Physical unclonable function

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Physical unclonable functions (also physically unclonable functions) or PUF for short are hardware structures in a semiconductor that enable the semiconductor to be uniquely identified or to secure keys for cryptographic processes . Semiconductors , referred to below as systems, can be complete electronic chip cards or microprocessors , in particular those with a hardware security module ( HSM ) for cryptographic tasks. Like a fingerprint, the PUF is an individual feature that is linked to a physical object . PUFs are classified as a physical primitive (based on a cryptographic primitive ).

history

Initial tests with PUFs consisted of a disc made of a translucent material, into the melt of which reflective particles had already been mixed. The disc was illuminated and sensors recorded the reflected light. The manufacturing process and the structure of the light source and sensors were always the same, but each pane provided the sensors with a different image. The basic principle could later be transferred to semiconductor circuits.

Applications

Possible applications are seen in the following areas:

  • In cryptography for producing an AES key
  • Clear identification of goods in order to identify counterfeit products ( product piracy )
  • Authentication in the challenge-response procedure
  • Authentication certificates for mobile devices

Working principle

The PUFs are based on the fact that due to the smallest fluctuations in the production process, certain assemblies show an individual behavior, although the production process should result in absolutely identical parts. Systems with a PUF unit are therefore all manufactured in absolutely the same production process and - at least with regard to the PUF - do not experience any individual processing.

The PUF unit in the hardware contains areas that process an input (challenge) with known methods (function) and generate a return value (response) from it. Part of this challenge-response procedure is the PUF, which, through its behavior, causes a change in the return value that is clear for the component.

In addition, the challenge-response method can be secured to the extent that the input and return value cannot be used to infer the behavior of the PUF , for example by using cryptographic hashes .

There are a number of possibilities in hardware, some of which are outlined below.

SRAM PUF

After being switched on, a register of an SRAM initially has a random assignment of the bits with 0 or 1. For the function as a PUF it is crucial that the same (or mostly the same) assignment with 0/1 is present every time it is switched on, that this assignment however differs from system to system.

Ring oscillator PUF

In a ring oscillator PUF, various elements are fed back with a time delay and, for example, applied to an input of a multiplexer . The duration of the oscillation again depends on small production tolerances and is individual for the PUF. The return value is obtained from the comparison of oscillator frequencies or from reading out a multiplexer at a specific point in time. By making a clever comparison, fluctuations in the ambient conditions can advantageously be eliminated.

Properties required for security applications

Various properties are required so that PUFs can be used in cryptographic applications:

  • Robustness means that when reading out external influences at the moment of reading (temperature, voltage, etc.) change only so little that with reliable measures for error correction the response always delivers the same behavior or result to a challenge. Error correction methods, for example, are used for this purpose.
  • Non-copying prevents, for example, a blank of a chip card from being made into a clone of another chip card. The PUF can no longer be changed and with a suitable design of the production process the probability of two similarly produced chip cards disappears.
  • Unpredictability means that the return (response) cannot be predicted from the input (challenge). This results in the expectation of a high entropy of the response, even if the ambient conditions change. After a cooling of the semiconductor (reduction of the thermal entropy ), a reduction of the informational entropy (according to Claude Shannon ) should not follow.
  • Tamper evidence means that the PUF reacts to invasive manipulations on the semiconductor and thereby reveals these or the response is no longer accepted.

Other procedures and advantages

PUFs fulfill the same function as semiconductors, which are individualized in a non-volatile memory after production via the targeted burning of some semiconductor components ( fuse bit ) or via a key stored in software.

The advantage of the PUF lies in the low costs, since at the end of the production process (as part of the functional test) the PUF only needs to be read out in order to store the key or a certain number of challenges and responses in a database , so that the semiconductor can be found at any time later to identify or authenticate via the PUF.

In addition, some simple attacks on the system can be ruled out. A change in the PUF means a manipulation of the microscopic components on the circuit, whereupon some PUF types change their properties irreversibly and noticeably.

