Browse Prior Art Database

Physically Unclonable Function Enhancement to Guarantee Repeatable Behavior

IP.com Disclosure Number: IPCOM000199382D
Publication Date: 2010-Aug-31
Document File: 4 page(s) / 175K

Publishing Venue

The IP.com Prior Art Database

Abstract

Described is a method to connect the output of the physically unclonable function (PUF) circuit into a comparator that can perform the PUF output comparison multiple times. If the comparison is always the same result, then this circuit is tagged as repeatable and used to implement the PUF function. If the comparator gives inconsistent results, then that particular PUF circuit is tagged as unrepeatable and not used. The output is then optionally run through a compression circuit to filter only the repeatable bits to the output.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 58% of the total text.

Page 1 of 4

Ȉ ˇ

Ȉ ˇ Ȉ ˇ

For security reasons, it is desirable to implement physically unclonable functions (PUF) in integrated circuits. This enables one to implement different functions or security keys in two chips where the differences in the two chips are physically undetectable. Physically unclonable functions can be used to implement challenge-response authentication. There are many ways to do this. One example is to power up an SRAM and hope that the data that is in the SRAM cells is consistent after every power-up. However, this method is very unreliable because random process variation will not make the SRAM cells strongly favor one state or another. This means that variation in temperature and voltage can make the SRAM initialize to different states [1, 2].

    Most parameter variation in semiconductor elements follows a Gaussian distribution. For a Gaussian distribution, 68.2% of the element variation is within 1 standard deviation of the mean (see Figure 1).

˄ ˙

    Examples are linewidth, gate oxide thickness, alignment, threshold voltage, and others. When designing PUF circuits to take advantage of this natural variation, the Gaussian nature of most variation will result in small amounts of variation between most physical elements. This can cause unrepeatable and inconsistent function which is undesirable in PUF circuits. This invention will result in filtering out the unrepeatable and inconsistent PUF circuits and allow only the ones with large natural variation to be used resulting in repeatable and consistent PUF circuit outputs.

    The main idea of this invention is to connect the output of the PUF circuit into a comparator that can perform the PUF output comparison multiple times. If the comparison is always the same result, then this circuit is tagged as repeatable and used to implement the PUF function. If the comparator gives inconsistent results, then that particular PUF circuit is tagged as unrepeatable and not used. Figure 2 is a circuit that implements the described function.

1

[This page contains 1 picture or other non-text object]

Page 2 of 4

˄ ˝

Sequence of operation:
1: 1st Read PUF of circuit (0 or 1 is read) into Latch New
2: 2nd Read PUF of circuit (0 or 1 is read), Latch New is transferred to Latch Previous and 2nd read is captured in Latch New
3: Reset pulses from 0 to 1 to 0. This precharges Repeatable

_b

to 1 when Reset goes to a 1 and

evaluates the XOR of Mux

_data

and New

_data

when Reset goes back to 0. If New

_data

and

Previous

_data

are the same, then Same

_b

is a 0 and Repeatable

_b

and REPEATABLE stay at a


1. If New

_data

and Previous

_...