mdw@git.distorted.org.uk Git - catacomb/blob - math/g-prime.c

   1 /* -*-c-*-
   2  *
   3  * Abstraction for prime groups
   4  *
   5  * (c) 2004 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <mLib/sub.h>
  31
  32 #include "mpmont.h"
  33 #include "pgen.h"
  34
  35 #define ge ge_prime
  36 #include "group-guts.h"
  37
  38 /*----- Main code ---------------------------------------------------------*/
  39
  40 /* --- Group operations --- */
  41
  42 static void gdestroygroup(group *gg) {
  43   gctx_prime *g = (gctx_prime *)gg;
  44   mp_drop(g->gen.x); mp_drop(g->g.r); mp_drop(g->g.h);
  45   mpmont_destroy(&g->mm);
  46   DESTROY(g);
  47 }
  48
  49 static ge_prime *gcreate(group *gg) {
  50   gctx_prime *g = (gctx_prime *)gg; ge_prime *x = CREATE(ge_prime);
  51   x->x = MP_COPY(g->i.x); return (x);
  52 }
  53
  54 static void gcopy(group *gg, ge_prime *d, ge_prime *x)
  55   { mp *t = MP_COPY(x->x); MP_DROP(d->x); d->x = t; }
  56
  57 static void gburn(group *gg, ge_prime *x) { x->x->f |= MP_BURN; }
  58
  59 static void gdestroy(group *gg, ge_prime *x) { MP_DROP(x->x); DESTROY(x); }
  60
  61 static int gsamep(group *gg, group *hh) {
  62   gctx_prime *g = (gctx_prime *)gg, *h = (gctx_prime *)hh;
  63   return (MP_EQ(g->mm.m, h->mm.m));
  64 }
  65
  66 static int geq(group *gg, ge_prime *x, ge_prime *y)
  67   { return (MP_EQ(x->x, y->x)); }
  68
  69 static const char *gcheck(group *gg, grand *gr) {
  70   gctx_prime *g = (gctx_prime *)gg; int rc; mp *t;
  71   if (!pgen_primep(g->mm.m, gr)) return ("p is not prime");
  72   t = mp_mul(MP_NEW, g->g.r, g->g.h); t = mp_add(t, t, MP_ONE);
  73   rc = MP_EQ(t, g->mm.m); MP_DROP(t); if (!rc) return ("not a subgroup");
  74   return (group_stdcheck(gg, gr));
  75 }
  76
  77 static void gmul(group *gg, ge_prime *d, ge_prime *x, ge_prime *y) {
  78   gctx_prime *g = (gctx_prime *)gg;
  79   d->x = mpmont_mul(&g->mm, d->x, x->x, y->x);
  80 }
  81
  82 static void gsqr(group *gg, ge_prime *d, ge_prime *x) {
  83   gctx_prime *g = (gctx_prime *)gg; mp *r = mp_sqr(d->x, x->x);
  84   d->x = mpmont_reduce(&g->mm, r, r);
  85 }
  86
  87 static void ginv(group *gg, ge_prime *d, ge_prime *x) {
  88   gctx_prime *g = (gctx_prime *)gg;
  89   mp *r = mpmont_reduce(&g->mm, d->x, x->x);
  90   r = mp_modinv(r, r, g->mm.m); d->x = mpmont_mul(&g->mm, r, r, g->mm.r2);
  91 }
  92
  93 static void gexp(group *gg, ge_prime *d, ge_prime *x, mp *n)
  94 {
  95   gctx_prime *g = (gctx_prime *)gg;
  96   d->x = mpmont_expr(&g->mm, d->x, x->x, n);
  97 }
  98
  99 static void gmexp(group *gg, ge_prime *d, const group_expfactor *f, size_t n)
 100 {
 101   gctx_prime *g = (gctx_prime *)gg; size_t i;
 102   mp_expfactor *ff = xmalloc(n * sizeof(mp_expfactor));
 103   for (i = 0; i < n; i++)
 104     { ff[i].base = f[i].base->x; ff[i].exp = f[i].exp; }
 105   d->x = mpmont_mexpr(&g->mm, d->x, ff, n); xfree(ff);
 106 }
 107
 108 static int gread(group *gg, ge_prime *d, const mptext_ops *ops, void *p) {
 109   gctx_prime *g = (gctx_prime *)gg; mp *t;
 110   if ((t = mp_read(MP_NEW, 0, ops, p)) == 0) return (-1);
 111   mp_drop(d->x); d->x = mpmont_mul(&g->mm, t, t, g->mm.r2); return (0);
