added MirOTR

git-svn-id: http://svn.miranda-ng.org/main/trunk@83 1316c22d-e87f-b044-9b9b-93d7a3e3ba9c

1 files changed, 709 insertions, 0 deletions

diff --git a/plugins/MirOTR/libgcrypt-1.4.6/mpi/ec.c b/plugins/MirOTR/libgcrypt-1.4.6/mpi/ec.c
new file mode 100644
index 0000000000..4a3a5f8c08
--- /dev/null
+++ b/plugins/MirOTR/libgcrypt-1.4.6/mpi/ec.c
@@ -0,0 +1,709 @@
+/* ec.c -  Elliptic Curve functions
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This file is part of Libgcrypt.
+  
+   Libgcrypt is free software; you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of
+   the License, or (at your option) any later version.
+  
+   Libgcrypt is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+  
+   You should have received a copy of the GNU Lesser General Public
+   License along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+   USA.  */
+
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "mpi-internal.h"
+#include "longlong.h"
+#include "g10lib.h"
+
+
+#define point_init(a)  _gcry_mpi_ec_point_init ((a))
+#define point_free(a)  _gcry_mpi_ec_point_free ((a))
+
+
+/* Object to represent a point in projective coordinates. */
+/* Currently defined in mpi.h */
+
+/* This context is used with all our EC functions. */
+struct mpi_ec_ctx_s
+{
+  /* Domain parameters.  */
+  gcry_mpi_t p;   /* Prime specifying the field GF(p).  */
+  gcry_mpi_t a;   /* First coefficient of the Weierstrass equation.  */
+
+  int a_is_pminus3;  /* True if A = P - 3. */
+
+  /* Some often used constants.  */
+  gcry_mpi_t one;
+  gcry_mpi_t two;
+  gcry_mpi_t three;
+  gcry_mpi_t four;
+  gcry_mpi_t eight;
+  gcry_mpi_t two_inv_p;
+
+  /* Scratch variables.  */
+  gcry_mpi_t scratch[11];
+  
+  /* Helper for fast reduction.  */
+/*   int nist_nbits; /\* If this is a NIST curve, the number of bits.  *\/ */
+/*   gcry_mpi_t s[10]; */
+/*   gcry_mpi_t c; */
+
+};
+
+
+
+/* Initialized a point object.  gcry_mpi_ec_point_free shall be used
+   to release this object.  */
+void
+_gcry_mpi_ec_point_init (mpi_point_t *p)
+{
+  p->x = mpi_new (0);
+  p->y = mpi_new (0);
+  p->z = mpi_new (0);
+}
+
+
+/* Release a point object. */
+void
+_gcry_mpi_ec_point_free (mpi_point_t *p)
+{
+  mpi_free (p->x); p->x = NULL;
+  mpi_free (p->y); p->y = NULL;
+  mpi_free (p->z); p->z = NULL;
+}
+
+/* Set the value from S into D.  */
+static void
+point_set (mpi_point_t *d, mpi_point_t *s)
+{
+  mpi_set (d->x, s->x);
+  mpi_set (d->y, s->y);
+  mpi_set (d->z, s->z);
+}
+
+
+
+static void
+ec_addm (gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, mpi_ec_t ctx)
+{
+  mpi_addm (w, u, v, ctx->p);
+}
+
+static void
+ec_subm (gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, mpi_ec_t ctx)
+{
+  mpi_subm (w, u, v, ctx->p);
+}
+
+static void
