Introduce device-specific derived key support#781
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jaybosamiya-ms merged 4 commits intomainfrom Apr 17, 2026
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Looks good to me. Thanks!
There are some minor comments.
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CI failures due to new Rust version released today which introduces new clippy lints, I'll open a PR to fix things soon. Those are unrelated to the changes in this PR. Edit: #782 |
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@sangho2 please resolve the comment if the tweak to support shim-level errors looks good to you, and it'll auto-merge, thanks! |
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🤖 SemverChecks 🤖 No breaking API changes detected Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered. |
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This PR adds support for derived keys through a
DerivedKeyProviderplatform trait. This design manages the tradeoffs between some requirements for OP-TEE and strictness of wrapping.The strictest version of this design looks similar to a TPM, in that the platform would never expose the root key to anything else, only ingesting context and outputting a derived key. However, this design does not fit some constraints required by the OP-TEE shim, which (for reasons) wants to specify its own key derivation function. The naive way to support this is through the platform revealing the device-specific key directly, but this (unsurprisingly) can lead to proliferation of key usage, rather than keeping it strictly confined. Indeed, direct exposing of such keys cannot even be supported by some platforms (e.g., TPM).
As a middle ground, the platform can choose to use a shim-provided KDF if it wishes to (if it makes sense for some shim/platform pairs) while for other more-distrustful platforms can choose to do their own KDF in addition to the shim-provided KDF, or even to ignore the shim-provided KDF entirely. Effectively, the platform is the true arbiter of how the secret gets protected.
This PR introduces this interface, as well as implements it for the Linux userland platform to demonstrate one concrete implementation of it.