JP4287398B2 - Encryption / decryption system, ciphertext generation program, and ciphertext decryption program - Google Patents

Description

  The present invention relates to an encryption / decryption system composed of a ciphertext generation apparatus and a ciphertext decryption apparatus that divide a plaintext / ciphertext into blocks having a predetermined length and perform encryption / decryption processing in units of blocks. The present invention relates to a ciphertext generation program and a ciphertext decryption program that implement each of the above devices in a system.

  Conventionally, stream cipher is used as a technique for encrypting contents such as digital broadcasting, movies or music. However, when streaming content, it is necessary to consider the situation of “interruption” such as when the communication path is interrupted for some reason during encrypted transfer or when the viewer intentionally pauses. is there. In response to “resumption” such as restoration of the communication path and playback request of the viewer, when resuming transfer from the interruption position, conventional general stream ciphers perform encryption / decryption from the top data to the interruption position. Recalculation was necessary. Therefore, especially when handling content with a large amount of data such as moving image data, it takes a relatively long time from the “resume” request until encryption / decryption becomes possible. It was impossible.

  For example, if the movie content is interrupted at the 4G byte data position from the beginning and the effective processing speed of the terminal is 10 Mbps, 4G / 10M = 200 [seconds] = 3 minutes 40 until encryption / decryption is possible A waiting time of seconds is required. This is a long time for human senses.

  Regarding the above interruption, a method of temporarily storing internal information during calculation in the encryption / decryption operation can be considered, and when using such a method, the stored calculation intermediate information is read at the time of resumption, Since the calculation from the interruption position is immediately possible, the recalculation from the head position is not necessary, and a flexible solution to the above problem can be provided. However, storing internal information in the middle of calculation in encryption / decryption to the outside increases the possibility of providing decryption information, and is not a desirable method in terms of security. Therefore, the method by recalculation was inevitable.

  For the above reasons, even when the recalculation method is adopted, the data can be divided into blocks and the encryption / decryption process is completed in blocks, so that only the recalculation from the beginning of the interrupted position block can be done at the time of restart. It is possible. According to this, since recalculation from the top position of the data becomes unnecessary, it is possible to shorten the time until the encryption / decryption process is restarted. However, in stream ciphers that perform exclusive OR on pseudorandom numbers and plaintext, when a fixed encryption key is used, the plaintext is exclusive ORed with respect to the same pseudorandom number pattern for each block. Therefore, it cannot be said that sufficient encryption strength is maintained. Although it is conceivable to randomly change the key for each block, it is necessary to prepare a pseudo-random number generation algorithm for changing the key separately, which causes a problem that the configuration becomes complicated.

For example, Patent Document 1 discloses a stream encryption system including an encryption bitstream generation unit, which performs frame counting by a frame counter insertion circuit before data encryption, and uses this to perform encryption unit However, it is not possible to immediately calculate from the interruption position.
JP 2001-345799 A

  This proposal proposes a stream that can generate different random number patterns for each block even when a fixed encryption key is used on both the sending and receiving sides in a system that uses a stream encryption method that assumes block unit processing. An encryption method is proposed, and an encryption / decryption system that enables smooth interruption / resumption processing without using a separate random number generation algorithm for key change is provided, and a ciphertext generation apparatus in this system is provided. And a ciphertext generation program and a ciphertext decryption program for realizing the ciphertext decryption apparatus.

The encryption / decryption system according to the present invention divides a plaintext into blocks having a predetermined length, and performs an operation for generating a ciphertext using a block key for each divided block to obtain a ciphertext. a unit, a counter for counting down the count-up or a predetermined value a predetermined value for each ciphertext generating end of block units, a ciphertext encrypted before predetermined block than the block that performs the ciphertext generating at present A ciphertext generating apparatus comprising: a block key generating unit that generates a block key to be applied to each block to be encrypted using the count value by the counter and the encryption key data, and gives the block key to the encryption unit; the ciphertext encrypted by the ciphertext generating apparatus is divided into blocks having a predetermined length, for decoding using the block key in the divided block unit A decoding unit for obtaining the plaintext by performing a calculation, predetermined than the block have done a counter that counts down the count-up or a predetermined value a predetermined value for each termination ciphertext decryption in block units, the ciphertext decryption at the present time A block key to be applied to each block to be decrypted is created using the undecrypted ciphertext used for decryption before the block, the count value by the counter, and the encryption key data, and is sent to the decryption unit gives constituted by the ciphertext decryption apparatus comprising a block key preparing means, the are both a control means is provided in the ciphertext generating apparatus and the ciphertext decryption apparatus, the control means of the ciphertext generating apparatus, encryption to restart the production of statements, data of said counter value and said predetermined block before ciphertext ciphertext decryption the ciphertext decryption apparatus sends the resume data to device Together to set the data, while setting the data of the counter value and the predetermined block previous ciphertext of the ciphertext generating apparatus, the control means of the ciphertext decryption apparatus, resumes decoding ciphertext In this case, resumption data is sent to the ciphertext generation apparatus to set the counter value of the ciphertext generation apparatus and ciphertext data before the predetermined block, and the counter of the ciphertext decryption apparatus And the ciphertext data before the predetermined block are set .

