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Generalize mbedtls_pk_setup_opaque beyond MBEDTLS_USE_PSA_CRYPTO

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It's useful in applications that want to use some PSA opaque keys regardless
of whether all pk operations go through PSA.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2024-01-17 10:07:55 +01:00
parent 9fe1c699a8
commit 32294044e1
1 changed files with 3 additions and 1 deletions
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4
docs/architecture/psa-migration/psa-legacy-bridges.md
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@ -163,7 +163,7 @@ There is a function `mbedtls_pk_setup_opaque` that mostly does this. However, it
* It creates a PK key of type `MBEDTLS_PK_OPAQUE` that wraps the PSA key. This is good enough in some scenarios, but not others. For example, it's ok for pkwrite, because we've upgraded the pkwrite code to handle `MBEDTLS_PK_OPAQUE`. That doesn't help users of third-party libraries that haven't yet been upgraded.
* It ties the lifetime of the PK object to the PSA key, which is error-prone: if the PSA key is destroyed but the PK object isn't, there is no way to reliably detect any subsequent misuse of the PK object.
* It is only available under `MBEDTLS_USE_PSA_CRYPTO`. (Not a priority concern: we generally expect people to activate `MBEDTLS_USE_PSA_CRYPTO` at an early stage of their migration to PSA.)
* It is only available under `MBEDTLS_USE_PSA_CRYPTO`. This is not a priority concern, since we generally expect people to activate `MBEDTLS_USE_PSA_CRYPTO` at an early stage of their migration to PSA. However, this function is useful to use specific PSA keys in X.509/TLS regardless of whether X.509/TLS use the PSA API for all cryptographic operations, so this is a wart in the current API.
It therefore appears that we need two ways to “convert” a PSA key to PK:
@ -305,6 +305,8 @@ Based on the [gap analysis](#using-a-psa-key-as-a-pk-context):
[ACTION] Clarify the documentation of `mbedtls_pk_setup_opaque` regarding which algorithms the resulting key will perform with `mbedtls_pk_sign`, `mbedtls_pk_verify`, `mbedtls_pk_encrypt`, `mbedtls_pk_decrypt`.
[ACTION] Provide `mbedtls_pk_setup_opaque` whenever `MBEDTLS_PSA_CRYPTO_CLIENT` is enabled, not just when `MBEDTLS_USE_PSA_CRYPTO` is enabled. This is nice-to-have, not critical. Update `use-psa-crypto.md` accordingly.
[OPEN] What about `mbedtls_pk_sign_ext` and `mbedtls_pk_verify_ext`?
#### API to convert between signature formats