Patent ID: 8457302

Claim:
A method for protecting secret data stored in a memory of a semiconductor chip of a data carrier, said secret data serving as input data for one or more operations executed on the semiconductor chip, the execution of the one or more operations causing signals detectable from outside of the data carrier, the signals being dependent on the one or more operations and on the input data for the one or more operations, said method comprising the steps of: falsifying the input data by combination with auxiliary data (Z) before execution of the one or more operations (ƒ) on the semiconductor chip, executing said one or more operations (ƒ) on the semiconductor chip, retrieving an auxiliary function value (ƒ(Z)) from said memory of said semiconductor chip of the data carrier, combining the output data determined by said executing of the one or more operations (ƒ) with said auxiliary function value (ƒ(Z)) in order to compensate for the falsification of the input data, wherein the auxiliary function value (ƒ(Z)) was previously determined by execution of the one or more operations (ƒ) with the auxiliary data (Z) as input data in safe surroundings and stored along with the auxiliary data (Z) in the memory of the semiconductor chip of the data carrier.