Return early from mbedtls_pk_write_pubkey_der - public opaque key
exporting is expected to contain all of the needed data, therefore it shouldn't
be written again.
mbedtls_cipher_setup_psa() should return
MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE when the requested
cipher is not supported by PSA, so that the caller can
try the original mbedtls_cipher_setup() instead.
The previous version of mbedtls_cipher_setup_psa(), however,
only attempted to translate the cipher mode (GCM, CCM, CBC,
ChaChaPoly, Stream), but didn't consider the underlying
cipher primitive. Hence, it wouldn't fail when attempting
to setup a cipher context for, say, 3DES-CBC, where CBC
is currently supported by PSA but 3DES isn't.
This commit adds a check to mbedtls_cipher_setup_psa()
for whether the requested cipher primitive is available
in the underlying PSA Crypto implementation, and fails
cleanly with MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE if
it is isn't.
For AEAD ciphers, the information contained in mbedtls_cipher_info
is not enough to deduce a PSA algorithm value of type psa_algorithm_t.
This is because mbedtls_cipher_info doesn't contain the AEAD tag
length, while values of type psa_algorithm_t do.
This commit adds the AEAD tag length as a separate parameter
to mbedtls_cipher_setup_psa(). For Non-AEAD ciphers, the value
must be 0.
This approach is preferred over passing psa_algorithm_t directly
in order to keep the changes in existing code using the cipher layer
small.
Mbed TLS cipher layer allows usage of keys for other purposes
than indicated in the `operation` parameter of `mbedtls_cipher_setkey()`.
The semantics of the PSA Crypto API, in contrast, checks key
usage against the key policy.
As a remedy, this commit modifies the PSA key slot setup to
always allow both encryption and decryption.
This commit implements the internal key slot management performed
by PSA-based cipher contexts. Specifically, `mbedtls_cipher_setkey()`
wraps the provided raw key material into a key slot, and
`mbedtls_cipher_free()` destroys that key slot.
This field determines whether a cipher context should
use an external implementation of the PSA Crypto API for
cryptographic operations, or Mbed TLS' own crypto library.
The commit also adds dummy implementations for the cipher API.
It's better for names in the API to describe the "what" (opaque keys) rather
than the "how" (using PSA), at least since we don't intend to have multiple
function doing the same "what" in different ways in the foreseeable future.
Unfortunately the can_do wrapper does not receive the key context as an
argument, so it cannot check psa_get_key_information(). Later we might want to
change our internal structures to fix this, but for now we'll just restrict
opaque PSA keys to be ECDSA keypairs, as this is the only thing we need for
now. It also simplifies testing a bit (no need to test each key type).
The code maintains the invariant that raw and opaque PSKs are never
configured simultaneously, so strictly speaking `ssl_conf_remove_psk()`
need not consider clearing the raw PSK if it has already cleared an
opaque one - and previously, it didn't. However, it doesn't come at
any cost to keep this check as a safe-guard to future unforeseen
situations where opaque and raw PSKs _are_ both present.
In multiple places, it occurrs as the fixed length of
the master secret, so use a constant with a descriptive
name instead. This is reinforced by the fact the some
further occurrences of '48' are semantically different.
Using finer grained control over include directories will allow differnt
targets to use different include files. This will be useful when the
`crypto` subcomponent wants to use its own include files instead of or in
addition to the top level ones.
