Changed ecp_mul() to always add the same point
diff --git a/library/ecp.c b/library/ecp.c
index 6812718..503f9d8 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -434,55 +434,42 @@
/*
* Integer multiplication: R = m * P
- * Using Montgomery's Ladder to avoid leaking information about m
+ * GECC 5.7 (SPA-resistant algorithm)
*/
int ecp_mul( const ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P )
{
int ret = 0;
size_t pos;
- ecp_point A, B;
+ ecp_point Q[2];
- ecp_point_init( &A ); ecp_point_init( &B );
+ ecp_point_init( &Q[0] ); ecp_point_init( &Q[1] );
/*
- * The general method works only for m >= 2
+ * The general method works only for m >= 1
*/
if( mpi_cmp_int( m, 0 ) == 0 ) {
ecp_set_zero( R );
goto cleanup;
}
- if( mpi_cmp_int( m, 1 ) == 0 ) {
- MPI_CHK( ecp_copy( R, P ) );
- goto cleanup;
- }
+ ecp_set_zero( &Q[0] );
- MPI_CHK( ecp_copy( &A, P ) );
- MPI_CHK( ecp_add( grp, &B, P, P ) );
-
- for( pos = mpi_msb( m ) - 2; ; pos-- )
+ for( pos = mpi_msb( m ) - 1; ; pos-- )
{
- if( mpi_get_bit( m, pos ) == 0 )
- {
- MPI_CHK( ecp_add( grp, &B, &A, &B ) );
- MPI_CHK( ecp_add( grp, &A, &A, &A ) ) ;
- }
- else
- {
- MPI_CHK( ecp_add( grp, &A, &A, &B ) );
- MPI_CHK( ecp_add( grp, &B, &B, &B ) ) ;
- }
+ MPI_CHK( ecp_add( grp, &Q[0], &Q[0], &Q[0] ) );
+ MPI_CHK( ecp_add( grp, &Q[1], &Q[0], P ) );
+ MPI_CHK( ecp_copy( &Q[0], &Q[ mpi_get_bit( m, pos ) ] ) );
if( pos == 0 )
break;
}
- MPI_CHK( ecp_copy( R, &A ) );
+ MPI_CHK( ecp_copy( R, &Q[0] ) );
cleanup:
- ecp_point_free( &A ); ecp_point_free( &B );
+ ecp_point_free( &Q[0] ); ecp_point_free( &Q[1] );
return( ret );
}