JP2011130312A - Ciphering device and deciphering device for stream cipher, ciphering method and deciphering method for stream cipher, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency of ciphering or deciphering processing for a short plain text or a short cipher text without adding a different logic. <P>SOLUTION: Initialization is performed using an initial key and an initial vector, and after completing the initialization processing, a bit sequence having the same length of the cipher text is selected from an internal state. Then, exclusive OR operation is performed between the selected bit sequence and the cipher text to output a plain text. Accordingly, a short cipher text is decrypted without processing of key-based sequence generation, so that the deciphering processing is made to be more efficient without requiring adding a different logic. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a stream cipher encryption apparatus, a stream cipher decryption apparatus, a stream cipher encryption method, a stream cipher decryption method, and a program.

  In recent years, various services using computers have been provided due to the remarkable spread of the Internet. Many of the services provided in this way use encryption to conceal the communication contents. Here, as the encryption method, a common key encryption method in which encryption and decryption are performed with one key is common, but this common key encryption method is roughly divided into a block encryption method and a stream encryption method. Is done.

  Since the stream encryption method can be expected to process faster than the block encryption method, for example, as a method for transmitting large-capacity data such as a movie in recent years, attention has been paid to the stream encryption method. There is a problem that the encryption process and the decryption process must be synchronized. For this reason, a self-synchronous stream cipher apparatus that automatically recovers synchronization using a ciphertext received without error of a certain size or more has been proposed (for example, see Patent Document 1).

JP 2001-16197 A

  However, in the stream cipher, the initial key is agitated by the initialization process, an initial internal state is generated, and each sequence of encryption is generated while sequentially updating the generated state. In the conventional stream cipher, the key sequence generation processing is further performed after initialization. Therefore, the conventional stream cipher has a problem that the encryption process cannot be performed unless the key sequence generation process is performed, and the process is redundant when a short plaintext is encrypted.

  Therefore, the present invention has been made in view of the above-described problems, and an encryption apparatus for stream cipher that improves the efficiency of encryption processing or decryption processing for short plaintext or ciphertext without adding different logic. An object of the present invention is to provide a stream cipher decryption device, a stream cipher encryption method, a stream cipher decryption method, and a program.

  The present invention proposes the following matters in order to solve the above problems. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.

  (1) The present invention provides an initialization processing means (for example, equivalent to the initialization processing unit 101 in FIG. 1) that performs an initialization process using an initial key and an initial vector, and an internal process after the initialization process is completed. A selection means (for example, corresponding to the bit selection unit 102 in FIG. 1) for selecting a bit string having the same length as the plaintext from the state, and performing an exclusive OR operation on the selected bit string and the plaintext, And a stream cipher encryption device characterized by comprising an operation means (for example, equivalent to the exclusive OR operation unit 103 in FIG. 1).

  According to the present invention, the initialization processing means performs the initialization process using the initial key and the initial vector. The selection means selects a bit string having the same length as the plaintext from the internal state after the initialization process is completed. The computing means performs an exclusive OR operation between the selected bit string and the plaintext, and outputs a ciphertext. Accordingly, since encryption is performed for a short plaintext without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the encryption process can be improved.

  (2) The stream cipher encryption apparatus according to (1), wherein the selected bit string is 1 bit or more and half or less of the internal state. Has proposed.

  According to the present invention, the selected bit string is 1 bit or more and half or less of the internal state. In other words, when encrypting a short plain text that is less than half of the internal state of the stream cipher, the processing load is reduced by directly using the bit string of the internal state.

  (3) The present invention relates to the stream cipher encryption device of (2), when the length of the plaintext is larger than half of the internal state, the plaintext of 1 bit or more and half or less of the internal state When the remaining plaintext is encrypted, the initialization processing means changes the initial vector and performs the initialization process again. ing.

  According to the present invention, when the length of the plaintext is longer than half of the internal state, processing is performed on a plaintext of 1 bit or more and half or less of the internal state, and the remaining plaintext is encrypted. The initialization processing means changes the initial vector and performs initialization processing again. That is, when the length of the plaintext is larger than half of the internal state, at least the bit string is divided into half or less of the internal state, and the initialization process is performed again for each, and the encryption process is executed. As a result, even if the plaintext length is longer than half of the internal state, encryption is performed without executing the key sequence generation process, so there is no need to add different logic and the efficiency of the encryption process Can be achieved.

  (4) The present invention relates to an initialization processing means (for example, equivalent to the initialization processing unit 101 in FIG. 5) for performing initialization processing using an initial key and an initial vector, and after the initialization processing, A selection means (for example, corresponding to the bit selection unit 102 in FIG. 5) for selecting a bit string having the same length as the ciphertext from the state, and performing an exclusive OR operation between the selected bit string and the ciphertext; A stream cipher decryption device characterized by comprising arithmetic means for outputting plaintext (for example, corresponding to the exclusive OR operation unit 201 in FIG. 5) is proposed.

  According to the present invention, the initialization processing means performs the initialization process using the initial key and the initial vector. The selection means selects a bit string having the same length as the plaintext from the internal state after the initialization process is completed. The computing means performs an exclusive OR operation between the selected bit string and the ciphertext, and outputs a plaintext. Therefore, since the short ciphertext is decrypted without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the decryption process can be improved.

  (5) The present invention relates to the stream cipher decryption device of (4), wherein the selected bit string is 1 bit or more and half or less of the internal state. Has proposed.

  According to the present invention, the selected bit string is 1 bit or more and half or less of the internal state. That is, when decrypting a ciphertext shorter than half of the internal state of the stream cipher, the processing load is reduced by directly using the bit string in the internal state.

  (6) The present invention relates to the decryption apparatus for stream cipher of (5), when the length of the ciphertext is larger than half of the internal state, it is 1 bit or more and half or less of the internal state A stream cipher decryption device characterized in that when processing is performed on ciphertext and the remaining ciphertext is decrypted, the initialization processing means changes the initial vector and performs initialization processing again. Has proposed.

  According to the present invention, when the length of the ciphertext is longer than half of the internal state, the ciphertext of 1 bit or more and half or less of the internal state is processed, and the remaining ciphertext is decrypted. In this case, the initialization processing means changes the initial vector and performs initialization processing again. In other words, if the length of the ciphertext is greater than half of the internal state, at least divide it into bit strings that are less than or equal to half of the internal state, perform initialization processing again, and execute decryption processing. . As a result, even if the length of the ciphertext is larger than half of the internal state, the decryption is performed without executing the key sequence generation process, so there is no need to add different logic and Efficiency can be improved.

  (7) The present invention is an encryption method for stream ciphers when the length of an input plaintext is 1 bit or more and half or less of the internal state, using an initial key and an initial vector, A first step (for example, corresponding to step S101 in FIG. 2), and a second step (for example, selecting a bit string having the same length as the plaintext from the internal state after the initialization process is completed) 2) and a third step (for example, equivalent to step S103 in FIG. 2) for performing an exclusive OR operation on the selected bit string and the plaintext and outputting a ciphertext. A stream cipher encryption method characterized by comprising the above is proposed.

  According to the present invention, an initialization process is performed using an initial key and an initial vector, and after completion of the initialization process, a bit string having the same length as the plaintext is selected from the internal state. Then, an exclusive OR operation of the selected bit string and plaintext is performed and ciphertext is output. Accordingly, since encryption is performed for a short plaintext without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the encryption process can be improved.

  (8) The present invention is an encryption method for stream ciphers when the length of an input plaintext is more than half of the internal state. The first method performs initialization using an initial key and an initial vector. Step (for example, corresponding to step S201 in FIG. 4) and a second step (for example, step S202 in FIG. 4) for selecting a bit string of 1 bit or more and half or less of the internal state after completion of the initialization process. And a third step (for example, corresponding to step S203 in FIG. 4) for performing an exclusive OR operation between the selected bit string and the plaintext and outputting a ciphertext, and changing only the initial vector. A fourth step (for example, corresponding to step S204 in FIG. 4) for performing the initialization process, and a fifth bit string for selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed. The (E.g., corresponding to step S205 in FIG. 4), and a sixth step (e.g., in step S206 in FIG. 4) that performs an exclusive OR operation on the selected bit string and the plaintext and outputs a ciphertext. And the seventh step of continuing the processing from the fourth step to the sixth step until the remaining plaintext length is 1 bit or more and half or less of the internal state (for example, 4) (equivalent to step S207 in FIG. 4), and an eighth step (for example, equivalent to step S208 in FIG. 4) of concatenating all the output ciphertexts and outputting ciphertext corresponding to the plaintext, And a stream cipher encryption method characterized by comprising:

