mpi-mpow.c
3 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
/* 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 err_out;
/* 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);
err_out:
return rc;
}