+ec_mulm (gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, mpi_ec_t ctx)
+{
+#if 0
+  /* NOTE: This code works only for limb sizes of 32 bit.  */
+  mpi_limb_t *wp, *sp;
+
+  if (ctx->nist_nbits == 192)
+    {
+      mpi_mul (w, u, v);
+      mpi_resize (w, 12);
+      wp = w->d;
+
+      sp = ctx->s[0]->d;
+      sp[0*2+0] = wp[0*2+0];
+      sp[0*2+1] = wp[0*2+1];
+      sp[1*2+0] = wp[1*2+0];
+      sp[1*2+1] = wp[1*2+1];
+      sp[2*2+0] = wp[2*2+0];
+      sp[2*2+1] = wp[2*2+1];
+
+      sp = ctx->s[1]->d;
+      sp[0*2+0] = wp[3*2+0];
+      sp[0*2+1] = wp[3*2+1];
+      sp[1*2+0] = wp[3*2+0];
+      sp[1*2+1] = wp[3*2+1];
+      sp[2*2+0] = 0;
+      sp[2*2+1] = 0;
+
+      sp = ctx->s[2]->d;
+      sp[0*2+0] = 0;
+      sp[0*2+1] = 0;
+      sp[1*2+0] = wp[4*2+0];
+      sp[1*2+1] = wp[4*2+1];
+      sp[2*2+0] = wp[4*2+0];
+      sp[2*2+1] = wp[4*2+1];
+
+      sp = ctx->s[3]->d;
+      sp[0*2+0] = wp[5*2+0];
+      sp[0*2+1] = wp[5*2+1];
+      sp[1*2+0] = wp[5*2+0];
+      sp[1*2+1] = wp[5*2+1];
+      sp[2*2+0] = wp[5*2+0];
+      sp[2*2+1] = wp[5*2+1];
+
+      ctx->s[0]->nlimbs = 6;
+      ctx->s[1]->nlimbs = 6;
+      ctx->s[2]->nlimbs = 6;
+      ctx->s[3]->nlimbs = 6;
+
+      mpi_add (ctx->c, ctx->s[0], ctx->s[1]);
+      mpi_add (ctx->c, ctx->c, ctx->s[2]);
+      mpi_add (ctx->c, ctx->c, ctx->s[3]);
+
+      while ( mpi_cmp (ctx->c, ctx->p ) >= 0 )
+        mpi_sub ( ctx->c, ctx->c, ctx->p );
+      mpi_set (w, ctx->c);
+    }
+  else if (ctx->nist_nbits == 384)
+    {
+      int i;
+      mpi_mul (w, u, v);
+      mpi_resize (w, 24);
+      wp = w->d;
+
+#define NEXT(a) do { ctx->s[(a)]->nlimbs = 12; \
+                     sp = ctx->s[(a)]->d; \
+                     i = 0; } while (0)
+#define X(a) do { sp[i++] = wp[(a)];} while (0)
+#define X0(a) do { sp[i++] = 0; } while (0)
+      NEXT(0); 
+      X(0);X(1);X(2);X(3);X(4);X(5);X(6);X(7);X(8);X(9);X(10);X(11);
+      NEXT(1);
+      X0();X0();X0();X0();X(21);X(22);X(23);X0();X0();X0();X0();X0();
+      NEXT(2);
+      X(12);X(13);X(14);X(15);X(16);X(17);X(18);X(19);X(20);X(21);X(22);X(23);
+      NEXT(3);
+      X(21);X(22);X(23);X(12);X(13);X(14);X(15);X(16);X(17);X(18);X(19);X(20);
+      NEXT(4);
+      X0();X(23);X0();X(20);X(12);X(13);X(14);X(15);X(16);X(17);X(18);X(19);
+      NEXT(5);
+      X0();X0();X0();X0();X(20);X(21);X(22);X(23);X0();X0();X0();X0();
+      NEXT(6);
+      X(20);X0();X0();X(21);X(22);X(23);X0();X0();X0();X0();X0();X0();
+      NEXT(7);
+      X(23);X(12);X(13);X(14);X(15);X(16);X(17);X(18);X(19);X(20);X(21);X(22);
+      NEXT(8);
+      X0();X(20);X(21);X(22);X(23);X0();X0();X0();X0();X0();X0();X0();
+      NEXT(9);
+      X0();X0();X0();X(23);X(23);X0();X0();X0();X0();X0();X0();X0();
+#undef X0
+#undef X
+#undef NEXT
+      mpi_add (ctx->c, ctx->s[0], ctx->s[1]);