  According to the present invention, initialization processing is performed using an initial key and an initial vector, and after completion of the initialization processing, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string The ciphertext is output by performing an exclusive OR operation with the plaintext. Next, only the initial vector is changed and initialization processing is performed. After the initialization processing is completed, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string and the plaintext are excluded. Perform logical OR operation and output ciphertext. The processing from the fourth step to the sixth step is continued until the remaining plaintext length is 1 bit or more and half or less of the internal state, and all the output ciphertexts are concatenated. The ciphertext corresponding to the plaintext is output. Therefore, if the length of the plaintext is larger than half of the internal state, at least the bit string of half or less of the internal state is divided and the initialization process is performed again for each to execute the encryption process. As a result, even if the plaintext length is longer than half of the internal state, encryption is performed without executing the key sequence generation process, so there is no need to add different logic and the efficiency of the encryption process Can be achieved.

  (9) The present invention is a method for decrypting a stream cipher when the length of the input ciphertext is 1 bit or more and half or less of the internal state, using an initial key and an initial vector, A first step for performing initialization processing (for example, corresponding to step S301 in FIG. 6), and a second step for selecting a bit string having the same length as the ciphertext from the internal state after completion of the initialization processing ( For example, this corresponds to step S302 in FIG. 6), and a third step (for example, corresponding to step S303 in FIG. 6) that performs an exclusive OR operation on the selected bit string and the ciphertext and outputs a plaintext. And a stream cipher decryption method characterized by comprising:

  According to the present invention, an initialization process is performed using an initial key and an initial vector, and after completion of the initialization process, a bit string having the same length as the ciphertext is selected from the internal state. Then, an exclusive OR operation between the selected bit string and the ciphertext is performed, and plaintext is output. Therefore, since the short ciphertext is decrypted without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the decryption process can be improved.

  (10) The present invention is a method for decrypting a stream cipher when the length of an input ciphertext is more than half of the internal state, and performs an initialization process using an initial key and an initial vector. 1 step (for example, corresponding to step S401 in FIG. 8) and a second step (for example, step in FIG. 8) for selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed. S402), a third step (for example, equivalent to step S403 in FIG. 8) of performing an exclusive OR operation on the selected bit string and the ciphertext and outputting plaintext, and changing only the initial vector Then, a fourth step (for example, corresponding to step S404 in FIG. 8) for performing the initialization process and a bit string equal to 1 bit or more and equal to or less than half of the internal state are selected after the initialization process is completed. A fifth step (for example, corresponding to step S405 in FIG. 8) and a sixth step (for example, the step in FIG. 8) that performs an exclusive OR operation on the selected bit string and the ciphertext and outputs plaintext And the seventh step of continuing the processing from the fourth step to the sixth step until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state. (E.g., corresponding to step S407 in FIG. 8) and an eighth step (for example, corresponding to step S408 in FIG. 8) of connecting all the output plaintexts and outputting plaintext corresponding to the ciphertext. And a stream cipher decryption method characterized by comprising:

  According to the present invention, initialization processing is performed using an initial key and an initial vector, and after completion of the initialization processing, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string And the ciphertext are subjected to an exclusive OR operation, and plaintext is output. Next, only the initial vector is changed and initialization processing is performed. After the initialization processing is completed, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string and the ciphertext are Performs an exclusive OR operation and outputs plaintext. The process from the fourth step to the sixth step is continued until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state, and all the output plaintexts are concatenated. The plaintext corresponding to the ciphertext is output. Therefore, when the length of the ciphertext is larger than half of the internal state, at least, it is divided into bit strings less than or equal to half of the internal state, and the initialization process is performed again for each to execute the decryption process. . As a result, even if the length of the ciphertext is larger than half of the internal state, the decryption is performed without executing the key sequence generation process, so there is no need to add different logic and Efficiency can be improved.

