34e4f738 |
1 | /* -*-c-*- |
2 | * |
3 | * $Id: mpbarrett-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $ |
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 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: mpbarrett-exp.c,v $ |
33 | * Revision 1.1 2004/04/01 12:50:09 mdw |
34 | * Add cyclic group abstraction, with test code. Separate off exponentation |
35 | * functions for better static linking. Fix a buttload of bugs on the way. |
36 | * Generally ensure that negative exponents do inversion correctly. Add |
37 | * table of standard prime-field subgroups. (Binary field subgroups are |
38 | * currently unimplemented but easy to add if anyone ever finds a good one.) |
39 | * |
40 | */ |
41 | |
42 | /*----- Header files ------------------------------------------------------*/ |
43 | |
44 | #include "mp.h" |
45 | #include "mpbarrett.h" |
46 | #include "mpbarrett-exp.h" |
47 | |
48 | /*----- Main code ---------------------------------------------------------*/ |
49 | |
50 | /* --- @mpbarrett_exp@ --- * |
51 | * |
52 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
53 | * @mp *d@ = fake destination |
54 | * @mp *a@ = base |
55 | * @mp *e@ = exponent |
56 | * |
57 | * Returns: Result, %$a^e \bmod m$%. |
58 | */ |
59 | |
60 | mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e) |
61 | { |
62 | mp *x = MP_ONE; |
63 | mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW; |
64 | |
65 | MP_COPY(a); |
66 | MP_SHRINK(e); |
67 | if (e->f & MP_NEG) { |
68 | mp *g = MP_NEW; |
69 | mp_gcd(&g, 0, &a, mb->m, a); |
70 | assert(MP_EQ(g, MP_ONE)); |
71 | mp_drop(g); |
72 | } |
73 | if (!MP_LEN(e)) |
74 | ; |
75 | else if (MP_LEN(e) < EXP_THRESH) |
76 | EXP_SIMPLE(x, a, e); |
77 | else |
78 | EXP_WINDOW(x, a, e); |
79 | mp_drop(d); |
80 | mp_drop(spare); |
81 | mp_drop(a); |
82 | return (x); |
83 | } |
84 | |
85 | /*----- Test rig ----------------------------------------------------------*/ |
86 | |
87 | #ifdef TEST_RIG |
88 | |
89 | static int vexp(dstr *v) |
90 | { |
91 | mp *m = *(mp **)v[0].buf; |
92 | mp *a = *(mp **)v[1].buf; |
93 | mp *b = *(mp **)v[2].buf; |
94 | mp *r = *(mp **)v[3].buf; |
95 | mp *mr; |
96 | int ok = 1; |
97 | |
98 | mpbarrett mb; |
99 | mpbarrett_create(&mb, m); |
100 | |
101 | mr = mpbarrett_exp(&mb, MP_NEW, a, b); |
102 | |
103 | if (!MP_EQ(mr, r)) { |
104 | fputs("\n*** barrett modexp failed", stderr); |
105 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
106 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
107 | fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); |
108 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
109 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
110 | fputc('\n', stderr); |
111 | ok = 0; |
112 | } |
113 | |
114 | mp_drop(m); |
115 | mp_drop(a); |
116 | mp_drop(b); |
117 | mp_drop(r); |
118 | mp_drop(mr); |
119 | mpbarrett_destroy(&mb); |
120 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
121 | return ok; |
122 | } |
123 | |
124 | static test_chunk tests[] = { |
125 | { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } }, |
126 | { 0, 0, { 0 } } |
127 | }; |
128 | |
129 | int main(int argc, char *argv[]) |
130 | { |
131 | sub_init(); |
132 | test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett"); |
133 | return (0); |
134 | } |
135 | |
136 | #endif |
137 | |
138 | /*----- That's all, folks -------------------------------------------------*/ |