A Montgomery multiplication device calculates a Montgomery product of an operand X and an operand Y with respect to a modulus M and includes a plurality of processing elements. In a first clock cycle, two intermediate partial sums are created by obtaining an input of length w−1 from a preceding processing element as w−1 least significant bits. The most significant bit is configured as either zero or one. Then, two partial sums are calculated using a word of the operand Y, a word of the modulus M, a bit of the operand X, and the two intermediate partial sums. In a second clock cycle, a selection bit is obtained from a subsequent processing element and one of the two partial sums is selected based on the value of the selection bit. Then, the selected partial sum is used for calculation of a word of the Montgomery product.
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