A non-volatile memory based physically unclonable function without helper data

Abstract

Stability across environmental variations such as temperature and voltage, is critically important for Physically Unclonable Functions (PUFs). Nearly all existing PUF systems to date need a mechanism to deal with “bit flips” when exact regeneration of the bitstring is required, e.g., for cryptographic applications. Error correction (ECC) and error avoidance schemes have been proposed but both of these require helper data to be stored for the regeneration process. Unfortunately, helper data adds time and area overhead to the PUF system and provides opportunities for adversaries to reverse engineer the secret bitstring. In this paper, we propose a non-volatile memory-based (NVM) PUF that is able to avoid bit flips without requiring any type of helper data. A voltage-to-digital converter technique is described for digitizing the analog entropy source and a robust median-finding algorithm is proposed as the reprograming strategy. Analysis on published experimental data is presented to demonstrate the practicability of our proposed strategy. We describe the technique in the context of emerging nano-devices, in particular, resistive random access memory (Memristor) cells, but the methodology is applicable to any type of NVM including Flash.