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SubjectRe: [PATCH v1 0/3] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys
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On 3/16/2021 7:02 PM, Ahmad Fatoum wrote:
> The Cryptographic Acceleration and Assurance Module (CAAM) is an IP core
> built into many newer i.MX and QorIQ SoCs by NXP.
>
> Its blob mechanism can AES encrypt/decrypt user data using a unique
> never-disclosed device-specific key. There has been multiple
> discussions on how to represent this within the kernel:
>
> - [RFC] crypto: caam - add red blobifier
> Steffen implemented[1] a PoC sysfs driver to start a discussion on how to
> best integrate the blob mechanism.
> Mimi suggested that it could be used to implement trusted keys.
> Trusted keys back then were a TPM-only feature.
>
> - security/keys/secure_key: Adds the secure key support based on CAAM.
> Udit added[2] a new "secure" key type with the CAAM as backend. The key
> material stays within the kernel only.
> Mimi and James agreed that this needs a generic interface, not specific
> to CAAM. Mimi suggested trusted keys. Jan noted that this could serve as
> basis for TEE-backed keys.
>
> - [RFC] drivers: crypto: caam: key: Add caam_tk key type
> Franck added[3] a new "caam_tk" key type based on Udit's work. The key
> material stays within the kernel only, but can optionally be user-set
> instead of coming from RNG. James voiced the opinion that there should
> be just one user-facing generic wrap/unwrap key type with multiple
> possible handlers. David suggested trusted keys.
>
The whole point was to use caam "black blobs", with the main advantage of
keys being kept encrypted in memory after "unsealing" the blobs.
(Keys in blobs are encrypted with a persistent BKEK - blob KEK, derived from
fuse-based OTPMK. OTOH black keys are keys encrypted with an ephemeral, random
KEK that is stored in an internal caam register. When a black blob is unsealed,
the key is practically rekeyed, the random key replacing the BKEK; key is never
exposed in plaintext, rekeying happens in caam).

Current implementation uses "red blobs", which means keys are left unprotected
in memory after blobs are unsealed.

> - Introduce TEE based Trusted Keys support
> Sumit reworked[4] trusted keys to support multiple possible backends with
> one chosen at boot time and added a new TEE backend along with TPM.
> This now sits in Jarkko's master branch to be sent out for v5.13
>
> This patch series builds on top of Sumit's rework to have the CAAM as yet another
> trusted key backend.
>
Shouldn't the description under TRUSTED_KEYS (in security/keys/Kconfig)
be updated to reflect the availability of multiple backends?

Thanks,
Horia

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