Rm subtraction from ecp_add_mixed()
diff --git a/library/ecp.c b/library/ecp.c
index f0dd7d2..39d0e8d 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1067,21 +1067,15 @@
}
/*
- * Addition or subtraction: R = P + Q or R = P - Q,
- * mixed affine-Jacobian coordinates (GECC 3.22)
+ * Addition: R = P + Q, mixed affine-Jacobian coordinates (GECC 3.22)
*
* The coordinates of Q must be normalized (= affine),
* but those of P don't need to. R is not normalized.
*
- * If sign >= 0, perform addition, otherwise perform subtraction,
- * taking advantage of the fact that, for Q != 0, we have
- * -Q = (Q.X, -Q.Y, Q.Z)
- *
* Cost: 1A := 8M + 3S
*/
static int ecp_add_mixed( const ecp_group *grp, ecp_point *R,
- const ecp_point *P, const ecp_point *Q,
- signed char sign )
+ const ecp_point *P, const ecp_point *Q )
{
int ret;
mpi T1, T2, T3, T4, X, Y, Z;
@@ -1092,26 +1086,14 @@
/*
* Trivial cases: P == 0 or Q == 0
- * (Check Q first, so that we know Q != 0 when we compute -Q.)
* This will never happen during ecp_mul() so we don't mind the branches.
*/
+ if( mpi_cmp_int( &P->Z, 0 ) == 0 )
+ return( ecp_copy( R, Q ) );
+
if( mpi_cmp_int( &Q->Z, 0 ) == 0 )
return( ecp_copy( R, P ) );
- if( mpi_cmp_int( &P->Z, 0 ) == 0 )
- {
- ret = ecp_copy( R, Q );
-
- /*
- * -R.Y mod P = P - R.Y unless R.Y == 0
- */
- if( ret == 0 && sign < 0)
- if( mpi_cmp_int( &R->Y, 0 ) != 0 )
- ret = mpi_sub_mpi( &R->Y, &grp->P, &R->Y );
-
- return( ret );
- }
-
/*
* Make sure Q coordinates are normalized
*/
@@ -1125,18 +1107,6 @@
MPI_CHK( mpi_mul_mpi( &T2, &T1, &P->Z ) ); MOD_MUL( T2 );
MPI_CHK( mpi_mul_mpi( &T1, &T1, &Q->X ) ); MOD_MUL( T1 );
MPI_CHK( mpi_mul_mpi( &T2, &T2, &Q->Y ) ); MOD_MUL( T2 );
-
- /*
- * For subtraction, -Q.Y should have been used instead of Q.Y,
- * so we replace T2 by -T2, which is P - T2 mod P
- * (Again, not used by ecp_mul(), so not worry about the branch.)
- */
- if( sign < 0 )
- {
- MPI_CHK( mpi_sub_mpi( &T2, &grp->P, &T2 ) );
- MOD_SUB( T2 );
- }
-
MPI_CHK( mpi_sub_mpi( &T1, &T1, &P->X ) ); MOD_SUB( T1 );
MPI_CHK( mpi_sub_mpi( &T2, &T2, &P->Y ) ); MOD_SUB( T2 );
@@ -1189,7 +1159,7 @@
{
int ret;
- MPI_CHK( ecp_add_mixed( grp, R, P, Q , 1 ) );
+ MPI_CHK( ecp_add_mixed( grp, R, P, Q ) );
MPI_CHK( ecp_normalize( grp, R ) );
cleanup:
@@ -1204,11 +1174,21 @@
const ecp_point *P, const ecp_point *Q )
{
int ret;
+ ecp_point mQ;
- MPI_CHK( ecp_add_mixed( grp, R, P, Q, -1 ) );
+ ecp_point_init( &mQ );
+
+ /* mQ = - Q */
+ ecp_copy( &mQ, Q );
+ if( mpi_cmp_int( &mQ.Y, 0 ) != 0 )
+ MPI_CHK( mpi_sub_mpi( &mQ.Y, &grp->P, &mQ.Y ) );
+
+ MPI_CHK( ecp_add_mixed( grp, R, P, &mQ ) );
MPI_CHK( ecp_normalize( grp, R ) );
cleanup:
+ ecp_point_free( &mQ );
+
return( ret );
}
@@ -1370,7 +1350,7 @@
j = i;
while( j-- )
{
- ecp_add_mixed( grp, &T[i + j], &T[j], &T[i], +1 );
+ ecp_add_mixed( grp, &T[i + j], &T[j], &T[i] );
TT[k++] = &T[i + j];
}
}
@@ -1443,7 +1423,7 @@
{
MPI_CHK( ecp_double_jac( grp, R, R ) );
MPI_CHK( ecp_select_comb( grp, &Txi, T, x[i] ) );
- MPI_CHK( ecp_add_mixed( grp, R, R, &Txi, +1 ) );
+ MPI_CHK( ecp_add_mixed( grp, R, R, &Txi ) );
}
cleanup: