1. A device for calculating a multiplication of a multiplier and a multiplicand with regard to a modulus using an iteration method comprising several iteration steps, including a preceding iteration step, a current iteration step and an iteration step following the current iteration step, comprising: a first performer adapted to perform an exact three operand addition in the preceding iteration step using a preceding intermediate result, the modulus and the multiplicand and using preceding look-ahead parameters to obtain an exact intermediate result for the current iteration step; a second performer adapted to perform an approximated operand addition in the preceding iteration step using the preceding intermediate result and the modulus and at least one part of the preceding look-ahead parameters in order to obtain an approximated intermediate result for the current iteration step; and a calculator adapted to calculate current look-ahead parameters in the preceding iteration step using the approximated intermediate result and the multiplier, wherein the first performer is implemented to perform an exact three operand addition in the current iteration step using the exact intermediate result for the current iteration step, the modulus, the multiplicand and the current look-ahead parameter calculated by the calculator, wherein the second performer is implemented to perform an approximated operand addition in the current iteration step using the current intermediate result and the modulus and at least part of the current look-ahead parameters to obtain an approximated intermediate result for the iteration step following the current iteration step; and wherein the calculator is implemented to obtain look-ahead parameters in the current iteration step for the iteration step following the current iteration step using the approximated intermediate result for the iteration step following the current iteration step and the multiplier; and a controller implemented to feed the first performer and the second performer in the preceding iteration step and in the current iteration step so that the two performers can operate in parallel.