ECP: Add mbedtls_ecp_tls_read_group_id()
`mbedtls_ecp_tls_read_group()` both parses the group ID and loads the
group into the structure provided. We want to support alternative
implementations of ECDH in the future and for that we need to parse the
group ID without populating an `mbedtls_ecp_group` structure (because
alternative implementations might not use that).
This commit moves the part that parses the group ID to a new function.
There is no need to test the new function directly, because the tests
for `mbedtls_ecp_tls_read_group()` are already implicitly testing it.
There is no intended change in behaviour in this commit.
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 2fb1af4..0e5b47f 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -632,7 +632,7 @@
/**
* \brief This function imports a point from a TLS ECPoint record.
*
- * \note On function return, \p buf is updated to point to immediately
+ * \note On function return, \p *buf is updated to point immediately
* after the ECPoint record.
*
* \param grp The ECP group used.
@@ -641,7 +641,8 @@
* \param len The length of the buffer.
*
* \return \c 0 on success.
- * \return An \c MBEDTLS_ERR_MPI_XXX error code on initialization failure.
+ * \return An \c MBEDTLS_ERR_MPI_XXX error code on initialization
+ * failure.
* \return #MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.
*/
int mbedtls_ecp_tls_read_point( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt,
@@ -687,20 +688,40 @@
/**
* \brief This function sets a group from a TLS ECParameters record.
*
- * \note \p buf is updated to point right after the ECParameters record
- * on exit.
+ * \note \p buf is updated to point right after the ECParameters
+ * record on exit.
*
* \param grp The destination group.
* \param buf The address of the pointer to the start of the input buffer.
* \param len The length of the buffer.
*
* \return \c 0 on success.
- * \return An \c MBEDTLS_ERR_MPI_XXX error code on initialization failure.
+ * \return An \c MBEDTLS_ERR_MPI_XXX error code on initialization
+ * failure.
* \return #MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.
+ * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the group is not
+ * recognised.
*/
int mbedtls_ecp_tls_read_group( mbedtls_ecp_group *grp, const unsigned char **buf, size_t len );
/**
+ * \brief This function reads a group from a TLS ECParameters record.
+ *
+ * \note \p buf is updated to point right after the ECParameters
+ * record on exit.
+ *
+ * \param grp Output parameter to hold the group id.
+ * \param buf The address of the pointer to the start of the input buffer.
+ * \param len The length of the buffer.
+ *
+ * \return \c 0 on success.
+ * \return #MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.
+ * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the group is not
+ * recognised.
+ */
+int mbedtls_ecp_tls_read_group_id( mbedtls_ecp_group_id *grp,
+ const unsigned char **buf, size_t len );
+/**
* \brief This function writes the TLS ECParameters record for a group.
*
* \param grp The ECP group used.
diff --git a/library/ecp.c b/library/ecp.c
index de5725c..49255b1 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -833,7 +833,24 @@
/*
* Set a group from an ECParameters record (RFC 4492)
*/
-int mbedtls_ecp_tls_read_group( mbedtls_ecp_group *grp, const unsigned char **buf, size_t len )
+int mbedtls_ecp_tls_read_group( mbedtls_ecp_group *grp,
+ const unsigned char **buf, size_t len )
+{
+ int ret;
+ mbedtls_ecp_group_id grp_id;
+
+ if( ( ret = mbedtls_ecp_tls_read_group_id( &grp_id, buf, len ) ) != 0 )
+ return( ret );
+
+ return mbedtls_ecp_group_load( grp, grp_id );
+}
+
+/*
+ * Read a group id from an ECParameters record (RFC 4492) and convert it to
+ * mbedtls_ecp_group_id.
+ */
+int mbedtls_ecp_tls_read_group_id( mbedtls_ecp_group_id *grp,
+ const unsigned char **buf, size_t len )
{
uint16_t tls_id;
const mbedtls_ecp_curve_info *curve_info;
@@ -860,7 +877,9 @@
if( ( curve_info = mbedtls_ecp_curve_info_from_tls_id( tls_id ) ) == NULL )
return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
- return mbedtls_ecp_group_load( grp, curve_info->grp_id );
+ *grp = curve_info->grp_id;
+
+ return( 0 );
}
/*