In the encryption / decryption system according to the present invention, in at least one of the ciphertext generation device and the ciphertext decryption device, a count value storage unit that stores a count value one previous to the current value of the counter, At least one of ciphertext storage units that store history information of one step before ciphertext data before a predetermined block, and the control means sends the restart data to the count value storage unit, the ciphertext storage unit, It is obtained from at least one of the above.

In the encryption / decryption system according to the present invention, the control means sets the value of the counter and the data of the ciphertext before the predetermined block at the time of initializing and restarting the ciphertext decryption. .

The ciphertext generation program according to the present invention divides a plaintext into blocks having a predetermined length to obtain a ciphertext from the plaintext, and generates a ciphertext using a block key for each divided block. Than the block that performs ciphertext generation at the present time, the encryption means that obtains the ciphertext by performing the above calculation, the count means that counts up or decreases the predetermined value every time ciphertext generation is completed in block units Using the ciphertext encrypted before the predetermined block, the count value obtained by the counting step, and the encryption key data, a block key to be applied to each block to be encrypted is created and given to the encryption means upon resumption of the block key preparing means and the ciphertext generating, for resumption Day said encryption means is the ciphertext decryption apparatus which is the destination of the ciphertext encrypted Sent together to set a predetermined block before the encrypted data using the block key creation unit value and dark ciphertext decryption apparatus counting means dark ciphertext decryption apparatus, and the counter of the counting means in the computer It is made to function as a control means which sets a value and the data of the ciphertext before the said predetermined block used by the said block key preparation means in the said computer .

In the ciphertext generation program according to the present invention, the control means sets the count value of the own device and ciphertext data before the predetermined block at the initial time and restart of ciphertext generation. .

The ciphertext decryption program according to the present invention divides a computer to decrypt a ciphertext, divides the encrypted ciphertext into blocks having a predetermined length, and uses a block key for each divided block. Decryption means for performing a decryption operation to obtain plaintext, a count means for counting up a predetermined value or counting down a predetermined value at the end of each block ciphertext decryption, and performing ciphertext decryption at the present time Block key applied to each block to be decrypted using the undecrypted ciphertext used for decryption before the predetermined block, the count value obtained by the counting step, and the encryption key data in the create and when the block key generation means and the ciphertext decryption give to the decoding means resumes transmission source of ciphertext for which the decoding means decodes Together to set the data in a predetermined block before ciphertext block key creation unit value and dark ciphertext generating apparatus of the count means of the ciphertext generating apparatus sends the resume data to the ciphertext generating apparatus uses that, the characterized in that to function as said counting means value and said predetermined block before the control means for setting the data of the ciphertext, wherein in the computer block key creation unit uses the computer.

The ciphertext decryption program according to the present invention is characterized in that the control means sets the count value and ciphertext data before the predetermined block when ciphertext decryption is initialized and resumed.

  In the present invention, a method of creating a block key for each block to be encrypted using a ciphertext encrypted before a predetermined block, a count value counted every time ciphertext generation is completed in block units, and cipher key data The control unit provided in both the ciphertext generation apparatus and the ciphertext decryption apparatus, when resuming ciphertext generation, sends the resumption data to the other apparatus and the value of the counter of the other apparatus And the ciphertext data before the predetermined block are set, and the value of the counter of the own device and the ciphertext data before the predetermined block are set, so that the key is changed in units of encryption blocks. The configuration is appropriately restarted when the ciphertext generation is restarted, and a different random number pattern can be generated for each block even after restarting. In addition, the ciphertext can be decrypted by an encryption method that generates such a random number pattern.

