Got started on ecp_add(): generic case done
diff --git a/library/ecp.c b/library/ecp.c
index 6c3b4a8..825db99 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -37,6 +37,19 @@
#include "polarssl/ecp.h"
/*
+ * Initialize a point
+ */
+void ecp_point_init( ecp_point *pt )
+{
+ if( pt == NULL )
+ return;
+
+ pt->is_zero = 1;
+ mpi_init( &( pt->X ) );
+ mpi_init( &( pt->Y ) );
+}
+
+/*
* Unallocate (the components of) a point
*/
void ecp_point_free( ecp_point *pt )
@@ -64,11 +77,21 @@
}
/*
+ * Set point to zero
+ */
+void ecp_set_zero( ecp_point *pt )
+{
+ pt->is_zero = 1;
+ mpi_free( &( pt->X ) );
+ mpi_free( &( pt->Y ) );
+}
+
+/*
* Copy the contents of Q into P
*/
int ecp_copy( ecp_point *P, const ecp_point *Q )
{
- int ret;
+ int ret = 0;
P->is_zero = Q->is_zero;
MPI_CHK( mpi_copy( &P->X, &Q->X ) );
@@ -78,6 +101,114 @@
return( ret );
}
+/*
+ * Addition: R = P + Q, generic case (P != Q, P != 0, Q != 0, R != 0)
+ * Cf SEC1 v2 p. 7, item 4
+ */
+static int ecp_add_generic( const ecp_group *grp, ecp_point *R,
+ const ecp_point *P, const ecp_point *Q )
+{
+ int ret = 0;
+ mpi DX, DY, K, L, LL, M, X, Y;
+
+ mpi_init( &DX ); mpi_init( &DY ); mpi_init( &K ); mpi_init( &L );
+ mpi_init( &LL ); mpi_init( &M ); mpi_init( &X ); mpi_init( &Y );
+
+ /*
+ * L = (Q.Y - P.Y) / (Q.X - P.X) mod p
+ */
+ MPI_CHK( mpi_sub_mpi( &DY, &Q->Y, &P->Y ) );
+ MPI_CHK( mpi_sub_mpi( &DX, &Q->X, &P->X ) );
+ MPI_CHK( mpi_inv_mod( &K, &DX, &grp->P ) );
+ MPI_CHK( mpi_mul_mpi( &K, &K, &DY ) );
+ MPI_CHK( mpi_mod_mpi( &L, &K, &grp->P ) );
+
+ /*
+ * LL = L^2 mod p
+ * M = L^2 - Q.X
+ * X = L^2 - P.X - Q.X
+ */
+ MPI_CHK( mpi_mul_mpi( &LL, &L, &L ) );
+ MPI_CHK( mpi_mod_mpi( &LL, &LL, &grp->P ) );
+ MPI_CHK( mpi_sub_mpi( &M, &LL, &Q->X ) );
+ MPI_CHK( mpi_sub_mpi( &X, &M, &P->X ) );
+
+ /*
+ * Y = L * (P.X - X) - P.Y = L * (-M) - P.Y
+ */
+ MPI_CHK( mpi_copy( &Y, &M ) );
+ Y.s = - Y.s;
+ MPI_CHK( mpi_mul_mpi( &Y, &Y, &L ) );
+ MPI_CHK( mpi_sub_mpi( &Y, &Y, &P->Y ) );
+
+ /*
+ * R = (X mod p, Y mod p)
+ */
+ R->is_zero = 0;
+ MPI_CHK( mpi_mod_mpi( &R->X, &X, &grp->P ) );
+ MPI_CHK( mpi_mod_mpi( &R->Y, &Y, &grp->P ) );
+
+cleanup:
+
+ mpi_free( &DX ); mpi_free( &DY ); mpi_free( &K ); mpi_free( &L );
+ mpi_free( &LL ); mpi_free( &M ); mpi_free( &X ); mpi_free( &Y );
+
+ return( ret );
+}
+
+/*
+ * Doubling: R = 2 * P, generic case (P != 0, R != 0)
+ *
+ * Returns POLARSSL_ERR_MPI_XXX on error.
+ */
+static int ecp_double_generic( const ecp_group *grp, ecp_point *R,
+ const ecp_point *P )
+{
+ int ret = 0;
+
+ (void) grp;
+ (void) R;
+ (void) P;
+
+ return( ret );
+}
+
+/*
+ * Addition: R = P + Q, cf p. 7 of SEC1 v2
+ */
+int ecp_add( const ecp_group *grp, ecp_point *R,
+ const ecp_point *P, const ecp_point *Q )
+{
+ int ret = 0;
+
+ if( P->is_zero )
+ {
+ ret = ecp_copy( R, Q );
+ }
+ else if( Q->is_zero )
+ {
+ ret = ecp_copy( R, P );
+ }
+ else if( mpi_cmp_mpi( &P->X, &Q->X ) != 0 )
+ {
+ ret = ecp_add_generic( grp, R, P, Q );
+ }
+ else if( mpi_cmp_int( &P->Y, 0 ) == 0 ||
+ mpi_cmp_mpi( &P->Y, &Q->Y ) != 0 )
+ {
+ ecp_set_zero( R );
+ }
+ else
+ {
+ /*
+ * P == Q
+ */
+ ret = ecp_double_generic( grp, R, P );
+ }
+
+ return ret;
+}
+
#if defined(POLARSSL_SELF_TEST)