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What is a Hardware Unique Key (HUK)?

A Hardware Unique Key (HUK) is the device-specific Key acting as the “root” of all other secret keys on a particular device. The HUK must be wholly unique to each device and secure to maintain the integrity of the Key chain it supports. Therefore, the HUK is the root that generates multiple secret keys on a device.

HUK must be unique to each device, different between devices, and unreadable by the external world, beyond the device.

Nowadays, there are two ways to provision a HUK; external key injection or internal key generation. However, the external key injection process requires additional costs to perform key provisioning in a secure clean room. In addition, the key injection procedure is vulnerable to secret data disclosure and requires further external secure storage for confidentiality protection.

The creation of HUK through internal key generation with a PUF, by contrast, eliminates those costs associated with external injection and enhances security at the same time. A PUF’s two main characteristics of being random between bits and unique between chips make a PUF the optimal solution for HUK generation. And by confining the entire key generation process within the chip, the manufacturer does not need to worry about key management and other associated costs after wafer processing/chip probing/final testing.  

While PUF values can be directly used as a HUK, a HUK could also be derived from a crypto engine (such as a TRNG), using PUF values for initial seeding. And by using the same type of crypto engine with two different devices that each have their own PUFs, a pre-shared key (PSK) can be created between the two, forming a shared secret that only the two parties would know.

The concept of a PUF providing the root key from which the other private keys of the device may be derived, with or without the help from installed crypto engines.

The above figure shows the concept of a PUF providing the root key from which the other private keys of the device may be derived, with or without the help from installed crypto engines.