  In the present invention, the purpose of enabling generation of a different random number pattern for each block without using a complicated and large-scale configuration is to count ciphertext encrypted before a predetermined block and ciphertext generation for each block. In order to achieve smooth interruption / resumption processing by creating a block key for each block to be encrypted using the counted value and encryption key data, the previous ciphertext block and counter This is achieved by storing the value for resumption and setting it at the time of resumption.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the configuration of the encryption / decryption system. The encryption / decryption system includes a ciphertext generation apparatus 100 and a ciphertext decryption apparatus 200. The ciphertext generation apparatus 100 includes a control unit 1 that performs overall control of the entire apparatus, and includes a plaintext storage unit 2, an encryption unit 3, a block key creation unit 4, an encryption key storage unit 5, a block counter 6, and a previous ciphertext supply. Unit 7, ciphertext output unit 8, ciphertext storage unit 9, and count value storage unit 10.

  The plaintext storage unit 2 stores plaintext (data before encryption) to be encrypted for each block (for example, for each byte) under the control of the control unit 1. The encryption unit 3 generates ciphertext by, for example, XOR (exclusive OR) operation based on the plaintext for each block and the block key created by the block key creation unit 4.

  The block key creation unit 4 is supplied with the output of the block counter 6, the ciphertext encrypted one step before supplied by the previous ciphertext supply unit 7, and the cipher key data from the cipher key storage unit 5. Here, the ciphertext encrypted before one step is given, but generally the ciphertext encrypted before the predetermined step is given. The block key creation unit 4 compresses the ciphertext supplied by the previous ciphertext supply unit 7 to the same key length, and performs an XOR (exclusive OR) operation on the ciphertext, the cipher key, and the output of the block counter 6 for each bit. To create a block key. As the above compression method, it is convenient to extract a predetermined bit portion in the ciphertext, but there is no particular limitation as to what method is used.

  The block counter 6 counts up or counts down by a predetermined value when the encryption unit 3 finishes encrypting one block of plaintext. The output bit length of the block counter 6 is assumed to be equal to the key length, for example. The count value storage unit 10 stores a count value one step before the count value of the block counter 6.

  The encryption key storage unit 5 stores a predetermined encryption key. The ciphertext output unit 8 transmits the ciphertext encrypted by the encryption unit 3 to the partner side. The ciphertext storage unit 9 stores at least one block of ciphertext encrypted by the immediately preceding step.

  The control unit 1 sets the value of the block counter 6 and predetermined ciphertext data in the previous ciphertext supply unit 7 at the initial and resumption of ciphertext generation in the overall control of the entire apparatus, and also stores the cipher key storage The encryption key is stored in the unit 5. Further, when the encryption unit 3 finishes encrypting one block of plaintext and all the next one block of plaintext is read from the plaintext storage unit 2, the control unit 1 transmits a new block of plaintext to the plaintext. Control to store in the storage unit 2 is performed.

  The ciphertext decryption apparatus 200 decrypts the ciphertext encrypted by the ciphertext generation apparatus, and the ciphertext decryption apparatus 200 includes a control unit 11 that performs overall control of the entire apparatus. Storage unit 12, decryption unit 13, block key creation unit 14, encryption key storage unit 15, block counter 16, previous ciphertext supply unit 17, decrypted text output unit 18, ciphertext storage unit 19, and count value storage unit 20 I have.

  The ciphertext storage unit 12 stores ciphertext data to be decrypted for each block (for example, for each byte) under the control of the control unit 11. The decryption unit 13 decrypts the ciphertext by, for example, an XOR (exclusive OR) operation based on the ciphertext for each block and the block key created by the block key creation unit 14.

  The block key generation unit 14 outputs the output of the block counter 16, the undecrypted ciphertext used for decryption one step before supplied by the previous ciphertext supply unit 17, and the cipher key data from the cipher key storage unit 15. (The same encryption key data as the encryption key data stored in the encryption key storage unit 5 of the ciphertext generation apparatus 100). Here, the ciphertext encrypted before one step is given, but generally the ciphertext before decryption used for decryption is given before a predetermined step. The block key creation unit 14 performs compression to align the ciphertext supplied by the previous ciphertext supply unit 17 with the key length, and performs an XOR (exclusive OR) operation on the ciphertext, the cipher key, and the output of the block counter 16 for each bit. To create a block key. As the above compression method, it is convenient to extract a predetermined bit portion in the ciphertext, but there is no particular limitation as to what method is used.

