Physically Unclonable Function (PUF) in CMVP Modules (G31a)
Physically Unclonable Functions (known as PUFs) are devices that can be integrated in hardware chips. They allow to rebuild a private/secret key or a public identifier, which is termed immutable. Their security requirements have been formalized in an internationally approved standard, namely ISO/IEC 20897. By design, PUFs contribute to reduce the attack surface on the keys as those vanish when the chip is not powered.
PUFs have received a lot of the attention by the industry and are now widespread. There is a variety of PUF architectures adapted to different use-cases: reliability (for automotive / space / nuclear), fast rebuilding time, low hardware footprint / low energy (for IoTs), etc. The question arises about the certifiability of cryptographic modules relying on PUF for the implementation of security functions.
In this presentation, the speaker will explain how CMVP scheme is already suitable for integrating PUFs. The speaker will first recall that the PUF parameters respectively consist of CSP (secret responses in the secret key setup) and protected PSP (the helper data needed to enhance the reliability of the CSPs).
Second, the speaker will present some use-cases. The first one is the secure boot protected by a master key spawned by a PUF. It is for instance possible to rebuild keys of different natures (symmetric or asymmeric) leveraging a KDF, and use them in approved digital signature or keyed message authentication code-based integrity test. The PUF key itself can be zeroized: either temporarily, for this powerup session, and even permanently, provided the chip has some OTP used to indicate whether a key is valid or revoked (this option works for those chips which have multiple PUF instances).
The speaker will also describe compliance requirements, such as self-tests, resistance to non-invasive security (in particular the protection of the key bits values when generated), and so-called “mitigation of other attacks”. This aspect is important when the PUF is leveraged in a secure-boot process: indeed, the boot sequence is known to be especially vulnerable because the device then is not yet fully functional, hence challenges to protect the key bits values in confidentiality (master key use-case) and in integrity (device identity use-case).