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1 | /* -*-c-*- |
2 | * |
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3 | * $Id$ |
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4 | * |
5 | * Modular exponentiation with Montgomery 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 "mpmont.h" |
34 | #include "mpmont-exp.h" |
35 | |
36 | /*----- Exponentiation ----------------------------------------------------*/ |
37 | |
38 | /* --- @mpmont_expr@ --- * |
39 | * |
40 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
41 | * @mp *d@ = fake destination |
42 | * @mp *a@ = base |
43 | * @mp *e@ = exponent |
44 | * |
45 | * Returns: Result, %$(a R^{-1})^e R \bmod m$%. |
46 | */ |
47 | |
48 | mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e) |
49 | { |
50 | mp *x = MP_COPY(mm->r); |
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 = mpmont_reduce(mm, a, a); |
60 | a = mp_modinv(a, a, mm->m); |
61 | a = mpmont_mul(mm, a, a, mm->r2); |
62 | } |
63 | if (MP_LEN(e) < EXP_THRESH) |
64 | EXP_SIMPLE(x, a, e); |
65 | else |
66 | EXP_WINDOW(x, a, e); |
67 | } |
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68 | mp_drop(d); |
69 | mp_drop(spare); |
70 | mp_drop(a); |
71 | return (x); |
72 | } |
73 | |
74 | /* --- @mpmont_exp@ --- * |
75 | * |
76 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
77 | * @mp *d@ = fake destination |
78 | * @mp *a@ = base |
79 | * @mp *e@ = exponent |
80 | * |
81 | * Returns: Result, %$a^e \bmod m$%. |
82 | */ |
83 | |
84 | mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e) |
85 | { |
86 | e = MP_COPY(e); |
87 | d = mpmont_mul(mm, d, a, mm->r2); |
88 | d = mpmont_expr(mm, d, d, e); |
89 | d = mpmont_reduce(mm, d, d); |
90 | MP_DROP(e); |
91 | return (d); |
92 | } |
93 | |
94 | /*----- Test rig ----------------------------------------------------------*/ |
95 | |
96 | #ifdef TEST_RIG |
97 | |
98 | static int texp(dstr *v) |
99 | { |
100 | mp *m = *(mp **)v[0].buf; |
101 | mp *a = *(mp **)v[1].buf; |
102 | mp *b = *(mp **)v[2].buf; |
103 | mp *r = *(mp **)v[3].buf; |
104 | mp *mr; |
105 | int ok = 1; |
106 | |
107 | mpmont mm; |
108 | mpmont_create(&mm, m); |
109 | |
110 | mr = mpmont_exp(&mm, MP_NEW, a, b); |
111 | |
112 | if (!MP_EQ(mr, r)) { |
113 | fputs("\n*** montgomery modexp failed", stderr); |
114 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
115 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
116 | fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); |
117 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
118 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
119 | fputc('\n', stderr); |
120 | ok = 0; |
121 | } |
122 | |
123 | MP_DROP(m); |
124 | MP_DROP(a); |
125 | MP_DROP(b); |
126 | MP_DROP(r); |
127 | MP_DROP(mr); |
128 | mpmont_destroy(&mm); |
129 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
130 | return ok; |
131 | } |
132 | |
133 | |
134 | static test_chunk tests[] = { |
135 | { "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } }, |
136 | { 0, 0, { 0 } }, |
137 | }; |
138 | |
139 | int main(int argc, char *argv[]) |
140 | { |
141 | sub_init(); |
142 | test_run(argc, argv, tests, SRCDIR "/tests/mpmont"); |
143 | return (0); |
144 | } |
145 | |
146 | #endif |
147 | |
148 | /*----- That's all, folks -------------------------------------------------*/ |