Cryptographic processing apparatus, cryptographic processing method, and computer program

A cryptographic processing apparatus for executing a common-key block cipher process, the cryptographic processing apparatus comprising:na cryptographic processing part configured to perform a data transformation process of repeating a round function for a plurality of rounds; anda key scheduling part configured to generate a round key to be applied in execution of the round function,wherein the key scheduling part is configured to include:an intermediate key generating part configured to generate an intermediate key by using a secret key transformation process,a register configured to store the generated intermediate key, anda data transformation part configured to execute the data transformation process on register-stored data that is stored in the register, the data transformation part being configured to execute a double-swap process of dividing the register-stored data into sets of data segments and swapping the data segments in each set to generate the round key, and thereafter repeatedly execute the double-swap process based on the round key generated in a previous iteration to generate a plurality of different round keys,

A cryptographic processing method for executing a common-key block cipher process using a cryptographic processing apparatus, the cryptographic processing method comprising:na round key generating step of, in a key scheduling part, generating a plurality of round keys to be applied in execution of round functions for a plurality of rounds that are executed in a cryptographic processing part; anda cryptographic processing step of, in the cryptographic processing part, performing a data transformation process of repeating for the plurality of rounds the round functions in which the round keys are applied,wherein the round key generating step is a step including:an intermediate-key generating step of generating an intermediate key by using a secret key transformation process and storing the generated intermediate key in a register, anda data transformation step in which a data transformation part executes a double-swap process of dividing register-stored data that is stored in the register into sets of data segments and swapping the data segments in each set to generate a round key, and thereafter repeatedly executes the double-swap process based on the round key generated in a previous iteration to generate a plurality of different round keys,a constant generation step in which a constant generation part generates a constant which is different for each round, the constant generation part being configured to generate small-number-of-bits data which is different for each round by performing a data transformation on small-number-of-bits data having a smaller number of bits than the constant to be generated, and generate the constant by using a combination of shifted data items of the generated small-number-of-bits data, andan exclusive-OR operation step in which an exclusive-OR operation part executes an exclusive-OR operation between the constant generated by the constant generation part and the register-stored data to generate the round key for each round.

A non-transitory, computer-readable storage medium storing a computer program that, when executed by a cryptographic processing apparatus, causes the cryptographic processing apparatus to perform a common-key block cipher process, the process comprising:na round key generating step of causing a key scheduling part to generate a plurality of round keys to be applied in execution of round functions for a plurality of rounds that are executed in a cryptographic processing part; anda cryptographic processing step of causing the cryptographic processing part to perform a data transformation process of repeating for the plurality of rounds the round functions in which the round keys are applied,wherein the round key generating step is a step of causing execution of:an intermediate-key generating step of generating an intermediate key by using a secret key transformation process and storing the generated intermediate key in a register,a data transformation step in which a data transformation part causes execution of a double-swap process of dividing register-stored data that is stored in the register into sets of data segments and swapping the data segments in each set to generate a round key, and thereafter repeated execution of the double-swap process based on the round key generated in a previous iteration to generate a plurality of different round keys,a constant generation step in which a constant generation part generates a constant which is different for each round, the constant generation part being configured to generate small-number-of-bits data which is different for each round by performing a data transformation on small-number-of-bits data having a smaller number of bits than the constant to be generated, and generate the constant by using a combination of shifted data items of the generated small-number-of-bits data, andan exclusive-OR operation step in which an exclusive-OR operation part executes an exclusive-OR operation between the constant generated by the constant generation part and the register-stored data to generate the round key for each round.