Stability analysis of a physical unclonable function based on metal resistance variations

Keying material for encryption is stored as digital bit-strings in non-volatile memory on FPGAs and ASICs in current technologies. However, secrets stored this way are not secure against a determined adversary, who can use probing attacks to steal the secret. Physical unclonable functions (PUFs) have emerged as an alternative. PUFs leverage random manufacturing variations as the source of entropy for generating random bit-strings, and incorporate an on-chip infrastructure for measuring and digitizing the corresponding variations in key electrical parameters, such as delay or voltage. PUFs are designed to reproduce a bitstring on demand and therefore eliminate the need for on-chip storage. In this paper, we evaluate the randomness, uniqueness and stability characteristics of a PUF based on metal wire resistance variations in a set of 63 chips fabricated in a 90 nm technology. The stability of the PUF and an on-chip voltage-to-digital converter are evaluated at 9 temperature-voltage corners.