  The block counter 16 counts up or down by the same predetermined value as the block counter 16 of the ciphertext generation apparatus when the decryption unit 13 finishes decrypting one block of ciphertext. The output bit length of the block counter 16 is assumed to be equal to the key length, for example. The count value storage unit 20 stores a count value one step before the count value of the block counter 16.

  The encryption key storage unit 15 stores a predetermined encryption key (the same encryption key data as the encryption key data stored in the encryption key storage unit 5 of the ciphertext generation apparatus). The decrypted text output unit 18 transmits the decrypted text decrypted by the decrypting unit 13 to, for example, a terminal that reproduces content, or sends the decrypted text to a processing unit that stores the content in a storage medium. The ciphertext storage unit 19 stores the ciphertext supplied at least one step before by the previous ciphertext supply unit 17.

  The control unit 11 sets the value of the block counter 16 and predetermined ciphertext data in the previous ciphertext supply unit 17 at the initial and restart of decryption text generation in the overall control of the entire apparatus, and also stores the cipher key storage The encryption key is stored in the unit 15. Furthermore, when the decryption unit 13 finishes decrypting one block of ciphertext and reads all the next one block of ciphertext from the ciphertext storage unit 12, the control unit 11 The ciphertext is sent to the previous ciphertext supply unit 17 and a new block of ciphertext is further stored in the ciphertext storage unit 12.

  The control means 1 and 11 in the ciphertext generation apparatus 100 and the ciphertext decryption apparatus 200 are configured to be able to send and receive information to and from each other via a transmission path. Also, one of the control means 1 and 11 in the ciphertext generation apparatus 100 and the ciphertext decryption apparatus 200, when the ciphertext generation is resumed, sends the resumption data to the other apparatus, and the other apparatus The block counter value and the previous ciphertext supply unit (7, 17) are set with the data of the ciphertext before the predetermined block, and the block counter value and the previous ciphertext supply unit (17, 7) in the own apparatus are set. ) And ciphertext data before a predetermined block.

  As described above, the ciphertext generating apparatus 100 configured by each unit is actually configured by a computer such as a personal computer or a workstation, and the ciphertext generating program corresponding to the flowchart shown in FIG. Is executed, the operations of the control unit 1, the encryption unit 3, the block key creation unit 4, the block counter 6, the previous ciphertext supply unit 7, and the ciphertext output unit 8 are realized. The operation will be described based on the flowchart shown in FIG.

  When the program is started by a transfer request for content sent from the ciphertext decryption apparatus 200, it is detected whether or not it is an initial start according to the input (S1). For example, in the case of a restart, a restart instruction and necessary data (such as a count value) are input. In the case of an initial start, only the start instruction is input, and therefore determination is performed based on these pieces of information.

  When the process branches to YES in step S1, the start count value set in advance in the program is set in the block counter 6 and the start value preset in the program is set in the previous ciphertext supply unit 7. Ciphertext data (arbitrary data) is set (S2: control step).

  On the other hand, when branching to NO in step S1, the restart count value given from the outside is set to the block counter 6, and the count value given from the outside to the previous ciphertext supply unit 7 is set. The ciphertext data for restart corresponding to is set (S3: control step).

  When the above step S2 or step S3 is completed, the encryption key data set in advance in the program is set in the encryption key storage unit 5 (S4). Next, the plaintext data for one block corresponding to the count value set in the block counter 6 is read to the plaintext storage unit 2 (S5). That is, in the case of the initial start, the plaintext data for the first block is stored in the plaintext storage unit 2, and in the case of restart, the plaintext is stored when the count value is set in the block counter 6. The plaintext data set in the unit 2 is stored in the plaintext storage unit 2.

  Subsequently, the encryption key data set in the encryption key storage unit 5, the count value set in the block counter 6, and the ciphertext data set in the previous ciphertext supply unit 7 are used as described above. Then, a block key is created (block key creation step), plaintext encryption is performed based on this block key (encryption step), and output as the ciphertext output unit 8 is performed (S6).

  Next, the block counter 6 is updated (a predetermined value is counted up or down) (S7: count step), and the ciphertext for one block encrypted at that time is set in the previous ciphertext supply unit 7 (S8). ). The ciphertext storage unit 9 sequentially stores the ciphertext stored in the previous ciphertext supply unit 7, and the count value storage unit 10 is overwritten with the count value of the block counter 6. Therefore, it is confirmed whether all plaintexts have been encrypted by detecting whether plaintext data to be encrypted remains in the storage medium or the like (S9).

