciphertext block of the immediately preceding block.

  In step 118, it is determined whether or not the encryption target block is the final block of the image file. If there is a block that has not been subjected to block encryption processing, in step 120, the next block in the image file is determined. Is set to the encryption target block, and the process returns to step 104. On the other hand, if the block encryption process has been performed for all the blocks of the image file, the encryption process routine is terminated.

  When the block encryption process is performed as described above, as shown in FIG. 9, the head sector storing the image file A in the HDD 22 is generated based on the common initial vector and the sector address of the head sector. A ciphertext block block-encrypted using the initial vector is stored, and for each of the second sector and the third sector, an initial vector generated based on the common initial vector and each sector address is stored. The ciphertext block that has been block-encrypted by use is stored. Similarly, for the other image file B, a ciphertext block that is block-encrypted using the initial vector generated based on the common initial vector and the sector address is stored.

  When the first sector of the image file A is extracted from the HDD 22, the decrypted plaintext block is extracted using the initial vector generated based on the common initial vector and the sector address of the first sector. It is.

  Further, when only the second sector or the third sector of the image file A is extracted from the HDD 22, the decoding is performed by using the initial vector generated based on the common initial vector and each sector address. The converted plaintext block is taken out.

  As described above, according to the copying machine according to the second embodiment, by performing block encryption for each sector unit using the initial vector for each sector unit, only the data in the middle of the encrypted file is stored. Can be extracted at high speed for each sector unit, and the initial vector used for each sector unit is generated based on the common initial vector and the sector address, thereby suppressing an increase in the storage area of the initial vector. it can. Also, by generating the initial vector using the common initial vector, it is only necessary to store the common initial vector, so that the storage area of the initial vector can be greatly reduced.

  In addition, when a block-encrypted and stored file is extracted by block decryption, even if the data to be extracted is data in the middle of the file, only the data in the middle of the file is obtained using the generated second initial vector. Decoding can be performed for each sector.

  In this embodiment, the case where functions for performing encryption and decryption are mounted on an LSI chip has been described as an example. However, the present invention is not limited to this, and functions for performing encryption and decryption are realized. The program may be stored in advance and executed by the CPU to perform the above-described encryption and decryption.

1 is a schematic diagram showing a configuration of a copier according to a first embodiment of the present invention. It is a block diagram which shows the function of the data processor which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating block encryption and block decryption in the data processor which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the content of the encryption process routine performed in the data processor which concerns on the 1st Embodiment of this invention. It is an image figure which shows the mode of the image file memorize | stored in HDD concerning the 1st Embodiment of this invention. It is a block diagram which shows the function of the data processor which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the content of the encryption process routine performed in the data processor which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the production | generation method of the initial vector in the data processor which concerns on the 2nd Embodiment of this invention. It is an image figure which shows the mode of the image file memorize | stored in HDD concerning the 2nd Embodiment of this invention.

Explanation of symbols

10 Copier 12 ROM
14 CPU
16 RAM
18, 128 Data processing device 22 HDD
24 Scanner 28 Operation Panel 30 Bus Interface 32 Initial Vector Storage Memory 34 Initial Vector Change Unit 36 Common Key Storage Memory 38 Encryption Unit 40 HDD Interface 130 Common Initial Vector Storage Memory 132 Address Storage Memory 134 Initial Vector Generation Unit

Claims (7)

File storage means for storing a file divided into predetermined storage units;
Initial vector storage means for storing a plurality of first initial vectors to be used for each file in block encryption for encrypting a file in a predetermined block unit;
By changing the first initial vector used for the file based on a predetermined rule, the second initial vector to be used for each predetermined storage unit in the block encryption of the file is used for the predetermined storage unit. Initial vector generation means for generating each;
When block encryption is performed on the first block in the predetermined storage unit when the input file is divided into the predetermined storage unit, the second initial vector generated by the initial vector generation means, the first block plaintext block, based on及beauty encryption key and block encryption the first block,
When block-encrypting a block that is not the first block in the predetermined storage unit, based on the ciphertext block obtained by block-encrypting the block immediately before the block, the plaintext block of the block, and the encryption key, An encryption means for block-encrypting the block;
Storage control means for storing the file encrypted by the encryption means in the file storage means;
An information processing apparatus including: When block decoding the head block in the predetermined storage unit when the file stored in the file storage unit is divided into the predetermined storage unit, the second block generated by the initial vector generation unit Based on the initial vector, the ciphertext block of the head block, and the encryption key, the head block is block decrypted,
When block decrypting a block that is not the first block in the predetermined storage unit, based on the ciphertext block obtained by block-encrypting the block immediately before the block, the ciphertext block of the block, and the encryption key, Further comprising decoding means for block decoding the block;
The initial vector generating means is used for each predetermined storage unit in the block decoding of the file by changing the first initial vector used for the file based on the predetermined rule. The information processing apparatus according to claim 1, wherein the second initial vector is generated for each predetermined storage unit.   When the encryption unit performs block encryption on the first block of the input file, the first initial vector stored in the initial vector storage unit, the plaintext block of the first block, and a predetermined encryption key The information processing apparatus according to claim 1, wherein the first block is block-encrypted based on the information. When block decrypting the first block of the file stored in the file storage means, based on the first initial vector used for the file, the ciphertext block of the first block, and the encryption key Block decoding the head block,
When block decoding the head block in the predetermined storage unit when the file is divided into the predetermined storage unit, the second initial vector generated by the initial vector generating means, the encryption of the head block Based on the sentence block and the encryption key, the first block is block decrypted,
When block decrypting a block that is not the first block of the file and is not the first block in the predetermined storage unit, a ciphertext block obtained by block-encrypting a block immediately before the block, and a ciphertext block of the block And decrypting means for block-decoding the block based on the encryption key,
The initial vector generating means is used for each predetermined storage unit in the block decoding of the file by changing the first initial vector used for the file based on the predetermined rule. The information processing apparatus according to claim 3, wherein the second initial vector is generated for each predetermined storage unit. The predetermined storage unit, the information processing apparatus of any one of claims 1 to 4, logical address division unit of said file storage means. The file storage means is a hard disk,
It said predetermined storage unit, the information processing apparatus of any one of claims 1 to 4, sector unit of the hard disk. File storage means for storing a computer by dividing a file into predetermined storage units;
Initial vector storage means for storing a plurality of first initial vectors to be used for each file in block encryption for encrypting a file in a predetermined block unit;
By changing the first initial vector used for the file based on a predetermined rule, the second initial vector to be used for each predetermined storage unit in the block encryption of the file is used for the predetermined storage unit. Initial vector generating means for generating each time,
When block encryption is performed on the first block in the predetermined storage unit when the input file is divided into the predetermined storage unit, the second initial vector generated by the initial vector generation means, the first block plaintext block, based on及beauty encryption key and block encryption the first block,
When block-encrypting a block that is not the first block in the predetermined storage unit, based on the ciphertext block obtained by block-encrypting the block immediately before the block, the plaintext block of the block, and the encryption key, An encryption means for block-encrypting a block, and a program for causing the file storage means to store a file block-encrypted by the encryption means in the file storage means.

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