+      mpi_add (ctx->c, ctx->c, ctx->s[1]);
+      mpi_add (ctx->c, ctx->c, ctx->s[2]);
+      mpi_add (ctx->c, ctx->c, ctx->s[3]);
+      mpi_add (ctx->c, ctx->c, ctx->s[4]);
+      mpi_add (ctx->c, ctx->c, ctx->s[5]);
+      mpi_add (ctx->c, ctx->c, ctx->s[6]);
+      mpi_sub (ctx->c, ctx->c, ctx->s[7]);
+      mpi_sub (ctx->c, ctx->c, ctx->s[8]);
+      mpi_sub (ctx->c, ctx->c, ctx->s[9]);
+
+      while ( mpi_cmp (ctx->c, ctx->p ) >= 0 )
+        mpi_sub ( ctx->c, ctx->c, ctx->p );
+      while ( ctx->c->sign )
+        mpi_add ( ctx->c, ctx->c, ctx->p );
+      mpi_set (w, ctx->c);
+    }
+  else
+#endif /*0*/
+    mpi_mulm (w, u, v, ctx->p);
+}
+
+static void
+ec_powm (gcry_mpi_t w, const gcry_mpi_t b, const gcry_mpi_t e,
+         mpi_ec_t ctx)
+{
+  mpi_powm (w, b, e, ctx->p);
+}
+
+static void
+ec_invm (gcry_mpi_t x, gcry_mpi_t a, mpi_ec_t ctx)
+{
+  mpi_invm (x, a, ctx->p);
+}
+
+
+
+/* This function returns a new context for elliptic curve based on the
+   field GF(p).  P is the prime specifying thuis field, A is the first
+   coefficient. 
+
+   This context needs to be released using _gcry_mpi_ec_free.  */
+mpi_ec_t 
+_gcry_mpi_ec_init (gcry_mpi_t p, gcry_mpi_t a)
+{
+  int i;
+  mpi_ec_t ctx;
+  gcry_mpi_t tmp;
+
+  mpi_normalize (p);
+  mpi_normalize (a);
+
+  /* Fixme: Do we want to check some constraints? e.g.
+     a < p
+  */
+
+  ctx = gcry_xcalloc (1, sizeof *ctx);
+
+  ctx->p = mpi_copy (p);
+  ctx->a = mpi_copy (a);
+
+  tmp = mpi_alloc_like (ctx->p);
+  mpi_sub_ui (tmp, ctx->p, 3);
+  ctx->a_is_pminus3 = !mpi_cmp (ctx->a, tmp);
+  mpi_free (tmp);
+
+
+  /* Allocate constants.  */
+  ctx->one   = mpi_alloc_set_ui (1);
+  ctx->two   = mpi_alloc_set_ui (2);
+  ctx->three = mpi_alloc_set_ui (3);
+  ctx->four  = mpi_alloc_set_ui (4);
+  ctx->eight = mpi_alloc_set_ui (8);
+  ctx->two_inv_p = mpi_alloc (0);
+  ec_invm (ctx->two_inv_p, ctx->two, ctx);
+
+  /* Allocate scratch variables.  */
+  for (i=0; i< DIM(ctx->scratch); i++)
+    ctx->scratch[i] = mpi_alloc_like (ctx->p);
+
+  /* Prepare for fast reduction.  */
+  /* FIXME: need a test for NIST values.  However it does not gain us
+     any real advantage, for 384 bits it is actually slower than using
+     mpi_mulm.  */
+/*   ctx->nist_nbits = mpi_get_nbits (ctx->p); */
+/*   if (ctx->nist_nbits == 192) */
+/*     { */
+/*       for (i=0; i < 4; i++) */
+/*         ctx->s[i] = mpi_new (192); */
+/*       ctx->c    = mpi_new (192*2); */
+/*     } */
+/*   else if (ctx->nist_nbits == 384) */
+/*     { */
+/*       for (i=0; i < 10; i++) */
+/*         ctx->s[i] = mpi_new (384); */
+/*       ctx->c    = mpi_new (384*2); */
+/*     } */
+
+  return ctx;
+}
+
+void
+_gcry_mpi_ec_free (mpi_ec_t ctx)
+{
+  int i;
+
+  if (!ctx)
+    return;
+
+  mpi_free (ctx->p);
+  mpi_free (ctx->a);
+
