A data conversion algorithm achieving efficient data diffusion is achieved. For example, in a configuration where a various processes are executed on two data segments which are resultants of dividing a rectangular matrix of data containing arranged one-byte data blocks into two parts to perform data conversion, efficient data scrambling with less operation cost is achieved by executing a linear conversion process on one of the data segments, an exclusive OR operation between the two data segments, a shift process on one of the data segments, and a swap process between the two data segments. Moreover, cryptographic processing with a high security level is achieved by including nonlinear conversion or key application operation on the data segments.