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Reword the builtin key language on persistency declaration

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Specifically allow the driver to override the persistency level of a
builtin key in cases where the driver is persistency-aware.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
This commit is contained in:
Steven Cooreman 2021-04-14 10:32:05 +02:00
parent 966db26779
commit 31e27af0cc
2 changed files with 7 additions and 2 deletions
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2
docs/proposed/psa-driver-interface.md
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@ -810,7 +810,7 @@ psa_status_t acme_get_builtin_key(psa_drv_slot_number_t slot_number,
If this function returns `PSA_SUCCESS` or `PSA_ERROR_BUFFER_TOO_SMALL`, it must fill `attributes` with the attributes of the key (except for the key identifier). On success, this function must also fill `key_buffer` with the key context.
On entry, `psa_get_key_lifetime(attributes)` is the location at which the driver was declared and the persistence level `#PSA_KEY_LIFETIME_PERSISTENT`. The driver entry point may change the lifetime to one with the same location but a different persistence level. The standard attributes other than the key identifier and lifetime have the value conveyed by `PSA_KEY_ATTRIBUTES_INIT`.
On entry, `psa_get_key_lifetime(attributes)` is the location at which the driver was declared and a persistence level with which the platform is attempting to register the key. The driver entry point may choose to change the lifetime (`psa_set_key_lifetime(attributes, lifetime)`) of the reported key attributes to one with the same location but a different persistence level, in case the driver has more specific knowledge about the actual persistence level of the key which is being retrieved. For example, if a driver knows it cannot delete a key, it may override the persistence level in the lifetime to `PSA_KEY_PERSISTENCE_READ_ONLY`. The standard attributes other than the key identifier and lifetime have the value conveyed by `PSA_KEY_ATTRIBUTES_INIT`.
The output parameter `key_buffer` points to a writable buffer of `key_buffer_size` bytes. If the driver has a [`"builtin_key_size"` property](#key-format-for-opaque-drivers) property, `key_buffer_size` has this value, otherwise `key_buffer_size` has the value determined from the key type and size.

7
include/psa/crypto_extra.h
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@ -778,7 +778,12 @@ static inline int psa_key_id_is_builtin( psa_key_id_t key_id )
* \param[out] lifetime On success, the lifetime associated with the key
* corresponding to \p key_id. Lifetime is a
* combination of which driver contains the key,
* and with what lifecycle the key can be used.
* and with what persistence level the key is
* intended to be used. If the platform
* implementation does not contain specific
* information about the intended key persistence
* level, the persistence level may be reported as
* #PSA_KEY_PERSISTENCE_DEFAULT.
* \param[out] slot_number On success, the slot number known to the driver
* registered at the lifetime location reported
* through \p lifetime which corresponds to the