The Impact of Aging on a Physical Unclonable Function

On-chip physical unclonable functions (PUFs) have shown promises to solve several security problems. A PUF's behavior needs to be robust against reversible as well as irreversible temporal variabilities in circuits so that noise in the PUF output is minimized. While the effect of the reversible temporal variabilities on PUFs is well studied, sufficient attention has not been given so far to analyze the effect of the irreversible temporal variabilities i.e., aging on PUFs. In this paper, we perform an accelerated aging test on a ring oscillator (RO) PUF and analyze how it affects the functionality of the PUF. With our experiment using a set of 90-nm field-programmable gate arrays, we observe that aging makes PUF responses unreliable. Additionally, simulations show that the randomness of PUF responses remains unaffected despite aging. We also show that a passive countermeasure technique using a configurable RO can mitigate aging effect on the PUF significantly.