An encryption processing system comprising: an encryption processing circuit configured to execute a round calculation on input data and generate output data; and a key schedule circuit configured to output key data used in the encryption processing circuit to the encryption processing circuit, wherein each round calculation executed by the encryption processing circuit includes a linear conversion process executed by a linear conversion circuit, and the linear conversion circuit changes a linear conversion mode of the linear conversion process according to a round transition, wherein the input data is a state formed by m*n components in which each component includes at least one bit, and wherein the linear conversion circuit is configured to execute the linear conversion process through matrix calculation in which a plurality of kinds of matrices M 0 to M k are used, characterised in that the linear conversion circuit switches and executes column diffusion calculation, first row diffusion calculation, and second row diffusion calculation according to the round transition, in the column diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each column in units of components of each column of the state in a specific order, in the first row diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each row in units of components of each row of the state in specific order A, and in the second row diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each row in units of components of each row of the state in specific order B different from the specific order A. an encryption processing circuit configured to execute a round calculation on input data and generate output data; and a key schedule circuit configured to output key data used in the encryption processing circuit to the encryption processing circuit, wherein each round calculation executed by the encryption processing circuit includes a linear conversion process executed by a linear conversion circuit, and the linear conversion circuit changes a linear conversion mode of the linear conversion process according to a round transition, wherein the input data is a state formed by m*n components in which each component includes at least one bit, and wherein the linear conversion circuit is configured to execute the linear conversion process through matrix calculation in which a plurality of kinds of matrices M 0 to M k are used, characterised in that the linear conversion circuit switches and executes column diffusion calculation, first row diffusion calculation, and second row diffusion calculation according to the round transition, in the column diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each column in units of components of each column of the state in a specific order, in the first row diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each row in units of components of each row of the state in specific order A, and in the second row diffusion calculation the linear conversion is executed by applying a selected matrix selected from the matrices M 0 to M k to each row in units of components of each row of the state in specific order B different from the specific order A.