Extracting Robust Keys from NAND Flash Physical Unclonable Functions Shijie Jia, Luning Xia, Zhan Wang, Jingqiang Lin, Guozhu Zhang and Yafei Ji Institute.

Extracting Robust Keys from NAND Flash

Physical Unclonable Functions

Shijie Jia, Luning Xia, Zhan Wang, Jingqiang Lin, Guozhu Zhang and Yafei Ji

Institute of Information Engineering, CAS, Beijing, China

ISC 2015

 11th September,2015

1

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion2

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion3

NAND Flash memory is ubiquitous

Smart phones, SD cards, USB memory stick, etc.

The keys used by electronic devices need be protected

contain many confidential information many applications need to identify and authenticate users

Motivation

4

Motivation

Physically uncloable function (PUF)

PUFs are hardware primitives which produce unpredictable and instantiation dependent outcomes.

Noises exist in the PUFs

PUF responses are generally not perfectly reproducible. In general, fuzzy extractors (ECC and hash function )are used

to ensure the reliability of the responses. As the error rate increases, the cost of fuzzy extractor is

rather high for devices with limited hardware resources.

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Motivation

Physically uncloable function (PUF)

PUFs are hardware primitives which produce unpredictable and instantiation dependent outcomes.

Noises exist in the PUFs

PUF responses are generally not perfectly reproducible. In general, fuzzy extractors (ECC and hash function )are used

to ensure the reliability of the responses. As the error rate increases, the cost of fuzzy extractor is

rather high for devices with limited hardware resources.

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We focus on

NAND Flash Physical Unclonable Function (NFPUF) Error reduction techniques

First, we present three methods to extract raw NFPUF numbers.

partial erasure partial programming program disturbance

Second, we introduce two methods to select the cells. bit-map position-map

Motivation

7

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion8

NAND Flash memory basics

Uncertain States of Cells

on account of variations in manufacturing processes, the threshold voltages vary from cell to cell. When the threshold voltage is not shifted sufficiently from the

programmed state to the erased state, and vice versa, the cell will be in an uncertain state. 9

NAND Flash memory basics

Uncertain States of Cells

on account of variations in manufacturing processes, the threshold voltages vary from cell to cell. When the threshold voltage is not shifted sufficiently from the

programmed state to the erased state, and vice versa, the cell will be in an uncertain state. 10

NAND Flash memory basics

Disturbance Related to Array Organization

During the programming operations ,there exists noises between the adjacent cells.

After many repeating operations, it makes the adjacent cells flip

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NAND Flash memory basics

Disturbance Related to Array Organization

During the programming operations ,there exists noises between the adjacent cells.

After many repeating operations, it makes the adjacent cells flip 12

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion13

Partial Erasure

Erase a block

program a page to “0”

perform fixed number (PENum) of

partial erasure operations (Te)

to the selected page

record the number of partial

erasure operations that the

selected cells need to flip

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Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0

0 1 0 0 1 0 0 0

0

1

1 1 0 0 1 0 1 0 2

1 1 0 1 1 1 1 0 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

Partial Erasure

Erase a block

program a page to “0”

perform fixed number (PENum) of

partial erasure operations (Te)

to the selected page

record the number of partial

erasure operations that the

selected cells need to flip

15

Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0

0 1 0 0 1 0 0 0

0

1

1 1 0 0 1 0 1 0 2

1 1 0 1 1 1 1 0 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

Partial Programming

Erase a block

perform fixed number (PPNum) of

partial programming operations (Tp)

to the selected page

record the number of partial

programming operations that the

selected cells need to flip

16

Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

1 0 1 1 0 1 1 1

0

1

0 0 1 1 0 1 0 1 2

0 0 1 0 0 0 0 1 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

Partial Programming

Erase a block

perform fixed number (PPNum) of

partial programming operations (Tp)

to the selected page

record the number of partial

programming operations that the

selected cells need to flip

17

Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

1 0 1 1 0 1 1 1

0

1

0 0 1 1 0 1 0 1 2

0 0 1 0 0 0 0 1 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

Program Disturbance

Erase a block

perform fixed number (PDNum) of

programming operations to the

selected page

record the number of programming

operations that the selected cells

in its physically adjacent page

need to flip

18

Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

1 0 1 1 0 1 1 1

0

1

0 0 1 1 0 1 0 1 2

0 0 1 0 0 0 0 1 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

Program Disturbance

Erase a block

perform fixed number (PDNum) of

programming operations to the

selected page

record the number of programming

operations that the selected cells

in its physically adjacent page

need to flip

19

Robust key generation ----Extracting Raw NFPUF Numbers

1 1 1 1 1 1 1 1

1 0 1 1 0 1 1 1

0

1

0 0 1 1 0 1 0 1 2

0 0 1 0 0 0 0 1 3Raw NFPUF Numbers: 2 1 4 3 1 3 2 4

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Robust key generation ----Extracting Robust Keys from Raw NFPUF Numbers

Fluctuations of raw NFPUF numbers from four cells of a MLC type NAND Flash memory chip

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Robust key generation ----Extracting Robust Keys from Raw NFPUF Numbers

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Robust key generation ----Extracting Robust Keys from Raw NFPUF Numbers

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Robust key generation ----Extracting Robust Keys from Raw NFPUF Numbers

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion24

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Experiments

Setup Platform: a Flash test board with an ARM Cortex-M3 controller

Tested NAND Flash memory chips

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Evaluation

The security and reliability of the keys

speed (for performance)

reproducibility (for reliability)

uniqueness (for security)

randomness (for high-entropy)

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Evaluation ——speed

The average throughput of the raw NFPUF numbers (Kbits/second)

Parameters setting of the raw NFPUF numbers extraction methods

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Evaluation ——speed

The average throughput of the raw NFPUF numbers (Kbits/second)

Parameters setting of the raw NFPUF numbers extraction methods

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Evaluation ——Reproducibility (Intra-chip variations)

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Evaluation ——Uniqueness (Inter-chip variations)

The inter-chip variations of the three proposed extraction methods

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Evaluation ——Randomness

The percentage of bit “1” with temperature changes

Outline

Motivation

NAND Flash memory basics

Robust key generation

Experiments and Evaluation

Conclusion32

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First, we proposed three methods to extract raw NFPUF numbers from NAND Flash memory chips.

Second, we utilized the bit-map or position-map method to select the cells with the most reliable relationship of the size between raw NFPUF numbers.

At last, we evaluated the primary characteristics of the key under various temperature and aging conditions.

Our key generator eschews the costly ECC overheads to generate robust and error-free keys.

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Thank you !