static initialize comb table
MBEDTLS_ECP_FIXED_POINT_OPTIM aims to speed up ecc multiplication performance.
We compute the comb table in runtime now. It is a costly operation.
This patch add a pre-computed table to initialize well-known curves. It speed up ECDSA signature verify process in runtime by using more ROM size.
Signed-off-by: kXuan <kxuanobj@gmail.com>
diff --git a/library/ecp.c b/library/ecp.c
index 194e448..1ad5b67 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -729,6 +729,18 @@
}
/*
+ * Check that the comb table (grp->T) is static initialized.
+ */
+static int ecp_group_is_static_comb_table( const mbedtls_ecp_group *grp ) {
+#if MBEDTLS_ECP_FIXED_POINT_OPTIM == 1
+ return grp->T != NULL && grp->T_size == 0;
+#else
+ (void) grp;
+ return 0;
+#endif
+}
+
+/*
* Unallocate (the components of) a group
*/
void mbedtls_ecp_group_free( mbedtls_ecp_group *grp )
@@ -747,7 +759,7 @@
mbedtls_mpi_free( &grp->N );
}
- if( grp->T != NULL )
+ if( !ecp_group_is_static_comb_table(grp) && grp->T != NULL )
{
for( i = 0; i < grp->T_size; i++ )
mbedtls_ecp_point_free( &grp->T[i] );
@@ -2245,11 +2257,16 @@
w++;
/*
- * Make sure w is within bounds.
+ * If static comb table may not be used (!p_eq_g) or static comb table does
+ * not exists, make sure w is within bounds.
* (The last test is useful only for very small curves in the test suite.)
+ *
+ * The user reduces MBEDTLS_ECP_WINDOW_SIZE does not changes the size of
+ * static comb table, because the size of static comb table is fixed when
+ * it is generated.
*/
#if( MBEDTLS_ECP_WINDOW_SIZE < 6 )
- if( w > MBEDTLS_ECP_WINDOW_SIZE )
+ if( (!p_eq_g || !ecp_group_is_static_comb_table(grp)) && w > MBEDTLS_ECP_WINDOW_SIZE )
w = MBEDTLS_ECP_WINDOW_SIZE;
#endif
if( w >= grp->nbits )