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