Keep numbers positive.

[u/mdw/catacomb] / calc / ec2.cal

/* -*-apcalc-*-
 *
 * $Id: ec2.cal,v 1.3 2004/04/01 12:50:27 mdw Exp $
 *
 * Testbed for elliptic curve arithmetic over binary fields
 *
 * (c) 2004 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * Catacomb 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 Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: ec2.cal,v $
 * Revision 1.3  2004/04/01 12:50:27  mdw
 * Remove debugging code.
 *
 * Revision 1.2  2004/03/21 22:52:06  mdw
 * Merge and close elliptic curve branch.
 *
 * Revision 1.1.2.1  2004/03/21 22:39:46  mdw
 * Elliptic curves on binary fields work.
 *
 * Revision 1.1.4.2  2004/03/20 00:13:31  mdw
 * Projective coordinates for prime curves
 *
 * Revision 1.1.4.1  2003/06/10 13:43:53  mdw
 * Simple (non-projective) curves over prime fields now seem to work.
 *
 * Revision 1.1  2000/10/08 16:01:37  mdw
 * Prototypes of various bits of code.
 *
 */

/*----- Object types ------------------------------------------------------*/

obj ec2_curve { a, b, p };
obj ec2_pt { x, y, e };
obj ecpp_pt { x, y, z, e };

/*----- Main code ---------------------------------------------------------*/

define ec2_curve(a, b, p)
{
  local obj ec2_curve e;
  e.a = a;
  e.b = b;
  e.p = p;
  return (e);
}

define ec2_pt(x, y, e)
{
  local obj ec2_pt p;
  p.x = x % e.p;
  p.y = y % e.p;
  p.e = e;
  return (p);
}

define ec2_pt_print(a)
{
  print "(" : a.x : ", " : a.y : ")" :;
}

define ec2_pt_add(a, b)
{
  local e, alpha;
  local obj ec2_pt d;

  if (a == 0)
    d = b;
  else if (b == 0)
    d = a;
  else if (!istype(a, b))
    quit "bad type arguments to ec2_pt_add";
  else if (a.e != b.e)
    quit "points from different curves in ec2_pt_add";
  else {
    e = a.e;
    if (a.x != b.x) {
      alpha = ((a.y + b.y) * gf_inv(a.x + b.x, e.p)) % e.p;
      d.x = (e.a + alpha^2 + alpha + a.x + b.x) % e.p;
    } else if (a.y != b.y || a.x == gf(0))
      return 0;
    else {
      alpha = a.x + a.y * gf_inv(a.x, e.p) % e.p;
      d.x = (e.a + alpha^2 + alpha) % e.p;
    }
    d.y = ((a.x + d.x) * alpha + d.x + a.y) % e.p;
    d.e = e;
  }

  return (d);
}

define ec2_pt_dbl(a)
{
  local e, alpha;
  local obj ec2_pt d;
  if (istype(a, 1))
    return (0);
  e = a.e;
  alpha = a.x + a.y * gf_inv(a.x, e.p) % e.p;
  d.x = (e.a + alpha^2 + alpha) % e.p;
  d.y = ((a.x + d.x) * alpha + d.x + a.y) % e.p;
  d.e = e;
  return (d);
}

define ec2_pt_sub(a, b) { return ec2_pt_add(a, ec2_pt_neg(b)); }

define ec2_pt_neg(a)
{
  local obj ec2_pt d;
  d.x = a.x;
  d.y = a.x + a.y;
  d.e = a.e;
  return (d);
}

define ec2_pt_check(a)
{
  local e;

  e = a.e;
  if ((a.y^2 + a.x * a.y) % e.p != (a.x^3 + e.a * a.x^2 + e.b) % e.p)
    quit "bad curve point";
}

define ec2_pt_mul(a, b)
{
  local p, n;
  local d;

  if (istype(a, 1)) {
    n = a;
    p = b;
  } else if (istype(b, 1)) {
    n = b;
    p = a;
  } else
    return (newerror("bad arguments to ec2_pt_mul"));

  d = 0;
  while (n) {
    if (n & 1)
      d += p;
    n >>= 1;
    p = ec2_pt_dbl(p);
  }
  return (d);
}

/*----- FIPS186-2 standard curves -----------------------------------------*/

b163 = ec2_curve(gf(1),gf(0x20a601907b8c953ca1481eb10512f78744a3205fd),
		 gf(0x800000000000000000000000000000000000000c9));
b163_r = 5846006549323611672814742442876390689256843201587;
b163_g = ec2_pt(0x3f0eba16286a2d57ea0991168d4994637e8343e36,
		0x0d51fbc6c71a0094fa2cdd545b11c5c0c797324f1, b163);

/*----- That's all, folks -------------------------------------------------*/