General robustification.

[u/mdw/catacomb] / g-prime.c

/* -*-c-*-
 *
 * $Id: g-prime.c,v 1.2 2004/04/03 03:32:05 mdw Exp $
 *
 * Abstraction for prime groups
 *
 * (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: g-prime.c,v $
 * Revision 1.2  2004/04/03 03:32:05  mdw
 * General robustification.
 *
 * Revision 1.1  2004/04/01 12:50:09  mdw
 * Add cyclic group abstraction, with test code.  Separate off exponentation
 * functions for better static linking.  Fix a buttload of bugs on the way.
 * Generally ensure that negative exponents do inversion correctly.  Add
 * table of standard prime-field subgroups.  (Binary field subgroups are
 * currently unimplemented but easy to add if anyone ever finds a good one.)
 *
 */

/*----- Header files ------------------------------------------------------*/

#include <mLib/sub.h>

#include "mpmont.h"
#include "pgen.h"

#define ge mp *
#include "group.h"

/*----- Data structures ---------------------------------------------------*/

typedef struct gctx {
  group g;
  mp *gen;
  mpmont mm;
} gctx;

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

/* --- Group operations --- */

static void gdestroygroup(group *gg) {
  gctx *g = (gctx *)gg;
  mp_drop(g->gen); mp_drop(g->g.r); mp_drop(g->g.h);
  mpmont_destroy(&g->mm);
  DESTROY(g);
}

static mp **gcreate(group *gg)
  { mp **x = CREATE(mp *); *x = MP_COPY(*gg->i); return (x); }

static void gcopy(group *gg, mp **d, mp **x)
  { mp *t = MP_COPY(*x); MP_DROP(*d); *d = t; }

static void gburn(group *gg, mp **x) { (*x)->f |= MP_BURN; }

static void gdestroy(group *gg, mp **x) { MP_DROP(*x); DESTROY(x); }

static int gsamep(group *gg, group *hh) {
  gctx *g = (gctx *)gg, *h = (gctx *)hh;
  return (MP_EQ(g->mm.m, h->mm.m));
}

static int geq(group *gg, mp **x, mp **y) { return (MP_EQ(*x, *y)); }

static const char *gcheck(group *gg, grand *gr) {
  gctx *g = (gctx *)gg; int rc; mp *t;
  if (!pgen_primep(g->mm.m, gr)) return ("p is not prime");
  t = mp_mul(MP_NEW, g->g.r, g->g.h); t = mp_add(t, t, MP_ONE);
  rc = MP_EQ(t, g->mm.m); MP_DROP(t); if (!rc) return ("not a subgroup");
  return (group_stdcheck(gg, gr));
}

static void gmul(group *gg, mp **d, mp **x, mp **y)
  { gctx *g = (gctx *)gg; *d = mpmont_mul(&g->mm, *d, *x, *y); }

static void gsqr(group *gg, mp **d, mp **x) {
  gctx *g = (gctx *)gg; mp *r = mp_sqr(*d, *x);
  *d = mpmont_reduce(&g->mm, r, r);
}

static void ginv(group *gg, mp **d, mp **x) {
  gctx *g = (gctx *)gg; mp *r = mpmont_reduce(&g->mm, *d, *x);
  mp_gcd(0, 0, &r, g->mm.m, r); *d = mpmont_mul(&g->mm, r, r, g->mm.r2);
}

static void gexp(group *gg, mp **d, mp **x, mp *n)
  { gctx *g = (gctx *)gg; *d = mpmont_expr(&g->mm, *d, *x, n); }

static void gmexp(group *gg, mp **d, const group_expfactor *f, size_t n) {
  gctx *g = (gctx *)gg; size_t i;
  mp_expfactor *ff = xmalloc(n * sizeof(mp_expfactor));
  for (i = 0; i < n; i++) { ff[i].base = *f[i].base; ff[i].exp = f[i].exp; }
  *d = mpmont_mexpr(&g->mm, *d, ff, n); xfree(ff);
}

static int gread(group *gg, mp **d, const mptext_ops *ops, void *p) {
  gctx *g = (gctx *)gg; mp *t;
  if ((t = mp_read(MP_NEW, 0, ops, p)) == 0) return (-1);
  mp_drop(*d); *d = mpmont_mul(&g->mm, t, t, g->mm.r2); return (0);
}

static int gwrite(group *gg, mp **x, const mptext_ops *ops, void *p) {
  gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
  int rc = mp_write(t, 10, ops, p); MP_DROP(t); return (rc);
}

static mp *gtoint(group *gg, mp *d, mp **x)
  { gctx *g = (gctx *)gg; return (mpmont_reduce(&g->mm, d, *x)); }

static int gfromint(group *gg, mp **d, mp *x) {
  gctx *g = (gctx *)gg; mp_div(0, &x, x, g->mm.m); mp_drop(*d);
  *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return (0);
}

static int gtobuf(group *gg, buf *b, mp **x) {
  gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
  int rc = buf_putmp(b, t); MP_DROP(t); return (rc);
}

static int gfrombuf(group *gg, buf *b, mp **d) {
  gctx * g = (gctx *)gg; mp *x; if ((x = buf_getmp(b)) == 0) return (-1);
  mp_div(0, &x, x, g->mm.m); mp_drop(*d);
  *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return(0);
}

/* --- @group_prime@ --- *
 *
 * Arguments:	@const gprime_param *gp@ = group parameters
 *
 * Returns:	A pointer to the group, or null.
 *
 * Use:		Constructs an abstract group interface for a subgroup of a
 *		prime field.  Group elements are @mp *@ pointers.
 */

static const group_ops gops = {
  GTY_PRIME,
  gdestroygroup, gcreate, gcopy, gburn, gdestroy,
  gsamep, geq, group_stdidentp,
  gcheck,
  gmul, gsqr, ginv, group_stddiv, gexp, gmexp,
  gread, gwrite,
  gtoint, gfromint, group_stdtoec, group_stdfromec, gtobuf, gfrombuf
};

group *group_prime(const gprime_param *gp)
{
  gctx *g;

  if (!MP_ISPOS(gp->p) || !MP_ISODD(gp->p))
    return (0);
  g = CREATE(gctx);
  g->g.ops = &gops;
  g->g.nbits = mp_bits(gp->p);
  g->g.noctets = (g->g.nbits + 7) >> 3;
  mpmont_create(&g->mm, gp->p);
  g->g.i = &g->mm.r;
  g->gen = mpmont_mul(&g->mm, MP_NEW, gp->g, g->mm.r2);
  g->g.g = &g->gen;
  g->g.r = MP_COPY(gp->q);
  g->g.h = MP_NEW; mp_div(&g->g.h, 0, gp->p, gp->q);
  return (&g->g);
}

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