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

   1 /* -*-c-*-
   2  *
   3  * $Id: f-prime.c,v 1.3.4.1 2003/06/10 13:43:53 mdw Exp $
   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 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: f-prime.c,v $
  33  * Revision 1.3.4.1  2003/06/10 13:43:53  mdw
  34  * Simple (non-projective) curves over prime fields now seem to work.
  35  *
  36  * Revision 1.3  2003/05/15 23:25:59  mdw
  37  * Make elliptic curve stuff build.
  38  *
  39  * Revision 1.2  2002/01/13 13:48:44  mdw
  40  * Further progress.
  41  *
  42  * Revision 1.1  2001/04/29 18:12:33  mdw
  43  * Prototype version.
  44  *
  45  */
  46
  47 /*----- Header files ------------------------------------------------------*/
  48
  49 #include <mLib/sub.h>
  50
  51 #include "field.h"
  52 #include "mpmont.h"
  53
  54 /*----- Data structures ---------------------------------------------------*/
  55
  56 typedef struct fctx {
  57   field f;
  58   mpmont mm;
  59 } fctx;
  60
  61 /*----- Main code ---------------------------------------------------------*/
  62
  63 /* --- Field operations --- */
  64
  65 static void fdestroy(field *ff)
  66 {
  67   fctx *f = (fctx *)ff;
  68   mpmont_destroy(&f->mm);
  69   DESTROY(f);
  70 }
  71
  72 static mp *fin(field *ff, mp *d, mp *x)
  73 {
  74   fctx *f = (fctx *)ff;
  75   mp_div(0, &d, x, f->mm.m);
  76   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
  77 }
  78
  79 static mp *fout(field *ff, mp *d, mp *x)
  80 {
  81   fctx *f = (fctx *)ff;
  82   return (mpmont_reduce(&f->mm, d, x));
  83 }
  84
  85 static mp *fneg(field *ff, mp *d, mp *x)
  86 {
  87   fctx *f = (fctx *)ff;
  88   return (mp_sub(d, f->mm.m, x));
  89 }
  90
  91 static mp *fadd(field *ff, mp *d, mp *x, mp *y)
  92 {
  93   fctx *f = (fctx *)ff;
  94   d = mp_add(d, x, y);
  95   if (d->f & MP_NEG)
  96     d = mp_add(d, d, f->mm.m);
  97   else if (MP_CMP(d, >, f->mm.m))
  98     d = mp_sub(d, d, f->mm.m);
  99   return (d);
 100 }
 101
 102 static mp *fsub(field *ff, mp *d, mp *x, mp *y)
 103 {
 104   fctx *f = (fctx *)ff;
 105   d = mp_sub(d, x, y);
 106   if (d->f & MP_NEG)
 107     d = mp_add(d, d, f->mm.m);
 108   else if (MP_CMP(d, >, f->mm.m))
 109     d = mp_sub(d, d, f->mm.m);
 110   return (d);
 111 }
 112
 113 static mp *fmul(field *ff, mp *d, mp *x, mp *y)
 114 {
 115   fctx *f = (fctx *)ff;
 116   return (mpmont_mul(&f->mm, d, x, y));
 117 }
 118
 119 static mp *fsqr(field *ff, mp *d, mp *x)
 120 {
 121   fctx *f = (fctx *)ff;
 122   d = mp_sqr(d, x);
 123   return (mpmont_reduce(&f->mm, d, d));
 124 }
 125
 126 static mp *finv(field *ff, mp *d, mp *x)
 127 {
 128   fctx *f = (fctx *)ff;
 129   d = mpmont_reduce(&f->mm, d, x);
 130   mp_gcd(0, 0, &d, f->mm.m, d);
 131   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 132 }
 133
 134 static mp *freduce(field *ff, mp *d, mp *x)
 135 {
 136   fctx *f = (fctx *)ff;
 137   mp_div(0, &d, x, f->mm.m);
 138   return (d);
 139 }
 140
 141 static mp *fdbl(field *ff, mp *d, mp *x)
 142 {
 143   fctx *f = (fctx *)ff;
 144   d = mp_lsl(d, x, 1);
 145   if (MP_CMP(d, >, f->mm.m))
 146     d = mp_sub(d, d, f->mm.m);
 147   return (d);
 148 }
 149
 150 static mp *ftpl(field *ff, mp *d, mp *x)
 151 {
 152   fctx *f = (fctx *)ff;
 153   MP_DEST(d, MP_LEN(x) + 1, x->f);
 154   MPX_UMULN(d->v, d->vl, x->v, x->vl, 3);
 155   while (MP_CMP(d, >, f->mm.m))
 156     d = mp_sub(d, d, f->mm.m);
 157   return (d);
 158 }
 159
 160 static mp *fsqrt(field *ff, mp *d, mp *x)
 161 {
 162   fctx *f = (fctx *)ff;
 163   d = mpmont_reduce(&f->mm, d, x);
 164   d = mp_modsqrt(d, d, f->mm.m);
 165   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 166 }
 167
 168 /* --- Field operations table --- */
 169
 170 static field_ops fops = {
 171   fdestroy,
 172   fin, fout,
 173   fneg, fadd, fsub, fmul, fsqr, finv, freduce,
 174   fdbl, ftpl, fsqrt
 175 };
 176
 177 /* --- @field_prime@ --- *
 178  *
 179  * Arguments:   @mp *p@ = the characteristic of the field
 180  *
 181  * Returns:     A pointer to the field.
 182  *
 183  * Use:         Creates a field structure for a prime field of size %$p$%,
 184  *              using Montgomery reduction for arithmetic.
 185  */
 186
 187 field *field_prime(mp *p)
 188 {
 189   fctx *f = CREATE(fctx);
 190   f->f.ops = &fops;
 191   mpmont_create(&f->mm, p);
 192   f->f.zero = MP_ZERO;
 193   f->f.one = f->mm.r;
 194   return (&f->f);
 195 }
 196
 197 /*----- That's all, folks -------------------------------------------------*/