git.distorted.org.uk Git - u/mdw/catacomb/blob - mp-modexp.c

   1 /* -*-c-*-
   2  *
   3  * $Id$
   4  *
   5  * General-purpose modular exponentiation
   6  *
   7  * (c) 2006 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 "mpmont.h"
  35
  36 /*----- Main code ---------------------------------------------------------*/
  37
  38 /* --- @mp_modexp@ --- *
  39  *
  40  * Arguments:   @mp *d@ = fake destination
  41  *              @mp *x@ = base of exponentiation
  42  *              @mp *e@ = exponent
  43  *              @mp *n@ = modulus (must be positive)
  44  *
  45  * Returns:     The value %$x^e \bmod n$%.
  46  */
  47
  48 mp *mp_modexp(mp *d, mp *x, mp *e, mp *n)
  49 {
  50   if (MP_ODDP(n)) {
  51     mpmont mm;
  52     mpmont_create(&mm, n);
  53     d = mpmont_exp(&mm, d, x, e);
  54     mpmont_destroy(&mm);
  55   } else {
  56     mpbarrett mb;
  57     mpbarrett_create(&mb, n);
  58     d = mpbarrett_exp(&mb, d, x, e);
  59     mpbarrett_destroy(&mb);
  60   }
  61   return (d);
  62 }
  63
  64 /*----- Test rig ----------------------------------------------------------*/
  65
  66 #ifdef TEST_RIG
  67
  68 static int tmodexp(dstr *v)
  69 {
  70   mp *a = *(mp **)v[0].buf;
  71   mp *b = *(mp **)v[1].buf;
  72   mp *m = *(mp **)v[2].buf;
  73   mp *r = *(mp **)v[3].buf;
  74   mp *mr;
  75   int ok = 1;
  76
  77   mr = mp_modexp(MP_NEW, a, b, m);
  78
  79   if (!MP_EQ(mr, r)) {
  80     fputs("\n*** modexp failed", stderr);
  81     fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
  82     fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
  83     fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
  84     fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
  85     fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
  86     fputc('\n', stderr);
  87     ok = 0;
  88   }
  89
  90   MP_DROP(m);
  91   MP_DROP(a);
  92   MP_DROP(b);
  93   MP_DROP(r);
  94   MP_DROP(mr);
  95   assert(mparena_count(MPARENA_GLOBAL) == 0);
  96   return ok;
  97 }
  98
  99 static test_chunk tests[] = {
 100   { "modexp", tmodexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
 101   { 0, 0, { 0 } }
 102 };
 103
 104 int main(int argc, char *argv[])
 105 {
 106   sub_init();
 107   test_run(argc, argv, tests, SRCDIR "/tests/mp");
 108   return (0);
 109 }
 110
 111 #endif
 112
 113 /*----- That's all, folks -------------------------------------------------*/