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A Physical Unclonable Function (PUF) can be any physical object that, for a given input and condition (challenge), provides a physically defined ¡°digital fingerprint¡± output (response) that serves as a unique identifier, most often for a semiconductor device such as a microprocessor.
Our focus here is on the best-known subset of PUFs, which are silicon PUFs. As the name suggests, this type of PUF gets its instance-specific measurements from silicon, meaning these PUFs are part of an integrated circuit (IC).
Due to deep submicron manufacturing process variations, every transistor in an IC has slightly different physical properties. These variations lead to small but measurable differences in electronic properties, such as transistor threshold voltages and gain factor. Since these process variations are not fully controllable during manufacturing, these physical device properties cannot be copied or cloned.
By utilizing these inherent variations, PUFs are very valuable for use as a unique identifier for any given IC. They do this through circuitry within the IC that converts the tiny variations into a digital pattern of 0s and 1s, which is unique for that specific chip and is repeatable over time. This pattern is a ¡°silicon fingerprint,¡± comparable to its human biometric counterpart..
Utilizing a PUF for security and identification purposes is done through very specific algorithms that turn the silicon fingerprint into a cryptographic key. This key is unique for that individual chip and is used as its root key. The root key is reliably reconstructed from the PUF whenever it is needed by the system, without a need for storing the key in any form of memory. When the device is powered off, no secret key is present in any form of memory; in effect, the root key is ¡°invisible¡± to attackers, which makes the storage of keys with PUFs very secure.
So, PUF implementations require processing algorithms to turn the silicon fingerprint into a cryptographic root key. This is because the silicon fingerprint will be slightly noisy between different measurements, as in addition to innate process variations, the electronic properties will also be influenced by ambient conditions, such as temperature and power supply. Hence, a good PUF implementation needs to turn this noisy fingerprint into a fully stable and fully random string of 0s and 1s, for it to qualify as a cryptographic key. For this purpose, most PUF implementations use two processes:
The benefits of using PUF technology are:
Usage of this technology varies from PUFs for IoT security, where the technology¡¯s low cost and flexible implementation offer great benefits, all the way to PUFs for Aerospace & Government, proving that the technology is capable of delivering the highest level of security.
Synopsys offers industry-leading PUF IP solutions, including:
Enabling Authentication with PUF-based Security
Certified PUF IP provides SRAM-based device security with unique cryptographic keys.
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