1 /* mpi-mpow.c - MPI functions
2 * Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
4 * This file is part of GnuPG.
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.
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.
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
21 #include "mpi-internal.h"
24 static int build_index(const MPI *exparray, int k, int i, int t)
30 for (j = k - 1; j >= 0; j--) {
32 if (mpi_test_bit(exparray[j], bitno))
39 * RES = (BASE[0] ^ EXP[0]) * (BASE[1] ^ EXP[1]) * ... * mod M
41 int mpi_mulpowm(MPI res, MPI *basearray, MPI *exparray, MPI m)
44 int k; /* number of elements */
45 int t; /* bit size of largest exponent */
47 MPI *G = NULL; /* table with precomputed values of size 2^k */
50 for (k = 0; basearray[k]; k++)
53 pr_emerg("mpi_mulpowm: assert(k) failed\n");
56 for (t = 0, i = 0; (tmp = exparray[i]); i++) {
57 j = mpi_get_nbits(tmp);
62 pr_emerg("mpi_mulpowm: assert(i==k) failed\n");
66 pr_emerg("mpi_mulpowm: assert(t) failed\n");
70 pr_emerg("mpi_mulpowm: assert(k<10) failed\n");
74 G = kzalloc((1 << k) * sizeof *G, GFP_KERNEL);
79 tmp = mpi_alloc(mpi_get_nlimbs(m) + 1);
82 if (mpi_set_ui(res, 1) < 0)
84 for (i = 1; i <= t; i++) {
85 if (mpi_mulm(tmp, res, res, m) < 0)
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");
94 G[0] = mpi_alloc_set_ui(1);
98 for (j = 0; j < k; j++) {
99 if ((idx & (1 << j))) {
115 G[idx] = mpi_alloc(0);
121 if (mpi_mulm(res, tmp, G[idx], m) < 0)
129 for (i = 0; i < (1 << k); i++)