In a Montgomery multiplier, a modulus product generator may select a modulus product from a plurality of selectable n-bit modulus numbers M, a given modulus number M being formed from a currently input extended chunk of bits among the n-bit modulus numbers. A partial product generator may select a multiplicand number from a plurality of selectable n-bit multiplicands A as a partial product, a given multiplicand A being formed from a currently input extended chunk of bits among the n-bit multiplicands. An accumulator may accumulate the selected modulus product and partial product to generate a multiplication result. The Montgomery multiplier may be part of an operation unit that may include a memory and host, and may be adapted to perform a Montgomery multiplication operation and a normal multiplication operation based on a logic state of a control signal input thereto.