As system security demands continue to evolve, Physically Unclonable Functions (PUFs) are a promising solution for secure storage on Integrated Circuits (ICs). SRAM PUFs are among the most popular types of PUFs, since they require no additional circuitry and can be implemented with on-die memories such as caches and data memory that are readily available on both ASICs and FPGAs. This work demonstrates that SRAM PUFs are not well suited as PUFs, as they do not meet several requirements that constitute an ideal PUF. The compact nature of SRAM, standard interconnects and resiliency to environmental effects make SRAM PUFs particularly easy to clone. We consider several ways in which SRAM PUFs can be characterized and demonstrate a Focused Ion Beam circuit edit with which we were able to produce a physical clone of our Proof-of-Concept SRAM PUF implementation. As a result of the circuit edit, when challenged, the physical clone produced an identical physical response to the original device. To the best of our knowledge, this is the first work in which a physical clone of a Physically Unclonable Function was produced.
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