Some embodiments include apparatus and methods using a first ring oscillator, a second ring oscillator, and circuit coupled to the first and second ring oscillators. The first ring oscillator includes a first memory cell and a first plurality of stages coupled to the first memory cell. The second ring oscillator includes a second memory cell and a second plurality of stages coupled to the second memory cell. The circuit includes a first input node coupled to an output node of the first ring oscillator and a second input node coupled to an output node of the second ring oscillator. In one of such embodiments, the circuit can operate to generate identification information to authenticate the apparatus.