/* RESULT = P1 + P2 */
void
_gcry_mpi_ec_add_points (mpi_point_t result,
mpi_point_t p1, mpi_point_t p2,
mpi_ec_t ctx)
{
#define x1 (p1->x )
#define y1 (p1->y )
#define z1 (p1->z )
#define x2 (p2->x )
#define y2 (p2->y )
#define z2 (p2->z )
#define x3 (result->x)
#define y3 (result->y)
#define z3 (result->z)
#define l1 (ctx->t.scratch[0])
#define l2 (ctx->t.scratch[1])
#define l3 (ctx->t.scratch[2])
#define l4 (ctx->t.scratch[3])
#define l5 (ctx->t.scratch[4])
#define l6 (ctx->t.scratch[5])
#define l7 (ctx->t.scratch[6])
#define l8 (ctx->t.scratch[7])
#define l9 (ctx->t.scratch[8])
#define t1 (ctx->t.scratch[9])
#define t2 (ctx->t.scratch[10])
if ( (!mpi_cmp (x1, x2)) && (!mpi_cmp (y1, y2)) && (!mpi_cmp (z1, z2)) )
{
/* Same point; need to call the duplicate function. */
_gcry_mpi_ec_dup_point (result, p1, ctx);
}
else if (!mpi_cmp_ui (z1, 0))
{
/* P1 is at infinity. */
mpi_set (x3, p2->x);
mpi_set (y3, p2->y);
mpi_set (z3, p2->z);
}
else if (!mpi_cmp_ui (z2, 0))
{
/* P2 is at infinity. */
mpi_set (x3, p1->x);
mpi_set (y3, p1->y);
mpi_set (z3, p1->z);
}
else
{
int z1_is_one = !mpi_cmp_ui (z1, 1);
int z2_is_one = !mpi_cmp_ui (z2, 1);
/* l1 = x1 z2^2 */
/* l2 = x2 z1^2 */
if (z2_is_one)
mpi_set (l1, x1);
else
{
ec_powm (l1, z2, mpi_const (MPI_C_TWO), ctx);
ec_mulm (l1, l1, x1, ctx);
}
if (z1_is_one)
mpi_set (l2, x2);
else
{
ec_powm (l2, z1, mpi_const (MPI_C_TWO), ctx);
ec_mulm (l2, l2, x2, ctx);
}
/* l3 = l1 - l2 */
ec_subm (l3, l1, l2, ctx);
/* l4 = y1 z2^3 */
ec_powm (l4, z2, mpi_const (MPI_C_THREE), ctx);
ec_mulm (l4, l4, y1, ctx);
/* l5 = y2 z1^3 */
ec_powm (l5, z1, mpi_const (MPI_C_THREE), ctx);
ec_mulm (l5, l5, y2, ctx);
/* l6 = l4 - l5 */
ec_subm (l6, l4, l5, ctx);
if (!mpi_cmp_ui (l3, 0))
{
if (!mpi_cmp_ui (l6, 0))
{
/* P1 and P2 are the same - use duplicate function. */
_gcry_mpi_ec_dup_point (result, p1, ctx);
}
else
{
/* P1 is the inverse of P2. */
mpi_set_ui (x3, 1);
mpi_set_ui (y3, 1);
mpi_set_ui (z3, 0);
}
}
else
{
/* l7 = l1 + l2 */
ec_addm (l7, l1, l2, ctx);
/* l8 = l4 + l5 */
ec_addm (l8, l4, l5, ctx);
/* z3 = z1 z2 l3 */
ec_mulm (z3, z1, z2, ctx);
ec_mulm (z3, z3, l3, ctx);
/* x3 = l6^2 - l7 l3^2 */
ec_powm (t1, l6, mpi_const (MPI_C_TWO), ctx);
ec_powm (t2, l3, mpi_const (MPI_C_TWO), ctx);
ec_mulm (t2, t2, l7, ctx);
ec_subm (x3, t1, t2, ctx);
/* l9 = l7 l3^2 - 2 x3 */
ec_mulm (t1, x3, mpi_const (MPI_C_TWO), ctx);
ec_subm (l9, t2, t1, ctx);
/* y3 = (l9 l6 - l8 l3^3)/2 */
ec_mulm (l9, l9, l6, ctx);
ec_powm (t1, l3, mpi_const (MPI_C_THREE), ctx); /* fixme: Use saved value*/
ec_mulm (t1, t1, l8, ctx);
ec_subm (y3, l9, t1, ctx);
ec_mulm (y3, y3, ec_get_two_inv_p (ctx), ctx);
}
}
#undef x1
#undef y1
#undef z1
#undef x2
#undef y2
#undef z2
#undef x3
#undef y3
#undef z3
#undef l1
#undef l2
#undef l3
#undef l4
#undef l5
#undef l6
#undef l7
#undef l8
#undef l9
#undef t1
#undef t2
}
/* Scalar point multiplication - the main function for ECC. If takes
an integer SCALAR and a POINT as well as the usual context CTX.
