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Defer static keystore to 3.6.3

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Signed-off-by: David Horstmann <david.horstmann@arm.com>
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David Horstmann 2024-10-11 17:24:16 +01:00
parent 182936ec4c
commit 480f71f9ad
1 changed files with 2 additions and 2 deletions
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docs/architecture/psa-keystore-design.md
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@ -67,7 +67,7 @@ Note that a slot must not be moved in memory while it is being read or written.
There are three variants of the key store implementation, responding to different needs.
* Hybrid key store ([static key slots](#static-key-store) with dynamic key data): the key store is a statically allocated array of slots, of size `MBEDTLS_PSA_KEY_SLOT_COUNT`. Key material is allocated on the heap. This is the historical implementation. It remains the default in the Mbed TLS 3.6 long-time support (LTS) branch when using a handwritten `mbedtls_config.h`, as is common on resource-constrained platforms, because the alternatives have tradeoffs (key size limit and larger RAM usage at rest for the static key store, larger code size and more risk due to code complexity for the dynamic key store).
* Fully [static key store](#static-key-store) (since Mbed TLS 3.6.2): the key store is a statically allocated array of slots, of size `MBEDTLS_PSA_KEY_SLOT_COUNT`. Each key slot contains the key representation directly, and the key representation must be no more than `MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE` bytes. This is intended for very constrained devices that do not have a heap.
* Fully [static key store](#static-key-store) (since Mbed TLS 3.6.3): the key store is a statically allocated array of slots, of size `MBEDTLS_PSA_KEY_SLOT_COUNT`. Each key slot contains the key representation directly, and the key representation must be no more than `MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE` bytes. This is intended for very constrained devices that do not have a heap.
* [Dynamic key store](#dynamic-key-store) (since Mbed TLS 3.6.1): the key store is dynamically allocated as multiple slices on the heap, with a size that adjusts to the application's usage. Key material is allocated on the heap. Compared to the hybrid key store, the code size and RAM consumption are larger. This is intended for higher-end devices where applications are not expected to have a highly predicatable resource usage. This is the default implementation when using the default `mbedtls_config.h` file, as is common on platforms such as Linux, starting with Mbed TLS 3.6.1.
#### Future improvement: merging the key store variants
@ -95,7 +95,7 @@ When creating a volatile key, the slice containing the slot and index of the slo
The static key store is the historical implementation. The key store is a statically allocated array of slots, of size `MBEDTLS_PSA_KEY_SLOT_COUNT`. This value is an upper bound for the total number of volatile keys plus loaded keys.
Since Mbed TLS 3.6.2, there are two variants for the static key store: a hybrid variant (default), and a fully-static variant enabled by the configuration option `MBEDTLS_PSA_STATIC_KEY_SLOTS`. The two variants have the same key store management: the only difference is in how the memory for key data is managed. With fully static key slots, the key data is directly inside the slot, and limited to `MBEDTLS_PSA_KEY_SLOT_BUFFER_SIZE` bytes. With the hybrid key store, the slot contains a pointer to the key data, which is allocated on the heap.
Since Mbed TLS 3.6.3, there are two variants for the static key store: a hybrid variant (default), and a fully-static variant enabled by the configuration option `MBEDTLS_PSA_STATIC_KEY_SLOTS`. The two variants have the same key store management: the only difference is in how the memory for key data is managed. With fully static key slots, the key data is directly inside the slot, and limited to `MBEDTLS_PSA_KEY_SLOT_BUFFER_SIZE` bytes. With the hybrid key store, the slot contains a pointer to the key data, which is allocated on the heap.
#### Volatile key identifiers in the static key store