An Integrated Montgomery Calculation Engine (IMCE), for multiplying two multiplicands modulo a predefined number, includes a Carry Save Adder (CSA) circuit and control circuitry. The CSA circuit has multiple inputs, and has outputs including a sum output and a carry output. The control circuitry is coupled to the inputs and the outputs of the CSA circuit and is configured to operate the CSA circuit in at least (i) a first setting that calculates a Montgomery precompute value and (ii) a second setting that calculates a Montgomery multiplication of the two multiplicands.