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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   4  *
   5  * Prime fields with Montgomery arithmetic
   6  *
   7  * (c) 2001 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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <mLib/sub.h>
  33
  34 #include "field.h"
  35 #include "mprand.h"
  36 #include "field-guts.h"
  37
  38 /*----- Main code ---------------------------------------------------------*/
  39
  40 /* --- Field operations --- */
  41
  42 static void fdestroy(field *ff) {
  43   fctx_prime *f = (fctx_prime *)ff;
  44   mpmont_destroy(&f->mm);
  45   DESTROY(f);
  46 }
  47
  48 static mp *frand(field *ff, mp *d, grand *r) {
  49   fctx_prime *f = (fctx_prime *)ff;
  50   return (mprand_range(d, f->mm.m, r, 0));
  51 }
  52
  53 static mp *fin(field *ff, mp *d, mp *x) {
  54   fctx_prime *f = (fctx_prime *)ff;
  55   mp_div(0, &d, x, f->mm.m);
  56   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
  57 }
  58
  59 static mp *fout(field *ff, mp *d, mp *x) {
  60   fctx_prime *f = (fctx_prime *)ff;
  61   return (mpmont_reduce(&f->mm, d, x));
  62 }
  63
  64 static int fzerop(field *ff, mp *x) { return (MP_ZEROP(x)); }
  65
  66 static mp *fneg(field *ff, mp *d, mp *x) {
  67   fctx_prime *f = (fctx_prime *)ff;
  68   return (mp_sub(d, f->mm.m, x));
  69 }
  70
  71 static mp *fadd(field *ff, mp *d, mp *x, mp *y) {
  72   fctx_prime *f = (fctx_prime *)ff; d = mp_add(d, x, y);
  73   if (MP_NEGP(d)) d = mp_add(d, d, f->mm.m);
  74   else if (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m);
  75   return (d);
  76 }
  77
  78 static mp *fsub(field *ff, mp *d, mp *x, mp *y) {
  79   fctx_prime *f = (fctx_prime *)ff; d = mp_sub(d, x, y);
  80   if (MP_NEGP(d)) d = mp_add(d, d, f->mm.m);
  81   else if (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m);
  82   return (d);
  83 }
  84
  85 static mp *fmul(field *ff, mp *d, mp *x, mp *y) {
  86   fctx_prime *f = (fctx_prime *)ff;
  87   return (mpmont_mul(&f->mm, d, x, y));
  88 }
  89
  90 static mp *fsqr(field *ff, mp *d, mp *x) {
  91   fctx_prime *f = (fctx_prime *)ff; d = mp_sqr(d, x);
  92   return (mpmont_reduce(&f->mm, d, d));
  93 }
  94
  95 static mp *finv(field *ff, mp *d, mp *x) {
  96   fctx_prime *f = (fctx_prime *)ff; d = mpmont_reduce(&f->mm, d, x);
  97   d = mp_modinv(d, d, f->mm.m); return (mpmont_mul(&f->mm, d, d, f->mm.r2));
  98 }
  99
 100 static mp *freduce(field *ff, mp *d, mp *x) {
 101   fctx_prime *f = (fctx_prime *)ff;
 102   mp_div(0, &d, x, f->mm.m);
 103   return (d);
 104 }
 105
 106 static mp *fsqrt(field *ff, mp *d, mp *x) {
 107   fctx_prime *f = (fctx_prime *)ff; d = mpmont_reduce(&f->mm, d, x);
 108   d = mp_modsqrt(d, d, f->mm.m); if (!d) return (d);
 109   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 110 }
 111
 112 static mp *fdbl(field *ff, mp *d, mp *x) {
 113   fctx_prime *f = (fctx_prime *)ff; d = mp_lsl(d, x, 1);
 114   if (MP_CMP(d, >=, f->mm.m)) d = mp_sub(d, d, f->mm.m);
 115   return (d);
 116 }
 117
 118 static mp *ftpl(field *ff, mp *d, mp *x) {
 119   fctx_prime *f = (fctx_prime *)ff; MP_DEST(d, MP_LEN(x) + 1, x->f);
 120   MPX_UMULN(d->v, d->vl, x->v, x->vl, 3); d->f &= ~MP_UNDEF;
 121   while (MP_CMP(d, >=, f->mm.m)) d = mp_sub(d, d, f->mm.m);
 122   return (d);
 123 }
 124
 125 static mp *fqdl(field *ff, mp *d, mp *x) {
 126   fctx_prime *f = (fctx_prime *)ff; d = mp_lsl(d, x, 2);
 127   while (MP_CMP(d, >=, f->mm.m)) d = mp_sub(d, d, f->mm.m);
 128   return (d);
 129 }
 130
 131 static mp *fhlv(field *ff, mp *d, mp *x) {
 132   fctx_prime *f = (fctx_prime *)ff;
 133   if (MP_ZEROP(x)) { MP_COPY(x); MP_DROP(d); return (x); }
 134   if (x->v[0] & 1) { d = mp_add(d, x, f->mm.m); x = d; }
 135   return (mp_lsr(d, x, 1));
 136 }
 137
 138 /* --- Field operations table --- */
 139
 140 static const field_ops fops = {
 141   FTY_PRIME, "prime",
 142   fdestroy, frand, field_stdsamep,
 143   fin, fout,
 144   fzerop, fneg, fadd, fsub, fmul, fsqr, finv, freduce, fsqrt,
 145   0,
 146   fdbl, ftpl, fqdl, fhlv
 147 };
 148
 149 /* --- @field_prime@ --- *
 150  *
 151  * Arguments:   @mp *p@ = the characteristic of the field
 152  *
 153  * Returns:     A pointer to the field or null.
 154  *
 155  * Use:         Creates a field structure for a prime field of size %$p$%,
 156  *              using Montgomery reduction for arithmetic.
 157  */
 158
 159 field *field_prime(mp *p)
 160 {
 161   fctx_prime *f;
 162
 163   f = CREATE(fctx_prime);
 164   f->f.ops = &fops;
 165   if (mpmont_create(&f->mm, p)) {
 166     DESTROY(f);
 167     return (0);
 168   }
 169   f->f.zero = MP_ZERO;
 170   f->f.one = f->mm.r;
 171   f->f.m = f->mm.m;
 172   f->f.nbits = mp_bits(p);
 173   f->f.noctets = (f->f.nbits + 7) >> 3;
 174   f->f.q = f->mm.m;
 175   return (&f->f);
 176 }
 177
 178 /*----- That's all, folks -------------------------------------------------*/