Noise-Resilient SRAM Physically Unclonable Function Design for Security

Physically Unclonable Function (PUF) circuits are designed to provide part-specific responses that are random across different copies of the circuit by exploiting the unavoidable process variations in nanometer scale fabrication. This property can be used as an important building block in security and cryptographic applications including key generation and challenge-response authentication. A major problem, however, is to ensure PUF response stability and reliability in the presence of circuit and environmental noise. SRAM based PUFs are most promising in this regard but still require extensive output error correction because the response of many cells in the memory array is not consistent. Unfortunately, all such "weak" cells cannot be determined in advance to allow their unstable responses to be masked out. In this paper we present a new SRAM PUF design that allows all the unstable weak cells to be reliably identified over the full range of operating conditions including temperature, electrical noise, and aging. By using the remaining "strong" cells, each instantiation of our SRAM PUF provides the same consistent and repeatable response every time it is challenged, without any need for error correction. Experiments reported here show that relatively few (of the order of 10%) SRAM PUF cells are truly stable in the presence of realistic circuit noise; in addition to the expected noise level, this number also depends on the random variability in the manufacturing process. Our simulation results show that the new SRAM PUF can be designed to maintain good robustness against any level of expect circuit and environmental noise, and is resilient to aging.