Enhanced TERO-PUF Implementations and Characterization on FPGAs (Abstract Only)

Physical unclonable functions (PUF) are a promising approach in design for trust and security. A PUF derives a unique identifier using physical characteristics of different dies containing an identical circuit, so it can be used to authenticate chips and for identification. The transient effect ring oscillator (TERO) PUF is based on the extraction of entropy due to process variations by comparing TERO cells characteristics. The TERO cell is designed and implemented with a symmetric structure that requires special selection of the gates used and the delays of all connections inside the cell. Implementing this cell in FPGAs is challenging because the structure of FPGAs does not automatically allow designers to choose connections between elements. However, by manually specifying constraints and using specific features of the target FPGA family, the symmetry of the TERO cell can be established and reproduced in larger designs. In this work, the design of the TERO cell is described for two different FGPA technologies (45nm Xilinx Spartan 6 and 28nm Altera Cyclone V). The statistical characterization of the TERO-PUF with the two targeted FPGAs has resulted in a uniqueness of 48.46% with Spartan 6 and 47.62% with Cyclone V. The result for the steadiness is 2.63% with Spartan 6 and 1.8% with Cyclone V. These results are close to the results obtained by several works that use ring oscillator RO-PUF which are considered the best candidate for PUF implementation on FPGAs. However, TERO-PUF is less sensitive to electromagnetic analysis than RO-PUF. Additionally, unlike RO-PUF, TERO-PUF is able to generate multiple bits per challenge (from one to three) and we have shown during the statistical characterization that the TERO-PUF provides from 0.85 to 1 bits of entropy per response bit. As a conclusion, our work clearly shows that TERO-PUF is an serious alternative to RO-PUF for PUF implementation on FPGAs with strong statistical characteristics and more security than RO-PUF.