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/include/mbedtls/hkdf.h b/include/mbedtls/hkdf.h
index 40ee64e..ebf5e12 100644
--- a/include/mbedtls/hkdf.h
+++ b/include/mbedtls/hkdf.h
@@ -70,7 +70,7 @@
* \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
* MD layer.
*/
-int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
+int mbedtls_hkdf( mbedtls_md_handle_t md, const unsigned char *salt,
size_t salt_len, const unsigned char *ikm, size_t ikm_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len );
@@ -99,7 +99,7 @@
* \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
* MD layer.
*/
-int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
+int mbedtls_hkdf_extract( mbedtls_md_handle_t md,
const unsigned char *salt, size_t salt_len,
const unsigned char *ikm, size_t ikm_len,
unsigned char *prk );
@@ -130,7 +130,7 @@
* \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
* MD layer.
*/
-int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
+int mbedtls_hkdf_expand( mbedtls_md_handle_t md, const unsigned char *prk,
size_t prk_len, const unsigned char *info,
size_t info_len, unsigned char *okm, size_t okm_len );