A Montgomery multiplier for providing security of information used in smart cards from hacking by a differential power analysis attack by minimizing power consumption difference by the input data. More particularly, the Montgomery multiplier applies an asynchronous dual rail lines method wherein two lines DATAFALSE and DATATRUE are used to represent one binary data such that in order to represent binary data `0`, a logical high signal is applied to the DATAFALSE line, and a logical low signal is applied to the DATATRUE line. Conversely, to represent binary data `1`, a logical low signal is applied to the DATAFALSE line, and a logical high signal is applied to the DATATRUE line. That is, when the data is represented by the asynchronous dual rail lines method, whatever the binary data value is, the same number of logical high states and logical low states are generated. As a result, whatever binary data is to be operated, the power consumption difference of the circuit is minimized.