lib/mpi/mpi-mpow.c

   1 /* mpi-mpow.c  -  MPI functions
   2  * Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include "mpi-internal.h"
  22 #include "longlong.h"
  23
  24 static int build_index(const MPI *exparray, int k, int i, int t)
  25 {
  26         int j, bitno;
  27         int index = 0;
  28
  29         bitno = t - i;
  30         for (j = k - 1; j >= 0; j--) {
  31                 index <<= 1;
  32                 if (mpi_test_bit(exparray[j], bitno))
  33                         index |= 1;
  34         }
  35         return index;
  36 }
  37
  38 /****************
  39  * RES = (BASE[0] ^ EXP[0]) *  (BASE[1] ^ EXP[1]) * ... * mod M
  40  */
  41 int mpi_mulpowm(MPI res, MPI *basearray, MPI *exparray, MPI m)
  42 {
  43         int rc = -ENOMEM;
  44         int k;                  /* number of elements */
  45         int t;                  /* bit size of largest exponent */
  46         int i, j, idx;
  47         MPI *G = NULL;          /* table with precomputed values of size 2^k */
  48         MPI tmp = NULL;
  49
  50         for (k = 0; basearray[k]; k++)
  51                 ;
  52         if (!k) {
  53                 pr_emerg("mpi_mulpowm: assert(k) failed\n");
  54                 BUG();
  55         }
  56         for (t = 0, i = 0; (tmp = exparray[i]); i++) {
  57                 j = mpi_get_nbits(tmp);
  58                 if (j > t)
  59                         t = j;
  60         }
  61         if (i != k) {
  62                 pr_emerg("mpi_mulpowm: assert(i==k) failed\n");
  63                 BUG();
  64         }
  65         if (!t) {
  66                 pr_emerg("mpi_mulpowm: assert(t) failed\n");
  67                 BUG();
  68         }
  69         if (k >= 10) {
  70                 pr_emerg("mpi_mulpowm: assert(k<10) failed\n");
  71                 BUG();
  72         }
  73
  74         G = kzalloc((1 << k) * sizeof *G, GFP_KERNEL);
  75         if (!G)
  76                 goto err_out;
  77
  78         /* and calculate */
  79         tmp = mpi_alloc(mpi_get_nlimbs(m) + 1);
  80         if (!tmp)
  81                 goto nomem;
  82         if (mpi_set_ui(res, 1) < 0)
  83                 goto nomem;
  84         for (i = 1; i <= t; i++) {
  85                 if (mpi_mulm(tmp, res, res, m) < 0)
  86                         goto nomem;
  87                 idx = build_index(exparray, k, i, t);
  88                 if (!(idx >= 0 && idx < (1 << k))) {
  89                         pr_emerg("mpi_mulpowm: assert(idx >= 0 && idx < (1<<k)) failed\n");
  90                         BUG();
  91                 }
  92                 if (!G[idx]) {
  93                         if (!idx) {
  94                                 G[0] = mpi_alloc_set_ui(1);
  95                                 if (!G[0])
  96                                         goto nomem;
  97                         } else {
  98                                 for (j = 0; j < k; j++) {
  99                                         if ((idx & (1 << j))) {
 100                                                 if (!G[idx]) {
 101                                                         if (mpi_copy
 102                                                             (&G[idx],
 103                                                              basearray[j]) < 0)
 104                                                                 goto nomem;
 105                                                 } else {
 106                                                         if (mpi_mulm
 107                                                             (G[idx], G[idx],
 108                                                              basearray[j],
 109                                                              m) < 0)
 110                                                                 goto nomem;
 111                                                 }
 112                                         }
 113                                 }
 114                                 if (!G[idx]) {
 115                                         G[idx] = mpi_alloc(0);
 116                                         if (!G[idx])
 117                                                 goto nomem;
 118                                 }
 119                         }
 120                 }
 121                 if (mpi_mulm(res, tmp, G[idx], m) < 0)
 122                         goto nomem;
 123         }
 124
 125         rc = 0;
 126 nomem:
 127         /* cleanup */
 128         mpi_free(tmp);
 129         for (i = 0; i < (1 << k); i++)
 130                 mpi_free(G[i]);
 131         kfree(G);
 132 err_out:
 133         return rc;
 134 }