Analysis and Enhancement of Ring Oscillators Based Physical Unclonable Functions in FPGAs

Abstract

International audienceThe paper analyzes and proposes some enhancements of Ring Oscillator based Physical Unclonable Functions (PUFs) that are used to extract a unique signature of an integrated circuit in order to be used for device authentication purposes and/or key generation. We analyze in more details the concept developed by Suh et al. in 2007. Contrary to what authors claim, we show that the designer of the Ring Oscillator PUFs implemented in FPGAs needs precise control of placement and routing in order to get unique responses and repeatable results for each individual device, especially when the rest of the reconfigurable device should remain upgradable. One main disadvantage of the original design is its high power consumption. We propose a simple improvement that reduces the consumption of the PUF published by Suh et al. by up to 96.6%. Last but not least, we point out that ring oscillators significantly influence one another and can even be locked. This questions the reliability of the PUF and should be taken into account during the design

Implementation of Ring-Oscillators-Based Physical Unclonable Functions with Independent Bits in the Response

“…In comparison to our previous results in [15], intrachip variations were underestimated because the mean was computed on a 256-bit response ignoring dependency between bits. According to our method, we identify 31 bits of information in the response.…”

“…Thus the intrachip variation must be computed on these bits. This explains why the ratio intrachip variation in [15] intrachip variation in this paper ≈ 256 31 .…”

ASIC implementation of a hardware‐embedded physical unclonable function

“…Proposed entropy sources include variations in transistor threshold voltages [2], in propagation delays in inverter chains and ROs [1,[3][4][5][6][7][8][9][10][11], in power up patterns in static random-access memories (SRAMs) [12], in leakage current [13], in metal resistance [14], in non-volatile memory memory [15] and many others. The hardware-embedded delay PUF (HELP) that we investigate in this paper leverages path stability characteristics and within-die delay variations in core logic macros.…”