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

   1 /* -*-c-*-
   2  *
   3  * $Id: g-prime.c,v 1.2 2004/04/03 03:32:05 mdw Exp $
   4  *
   5  * Abstraction for prime groups
   6  *
   7  * (c) 2004 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: g-prime.c,v $
  33  * Revision 1.2  2004/04/03 03:32:05  mdw
  34  * General robustification.
  35  *
  36  * Revision 1.1  2004/04/01 12:50:09  mdw
  37  * Add cyclic group abstraction, with test code.  Separate off exponentation
  38  * functions for better static linking.  Fix a buttload of bugs on the way.
  39  * Generally ensure that negative exponents do inversion correctly.  Add
  40  * table of standard prime-field subgroups.  (Binary field subgroups are
  41  * currently unimplemented but easy to add if anyone ever finds a good one.)
  42  *
  43  */
  44
  45 /*----- Header files ------------------------------------------------------*/
  46
  47 #include <mLib/sub.h>
  48
  49 #include "mpmont.h"
  50 #include "pgen.h"
  51
  52 #define ge mp *
  53 #include "group.h"
  54
  55 /*----- Data structures ---------------------------------------------------*/
  56
  57 typedef struct gctx {
  58   group g;
  59   mp *gen;
  60   mpmont mm;
  61 } gctx;
  62
  63 /*----- Main code ---------------------------------------------------------*/
  64
  65 /* --- Group operations --- */
  66
  67 static void gdestroygroup(group *gg) {
  68   gctx *g = (gctx *)gg;
  69   mp_drop(g->gen); mp_drop(g->g.r); mp_drop(g->g.h);
  70   mpmont_destroy(&g->mm);
  71   DESTROY(g);
  72 }
  73
  74 static mp **gcreate(group *gg)
  75   { mp **x = CREATE(mp *); *x = MP_COPY(*gg->i); return (x); }
  76
  77 static void gcopy(group *gg, mp **d, mp **x)
  78   { mp *t = MP_COPY(*x); MP_DROP(*d); *d = t; }
  79
  80 static void gburn(group *gg, mp **x) { (*x)->f |= MP_BURN; }
  81
  82 static void gdestroy(group *gg, mp **x) { MP_DROP(*x); DESTROY(x); }
  83
  84 static int gsamep(group *gg, group *hh) {
  85   gctx *g = (gctx *)gg, *h = (gctx *)hh;
  86   return (MP_EQ(g->mm.m, h->mm.m));
  87 }
  88
  89 static int geq(group *gg, mp **x, mp **y) { return (MP_EQ(*x, *y)); }
  90
  91 static const char *gcheck(group *gg, grand *gr) {
  92   gctx *g = (gctx *)gg; int rc; mp *t;
  93   if (!pgen_primep(g->mm.m, gr)) return ("p is not prime");
  94   t = mp_mul(MP_NEW, g->g.r, g->g.h); t = mp_add(t, t, MP_ONE);
  95   rc = MP_EQ(t, g->mm.m); MP_DROP(t); if (!rc) return ("not a subgroup");
  96   return (group_stdcheck(gg, gr));
  97 }
  98
  99 static void gmul(group *gg, mp **d, mp **x, mp **y)
 100   { gctx *g = (gctx *)gg; *d = mpmont_mul(&g->mm, *d, *x, *y); }
 101
 102 static void gsqr(group *gg, mp **d, mp **x) {
 103   gctx *g = (gctx *)gg; mp *r = mp_sqr(*d, *x);
 104   *d = mpmont_reduce(&g->mm, r, r);
 105 }
 106
 107 static void ginv(group *gg, mp **d, mp **x) {
 108   gctx *g = (gctx *)gg; mp *r = mpmont_reduce(&g->mm, *d, *x);
 109   mp_gcd(0, 0, &r, g->mm.m, r); *d = mpmont_mul(&g->mm, r, r, g->mm.r2);
 110 }
