Multistage physical unclonable function system

When a physical unclonable function (PUF) system, which includes a plurality of PUF cells and in which the length of an inputted challenge bit and a created response bit is fixed is called a basic PUF system, a multistage PUF system of the present invention includes: a control unit which generates a control signal required for the operation of the multistage PUF system; a random number generating unit which includes one or more basic PUF systems and is configured in multistage in a manner of allowing a first basic PUF system to receive a challenge bit and create a response bit and of allowing a second basic PUF system to receive the response bit, created by the first basic PUF system, and create a response bit; and a selection unit which selects either a response bit or a challenge bit created by the last step of a basic PUF system in the random number generating unit and provides the selected one as an input to the first basic PUF system, according to a control signal of the control unit.