  (11) The present invention is a program for causing a computer to execute a stream cipher encryption method when the length of an input plaintext is 1 bit or more and half or less of the internal state, A first step (for example, corresponding to step S101 in FIG. 2) for performing initialization processing using an initial vector, and after completion of the initialization processing, a bit string having the same length as plain text is selected from the internal state A second step (for example, corresponding to step S102 in FIG. 2), and a third step (for example, in FIG. 2) that performs an exclusive OR operation between the selected bit string and the plaintext, and outputs a ciphertext. (Corresponding to step S103) is proposed.

  According to the present invention, an initialization process is performed using an initial key and an initial vector, and after completion of the initialization process, a bit string having the same length as the plaintext is selected from the internal state. Then, an exclusive OR operation of the selected bit string and plaintext is performed and ciphertext is output. Accordingly, since encryption is performed for a short plaintext without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the encryption process can be improved.

  (12) The present invention is a program for causing a computer to execute a stream cipher encryption method when the length of input plaintext is more than half of the internal state, using an initial key and an initial vector. First step for performing initialization process (for example, corresponding to step S201 in FIG. 4) and second step for selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed (For example, corresponding to step S202 in FIG. 4) and a third step (for example, corresponding to step S203 in FIG. 4) that performs an exclusive OR operation on the selected bit string and the plaintext and outputs a ciphertext. And a fourth step (for example, corresponding to step S204 in FIG. 4) in which only the initial vector is changed and the initialization process is performed, and one bit or more after the initialization process is completed. A fifth step (for example, corresponding to step S205 in FIG. 4) for selecting a bit string less than half of the state, an exclusive OR operation of the selected bit string and the plaintext, and outputting a ciphertext (For example, corresponding to step S206 in FIG. 4) and the processing from the fourth step to the sixth step, the remaining plaintext length is 1 bit or more and half or less of the internal state. Up to the seventh step (for example, corresponding to step S207 in FIG. 4) and the eighth step (for example, for outputting the ciphertext corresponding to the plaintext by concatenating all the ciphertexts output) , Which corresponds to step S208 in FIG. 4), is proposed.

  According to the present invention, initialization processing is performed using an initial key and an initial vector, and after completion of the initialization processing, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string The ciphertext is output by performing an exclusive OR operation with the plaintext. Next, only the initial vector is changed and initialization processing is performed. After the initialization processing is completed, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string and the plaintext are excluded. Perform logical OR operation and output ciphertext. The processing from the fourth step to the sixth step is continued until the remaining plaintext length is 1 bit or more and half or less of the internal state, and all the output ciphertexts are concatenated. The ciphertext corresponding to the plaintext is output. Therefore, if the length of the plaintext is larger than half of the internal state, at least the bit string of half or less of the internal state is divided and the initialization process is performed again for each to execute the encryption process. As a result, even if the plaintext length is longer than half of the internal state, encryption is performed without executing the key sequence generation process, so there is no need to add different logic and the efficiency of the encryption process Can be achieved.

  (13) The present invention is a program for causing a computer to execute a method for decrypting a stream cipher when the length of an input ciphertext is 1 bit or more and half or less of the internal state, and an initial key And the initial step using the initial vector (for example, corresponding to step S301 in FIG. 6), and after completion of the initialization process, a bit string having the same length as the ciphertext from the internal state A second step (for example, corresponding to step S302 in FIG. 6), and a third step (for example, FIG. 6) that performs an exclusive OR operation on the selected bit string and the ciphertext and outputs plaintext. 6 is equivalent to step S303 in FIG. 6).

  According to the present invention, an initialization process is performed using an initial key and an initial vector, and after completion of the initialization process, a bit string having the same length as the ciphertext is selected from the internal state. Then, an exclusive OR operation between the selected bit string and the ciphertext is performed, and plaintext is output. Therefore, since the short ciphertext is decrypted without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the decryption process can be improved.

