ECC import: more useful choice of INVALID_ARGUMENT vs NOT_SUPPORTED
Attempting to create an ECC key with a curve specification that is not
valid can plausibly fail with PSA_ERROR_INVALID_ARGUMENT ("this is not
a curve specification at all") or PSA_ERROR_NOT_SUPPORTED ("this may
be a curve specification, but not one I support"). The choice of error
is somewhat subjective.
Before this commit, due to happenstance in the implementation, an
attempt to use a curve that is declared in the PSA API but not
implemented in Mbed TLS returned PSA_ERROR_INVALID_ARGUMENT, whereas
an attempt to use a curve that Mbed TLS supports but for which support
was disabled at compile-time returned PSA_ERROR_NOT_SUPPORTED. This
inconsistency made it difficult to write negative tests that could
work whether the curve is implemented via Mbed TLS code or via a
driver.
After this commit, any attempt to use parameters that are not
recognized fails with NOT_SUPPORTED, whether a curve with the
specified size might plausibly exist or not, because "might plausibly
exist" is not something Mbed TLS can determine.
To keep returning INVALID_ARGUMENT when importing an ECC key with an
explicit "bits" attribute that is inconsistent with the size of the
key material, this commit changes the way mbedtls_ecc_group_of_psa()
works: it now works on a size in bits rather than bytes, with an extra
flag indicating whether the bit-size must be exact or not.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/src/drivers/key_management.c b/tests/src/drivers/key_management.c
index 98990d1..be6a814 100644
--- a/tests/src/drivers/key_management.c
+++ b/tests/src/drivers/key_management.c
@@ -76,7 +76,7 @@
mbedtls_ecp_group_id grp_id =
mbedtls_ecc_group_of_psa(
curve,
- PSA_BITS_TO_BYTES( psa_get_key_bits( attributes ) ) );
+ psa_get_key_bits( attributes ), 0 );
const mbedtls_ecp_curve_info *curve_info =
mbedtls_ecp_curve_info_from_grp_id( grp_id );
mbedtls_ecp_keypair ecp;