# US 10,771,246 B2 · Systems and methods for stable physically unclonable functions

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- Number: US 10,771,246 B2
- Document ID: US10771246B2
- Status: Granted
- Kind: B2
- Application number: 15/264,872
- Filed: 2016-09-14
- Published: 2018-06-07
- Granted: 2020-09-08
- Earliest claimed: 2015-10-13
- Assignees: Maxim Integrated Products, Inc.
- Applicants: Maxim Integrated Products, Inc.
- Inventors: Sung Ung Kwak
- Web page: https://patentgrep.com/patent/US10771246B2

## CPC

- G09C 1/00: Apparatus or methods whereby a given sequence of signs, e.g. an intelligible text, is transformed into an unintelligible sequence of signs by transposing the signs or groups of signs or by replacing them by others according to a predetermined system (cryptographic typewriters G09C3/00)
- H04L 9/0869: {involving random numbers or seeds}
- H04L 9/0866: {involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics}
- H04L 9/3278: {using physically unclonable functions [PUF]}
- G09C: CIPHERING OR DECIPHERING APPARATUS FOR CRYPTOGRAPHIC OR OTHER PURPOSES INVOLVING THE NEED FOR SECRECY
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

Systems and methods allow to take advantage of the natural statistical variation of physical properties in a semiconductor device in order to create truly random, repeatable, and hard to detect cryptographic bits. This may be accomplished by recursively pairing mismatch values of Physically Unclonable Functions (PUF) elements so as to ensure that generated PUF key bits remain insensitive to environmental errors, without affecting the utilization rate of available PUF elements. The pairing process may be applied to any given hardware to generate more stable PUF bit sequences that provide a higher margin of error, increase the number of bits for a given margin of error, or any combination thereof.

## Claims

### Claim 1

An apparatus to generate Physically Unclonable Function (PUF) key bits, the apparatus comprising:
a sensing element configured to detect mismatches in physical characteristics between PUF elements and to output signals associated with the mismatches;
a data converter coupled to the sense element, the data converter converts the output signals into mismatch data being associated with a first distribution;
a sorting module coupled to receive the mismatch data from the data converter, the selection module sorts at least some of the mismatch data by magnitude and polarity to generate sorted mismatch values;
a paring module to pair at least two sorted mismatch values to generate a paired value that is associated with a second distribution; and
a sequence generator that generates a bit sequence using the paired value, wherein the paired value is generated by combining a first sorted mismatch value associated with a large positive number with a second sorted mismatch value associated with a relatively smaller negative number, the paired value.

### Claim 2 (depends on 1)

The apparatus according to claim 1, wherein the paring module pairs sorted mismatch values to generate a first paired value that is associated with a second distribution, a second paired value that is associated with a third distribution, and uses the first and second paired values to generate a fourth distribution.

### Claim 3 (depends on 1)

The apparatus according to claim 1, further comprising a switching module to switch an order of at least some of the sorted mismatch values to assign to the paired value a polarity that represents one of a zero and a 1.

### Claim 4 (depends on 1)

The apparatus according to claim 1, wherein a difference between two paired values is equal to or exceeds predetermined value.

### Claim 5 (depends on 1)

The apparatus according to claim 1, wherein the plurality of PUF elements are located on independent arrays.

### Claim 6 (depends on 5)

The apparatus according to claim 5, wherein the first sorted mismatch value is associated with a first array and the second sorted mismatch value is associated with a second array.

### Claim 7 (depends on 1)

The apparatus according to claim 1, wherein the mismatch data is stored in a first memory and overwritten when a second memory stores the paired data.

### Claim 8 (depends on 7)

The apparatus according to claim 7, wherein the first memory comprises a register that receives the mismatch data.

### Claim 9 (depends on 1)

The apparatus according to claim 1, wherein at least one of the sorting module and the paring module is implemented in software.

### Claim 10 (depends on 1)

The apparatus according to claim 1, wherein the sensing element detects mismatches at a start-up condition.

### Claim 11 (depends on 1)

The apparatus according to claim 1, wherein the data converter digitizes the mismatch data prior to sorting a pairing.

### Claim 12 (depends on 9)

The apparatus according to claim 9, wherein switching module comprises a summation module that subtracts the switched sorted mismatch values based on the output signals.

### Claim 13

A method of reliably reproducing randomly generated unique bit sequences, the method comprising:
determining mismatch data related to at least one physical characteristic of a plurality of Physically Unclonable Function (PUF) elements, the mismatch data being associated with a first distribution;
sorting at least some of the mismatch data by magnitude and polarity to generate sorted mismatch values;
pairing sorted mismatch values to generate a paired value that is associated with a second distribution; and
generating a bit sequence using the paired value, wherein the paired value is generated by combining a first sorted mismatch value associated with a large positive number with a second sorted mismatch value associated with a relatively smaller negative number, the paired value.

### Claim 14 (depends on 13)

The method according to claim 13, wherein the first sorted mismatch value is associated with a first array and the second sorted mismatch value is associated with a second array, the first and second array being independent from each other.

### Claim 15 (depends on 13)

The method according to claim 13, further comprising switching an order of at least some of the sorted mismatch values to assign a polarity to the paired value, the polarity represents one of a zero and a 1.

### Claim 16 (depends on 13)

The method according to claim 13, wherein the first distribution is a normal distribution and the second distribution is a bi-modal distribution.

### Claim 17

A method of reliably reproducing randomly generated unique bit sequences, the method comprising:
determining mismatch data related to at least one physical characteristic of a plurality of Physically Unclonable Function (PUF) elements, the mismatch data being associated with a first distribution;
sorting at least some of the mismatch data by magnitude and polarity to generate sorted mismatch values;
pairing sorted mismatch values to generate a first paired value that is associated with a second distribution and a second paired value that is associated with a third distribution;
pairing the first and second paired values to generate a fourth distribution; and
generating a bit sequence using the first and second paired values.

### Claim 18 (depends on 17)

The method according to claim 17, wherein a first separation of the fourth distribution is at least twice as large as a second separation of the first distribution.