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.
The test suites `test_suite_gcm.aes{128,192,256}_en.data` contains
numerous NIST test vectors for AES-*-GCM against which the GCM
API mbedtls_gcm_xxx() is tested.
However, one level higher at the cipher API, no tests exist which
exercise mbedtls_cipher_auth_{encrypt/decrypt}() for GCM ciphers,
although test_suite_cipher.function contains the test auth_crypt_tv
which does precisely that and is already used e.g. in
test_suite_cipher.ccm.
This commit replicates the test vectors from
test_suite_gcm.aes{128,192,256}_en.data in test_suite_cipher.gcm.data
and adds a run of auth_crypt_tv for each of them.
The conversion was mainly done through the sed command line
```
s/gcm_decrypt_and_verify:\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):
\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\)/auth_crypt_tv:
\1:\2:\4:\5:\3:\7:\8:\9/
```
Revived from a previous PR by Gilles, see:
https://github.com/ARMmbed/mbedtls/pull/1293/files#diff-568ef321d275f2035b8b26a70ee9af0bR71
This will be useful in eliminating temporary stack buffers for transcoding the
signature: in order to do that in place we need to be able to make assumptions
about the size of the output buffer, which this macro will provide. (See next
commit.)
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).
While at it, clarify who's responsible for destroying the underlying key. That
can't be us because some keys cannot be destroyed and we wouldn't know. So
let's leave that up to the caller.
Otherwise, if `mbedtls_psa_get_free_key_slot()` fails to find a fresh
key slot, the slot value will be undefined, and the call to
`psa_destroy_key()` at the end of `main()` is undefined behavior.
Previously, command line arguments `psk_slot` and `psk_list_slot`
could be used to indicate the PSA key slots that the example
applications should use to store the PSK(s) provided.
This commit changes this approach to use the utility function
`mbedtls_psa_get_free_key_slot()` to obtain free key slots from
the PSA Crypto implementation automatically, so that users only
need to pass boolean flags `psk_opaque` and `psk_list_opaque`
on the command line to enable / disable PSA-based opaque PSKs.