See also

literature

  • Dr. André Schaller: Chip fingerprint . In: c't . No. 26/2018 . Heise-Verlag, 2018, ISSN  0724-8679 , p. 158-162 .
  • Shahin Tajik: On the Physical Security of Physically Unclonable Functions . 1st edition. Springer International Publishing AG, Cham (CH) 2019, ISBN 978-3-319-75819-0 (English, published in mid-2018, year of publication according to imprint 2019).
  • Ioannis Papakonstantinou, Nicolas Sklavos: Computer and Network Security Essentials . Ed .: Kevin Daimi. Springer International Publishing, Cham (CH) 2018, ISBN 978-3-319-58423-2 , 24: Physical Unclonable Functions (PUFs) Design Technologies: Advantages and Trade Offs (English).
  • Basel Halak: Physically Unclonable Functions - From Basic Design Principles to Advanced Hardware Security Applications . 1st edition. Springer International Publishing AG, 2018, ISBN 978-3-319-76803-8 (English).
  • Fatemeh Ganji: On the Learnability of Physically Unclonable Functions . 1st edition. Springer International Publishing AG, 2018, ISBN 978-3-319-76716-1 (English).
  • Roel Maes: Physically Unclonable Functions - Constructions, Properties and Applications . Springer-Verlag, Berlin, Heidelberg 2013, ISBN 978-3-642-41394-0 (English). Based on the author's dissertation.
  • Matthias Hiller, Michael Pehl, Georg Sigl: Error correction method for secure key generation with physical unclonable functions . Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, April 2015, ISSN  1614-0702 , pp. 229–233 .
  • Swarup Bhunia; Sandip Ray; Susmita Sur-Kolay (Ed.): Fundamentals of IP and SoC Security . Springer International Publishing, 2017, ISBN 978-3-319-50055-3 (English).
    • Chapter 6: PUF-Based Authentication (Jim Plusquellic)
    • Chapter 8: Physical Unclonable Functions and Intellectual Property Protection Techniques (Ramesh Karri, Ozgur Sinanoglu, Jeyavijayan Rajendran)
  • Dominik Merli, Georg Sigl: Physical Unclonable Functions - CMOS implementations and hardware attacks . Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, December 2012, ISSN  1614-0702 , pp. 876–880 .

Web links

Individual evidence

  1. ↑ Roel Maes: Physically Unclonable Functions - Constructions, Properties and Applications . 1st edition. Springer-Verlag, Berlin, Heidelberg 2013, ISBN 978-3-642-41394-0 , section 2.3.1 (English).
  2. ↑ Roel Maes: Physically Unclonable Functions - Constructions, Properties and Applications . 1st edition. Springer-Verlag, Berlin, Heidelberg 2013, ISBN 978-3-642-41394-0 , section 2.1.1 (English).
  3. ↑ Swarup Bhunia; Sandip Ray; Susmita Sur-Kolay (Ed.): Fundamentals of IP and SoC Security . Springer International Publishing, 2017, ISBN 978-3-319-50055-3 , Section 6.1 (English).
  4. ↑ Rainer Plaga: What are "Physical Unclonable Functions" and what are their goals? Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, April 2015, ISSN  1614-0702 , Section 1. Introduction, pp. 219–223 .
  5. ↑ UMABASA project according to Rainer Plaga: What are "Physical Unclonable Functions" and what are their goals? Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, April 2015, ISSN  1614-0702 , pp. 219–223, system according to Figure 3 .
  6. ↑ Patent CN000204291000 : Advanced encryption standard (AES) secret key generation structure based on physical unclonable function (PUF) of latch-type voltage sensitive amplifier. Filed December 15 , published April 22 , applicant: UNIV TIANJIN, inventor: HE JIAJI; SHU QINGRAN; YANG SONG; ZHAO YIQIANG. ‌
  7. ↑ Patent EU000002911335 : Physically unclonable, function-based anti-counterfeiting system. Registered on February 21, 2014 , published on August 26, 2015 , applicant: European Union represented by the European Commiss, BE, inventors: Baldini Gianmarco (IT), Nai Fovino Igor (IT), Sanchez Martin Jose Ignacio (IT). ‌
  8. ↑ Patent EP000001941652 : Integrated Physical Unclonable Function (Puf) with Combined Sensor and Display. Filed October 2 , published September 25 , Applicant: Koninkl Philips Electronics NV, NL, Inventor: Akkermans Antonius Hermanus Maria, NL; Ophey Willem Gerard, NL; Skoric Boris, NL; Tuyls Pim Theo, NL. ‌
  9. ↑ Patent DE102013202001 : Method for providing a mobile device with an authentication certificate . Registered on February 7, 2013 , published on August 10, 2017 , applicant: Bundesdruckerei GmbH, 10969, Berlin, DE; Fraunhofer Society for the Promotion of Applied Research e. V., 80686, Munich, DE, inventor: Dietrich, Frank, 12437, Berlin, DE; Eckert, Claudia, Prof. Dr., 85748, Garching, DE; Krauss, Christoph, Dr., 85748, Garching, DE; Paeschke, Manfred, Dr., 16348, Wandlitz, DE; Stumpf, Frederic, Dr., 85748, Garching, DE. ‌
  10. ↑ Rainer Plaga: What are "Physical Unclonable Functions" and what are their goals? Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, April 2015, ISSN  1614-0702 , 2.1 PUF circuit, pp. 219–223 .
  11. ↑ Stefan Katzenbeisser, André Schaller: Physical Unclonable Functions - Security Properties and Applications . Ed .: DuD - data protection and data security. Springer Gabler / Springer Fachmedien, December 2012, ISSN  1614-0702 , pp. 881–885 .
  12. ↑ Patent EP10012987 : Error correction for physically unclonable functions. Filed April 14 , published October 5 , applicant: MASSACHUSETTS INST TECHNOLOGY, US, inventor: CLARKE DWAINE, BB; DEVADAS SRINIVAS, US; GASSEND BLAISE, US. ‌