  If there is a plaintext remaining unencrypted in step S9, the process returns to step S5 to proceed to encryption for the next one block of plaintext. In this way, the routine proceeds from step S5 to step S9, and the routine returning from step S9 to step S5 is repeated, and when it is confirmed in step S9 that all plaintexts have been encrypted, the processing is ended.

  As described with reference to FIG. 1, the ciphertext decryption apparatus 200 configured by each unit is actually configured by a computer such as a personal computer or a workstation, and the ciphertext corresponding to the flowchart shown in FIG. Since the computer executes the decryption program, the operations of the control unit 11, the decryption unit 13, the block key creation unit 14, the block counter 16, the previous ciphertext supply unit 17, and the decrypted text output unit 18 are realized. The operation will be described below based on the flowchart shown in FIG.

  For example, when a program is started by sending a content transfer request to the ciphertext generation apparatus 100, it is detected whether or not the program is an initial start according to an input from the outside (S11). For example, in the case of a restart, a restart instruction and necessary data (count value, etc.) are input. In the case of an initial start, only the start instruction is input, so the determination in step S11 is based on the above information. Done.

  When branching to YES in step S11, a start count value set in advance in the program (the same count value as that of the cipher generation program) is set to the block counter 16, and the previous ciphertext supply unit 17 is set. On the other hand, cipher text data for start (arbitrary data: the same data as that of the cipher generation program) set in the program in advance is set (S12: control step).

  On the other hand, when branching to NO in the above step S11, a restart count value is set to the block counter 16, and the restart ciphertext data corresponding to the count value is set to the previous ciphertext supply unit 17. Set (S13: control step).

  When the processing in step S12 or step S13 is completed, the encryption key data set in advance in the program is set in the encryption key storage unit 15 (S14). Next, ciphertext data for one block corresponding to the count value set in the block counter 16 is read out to the ciphertext storage unit 12 (S15). That is, in the case of an initial start, the ciphertext data for the first block is stored in the ciphertext storage unit 12, and in the case of a restart, when the count value is set in the block counter 16, The ciphertext data set in the ciphertext storage unit 12 is stored in the ciphertext storage unit 12.

  Subsequently, the encryption key data set in the encryption key storage unit 15, the count value set in the block counter 16, and the ciphertext data set in the previous ciphertext supply unit 17 are used. A block key is created as described above (block key creation step), and the ciphertext is decrypted (processing opposite to encryption) based on this block key (decryption step), and output as the decrypted text output unit 18 Is performed (S16).

  Next, the block counter 16 is updated (a predetermined value is counted up or down) (S17: count step), and the encrypted text before decryption for one block decrypted at that time is encrypted in the previous ciphertext supply unit 17. Transferred from the sentence storage unit 12 and set (S18). The ciphertext storage unit 19 sequentially stores the ciphertext stored in the previous ciphertext supply unit 17, and the count value storage unit 20 is overwritten with the count value of the block counter 16. Therefore, it is confirmed whether or not all ciphertexts have been decrypted by detecting whether or not ciphertext data to be decrypted remains in the storage medium or the like (S19).

  If there is a decrypted text that remains without being decrypted in step S19, the process returns to step S15 to proceed to decryption of the next one block of ciphertext. In this way, the routine proceeds from step S15 to step S19, and the routine returning from step S19 to step S15 is repeated, and when it is confirmed in step S19 that all the ciphertexts have been decrypted, the process is ended.

  The content is encrypted and transferred by the process by the ciphertext generation apparatus 100 or the ciphertext generation program as described above and received by the ciphertext decryption apparatus 200, and the problem is caused by the process by the ciphertext decryption apparatus 200 or the ciphertext decryption program. FIG. 4 shows an example of a communication sequence related to the case where all ciphertexts are decrypted. In this example, the ciphertext decryption apparatus 200 transfers the transfer request (301) to the ciphertext generation apparatus 100 and the processing is started, and initialization is performed in the ciphertext generation apparatus 100 and the ciphertext decryption apparatus 200. (302). Thereafter, the ciphertext generation apparatus 100 performs encryption processing and ciphertext transmission, and the ciphertext decryption apparatus 200 receives ciphertext and decrypts the ciphertext (303 to 306). When the blocks up to the nth block are normally sent, the ciphertext generation apparatus 100 sends an end notification to the ciphertext decryption apparatus 200, and the ciphertext generation apparatus 100 and the ciphertext decryption apparatus 200 complete the processing (307). 308). When the process ends normally as described above, the process in step S3 in FIG. 2 and the process in step S13 in FIG. 3 are not performed.