+  mpi_free (ctx->one);
+  mpi_free (ctx->two);
+  mpi_free (ctx->three);
+  mpi_free (ctx->four);
+  mpi_free (ctx->eight);
+
+  mpi_free (ctx->two_inv_p);
+
+  for (i=0; i< DIM(ctx->scratch); i++)
+    mpi_free (ctx->scratch[i]);
+
+/*   if (ctx->nist_nbits == 192) */
+/*     { */
+/*       for (i=0; i < 4; i++) */
+/*         mpi_free (ctx->s[i]); */
+/*       mpi_free (ctx->c); */
+/*     } */
+/*   else if (ctx->nist_nbits == 384) */
+/*     { */
+/*       for (i=0; i < 10; i++) */
+/*         mpi_free (ctx->s[i]); */
+/*       mpi_free (ctx->c); */
+/*     } */
+
+  gcry_free (ctx);
+}
+
+/* Compute the affine coordinates from the projective coordinates in
+   POINT.  Set them into X and Y.  If one coordinate is not required,
+   X or Y may be passed as NULL.  CTX is the usual context. Returns: 0
+   on success or !0 if POINT is at infinity.  */
+int
+_gcry_mpi_ec_get_affine (gcry_mpi_t x, gcry_mpi_t y, mpi_point_t *point,
+                         mpi_ec_t ctx)
+{
+  gcry_mpi_t z1, z2, z3;
+
+  if (!mpi_cmp_ui (point->z, 0))
+    return -1;
+
+  z1 = mpi_new (0);
+  z2 = mpi_new (0);
+  ec_invm (z1, point->z, ctx);  /* z1 = z^(-1) mod p  */
+  ec_mulm (z2, z1, z1, ctx);    /* z2 = z^(-2) mod p  */
+
+  if (x)
+    ec_mulm (x, point->x, z2, ctx);
+
+  if (y)
+    {
+      z3 = mpi_new (0);
+      ec_mulm (z3, z2, z1, ctx);      /* z3 = z^(-3) mod p  */
+      ec_mulm (y, point->y, z3, ctx);
+      mpi_free (z3);
+    }
+
+  mpi_free (z2);
+  mpi_free (z1);
+  return 0;
+}
+
+
+
+
+
+/*  RESULT = 2 * POINT  */
+void
+_gcry_mpi_ec_dup_point (mpi_point_t *result, mpi_point_t *point, mpi_ec_t ctx)
+{
+#define x3 (result->x)
+#define y3 (result->y)
+#define z3 (result->z)
+#define t1 (ctx->scratch[0])
+#define t2 (ctx->scratch[1])
+#define t3 (ctx->scratch[2])
+#define l1 (ctx->scratch[3])
+#define l2 (ctx->scratch[4])
+#define l3 (ctx->scratch[5])
+
+  if (!mpi_cmp_ui (point->y, 0) || !mpi_cmp_ui (point->z, 0))
+    {                      
+      /* P_y == 0 || P_z == 0 => [1:1:0] */
+      mpi_set_ui (x3, 1);
+      mpi_set_ui (y3, 1);
+      mpi_set_ui (z3, 0);
+    }
+  else
+    {
+      if (ctx->a_is_pminus3)  /* Use the faster case.  */
+        {               
+          /* L1 = 3(X - Z^2)(X + Z^2) */
+          /*                          T1: used for Z^2. */
+          /*                          T2: used for the right term.  */
+          ec_powm (t1, point->z, ctx->two, ctx);   
+          ec_subm (l1, point->x, t1, ctx);   
+          ec_mulm (l1, l1, ctx->three, ctx);
+          ec_addm (t2, point->x, t1, ctx);   
+          ec_mulm (l1, l1, t2, ctx);   
+        }
+      else /* Standard case. */
+        {
+          /* L1 = 3X^2 + aZ^4 */
+          /*                          T1: used for aZ^4. */
+          ec_powm (l1, point->x, ctx->two, ctx); 
