Initial SRAM State as a Fingerprint and Source of True Random Numbers for RFID Tags

RFID applications create a need for low-cost security and privacy in potentially hostile environments. Our measurements show that initialization of SRAM produces a physical fingerprint. We propose a system of Fingerprint Extraction and Random Numbers in SRAM (FERNS) that harvests static identity and randomness from existing volatile CMOS storage. The identity results from manufacture-time physically random device threshold mismatch, and the random numbers result from run-time physically random noise. We use experimental data from virtual tags, microcontroller memory, and the WISP UHF RFID tag to validate the principles behind FERNS. We show that a 256byte SRAM can be used to identify circuits among a population of 160 virtual tags, and can potentially produce 128bit random numbers capable of passing cryptographic statistical tests.