Cryptographic processing apparatus, cryptographic-processing-algorithm constructing method, and cryptographic processing method, and computer program

A cryptographic processing method for performing a cryptographic process in a cryptographic processing apparatus, the method characterized by comprising

• a cryptographic processing step of performing a Feistel-type common-key block-cipher process of repeating an SP-type F-function in a plurality of rounds in a cryptographic processing section, the SP-type F-function performing a data transformation process including a non-linear transformation process and a linear transformation process,
• wherein the cryptographic processing step
• is a step of performing a cryptographic process to which an extended Feistel structure having a number of data lines:
• d that is set to an integer satisfying d≧2 is applied, and includes an operation step of performing operations in which a plurality of at least two or more different matrices are selectively applied to linear transformation processes that are performed in F-functions in respective rounds,
• wherein the plurality of different matrices, which are applied in the operation step, are a plurality of different matrices satisfying a condition in which a minimum number of branches for all of the data lines is equal to or more than a predetermined value, the minimum number of branches for all of the data lines being selected from among minimum numbers of branches corresponding to the data lines, each of the minimum numbers of branches corresponding to the data lines being based on linear transformation matrices included in F-functions that are input to a corresponding data line in the extended Feistel structure, and
• wherein the operation step
• is a step of performing linear transformation operations based on the plurality of different matrices in the F-functions that are input to the respective data lines in the extended Feistel structure.

A cryptographic-processing-algorithm constructing method for constructing a cryptographic processing algorithm in an information processing apparatus, the method characterized by comprising:

• a matrix-determining step in which, in a cryptographic-processing-algorithm configuration to which an extended Feistel structure having a number of data lines:
• d that is set to an integer satisfying d≧2 is applied, a control unit provided in the information processing apparatus determines a plurality of at least two or more different matrices that are to be applied to linear transformation processes performed in F-functions in respective rounds;
• and
• a matrix-setting step in which the control unit repeatedly arranges the plurality of different matrices, which are determined in the matrix-determining step, in the F-functions that are input to the respective data lines in the extended Feistel structure,
• wherein the matrix-determining step
• is a step of performing a process of determining, as the plurality of two or more different matrices, as matrices to be applied, a plurality of different matrices satisfying a condition in which a minimum number of branches for all of the data lines is equal to or more than a predetermined value, the minimum number of branches for all of the data lines being selected from among minimum numbers of branches corresponding to the data lines, each of the minimum numbers of branches corresponding to the data lines being based on linear transformation matrices included in F-functions that are input to a corresponding data line in the extended Feistel structure.

A computer program that causes a cryptographic processing apparatus to perform a cryptographic process, the program characterized by comprising

• a cryptographic processing step of causing a cryptographic processing section to perform a Feistel-type common-key block-cipher process of repeating an SP-type F-function in a plurality of rounds, the SP-type F-function performing a data transformation process including a non-linear transformation process and a linear transformation process,
• wherein the cryptographic processing step
• is a step of causing the cryptographic processing section to perform a cryptographic process to which an extended Feistel structure having a number of data lines:
• d that is set to an integer satisfying d≧2 is applied, and includes an operation step of performing operations in which a plurality of at least two or more different matrices are selectively applied to linear transformation processes that are performed in F-functions in respective rounds,
• wherein the plurality of different matrices, which are applied in the operation step, are a plurality of different matrices satisfying a condition in which a minimum number of branches for all of the data lines is equal to or more than a predetermined value, the minimum number of branches for all of the data lines being selected from among minimum numbers of branches corresponding to the data lines, each of the minimum numbers of branches corresponding to the data lines being based on linear transformation matrices included in F-functions that are input to a corresponding data line in the extended Feistel structure, and
• wherein the operation step
• is a step of performing linear transformation operations based on the plurality of different matrices in the F-functions that are input to the respective data lines in the extended Feistel structure.

A computer program that causes an information processing apparatus to construct a cryptographic processing algorithm, the program characterized by comprising:

• a matrix-determining step of causing, in a cryptographic-processing-algorithm configuration to which an extended Feistel structure having a number of data lines:
• d that is set to an integer satisfying d≧2 is applied, a control unit provided in the information processing apparatus to determine a plurality of at least two or more different matrices that are to be applied to linear transformation processes performed in F-functions in respective rounds;
• and
• a matrix-setting step of causing the control unit to repeatedly arrange the plurality of different matrices, which are determined in the matrix-determining step, in the F-functions that are input to the respective data lines in the extended Feistel structure,
• wherein the matrix-determining step
• is a step of performing a process of determining, as the plurality of two or more different matrices, as matrices to be applied, a plurality of different matrices satisfying a condition in which a minimum number of branches for all of the data lines is equal to or more than a predetermined value, the minimum number of branches for all of the data lines being selected from among minimum numbers of branches corresponding to the data lines, each of the minimum numbers of branches corresponding to the data lines being based on linear transformation matrices included in F-functions that are input to a corresponding data line in the extended Feistel structure.