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1 | /* -*-c-*- |
2 | * |
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3 | * Point multiplication for elliptic curves |
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 "ec.h" |
31 | #include "ec-exp.h" |
32 | |
33 | /*----- Main code ---------------------------------------------------------*/ |
34 | |
35 | /* --- @ec_imul@, @ec_mul@ --- * |
36 | * |
37 | * Arguments: @ec_curve *c@ = pointer to an elliptic curve |
38 | * @ec *d@ = pointer to the destination point |
39 | * @const ec *p@ = pointer to the generator point |
40 | * @mp *n@ = integer multiplier |
41 | * |
42 | * Returns: The destination @d@. |
43 | * |
44 | * Use: Multiplies a point by a scalar, returning %$n p$%. The |
45 | * @imul@ variant uses internal representations for argument |
46 | * and result. |
47 | */ |
48 | |
49 | ec *ec_imul(ec_curve *c, ec *d, const ec *p, mp *n) |
50 | { |
51 | ec t = EC_INIT; |
52 | |
53 | EC_COPY(&t, p); |
54 | if (t.x && (n->f & MP_BURN)) |
55 | t.x->f |= MP_BURN; |
56 | MP_SHRINK(n); |
57 | EC_SETINF(d); |
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58 | if (MP_ZEROP(n)) |
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59 | ; |
60 | else { |
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61 | if (MP_NEGP(n)) |
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62 | EC_NEG(c, &t, &t); |
63 | if (MP_LEN(n) < EXP_THRESH) |
64 | EXP_SIMPLE(*d, t, n); |
65 | else |
66 | EXP_WINDOW(*d, t, n); |
67 | } |
68 | EC_DESTROY(&t); |
69 | return (d); |
70 | } |
71 | |
72 | ec *ec_mul(ec_curve *c, ec *d, const ec *p, mp *n) |
73 | { |
74 | EC_IN(c, d, p); |
75 | ec_imul(c, d, d, n); |
76 | return (EC_OUT(c, d, d)); |
77 | } |
78 | |
79 | /* --- @ec_mmul@, @ec_immul@ --- * |
80 | * |
81 | * Arguments: @ec_curve *c@ = pointer to an elliptic curve |
82 | * @ec *d@ = pointer to the destination point |
83 | * @const ec_mulfactor *f@ = pointer to vector of factors |
84 | * @size_t n@ = number of factors |
85 | * |
86 | * Returns: The destination @d@. |
87 | * |
88 | * Use: Does simultaneous point multiplication. The @immul@ variant |
89 | * uses internal representations for arguments and result. |
90 | */ |
91 | |
92 | #undef EXP_WINSZ |
93 | #define EXP_WINSZ 3 |
94 | |
95 | static ec *immul(ec_curve *c, ec *d, ec_mulfactor *f, size_t n) |
96 | { |
97 | size_t i; |
98 | |
99 | for (i = 0; i < n; i++) { |
100 | MP_SHRINK(f[i].exp); |
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101 | if (MP_NEGP(f[i].exp)) |
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102 | EC_NEG(c, &f[i].base, &f[i].base); |
103 | if (f[i].base.x && f[i].exp->f & MP_BURN) |
104 | f[i].base.x->f |= MP_BURN; |
105 | } |
106 | EC_SETINF(d); |
107 | EXP_SIMUL(*d, f, n); |
108 | for (i = 0; i < n; i++) |
109 | EC_DESTROY(&f[i].base); |
110 | xfree(f); |
111 | return (d); |
112 | } |
113 | |
114 | ec *ec_immul(ec_curve *c, ec *d, const ec_mulfactor *f, size_t n) |
115 | { |
116 | ec_mulfactor *ff = xmalloc(n * sizeof(ec_mulfactor)); |
117 | size_t i; |
118 | |
119 | for (i = 0; i < n; i++) { |
120 | EC_CREATE(&ff[i].base); |
121 | EC_COPY(&ff[i].base, &f[i].base); |
122 | ff[i].exp = f[i].exp; |
123 | } |
124 | return (immul(c, d, ff, n)); |
125 | } |
126 | |
127 | ec *ec_mmul(ec_curve *c, ec *d, const ec_mulfactor *f, size_t n) |
128 | { |
129 | ec_mulfactor *ff = xmalloc(n * sizeof(ec_mulfactor)); |
130 | size_t i; |
131 | |
132 | for (i = 0; i < n; i++) { |
133 | EC_CREATE(&ff[i].base); |
134 | EC_IN(c, &ff[i].base, &f[i].base); |
135 | ff[i].exp = f[i].exp; |
136 | } |
137 | immul(c, d, ff, n); |
138 | return (EC_OUT(c, d, d)); |
139 | } |
140 | |
141 | /*----- That's all, folks -------------------------------------------------*/ |