Build-in self test (BIST) of PUF (Physical Unclonable Function) is researched. Generally output data is compared with the expected data in test. However, there is no expected data for PUF. Furthermore, don’t read the PUF output data to outside the chip is preferred for higher security. Thus BIST is very important for PUF.

 In PUF BIST, following three items must be tested: a) Randomness (randomness of each output data), b) Reproducibility (output data is always same), c) Uniqueness (output data differs each other). In this year we focused to a) and b).

a) Randomness test: Our SRAM PUFs are tested by NIST SP800-22 randomness test and autocorrelation Rxx(j) is also evaluated. The PUFs passed all 13 NIST test items except for 2 items where data length was not long enough. Distribution of Rxx(j) was also within reasonable range.

b) Reproducibility test: In order to accelerate the degradation of reproducibility by temperature change or long time use, our strategy is to add disturb during data evaluation. As a first step, SRAM PUF with pair VSS terminals are designed. By adding small bias to the terminals, it has been confirmed that this structure work well for the acceleration.