A memory system includes a plurality of memory cells at intersections between a plurality of word lines and a plurality of bit lines, and a plurality of bit line sense amplifiers connected to the plurality of bit lines, the plurality of bit line sense amplifiers configured to write data to or read data from the plurality of memory cells through the plurality of bit lines, a redundancy bit line sense amplifier among the plurality of bit line sense amplifiers configured to generate a physically unclonable function (PUF) key including a unique random digital value.