  On the other hand, an interruption request can be sent from the ciphertext decryption apparatus 200 to the ciphertext generation apparatus 100, whereby the processing can be interrupted. The communication sequence shown in FIG. 5 shows an example of this interruption. That is, as apparent from the comparison with FIG. 4, when the ciphertext of the third block is received by the ciphertext decryption apparatus 200, an interruption request (411) is sent from the ciphertext decryption apparatus 200, The sentence generation device 100 receives the information and makes an interruption determination (412), and each processing is completed. The ciphertext after the fourth block is received by the ciphertext decryption apparatus 200, but is discarded (415).

  Further, when a configuration is adopted in which normal reception information (512) is sent from the ciphertext decryption apparatus 200 to the ciphertext generation apparatus 100 every time a predetermined number of blocks of ciphertext are received, the communication sequence shown in FIG. Become. The control unit 1 of the ciphertext generating apparatus 100 that has received the normal reception information (512) performs the reception information reception (513) process, and monitors the reception information reception period (514) including the next predetermined time interval. If the state (515) where the cipher does not reach continues due to blockage of the communication path or abnormal termination (511) and the normal reception information (512) is not received during the reception information acceptance period (514) consisting of a predetermined time interval, The control unit 1 of the sentence generation device 100 performs an interruption process (516) and an end process.

  When the interruption shown in FIG. 5 or FIG. 6 occurs, a restart (restart) process is performed by the control unit 1 of the ciphertext generation apparatus 100 or the control unit 11 of the ciphertext decryption apparatus 200. When the restart (restart) process by the control unit 1 of the ciphertext generation apparatus 100 is performed, the ciphertext storage unit 19 and the count value storage unit 20 of the ciphertext decryption apparatus 200 illustrated in FIG. 1 are not necessarily essential. . Further, when a restart (restart) process is performed by the control unit 11 of the ciphertext decryption apparatus 200, the ciphertext storage unit 9 and the count value storage unit 10 of the ciphertext generation apparatus 100 illustrated in FIG. is not.

  A case where a restart (restart) process by the control unit 11 of the ciphertext decryption apparatus 200 is performed will be described. In such a case, the count value (m) that has been processed normally is stored in the count value storage unit 20 by interruption according to FIG. 5 or FIG. Therefore, the control unit 11 of the ciphertext decryption apparatus 200 sends a retransmission request (601) including the count value (m) to the control unit 1 of the ciphertext generation apparatus 100 as shown in FIG. The count value next to the value (m) (m + 1 is assumed to be incremented by 1) is set in the block counter 16, and the last ciphertext stored in the ciphertext storage unit 19 is stored in the previous ciphertext supply unit 17. The resumption initialization to be set to (step S13) is performed.

  The control unit 1 of the ciphertext generating apparatus 100 that has received the retransmission request (601) including the count value (m) performs the resumption initialization (602 in FIG. 7: corresponding to step S3) as follows. The count value (m + 1) obtained by adding 1 to the count value (m) is set in the block counter 6, the ciphertext storage unit 9 is searched, and the ciphertext stored at the position corresponding to the count value (m) (Ciphertext corresponding to m) is taken out and set in the previous ciphertext supply unit 7 and one block of plaintext corresponding to the count value (m + 1) of the block counter 6 is stored in the plaintext storage unit 2 for encryption processing. Is started (603). As a result, the (m + 1) th ciphertext is transmitted (604).

  Upon receiving the (m + 1) -th ciphertext (605), the control unit 11 of the ciphertext decryption apparatus 200 stores the ciphertext in the ciphertext storage unit 12 and performs decryption processing (606). Thereafter, when the final n-th block is normally sent, an end notification (607) is sent from the ciphertext generation apparatus 100 to the ciphertext decryption apparatus 200, and the ciphertext generation apparatus 100 and the ciphertext decryption apparatus 200 perform processing. Is completed (608).

