A method of performing a keyed cryptographic operation mapping an input message to an output message, wherein the cryptographic operation includes at least one round including a non-linear mapping function configured to map input data to output data, including: splitting the input data into n split input data, wherein the splitting of the input data varies based upon the value of the input message; inputting each split input data into the non-linear mapping function to obtain n split output data, wherein a combination the n split output data indicates an output data, wherein the output data results when the input data is input to the non-linear mapping function.