Extracting Robust Keys from NAND Flash Physical Unclonable Functions

Abstract

Physical unclonable functions PUFs are innovative primitives to extract secret keys from the unique submicron structure of integrated circuits. PUFs avoid storing the secret key in the nonvolatile memory directly, providing interesting advantages such as physical unclonability and tamper resistance. In general, Error-Correcting Codes ECC are used to ensure the reliability of the response bits. However, the ECC techniques have significant power, delay overheads and are subject to information leakage. In this paper, we introduce a PUF-based key generator for NAND Flash memory chips, while requiring no extra custom hardware circuits. First, we present three methods to extract raw PUF output numbers from NAND Flash memory chips, namely partial erasure, partial programming and program disturbance, which are all based on the NAND Flash Physical Unclonable Function NFPUF. Second, we use a bit-map or a position-map to select the cells with the most reliable relationship of the size between raw NFPUF output numbers. Only the selected cells are used for key generation. Finally, we describe the practical implementations with multiple off-the-shelf NAND Flash memory chips, and evaluate the reliability and security of the proposed key generator. Experimental results show that our NFPUF based key generator can generate a cryptographically secure 128-bit key with a failure rate $$<10^{-6}$$<10-6 in 93.83i?źms.