  (14) The present invention is a program for causing a computer to execute a stream cipher decryption method when the length of an input ciphertext is more than half of the internal state, and uses an initial key and an initial vector. The first step (for example, corresponding to step S401 in FIG. 8) for performing the initialization process, and the second sequence for selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed Step (for example, equivalent to step S402 in FIG. 8) and a third step (for example, equivalent to step S403 in FIG. 8) that performs an exclusive OR operation on the selected bit string and the ciphertext and outputs plaintext ), A fourth step (for example, corresponding to step S404 in FIG. 8) for performing initialization processing by changing only the initial vector, and after completion of the initialization processing, 1 bit or more, and A fifth step (for example, corresponding to step S405 in FIG. 8) for selecting a bit string equal to half or less of the partial state, an exclusive OR operation between the selected bit string and the ciphertext, and outputting plaintext The sixth step (e.g., corresponding to step S406 in FIG. 8) and the processing from the fourth step to the sixth step are the remaining ciphertext length of 1 bit or more and half of the internal state. A seventh step to be continued until the following is satisfied (for example, corresponding to step S407 in FIG. 8), and an eighth step in which all the output plaintexts are concatenated and a plaintext corresponding to the ciphertext is output. (For example, corresponding to step S408 in FIG. 8) is proposed.

  According to the present invention, initialization processing is performed using an initial key and an initial vector, and after completion of the initialization processing, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string And the ciphertext are subjected to an exclusive OR operation, and plaintext is output. Next, only the initial vector is changed and initialization processing is performed. After the initialization processing is completed, a bit string of 1 bit or more and half or less of the internal state is selected, and the selected bit string and the ciphertext are Performs an exclusive OR operation and outputs plaintext. The process from the fourth step to the sixth step is continued until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state, and all the output plaintexts are concatenated. The plaintext corresponding to the ciphertext is output. Therefore, when the length of the ciphertext is larger than half of the internal state, at least, it is divided into bit strings less than or equal to half of the internal state, and the initialization process is performed again for each to execute the decryption process. . As a result, even if the length of the ciphertext is larger than half of the internal state, the decryption is performed without executing the key sequence generation process, so there is no need to add different logic and Efficiency can be improved.

  According to the present invention, when a short plaintext or ciphertext is encrypted or decrypted with respect to the internal state of the stream cipher, the processing load can be reduced by directly using the bit string of the internal state. is there.

It is a figure which shows the structure of the encryption apparatus which concerns on 1st Embodiment. It is a figure which shows the process of the encryption apparatus which concerns on 1st Embodiment. It is a figure which shows the structure of the encryption apparatus which concerns on 2nd Embodiment. It is a figure which shows the process of the encryption apparatus which concerns on 2nd Embodiment. It is a figure which shows the structure of the decoding apparatus which concerns on 3rd Embodiment. It is a figure which shows the process of the decoding apparatus which concerns on 3rd Embodiment. It is a figure which shows the structure of the decoding apparatus which concerns on 4th Embodiment. It is a figure which shows the process of the decoding apparatus which concerns on 4th Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Note that the constituent elements in the present embodiment can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the present embodiment does not limit the contents of the invention described in the claims.

<First Embodiment>
A stream cipher encryption apparatus according to this embodiment will be described with reference to FIGS. 1 and 2.

<Configuration of Stream Cipher Encryption Device>
As shown in FIG. 1, the encryption device for stream encryption according to the present embodiment includes an initialization processing unit 101, a bit selection unit 102, and an exclusive OR operation unit 103. The stream cipher encryption apparatus according to this embodiment is an encryption apparatus suitable for short plaintext.

  The initialization processing unit 101 performs initialization processing using an initial key and an initial vector. The bit selection unit 102 selects a bit string having the same length as the plain text from the internal state after the initialization process is completed. The exclusive OR operation unit 103 performs an exclusive OR operation on the selected bit string and plaintext, and outputs a ciphertext. In the present embodiment, in order to ensure safety, it is desirable that the length of the plaintext is not more than half of the size of the internal state.

<Processing of encryption device for stream cipher>
The processing of the stream cipher encryption apparatus according to this embodiment will be described with reference to FIG.
The initialization processing unit 101 performs initialization processing using the initial key and the initial vector (step S101). After completion of the initialization process, the bit selection unit 102 selects a bit string having the same length as the plain text from the internal state (step S102). Then, the exclusive OR operation unit 103 performs an exclusive OR operation between the selected bit string and the plaintext, and outputs a ciphertext (step S103).

