git.distorted.org.uk Git - u/mdw/catacomb/blob - mpbarrett-exp.c

   1 /* -*-c-*-
   2  *
   3  * $Id$
   4  *
   5  * Modular exponentiation using Barrett reduction
   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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include "mp.h"
  33 #include "mpbarrett.h"
  34 #include "mpbarrett-exp.h"
  35
  36 /*----- Main code ---------------------------------------------------------*/
  37
  38 /* --- @mpbarrett_exp@ --- *
  39  *
  40  * Arguments:   @mpbarrett *mb@ = pointer to Barrett reduction context
  41  *              @mp *d@ = fake destination
  42  *              @mp *a@ = base
  43  *              @mp *e@ = exponent
  44  *
  45  * Returns:     Result, %$a^e \bmod m$%.
  46  */
  47
  48 mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
  49 {
  50   mp *x = MP_ONE;
  51   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
  52
  53   MP_COPY(a);
  54   MP_SHRINK(e);
  55   if (MP_ZEROP(e))
  56     ;
  57   else {
  58     if (MP_NEGP(e))
  59       a = mp_modinv(a, a, mb->m);
  60     if (MP_LEN(e) < EXP_THRESH)
  61       EXP_SIMPLE(x, a, e);
  62     else
  63       EXP_WINDOW(x, a, e);
  64   }
  65   mp_drop(d);
  66   mp_drop(spare);
  67   mp_drop(a);
  68   return (x);
  69 }
  70
  71 /*----- Test rig ----------------------------------------------------------*/
  72
  73 #ifdef TEST_RIG
  74
  75 static int vexp(dstr *v)
  76 {
  77   mp *m = *(mp **)v[0].buf;
  78   mp *a = *(mp **)v[1].buf;
  79   mp *b = *(mp **)v[2].buf;
  80   mp *r = *(mp **)v[3].buf;
  81   mp *mr;
  82   int ok = 1;
  83
  84   mpbarrett mb;
  85   mpbarrett_create(&mb, m);
  86
  87   mr = mpbarrett_exp(&mb, MP_NEW, a, b);
  88
  89   if (!MP_EQ(mr, r)) {
  90     fputs("\n*** barrett modexp failed", stderr);
  91     fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
  92     fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
  93     fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
  94     fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
  95     fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
  96     fputc('\n', stderr);
  97     ok = 0;
  98   }
  99
 100   mp_drop(m);
 101   mp_drop(a);
 102   mp_drop(b);
 103   mp_drop(r);
 104   mp_drop(mr);
 105   mpbarrett_destroy(&mb);
 106   assert(mparena_count(MPARENA_GLOBAL) == 0);
 107   return ok;
 108 }
 109
 110 static test_chunk tests[] = {
 111   { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
 112   { 0, 0, { 0 } }
 113 };
 114
 115 int main(int argc, char *argv[])
 116 {
 117   sub_init();
 118   test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett");
 119   return (0);
 120 }
 121
 122 #endif
 123
 124 /*----- That's all, folks -------------------------------------------------*/