  In this example, the retransmission request (601) including the count value (m) is used, but the retransmission request including the count value (m) and the ciphertext corresponding to the count value (m) is sent to the ciphertext generation apparatus 100. You may do it. In this way, the ciphertext storage unit 9 and the count value storage unit 10 of the ciphertext generation apparatus 100 are unnecessary. Further, when a retransmission request (601) including the count value (m) is sent, the ciphertext storage unit 9 is searched and the ciphertext (stored at the position corresponding to the count value (m) ( The ciphertext corresponding to m) can be taken out and returned to the ciphertext decryption apparatus 200. In such a case, the ciphertext storage unit 19 of the ciphertext decryption apparatus 200 is not necessary. Further, as long as the count value (m) is sent to the ciphertext generation apparatus 100, the count value storage unit 10 is not necessary. When the ciphertext storage unit 9 of the ciphertext generation apparatus 100 stores ciphertext up to the point of interruption corresponding to the count value, a retransmission request including the ciphertext is sent to the ciphertext generation apparatus 100. Also good. In response to this, the control unit 1 of the ciphertext generation apparatus 100 searches the ciphertext storage unit 9 to detect the count value (m) and sets it in the block counter 6.

  When the restart (restart) process by the control unit 1 of the ciphertext generation apparatus 100 is performed, the control unit 1 of the ciphertext generation apparatus 100 responds to the restart request from the ciphertext decryption apparatus 200. It is assumed that ciphertext corresponding to the count value (m) or the count value (m) and the count value (m) is sent to the control unit 11. The count value (m) is set to a value that is 1 less than the count value (m + 1) of the block counter 6 at the time of encryption before a predetermined step from the time when the control unit 1 of the ciphertext generating apparatus 100 determines interruption.

  Upon receiving the count value (m), the control unit 11 of the ciphertext decryption apparatus 200 sets the count value next to the count value (m) (m + 1 is incremented by 1) in the block counter 16, and The resumption initialization (step S13) is performed in which one block of ciphertext stored in the position corresponding to the count value (m) in the text storage unit 19 is extracted and set in the previous ciphertext supply unit 17. In this case, the ciphertext storage unit 19 needs to store ciphertexts of a certain amount of step text, but the count value storage unit 20 is unnecessary. In addition, when the control unit 1 of the ciphertext generation apparatus 100 sends the ciphertext corresponding to the count value (m) and the count value (m) and the control unit 11 of the ciphertext decryption apparatus 200 receives the ciphertext, the control unit 1 The unit 11 sets the next count value (m + 1 assuming that the count value is incremented one by one) to the block counter 16 and sets the ciphertext corresponding to the count value (m) to the previous ciphertext supply unit 17. Shall be set to In this case, the count value storage unit 20 and the ciphertext storage unit 19 are not necessary.

  As described above, the ciphertext storage unit 19 and the count value storage unit 20 of the ciphertext decryption apparatus 200 shown in FIG. 1, and the ciphertext storage unit 9 and the count value storage unit 10 of the ciphertext generation apparatus 100 Since a configuration that can be restarted based on the count value stored by providing the required configuration is adopted, for example, when re-encryption or re-decryption is necessary due to a failure in the transmission path, etc. It is possible to respond quickly.

The block diagram which shows the structure of the Example of the encryption / decryption system which concerns on this invention. The flowchart which shows the process by the ciphertext production | generation program in the case of implement | achieving the ciphertext production | generation apparatus of the encryption / decryption system which concerns on this invention with a computer. The flowchart which shows the process by the ciphertext decryption program in the case of implement | achieving the ciphertext decryption apparatus of the encryption / decryption system which concerns on this invention with a computer. The figure which shows the example of a communication sequence corresponding to the case where the ciphertext encrypted in the encryption / decryption system which concerns on this invention is normally transmitted, and is finally decoded appropriately. The figure which shows the example of the communication sequence corresponding to the case where the interruption request | requirement is sent out from the ciphertext decoding apparatus in the encryption / decryption system which concerns on this invention, and is interrupted. The figure which shows the example of a communication sequence corresponding to the case where the ciphertext decoding apparatus is interrupted by not receiving normal reception information during a reception information reception period consisting of a predetermined time interval in the encryption / decryption system according to the present invention. The figure which shows the example of a communication sequence corresponding to the case where the restart process from interruption is performed in the encryption / decryption system which concerns on this invention.

