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Clarify documentation to match implementation and intention of UDS (#… #234

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Oct 11, 2024
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Clarify documentation to match implementation and intention of UDS (#… #234

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6 changes: 3 additions & 3 deletions doc/caliptra_1x/Caliptra.md
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Expand Up @@ -286,13 +286,13 @@ Caliptra must provide its runtime (RT) code with a cryptographic identity in acc

### UDS

A combination of mask ROM and HW macros must implement the DICE key derivation and power-on latch, hiding the UDS and only making the CDI-derived signing key visible to firmware.
A combination of mask ROM and HW macros must implement the DICE key derivation and power-on latch, hiding the UDS seed and only making the CDI-derived signing public key visible to ROM and private key 'handle' available to ROM. Real UDS will only be calculated during the cold boot, used for CDI derivation and immediately gets cleared.

The Caliptra UDS is stored as ciphertext in fuses, obfuscated at rest by a secret obfuscation key[^2] known only to the Caliptra ROM. Once read by Caliptra ROM at boot, the unobfuscated UDS is then used to derive the IDevID identity.
The Caliptra UDS seed is stored as ciphertext in fuses, deobfuscated only on cold boot using an obfuscation key[^2] known only to the Caliptra Hardware. Once read by Caliptra HW at boot, the unobfuscated UDS is then used to derive the IDevID identity and immediately cleared by hardware.

### IDevID key

Caliptra's IDevID key is a hardware identity generated by Caliptra ROM during manufacturing. This key must be solely wielded by Caliptra ROM, and shall never be exposed externally at any phase of the Caliptra lifecycle. IDevID is used to endorse LDevID. The [IDevID certificate](#idevid-certificate) is endorsed by the vendor’s provisioning CA (pCA) that is implemented via a HSM appliance connected to High Volume Manufacturing (HVM) flows (see provisioning CA in [Reference 8](#ref-8)).
Caliptra's IDevID key is a hardware identity generated by Caliptra ROM during manufacturing. This key "handle" must be solely wielded by Caliptra ROM, and shall never be exposed externally at any phase of the Caliptra lifecycle. IDevID is used to endorse LDevID. The [IDevID certificate](#idevid-certificate) is endorsed by the vendor’s provisioning CA (pCA) that is implemented via a HSM appliance connected to High Volume Manufacturing (HVM) flows (see provisioning CA in [Reference 8](#ref-8)).

See [Provisioning IDevID During Manufacturing](#provisioning-idevid-during-manufacturing) for further details on IDevID provisioning.

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