 111
 112 static void gexp(group *gg, mp **d, mp **x, mp *n)
 113   { gctx *g = (gctx *)gg; *d = mpmont_expr(&g->mm, *d, *x, n); }
 114
 115 static void gmexp(group *gg, mp **d, const group_expfactor *f, size_t n) {
 116   gctx *g = (gctx *)gg; size_t i;
 117   mp_expfactor *ff = xmalloc(n * sizeof(mp_expfactor));
 118   for (i = 0; i < n; i++) { ff[i].base = *f[i].base; ff[i].exp = f[i].exp; }
 119   *d = mpmont_mexpr(&g->mm, *d, ff, n); xfree(ff);
 120 }
 121
 122 static int gread(group *gg, mp **d, const mptext_ops *ops, void *p) {
 123   gctx *g = (gctx *)gg; mp *t;
 124   if ((t = mp_read(MP_NEW, 0, ops, p)) == 0) return (-1);
 125   mp_drop(*d); *d = mpmont_mul(&g->mm, t, t, g->mm.r2); return (0);
 126 }
 127
 128 static int gwrite(group *gg, mp **x, const mptext_ops *ops, void *p) {
 129   gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
 130   int rc = mp_write(t, 10, ops, p); MP_DROP(t); return (rc);
 131 }
 132
 133 static mp *gtoint(group *gg, mp *d, mp **x)
 134   { gctx *g = (gctx *)gg; return (mpmont_reduce(&g->mm, d, *x)); }
 135
 136 static int gfromint(group *gg, mp **d, mp *x) {
 137   gctx *g = (gctx *)gg; mp_div(0, &x, x, g->mm.m); mp_drop(*d);
 138   *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return (0);
 139 }
 140
 141 static int gtobuf(group *gg, buf *b, mp **x) {
 142   gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
 143   int rc = buf_putmp(b, t); MP_DROP(t); return (rc);
 144 }
 145
 146 static int gfrombuf(group *gg, buf *b, mp **d) {
 147   gctx * g = (gctx *)gg; mp *x; if ((x = buf_getmp(b)) == 0) return (-1);
 148   mp_div(0, &x, x, g->mm.m); mp_drop(*d);
 149   *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return(0);
 150 }
 151
 152 /* --- @group_prime@ --- *
 153  *
 154  * Arguments:   @const gprime_param *gp@ = group parameters
 155  *
 156  * Returns:     A pointer to the group, or null.
 157  *
 158  * Use:         Constructs an abstract group interface for a subgroup of a
 159  *              prime field.  Group elements are @mp *@ pointers.
 160  */
 161
 162 static const group_ops gops = {
 163   GTY_PRIME,
 164   gdestroygroup, gcreate, gcopy, gburn, gdestroy,
 165   gsamep, geq, group_stdidentp,
 166   gcheck,
 167   gmul, gsqr, ginv, group_stddiv, gexp, gmexp,
 168   gread, gwrite,
 169   gtoint, gfromint, group_stdtoec, group_stdfromec, gtobuf, gfrombuf
 170 };
 171
 172 group *group_prime(const gprime_param *gp)
 173 {
 174   gctx *g;
 175
 176   if (!MP_ISPOS(gp->p) || !MP_ISODD(gp->p))
 177     return (0);
 178   g = CREATE(gctx);
 179   g->g.ops = &gops;
 180   g->g.nbits = mp_bits(gp->p);
 181   g->g.noctets = (g->g.nbits + 7) >> 3;
 182   mpmont_create(&g->mm, gp->p);
 183   g->g.i = &g->mm.r;
 184   g->gen = mpmont_mul(&g->mm, MP_NEW, gp->g, g->mm.r2);
 185   g->g.g = &g->gen;
 186   g->g.r = MP_COPY(gp->q);
 187   g->g.h = MP_NEW; mp_div(&g->g.h, 0, gp->p, gp->q);
 188   return (&g->g);
 189 }
 190
 191 /*----- That's all, folks -------------------------------------------------*/