1. Field of the Invention
The present invention relates to electronic security systems and, more specifically, to a physically unclonable function for device security.
2. Description of the Related Art
Device authentication is a critical challenge in the area of electronics security. With the advent of cloud computing, Internet of Things (IOTs), and proliferation of smart computing devices (smart phones, tablets, smart TVs, game-consoles, e-readers etc.), the security of smart devices has become a major concern as a majority of these smart devices are operated in insecure environment. Until recently, security concerns were mainly handled in software. However, hardware enforced security solutions can offer better protection than software only solutions.
Physically unclonable functions (PUFs) are hardware enforced security devices that are virtually impossible to reverse engineer. Physically Unclonable Functions (PUFs) have been proposed as a way of implementing security in modern ICs. PUFs are hardware designs that exploit the randomness in silicon manufacturing processes to create IC-specific signatures for silicon authentication.
Security for Systems-on-Chips (SoCs) has emerged as a major research topic in the last decade. A key thrust has been to find ways to detect insertion of malicious ICs into system designs by third-party manufacturing sources. To this end PUFs have been proposed as a mechanism for authenticating ICs prior to insertion in system level designs and for hardware key.
A PUF can be predicated on any physical parameter that varies randomly during silicon manufacturing. The most common physical parameters that have been exploited to build PUFs are as follows: 1) delay of an inverter (Arbiter, Ring Oscillator PUF), 2) SRAM start-up behavior (SRAM PUF), 3) glitch in digital circuitry (Glitch PUF), 4) Sub-threshold transistor current, 5) matrix material doped with random dielectric particles (coating PUF), 6) cross coupled circuit elements (Butterfly PUF), 7) power distribution system equivalent resistance variation. Though the above list is not exhaustive, it broadly classifies the sources of variations in CMOS manufacturing process that are used to design PUFs.
One way to determine the quality of a PUF is by virtue of the number of challenge-response pairs (CRPs) that can be realized from the PUF design. Weak PUFs are those that have small numbers of CRPs while strong PUFs are those that have large numbers of CRPs. Ideally, the number of CRPs for a strong PUF grows exponentially with the size of the PUF. Some PUFs may be reverse engineered due by careful analysis of their structures.
The use of smart cards at present is ubiquitous. From banking and telecommunication applications, it has now forayed into electronic passports, electronic IDs, anti-counterfeiting devices, smart grid applications and many more. Storing an authentication key inside smart card IC, makes smart cards and NFC enabled communication (electronic wallet) vulnerable to security threats. Generating keys on the fly by a PUF is heavily used in today's smart card and radio frequency identification (RFID) tag applications. In the future PUF will likely also be used to protect external memory. With the advance of the Internet of Things (IOTs) and cloud computing, the need for hardware device authentication and data encrypting/decrypting is increasing rapidly. PUFs are an excellent fit for generating and hiding the authentication signature or cryptographic key for IOT and cloud computing. PUFs can also be used in software licensing, replacing hardware dongles and the like.
Physical one way functions (POWF) and physical random function were precursors to PUFs. Operation of PUFs is predicated on any physical parameter that varies randomly in IC manufacturing. The reported physical parameters that have been exploited to build PUFs are as follows: 1) delay of logic paths (arbiter, ring oscillator PUF), 2) SRAM start-up behavior (SRAM PUF), 3) glitches in digital circuitry (Glitch PUF), 4) Sub-threshold transistor current fluctuation due to threshold voltage variation, 5) matrix material doped with random dielectric particles (coating PUF), 6) cross coupled circuit elements (Butterfly PUF), 7) power distribution system equivalent resistance variation. Due to random dopant fluctuation (RDF), threshold voltage of a transistor shows spatially uncorrelated variability. In the sub-threshold region of operation current and threshold voltage of a transistor are exponentially related (random variability is exponentially multiplied).
Existing PUF designs suffer from several disadvantages, including their relatively low uniqueness of the system and their limited number of challenge/response pairs.
Therefore, there is a need for a PUF that is highly unique and that has a high number of challenge/response pairs.