Some operations are not supported with Curve25519
diff --git a/include/polarssl/ecp.h b/include/polarssl/ecp.h
index 4391914..e4fce69 100644
--- a/include/polarssl/ecp.h
+++ b/include/polarssl/ecp.h
@@ -444,6 +444,9 @@
*
* \return 0 if successful,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
+ *
+ * \note This function does not support Montgomery curves, such as
+ * Curve25519.
*/
int ecp_add( const ecp_group *grp, ecp_point *R,
const ecp_point *P, const ecp_point *Q );
@@ -458,6 +461,9 @@
*
* \return 0 if successful,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
+ *
+ * \note This function does not support Montgomery curves, such as
+ * Curve25519.
*/
int ecp_sub( const ecp_group *grp, ecp_point *R,
const ecp_point *P, const ecp_point *Q );