An apparatus for calculating a result of a scalar multiplication of a reference number with a reference point on an elliptic curve includes a random number generator and processor. The random number generator generates a random bit. The processor calculates the result of the scalar multiplication based on a calculation algorithm using a first auxiliary variable storing a first interim result representing an integer multiple of the reference point or a coordinate of an integer multiple of the reference point and a second auxiliary variable storing a second interim result representing another integer multiple of the reference point or a coordinate of another integer multiple of the reference point. The processor swaps a value stored by the first auxiliary variable and a value stored by the second auxiliary variable during calculation of the result of the scalar multiplication, if a swap condition depending on the generated random bit is fulfilled.