 112 }
 113
 114 static int gwrite(group *gg, ge_prime *x, const mptext_ops *ops, void *p) {
 115   gctx_prime *g = (gctx_prime *)gg;
 116   mp *t = mpmont_reduce(&g->mm, MP_NEW, x->x);
 117   int rc = mp_write(t, 10, ops, p); MP_DROP(t); return (rc);
 118 }
 119
 120 static mp *gtoint(group *gg, mp *d, ge_prime *x) {
 121   gctx_prime *g = (gctx_prime *)gg;
 122   return (mpmont_reduce(&g->mm, d, x->x));
 123 }
 124
 125 static int gfromint(group *gg, ge_prime *d, mp *x) {
 126   gctx_prime *g = (gctx_prime *)gg; mp_div(0, &d->x, x, g->mm.m);
 127   d->x = mpmont_mul(&g->mm, d->x, d->x, g->mm.r2); return (0);
 128 }
 129
 130 static int gtobuf(group *gg, buf *b, ge_prime *x) {
 131   gctx_prime *g = (gctx_prime *)gg;
 132   mp *t = mpmont_reduce(&g->mm, MP_NEW, x->x);
 133   int rc = buf_putmp(b, t); MP_DROP(t); return (rc);
 134 }
 135
 136 static int gfrombuf(group *gg, buf *b, ge_prime *d) {
 137   gctx_prime * g = (gctx_prime *)gg; mp *x;
 138   if ((x = buf_getmp(b)) == 0) return (-1);
 139   mp_div(0, &x, x, g->mm.m); mp_drop(d->x);
 140   d->x = mpmont_mul(&g->mm, x, x, g->mm.r2); return(0);
 141 }
 142
 143 static int gtoraw(group *gg, buf *b, ge_prime *x) {
 144   gctx_prime *g = (gctx_prime *)gg; octet *q;
 145   mp *t = mpmont_reduce(&g->mm, MP_NEW, x->x);
 146   if ((q = buf_get(b, g->g.noctets)) == 0) { MP_DROP(t); return (-1); }
 147   mp_storeb(t, q, g->g.noctets); MP_DROP(t); return (0);
 148 }
 149
 150 static int gfromraw(group *gg, buf *b, ge_prime *d) {
 151   gctx_prime * g = (gctx_prime *)gg; mp *x; octet *q;
 152   if ((q = buf_get(b, g->g.noctets)) == 0) return (-1);
 153   x = mp_loadb(MP_NEW, q, g->g.noctets);
 154   mp_div(0, &x, x, g->mm.m); mp_drop(d->x);
 155   d->x = mpmont_mul(&g->mm, x, x, g->mm.r2); return(0);
 156 }
 157
 158 /* --- @group_prime@ --- *
 159  *
 160  * Arguments:   @const gprime_param *gp@ = group parameters
 161  *
 162  * Returns:     A pointer to the group, or null.
 163  *
 164  * Use:         Constructs an abstract group interface for a subgroup of a
 165  *              prime field.  Group elements are @mp *@ pointers.
 166  */
 167
 168 static const group_ops gops = {
 169   GTY_PRIME, "prime",
 170   gdestroygroup, gcreate, gcopy, gburn, gdestroy,
 171   gsamep, geq, group_stdidentp,
 172   gcheck,
 173   gmul, gsqr, ginv, group_stddiv, gexp, gmexp,
 174   gread, gwrite,
 175   gtoint, gfromint, group_stdtoec, group_stdfromec, gtobuf, gfrombuf,
 176   gtoraw, gfromraw
 177 };
 178
 179 group *group_prime(const gprime_param *gp)
 180 {
 181   gctx_prime *g;
 182
 183   if (!MP_POSP(gp->p) || !MP_ODDP(gp->p))
 184     return (0);
 185   g = CREATE(gctx_prime);
 186   g->g.ops = &gops;
 187   g->g.nbits = mp_bits(gp->p);
 188   g->g.noctets = (g->g.nbits + 7) >> 3;
 189   mpmont_create(&g->mm, gp->p);
 190   g->i.x = g->mm.r; g->g.i = &g->i;
 191   g->gen.x = mpmont_mul(&g->mm, MP_NEW, gp->g, g->mm.r2);
 192   g->g.g = &g->gen;
 193   g->g.r = MP_COPY(gp->q);
 194   g->g.h = MP_NEW; mp_div(&g->g.h, 0, gp->p, gp->q);
 195   return (&g->g);
 196 }
 197
 198 /*----- That's all, folks -------------------------------------------------*/