  Therefore, according to this embodiment, since encryption is performed for a short plaintext without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the encryption process can be improved.

<Second Embodiment>
A stream cipher encryption apparatus according to this embodiment will be described with reference to FIGS. 3 and 4.

<Configuration of Stream Cipher Encryption Device>
As shown in FIG. 3, the encryption device for stream cipher according to the present embodiment includes an initialization processing unit 101, a bit selection unit 102, an exclusive OR operation unit 103, an initial vector supply unit 104, Part 105. The stream cipher encryption apparatus according to the present embodiment is an encryption apparatus suitable for a case where the total length of plaintext is longer than half of the internal state. In addition, since components having the same reference numerals as those in the first embodiment have the same functions, detailed descriptions thereof are omitted.

  The initial vector supply unit 104 supplies a new initial vector to the initialization processing unit 101 when the total length of the plaintext is longer than half of the internal state and the remaining part is encrypted. Thereby, the initialization process part 101 performs an initialization process again. When the total length of the plaintext is larger than half of the internal state and the encryption is divided into several times, the combining unit 105 sequentially outputs the ciphertexts output from the exclusive OR operation unit 103. Combine to generate the final ciphertext.

<Processing of encryption device for stream cipher>
The processing of the stream cipher encryption apparatus according to this embodiment will be described with reference to FIG.
The initialization processing unit 101 performs initialization processing using the initial key and the initial vector (step S201). The bit selection unit 102 selects a bit string of 1 bit or more and half or less of the internal state after completion of the initialization process (step S202).

  The exclusive OR operation unit 103 performs an exclusive OR operation between the selected bit string and the plaintext, and outputs a ciphertext (step S203). Next, if the total length of the plaintext is larger than half of the internal state, the initial vector supply unit 104 changes only the initial vector to encrypt the remaining plaintext, and the initialization processing unit 101 performs the initialization process again (step S204).

  After completion of the initialization process, the bit selection unit 102 selects a bit string of 1 bit or more and half or less of the internal state (step S205). The exclusive OR operation unit 103 performs an exclusive OR operation between the selected bit string and the plaintext, and outputs a ciphertext (step S206).

  Then, the processing from step S204 to step S206 is continued until the length of the remaining plaintext is 1 bit or more and half or less of the internal state (step S207). Then, all the ciphertexts sequentially output from the exclusive OR operation unit 103 are connected by the combining unit 105, and a ciphertext corresponding to the plaintext is output (step S208).

  Therefore, according to the present embodiment, when the length of the plaintext is larger than half of the internal state, the bit string is divided into at least half of the internal state and the initialization process is performed again for each of them. Execute the process. As a result, even if the plaintext length is longer than half of the internal state, encryption is performed without executing the key sequence generation process, so there is no need to add different logic and the efficiency of the encryption process Can be achieved.

<Third Embodiment>
The stream cipher decoding apparatus according to this embodiment will be described with reference to FIGS.

<Configuration of Decryption Device for Stream Cipher>
As shown in FIG. 5, the stream cipher decryption apparatus according to the present embodiment includes an initialization processing unit 101, a bit selection unit 102, and an exclusive OR operation unit 201. The stream cipher decryption apparatus according to the present embodiment is a decryption apparatus suitable for short plaintext. In addition, since components having the same reference numerals as those in the first embodiment have the same functions, detailed descriptions thereof are omitted.

  The exclusive OR operation unit 201 performs an exclusive OR operation on the bit string selected by the bit selection unit 102 and the ciphertext, and outputs a plaintext. In the present embodiment, in order to ensure safety, it is desirable that the length of the plaintext is not more than half of the size of the internal state.

<Processing of Decryption Device for Stream Cipher>
With reference to FIG. 6, the processing of the decryption apparatus for the stream cipher according to this embodiment will be described.
The initialization processing unit 101 performs initialization processing using the initial key and the initial vector (step S301). After completion of the initialization process, the bit selection unit 102 selects a bit string having the same length as the ciphertext from the internal state (step S302). Then, the exclusive OR operation unit 201 performs an exclusive OR operation between the selected bit string and the ciphertext, and outputs a plaintext (step S303).

