We present a Resistive Random Access Memory based Physical Unclonable Function design that gives near-ideal characteristics with high reliability when operating in extreme temperature conditions. By injecting the cells with electric currents, the resistances are much lower than they are in the pristine state and significantly vary cell-to-cell. This property can be exploited to design cryptographic key generators and create quasi-infinite possible digital fingerprints for the same array. The physical unclonable functions operate at low power, in a range that does not disturb the cells; unlike what is done by forming permanently conductive filaments, and the SET/RESET program/erase processes, this design does not modify permanently the resistance of each cell. The novelty of this architecture is to exploit the physical properties of this memory technology by forming gentle ephemeral conductive paths. We evaluate the proposed device’s performance by various stress tests on 1 kb–180 nm ReRAM Technology.