RESULT will be set to the resulting point. */
void
_gcry_mpi_ec_mul_point (mpi_point_t result,
gcry_mpi_t scalar, mpi_point_t point,
mpi_ec_t ctx)
{
#if 0
/* Simple left to right binary method. GECC Algorithm 3.27 */
unsigned int nbits;
int i;
nbits = mpi_get_nbits (scalar);
mpi_set_ui (result->x, 1);
mpi_set_ui (result->y, 1);
mpi_set_ui (result->z, 0);
for (i=nbits-1; i >= 0; i--)
{
_gcry_mpi_ec_dup_point (result, result, ctx);
if (mpi_test_bit (scalar, i) == 1)
_gcry_mpi_ec_add_points (result, result, point, ctx);
}
#else
gcry_mpi_t x1, y1, z1, k, h, yy;
unsigned int i, loops;
mpi_point_struct p1, p2, p1inv;
x1 = mpi_alloc_like (ctx->p);
y1 = mpi_alloc_like (ctx->p);
h = mpi_alloc_like (ctx->p);
k = mpi_copy (scalar);
yy = mpi_copy (point->y);
if ( mpi_is_neg (k) )
{
k->sign = 0;
ec_invm (yy, yy, ctx);
}
if (!mpi_cmp_ui (point->z, 1))
{
mpi_set (x1, point->x);
mpi_set (y1, yy);
}
else
{
gcry_mpi_t z2, z3;
z2 = mpi_alloc_like (ctx->p);
z3 = mpi_alloc_like (ctx->p);
ec_mulm (z2, point->z, point->z, ctx);
ec_mulm (z3, point->z, z2, ctx);
ec_invm (z2, z2, ctx);
ec_mulm (x1, point->x, z2, ctx);
ec_invm (z3, z3, ctx);
ec_mulm (y1, yy, z3, ctx);
mpi_free (z2);
mpi_free (z3);
}
z1 = mpi_copy (mpi_const (MPI_C_ONE));
mpi_mul (h, k, mpi_const (MPI_C_THREE)); /* h = 3k */
loops = mpi_get_nbits (h);
if (loops < 2)
{
/* If SCALAR is zero, the above mpi_mul sets H to zero and thus
LOOPs will be zero. To avoid an underflow of I in the main
loop we set LOOP to 2 and the result to (0,0,0). */
loops = 2;
mpi_clear (result->x);
mpi_clear (result->y);
mpi_clear (result->z);
}
else
{
mpi_set (result->x, point->x);
mpi_set (result->y, yy);
mpi_set (result->z, point->z);
}
mpi_free (yy); yy = NULL;
p1.x = x1; x1 = NULL;
p1.y = y1; y1 = NULL;
p1.z = z1; z1 = NULL;
point_init (&p2);
point_init (&p1inv);
for (i=loops-2; i > 0; i--)
{
_gcry_mpi_ec_dup_point (result, result, ctx);
if (mpi_test_bit (h, i) == 1 && mpi_test_bit (k, i) == 0)
{
point_set (&p2, result);
_gcry_mpi_ec_add_points (result, &p2, &p1, ctx);
}
if (mpi_test_bit (h, i) == 0 && mpi_test_bit (k, i) == 1)
{
point_set (&p2, result);
/* Invert point: y = p - y mod p */
point_set (&p1inv, &p1);
ec_subm (p1inv.y, ctx->p, p1inv.y, ctx);
_gcry_mpi_ec_add_points (result, &p2, &p1inv, ctx);
}
}
point_free (&p1);
point_free (&p2);
point_free (&p1inv);
mpi_free (h);
mpi_free (k);
#endif
}
void
gcry_mpi_ec_dup (gcry_mpi_point_t w, gcry_mpi_point_t u, gcry_ctx_t ctx)
{
_gcry_mpi_ec_dup_point (w, u, _gcry_ctx_get_pointer (ctx, CONTEXT_TYPE_EC));
}