  Therefore, according to this embodiment, since a short ciphertext is decrypted without executing the key sequence generation process, it is not necessary to add different logic, and the efficiency of the decryption process can be improved.

<Fourth Embodiment>
The stream cipher decryption apparatus according to this embodiment will be described with reference to FIGS.

<Configuration of Decryption Device for Stream Cipher>
As shown in FIG. 7, the decryption / encryption device for stream cipher according to the present embodiment includes an initialization processing unit 101, a bit selection unit 102, an initial vector supply unit 104, an exclusive OR operation unit 201, It is comprised from the coupling | bond part 202. FIG. The stream cipher decryption apparatus according to the present embodiment is a decryption apparatus suitable for a case where the total length of ciphertext is larger than half of the internal state. In addition, since components having the same reference numerals as those in the second and third embodiments have the same functions, detailed descriptions thereof are omitted.

  When the combined length of the ciphertext is larger than half of the internal state and decryption is performed in several times, the combining unit 202 sequentially outputs plaintexts output from the exclusive OR operation unit 201. Combine to generate the final plaintext.

<Processing of Decryption Device for Stream Cipher>
The processing of the decryption apparatus for stream cipher according to the present embodiment will be described with reference to FIG.
The initialization processing unit 101 performs initialization processing using the initial key and the initial vector (step S401). After completing the initialization process, the bit selection unit 102 selects a bit string of 1 bit or more and half or less of the internal state (step S402).

  The exclusive OR operation unit 201 performs an exclusive OR operation between the selected bit string and the ciphertext, and outputs a plaintext (step S403). Next, when the total length of the ciphertext is larger than half of the internal state, the initial vector supply unit 104 changes only the initial vector and initializes it in order to decrypt the remaining ciphertext. The processing unit 101 performs initialization processing again (step S404).

  After completing the initialization process, the bit selection unit 102 selects a bit string of 1 bit or more and half or less of the internal state (step S405). The exclusive OR operation unit 201 performs an exclusive OR operation between the selected bit string and the ciphertext, and outputs a plaintext (step S406).

  Then, the processing from step S404 to step S406 is continued until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state (step S407). Then, all the plaintexts sequentially output from the exclusive OR operation unit 201 are connected by the combining unit 203, and a plaintext corresponding to the ciphertext is output (step S408).

  Therefore, according to the present embodiment, when the length of the ciphertext is larger than half of the internal state, at least, it is divided into bit strings equal to or less than half of the internal state, and the initialization process is performed again for each. The decryption process is executed. As a result, even if the length of the ciphertext is larger than half of the internal state, the decryption is performed without executing the key sequence generation process, so there is no need to add different logic and Efficiency can be improved.

  The processing of the stream cipher encryption device and the stream cipher decryption device is recorded on a computer-readable recording medium, and the program recorded on the recording medium is stored in the stream cipher encryption device and the stream cipher decryption device. The stream cipher encryption apparatus and the stream cipher decryption apparatus according to the present invention can be realized by reading and executing the above. The computer system here includes an OS and hardware such as peripheral devices.

  Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW (World Wide Web) system is used. The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.

  The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and includes designs and the like that do not depart from the gist of the present invention.

101; initialization processing unit 102; bit selection unit 103; exclusive OR operation unit 104; initial vector supply unit 105; combining unit 201; exclusive OR operation unit 202; combining unit

Claims (14)

Initialization processing means for performing initialization processing using the initial key and the initial vector;
A selection means for selecting a bit string having the same length as the plaintext from the internal state after the initialization process is completed;
An arithmetic means for performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A stream cipher encryption apparatus comprising:   The stream cipher encryption apparatus according to claim 1, wherein the selected bit string is 1 bit or more and half or less of the internal state.   When the length of the plaintext is larger than half of the internal state, processing is performed on a plaintext of 1 bit or more and half or less of the internal state, and when the remaining plaintext is encrypted, the initialization is performed. 3. The stream cipher encryption apparatus according to claim 2, wherein the processing means changes the initial vector and performs the initialization process again. Initialization processing means for performing initialization processing using the initial key and the initial vector;
A selection means for selecting a bit string having the same length as the ciphertext from the internal state after the initialization process is completed;
An arithmetic means for performing an exclusive OR operation between the selected bit string and the ciphertext, and outputting plaintext;
An apparatus for decrypting a stream cipher, comprising:   5. The stream cipher decoding apparatus according to claim 4, wherein the selected bit string is 1 bit or more and half or less of the internal state.   When the length of the ciphertext is larger than half of the internal state, the ciphertext of 1 bit or more and half or less of the internal state is processed, and when the remaining ciphertext is decrypted, 6. The apparatus for decrypting a stream cipher according to claim 5, wherein the initialization processing means changes the initial vector and performs the initialization process again. An encryption method of stream cipher when the length of input plaintext is 1 bit or more and half or less of the internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string having the same length as the plaintext from the internal state after the initialization process is completed;
A third step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A stream cipher encryption method characterized by comprising: An encryption method of stream cipher when the length of plaintext to be input is more than half of the internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process;
A third step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A fourth step of performing initialization processing by changing only the initial vector;
A fifth step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed;
A sixth step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A seventh step of continuing the processing from the fourth step to the sixth step until the length of the remaining plaintext is 1 bit or more and half or less of the internal state;
An eighth step of concatenating all the output ciphertexts and outputting ciphertexts corresponding to the plaintexts;
A stream cipher encryption method characterized by comprising: A method of decrypting a stream cipher when the length of an input ciphertext is 1 bit or more and half or less of an internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string having the same length as the ciphertext from the internal state after the initialization process is completed;
A third step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A method of decrypting a stream cipher, comprising: A method for decrypting a stream cipher when the length of the input ciphertext is more than half of the internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process;
A third step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A fourth step of performing initialization processing by changing only the initial vector;
A fifth step of selecting a bit string equal to 1 bit or more and equal to or less than half of the internal state after the initialization process is completed;
A sixth step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A seventh step of continuing the processing from the fourth step to the sixth step until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state;
An eighth step of concatenating all the output plaintexts and outputting plaintext corresponding to the ciphertext;
A method of decrypting a stream cipher, comprising: A program for causing a computer to execute a stream cipher encryption method when the length of an input plaintext is 1 bit or more and half or less of an internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string having the same length as the plaintext from the internal state after the initialization process is completed;
A third step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A program that causes a computer to execute. A program for causing a computer to execute a stream cipher encryption method when the length of an input plaintext is more than half of the internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process;
A third step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A fourth step of performing initialization processing by changing only the initial vector;
A fifth step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process is completed;
A sixth step of performing an exclusive OR operation between the selected bit string and the plaintext, and outputting a ciphertext;
A seventh step of continuing the processing from the fourth step to the sixth step until the length of the remaining plaintext is 1 bit or more and half or less of the internal state;
An eighth step of concatenating all the output ciphertexts and outputting ciphertexts corresponding to the plaintexts;
A program that causes a computer to execute. A program for causing a computer to execute a stream cipher decryption method when the length of an input ciphertext is 1 bit or more and half or less of an internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string having the same length as the ciphertext from the internal state after the initialization process is completed;
A third step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A program that causes a computer to execute. A program for causing a computer to execute a method for decrypting a stream cipher when the length of an input ciphertext is more than half of the internal state,
A first step of performing an initialization process using an initial key and an initial vector;
A second step of selecting a bit string of 1 bit or more and half or less of the internal state after the initialization process;
A third step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A fourth step of performing initialization processing by changing only the initial vector;
A fifth step of selecting a bit string equal to 1 bit or more and equal to or less than half of the internal state after the initialization process is completed;
A sixth step of performing an exclusive OR operation between the selected bit string and the ciphertext and outputting plaintext;
A seventh step of continuing the processing from the fourth step to the sixth step until the length of the remaining ciphertext is 1 bit or more and half or less of the internal state;
An eighth step of concatenating all the output plaintexts and outputting plaintext corresponding to the ciphertext;
A program that causes a computer to execute.

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