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1 | /* -*-c-*- |
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2 | * |
3 | * Modular exponentiation with Montgomery reduction |
4 | * |
5 | * (c) 2004 Straylight/Edgeware |
6 | */ |
7 | |
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8 | /*----- Licensing notice --------------------------------------------------* |
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9 | * |
10 | * This file is part of Catacomb. |
11 | * |
12 | * Catacomb is free software; you can redistribute it and/or modify |
13 | * it under the terms of the GNU Library General Public License as |
14 | * published by the Free Software Foundation; either version 2 of the |
15 | * License, or (at your option) any later version. |
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16 | * |
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17 | * Catacomb is distributed in the hope that it will be useful, |
18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
20 | * GNU Library General Public License for more details. |
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21 | * |
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22 | * You should have received a copy of the GNU Library General Public |
23 | * License along with Catacomb; if not, write to the Free |
24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
25 | * MA 02111-1307, USA. |
26 | */ |
27 | |
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28 | /*----- Header files ------------------------------------------------------*/ |
29 | |
30 | #include "mp.h" |
31 | #include "mpmont.h" |
32 | #include "mpmont-exp.h" |
33 | |
34 | /*----- Exponentiation ----------------------------------------------------*/ |
35 | |
36 | /* --- @mpmont_expr@ --- * |
37 | * |
38 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
39 | * @mp *d@ = fake destination |
40 | * @mp *a@ = base |
41 | * @mp *e@ = exponent |
42 | * |
43 | * Returns: Result, %$(a R^{-1})^e R \bmod m$%. |
44 | */ |
45 | |
46 | mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e) |
47 | { |
48 | mp *x = MP_COPY(mm->r); |
49 | mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW; |
50 | |
51 | MP_COPY(a); |
52 | MP_SHRINK(e); |
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53 | if (MP_ZEROP(e)) |
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54 | ; |
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55 | else { |
56 | if (MP_NEGP(e)) { |
57 | a = mpmont_reduce(mm, a, a); |
58 | a = mp_modinv(a, a, mm->m); |
59 | a = mpmont_mul(mm, a, a, mm->r2); |
60 | } |
61 | if (MP_LEN(e) < EXP_THRESH) |
62 | EXP_SIMPLE(x, a, e); |
63 | else |
64 | EXP_WINDOW(x, a, e); |
65 | } |
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66 | mp_drop(d); |
67 | mp_drop(spare); |
68 | mp_drop(a); |
69 | return (x); |
70 | } |
71 | |
72 | /* --- @mpmont_exp@ --- * |
73 | * |
74 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
75 | * @mp *d@ = fake destination |
76 | * @mp *a@ = base |
77 | * @mp *e@ = exponent |
78 | * |
79 | * Returns: Result, %$a^e \bmod m$%. |
80 | */ |
81 | |
82 | mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e) |
83 | { |
84 | e = MP_COPY(e); |
85 | d = mpmont_mul(mm, d, a, mm->r2); |
86 | d = mpmont_expr(mm, d, d, e); |
87 | d = mpmont_reduce(mm, d, d); |
88 | MP_DROP(e); |
89 | return (d); |
90 | } |
91 | |
92 | /*----- Test rig ----------------------------------------------------------*/ |
93 | |
94 | #ifdef TEST_RIG |
95 | |
96 | static int texp(dstr *v) |
97 | { |
98 | mp *m = *(mp **)v[0].buf; |
99 | mp *a = *(mp **)v[1].buf; |
100 | mp *b = *(mp **)v[2].buf; |
101 | mp *r = *(mp **)v[3].buf; |
102 | mp *mr; |
103 | int ok = 1; |
104 | |
105 | mpmont mm; |
106 | mpmont_create(&mm, m); |
107 | |
108 | mr = mpmont_exp(&mm, MP_NEW, a, b); |
109 | |
110 | if (!MP_EQ(mr, r)) { |
111 | fputs("\n*** montgomery modexp failed", stderr); |
112 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
113 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
114 | fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); |
115 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
116 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
117 | fputc('\n', stderr); |
118 | ok = 0; |
119 | } |
120 | |
121 | MP_DROP(m); |
122 | MP_DROP(a); |
123 | MP_DROP(b); |
124 | MP_DROP(r); |
125 | MP_DROP(mr); |
126 | mpmont_destroy(&mm); |
127 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
128 | return ok; |
129 | } |
130 | |
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131 | static test_chunk tests[] = { |
132 | { "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } }, |
133 | { 0, 0, { 0 } }, |
134 | }; |
135 | |
136 | int main(int argc, char *argv[]) |
137 | { |
138 | sub_init(); |
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139 | test_run(argc, argv, tests, SRCDIR "/t/mpmont"); |
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140 | return (0); |
141 | } |
142 | |
143 | #endif |
144 | |
145 | /*----- That's all, folks -------------------------------------------------*/ |