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

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