Introduce MD handle type
As has been previously done for ciphersuites, this commit introduces
a zero-cost abstraction layer around the type
mbedtls_md_info const *
whose valid values represent implementations of message digest algorithms.
Access to a particular digest implementation can be requested by name or
digest ID through the API mbedtls_md_info_from_xxx(), which either returns
a valid implementation or NULL, representing failure.
This commit replaces such uses of `mbedtls_md_info const *` by an abstract
type `mbedtls_md_handle_t` whose valid values represent digest implementations,
and which has a designated invalid value MBEDTLS_MD_INVALID_HANDLE.
The purpose of this abstraction layer is to pave the way for builds which
support precisely one digest algorithm. In this case, mbedtls_md_handle_t
can be implemented as a two-valued type, with one value representing the
invalid handle, and the unique valid value representing the unique enabled
digest.
diff --git a/library/ecdsa.c b/library/ecdsa.c
index 58e1a5f..94bb7f0 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -412,11 +412,14 @@
mbedtls_hmac_drbg_context *p_rng = &rng_ctx;
unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
size_t grp_len = ( grp->nbits + 7 ) / 8;
- const mbedtls_md_info_t *md_info;
+ mbedtls_md_handle_t md_info;
mbedtls_mpi h;
- if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
+ if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) ==
+ MBEDTLS_MD_INVALID_HANDLE )
+ {
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
+ }
mbedtls_mpi_init( &h );
mbedtls_hmac_drbg_init( &rng_ctx );