+          ec_mulm (l1, l1, ctx->three, ctx);  
+          ec_powm (t1, point->z, ctx->four, ctx); 
+          ec_mulm (t1, t1, ctx->a, ctx);    
+          ec_addm (l1, l1, t1, ctx); 
+        }
+      /* Z3 = 2YZ */
+      ec_mulm (z3, point->y, point->z, ctx);
+      ec_mulm (z3, z3, ctx->two, ctx);       
+
+      /* L2 = 4XY^2 */
+      /*                              T2: used for Y2; required later. */
+      ec_powm (t2, point->y, ctx->two, ctx);
+      ec_mulm (l2, t2, point->x, ctx);
+      ec_mulm (l2, l2, ctx->four, ctx);
+
+      /* X3 = L1^2 - 2L2 */
+      /*                              T1: used for L2^2. */
+      ec_powm (x3, l1, ctx->two, ctx);
+      ec_mulm (t1, l2, ctx->two, ctx);
+      ec_subm (x3, x3, t1, ctx);
+      
+      /* L3 = 8Y^4 */
+      /*                              T2: taken from above. */
+      ec_powm (t2, t2, ctx->two, ctx); 
+      ec_mulm (l3, t2, ctx->eight, ctx);
+
+      /* Y3 = L1(L2 - X3) - L3 */
+      ec_subm (y3, l2, x3, ctx);
+      ec_mulm (y3, y3, l1, ctx);
+      ec_subm (y3, y3, l3, ctx);
+    }
+
+#undef x3
+#undef y3
+#undef z3
+#undef t1
+#undef t2
+#undef t3
+#undef l1
+#undef l2
+#undef l3
+}
+
+
+
+/* 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->scratch[0])
+#define l2 (ctx->scratch[1])
+#define l3 (ctx->scratch[2])
+#define l4 (ctx->scratch[3])
+#define l5 (ctx->scratch[4])
+#define l6 (ctx->scratch[5])
+#define l7 (ctx->scratch[6])
+#define l8 (ctx->scratch[7])
+#define l9 (ctx->scratch[8])
+#define t1 (ctx->scratch[9])
+#define t2 (ctx->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, ctx->two, ctx); 
+          ec_mulm (l1, l1, x1, ctx);
+        }
+      if (z1_is_one)
+        mpi_set (l2, x1);
+      else
+        {
+          ec_powm (l2, z1, ctx->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, ctx->three, ctx);
+      ec_mulm (l4, l4, y1, ctx);
+      /* l5 = y2 z1^3  */
+      ec_powm (l5, z1, ctx->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, ctx->two, ctx);
+          ec_powm (t2, l3, ctx->two, ctx);
+          ec_mulm (t2, t2, l7, ctx);
+          ec_subm (x3, t1, t2, ctx);
+          /* l9 = l7 l3^2 - 2 x3  */
+          ec_mulm (t1, x3, ctx->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, ctx->three, ctx); /* fixme: Use saved value*/
+          ec_mulm (t1, t1, l8, ctx);
+          ec_subm (y3, l9, t1, ctx);
+          ec_mulm (y3, y3, ctx->two_inv_p, 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_t 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 (ctx->one);
+
+  mpi_mul (h, k, ctx->three); /* h = 3k */
+  loops = mpi_get_nbits (h);
+
+  mpi_set (result->x, point->x);
+  mpi_set (result->y, yy); mpi_free (yy); yy = NULL;
+  mpi_set (result->z, point->z); 
+
+  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
+}
+