135 lines
3.0 KiB
C
135 lines
3.0 KiB
C
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/* mpi-mpow.c - MPI functions
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* Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* GnuPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include "mpi-internal.h"
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#include "longlong.h"
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static int build_index(const MPI *exparray, int k, int i, int t)
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{
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int j, bitno;
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int index = 0;
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bitno = t - i;
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for (j = k - 1; j >= 0; j--) {
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index <<= 1;
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if (mpi_test_bit(exparray[j], bitno))
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index |= 1;
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}
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return index;
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}
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/****************
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* RES = (BASE[0] ^ EXP[0]) * (BASE[1] ^ EXP[1]) * ... * mod M
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*/
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int mpi_mulpowm(MPI res, MPI *basearray, MPI *exparray, MPI m)
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{
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int rc = -ENOMEM;
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int k; /* number of elements */
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int t; /* bit size of largest exponent */
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int i, j, idx;
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MPI *G = NULL; /* table with precomputed values of size 2^k */
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MPI tmp = NULL;
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for (k = 0; basearray[k]; k++)
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;
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if (!k) {
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pr_emerg("mpi_mulpowm: assert(k) failed\n");
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BUG();
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}
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for (t = 0, i = 0; (tmp = exparray[i]); i++) {
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j = mpi_get_nbits(tmp);
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if (j > t)
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t = j;
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}
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if (i != k) {
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pr_emerg("mpi_mulpowm: assert(i==k) failed\n");
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BUG();
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}
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if (!t) {
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pr_emerg("mpi_mulpowm: assert(t) failed\n");
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BUG();
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}
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if (k >= 10) {
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pr_emerg("mpi_mulpowm: assert(k<10) failed\n");
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BUG();
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}
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G = kzalloc((1 << k) * sizeof *G, GFP_KERNEL);
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if (!G)
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goto err_out;
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/* and calculate */
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tmp = mpi_alloc(mpi_get_nlimbs(m) + 1);
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if (!tmp)
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goto nomem;
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if (mpi_set_ui(res, 1) < 0)
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goto nomem;
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for (i = 1; i <= t; i++) {
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if (mpi_mulm(tmp, res, res, m) < 0)
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goto nomem;
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idx = build_index(exparray, k, i, t);
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if (!(idx >= 0 && idx < (1 << k))) {
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pr_emerg("mpi_mulpowm: assert(idx >= 0 && idx < (1<<k)) failed\n");
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BUG();
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}
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if (!G[idx]) {
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if (!idx) {
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G[0] = mpi_alloc_set_ui(1);
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if (!G[0])
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goto nomem;
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} else {
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for (j = 0; j < k; j++) {
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if ((idx & (1 << j))) {
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if (!G[idx]) {
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if (mpi_copy
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(&G[idx],
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basearray[j]) < 0)
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goto nomem;
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} else {
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if (mpi_mulm
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(G[idx], G[idx],
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basearray[j],
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m) < 0)
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goto nomem;
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}
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}
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}
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if (!G[idx]) {
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G[idx] = mpi_alloc(0);
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if (!G[idx])
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goto nomem;
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}
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}
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}
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if (mpi_mulm(res, tmp, G[idx], m) < 0)
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goto nomem;
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}
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rc = 0;
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nomem:
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/* cleanup */
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mpi_free(tmp);
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for (i = 0; i < (1 << k); i++)
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mpi_free(G[i]);
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kfree(G);
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err_out:
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return rc;
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}
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