A physically unclonable function (PUF) device, with corresponding method, is provided for characterizing an integrated circuit. The PUF device includes a digital clock manager (DCM), a Butterfly circuit incorporated within the integrated circuit, and a shift register. The DCM receives a clock input signal (CLK) and imposes a temporal offset to produce a phase-shift signal (PS). The Butterfly circuit receives a first excite signal as said CLK and a second excite signal as said PS. In response, the Butterfly circuit produces an output that shifts state in response to a non-concurrent change in the CLK and PS. The shift register increments a shift count in response to the output.