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1 | /* -*-c-*- |
2 | * |
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3 | * $Id$ |
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4 | * |
5 | * Modular exponentiation using Barrett reduction |
6 | * |
7 | * (c) 2004 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of Catacomb. |
13 | * |
14 | * Catacomb is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * Catacomb is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with Catacomb; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
32 | #include "mp.h" |
33 | #include "mpbarrett.h" |
34 | #include "mpbarrett-exp.h" |
35 | |
36 | /*----- Main code ---------------------------------------------------------*/ |
37 | |
38 | /* --- @mpbarrett_exp@ --- * |
39 | * |
40 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
41 | * @mp *d@ = fake destination |
42 | * @mp *a@ = base |
43 | * @mp *e@ = exponent |
44 | * |
45 | * Returns: Result, %$a^e \bmod m$%. |
46 | */ |
47 | |
48 | mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e) |
49 | { |
50 | mp *x = MP_ONE; |
51 | mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW; |
52 | |
53 | MP_COPY(a); |
54 | MP_SHRINK(e); |
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55 | if (MP_ZEROP(e)) |
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56 | ; |
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57 | else { |
58 | if (MP_NEGP(e)) |
59 | a = mp_modinv(a, a, mb->m); |
60 | if (MP_LEN(e) < EXP_THRESH) |
61 | EXP_SIMPLE(x, a, e); |
62 | else |
63 | EXP_WINDOW(x, a, e); |
64 | } |
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65 | mp_drop(d); |
66 | mp_drop(spare); |
67 | mp_drop(a); |
68 | return (x); |
69 | } |
70 | |
71 | /*----- Test rig ----------------------------------------------------------*/ |
72 | |
73 | #ifdef TEST_RIG |
74 | |
75 | static int vexp(dstr *v) |
76 | { |
77 | mp *m = *(mp **)v[0].buf; |
78 | mp *a = *(mp **)v[1].buf; |
79 | mp *b = *(mp **)v[2].buf; |
80 | mp *r = *(mp **)v[3].buf; |
81 | mp *mr; |
82 | int ok = 1; |
83 | |
84 | mpbarrett mb; |
85 | mpbarrett_create(&mb, m); |
86 | |
87 | mr = mpbarrett_exp(&mb, MP_NEW, a, b); |
88 | |
89 | if (!MP_EQ(mr, r)) { |
90 | fputs("\n*** barrett modexp failed", stderr); |
91 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
92 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
93 | fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); |
94 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
95 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
96 | fputc('\n', stderr); |
97 | ok = 0; |
98 | } |
99 | |
100 | mp_drop(m); |
101 | mp_drop(a); |
102 | mp_drop(b); |
103 | mp_drop(r); |
104 | mp_drop(mr); |
105 | mpbarrett_destroy(&mb); |
106 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
107 | return ok; |
108 | } |
109 | |
110 | static test_chunk tests[] = { |
111 | { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } }, |
112 | { 0, 0, { 0 } } |
113 | }; |
114 | |
115 | int main(int argc, char *argv[]) |
116 | { |
117 | sub_init(); |
118 | test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett"); |
119 | return (0); |
120 | } |
121 | |
122 | #endif |
123 | |
124 | /*----- That's all, folks -------------------------------------------------*/ |