Key provisioning

Notes

Often done at final test or at a trusted OSAT; PUF-derived keys avoid the need to handle secrets outside the die at all.

Overview

Key provisioning is the process of giving each chip or device its own cryptographic keys, certificates and identity, and locking them into protected storage, usually during manufacturing and sometimes later in the field. It is what lets a device prove who it is, decrypt its own firmware and verify that updates are genuine. The aim is that no secret key is ever exposed in plain form to people, test equipment or factories that do not need to see it.

How it works

There are two broad approaches. In the first, the chip creates its own secret: a hardware random number generator produces a key on the device, which writes it into one-time programmable memory such as eFuses and then sets protection bits so software can no longer read it. Espressif's ESP32, for example, does this by default for its flash encryption key. In the second, keys or certificates are created outside the chip, in a hardware security module or a vendor's key management service, and injected during test or programming. Espressif warns that a key generated on the host is not suitable for production unless every device gets its own.

Public keys and their hashes are provisioned too. For secure boot, a digest of the manufacturer's signing key is burned into fuses so the boot ROM can check every bootloader against it. For device identity, a certificate chain is installed so that a cloud service or another device can authenticate the part, as with the Device Attestation Certificates used by the Matter smart home standard.

Because chips pass through foundries, test houses and contract manufacturers, provisioning is often split across the supply chain. Services such as NXP's EdgeLock 2GO generate credentials centrally and have a programming partner install them, so that security does not depend on every factory. Key management guidance from NIST, such as SP 800-57, sets out how keys should be generated, protected and retired.

Examples

• An ESP32 generating its own AES-256 flash encryption key on first boot and write- and read-protecting the eFuse that holds it.
• A manufacturer burning the hash of its secure boot signing key into device fuses so that only firmware it has signed will run.
• A smart home product receiving a unique Matter Device Attestation Certificate during manufacturing so that apps can confirm it is genuine.
• A chip vendor's cloud service generating per-device credentials that a programming partner installs before the parts reach the customer's factory.

Related terms

• OTP memory
• PUF
• Root of trust
• Supply chain attack
• EOL programming
• Remote attestation

Where it appears on the Hub

Used on 10 pages of the Hub. In each group, the pages that mention it most come first.