Explanation of symbols

1 11 Control unit
2 Plain text storage
3 Encryption Department
4 14 Block key generator
5 15 Encryption key storage
6 16 block counter
7 Previous Ciphertext Supply Department
8 Ciphertext output part
9 Ciphertext storage
10, 20 Count value storage unit
12 Ciphertext storage
13 Decryption unit
17 Previous Ciphertext Supply Department
18 Decrypted text output part
19 Ciphertext storage

Claims (7)

The plaintext is divided into blocks having a predetermined length, and an encryption unit that obtains ciphertext by performing an operation for ciphertext generation using the block key for each divided block, and ciphertext generation in units of blocks ends. A counter that counts up or down a predetermined value every time, a ciphertext encrypted before a block that is currently generating ciphertext, a count value by the counter, and encryption key data And a ciphertext generating device comprising a block key creating means for creating a block key to be applied to each block to be encrypted and giving the block key to the encryption unit;
The ciphertext encrypted by the ciphertext generating apparatus is divided into blocks having a predetermined length, the decoding unit to obtain the plaintext by performing an operation for the decrypted using the block key in the divided block unit A counter that counts up or down a predetermined value every time ciphertext decryption is completed in block units, and decryption that was used for decryption before the block that is currently decrypting ciphertext A cipher comprising: a block key creating unit that creates a block key to be applied to each block to be decrypted using the previous ciphertext, the count value by the counter, and the encryption key data, and supplies the block key to the decryption unit It consists of a sentence decryption device,
Both the ciphertext generation apparatus and the ciphertext decryption apparatus are provided with control means, and when the control means of the ciphertext generation apparatus resumes ciphertext generation , the ciphertext generation apparatus resumes the ciphertext decryption apparatus. Data is sent to set the counter value of the ciphertext decryption apparatus and the ciphertext data before the predetermined block, and the counter value of the ciphertext generation apparatus and the ciphertext before the predetermined block When the control unit of the ciphertext decryption apparatus restarts decryption of the ciphertext, the resumption data is sent to the ciphertext generation apparatus and the counter value of the ciphertext generation apparatus is set. encryption condensate, wherein the predetermined block before with to set the data of the ciphertext, setting the data of the counter value and the predetermined block previous ciphertext of the ciphertext decryption apparatus and System. At least one of the ciphertext generation device and the ciphertext decryption device includes:
At least one of a count value storage unit that stores a count value one before the current value of the counter and a ciphertext storage unit that stores history information of one step before ciphertext data before the predetermined block is provided. And
2. The encryption / decryption system according to claim 1, wherein the control unit obtains resumption data from at least one of the count value storage unit and the ciphertext storage unit. 2. The encryption / decryption system according to claim 1, wherein the control unit sets the value of the counter and the data of the ciphertext before the predetermined block at the time of initializing and resuming the ciphertext decryption. . To get the ciphertext from plaintext,
An encryption unit that divides the plaintext into blocks having a predetermined length and obtains ciphertext by performing an operation for ciphertext generation using a block key for each divided block ;
Counting means for counting up a predetermined value or counting down a predetermined value every time ciphertext generation in a block unit is completed ;
Apply to each block to be encrypted using the ciphertext encrypted a predetermined block before the block for which ciphertext is currently generated, the count value obtained by the counting step, and the encryption key data A block key creating means for creating a block key and giving it to the encrypting means, and at the time of resuming ciphertext generation, sending the resumption data to the ciphertext decryption device to which the ciphertext encrypted by the encrypting means is sent The value of the counting means of the ciphertext decryption apparatus and the data of the ciphertext before the predetermined block used by the block key generation means of the ciphertext decryption apparatus are set, and the value of the counter of the counting means in the computer Control means for setting ciphertext data before the predetermined block used by the block key generating means in the computer;
Ciphertext generation program to make it function . 5. The ciphertext generation program according to claim 4, wherein the control means sets the count value of the own device and ciphertext data before the predetermined block at the initial and resumption of ciphertext generation. . A computer to decrypt the ciphertext,
A decryption unit that divides the encrypted ciphertext into blocks having a predetermined length , performs a decryption operation using a block key for each divided block, and obtains plaintext;
A counting means for counting up a predetermined value or counting down a predetermined value at the end of ciphertext decryption in units of blocks ;
Decryption using the undecrypted ciphertext used for decryption before the block that is currently decrypting the ciphertext, the count value obtained by the counting step, and the cipher key data A block key generating unit that generates a block key to be applied to each block to be performed and gives the block key to the decrypting unit, and a ciphertext that is a transmission source of the ciphertext to be decrypted by the decrypting unit when the decryption The restart data is sent to the generation device to set the value of the counting means of the ciphertext generation device and the data of the ciphertext before a predetermined block used by the block key generation means of the ciphertext generation device, and the computer in the computer It said predetermined block before the control hand set and data of the ciphertext counting means value and said block key generation means in the computer is used A ciphertext decryption program to function as a stage . 7. The ciphertext decryption program according to claim 6, wherein the control means sets the count value and ciphertext data before the predetermined block at the time of initial and resumption of ciphertext decryption.

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