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1 | /* -*-c-*- |
2 | * |
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3 | * $Id$ |
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4 | * |
5 | * Standard group operations |
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 "group.h" |
33 | #include "pgen.h" |
34 | |
35 | /*----- Handy functions ---------------------------------------------------*/ |
36 | |
37 | /* --- @group_check@ --- * |
38 | * |
39 | * Arguments: @group *g@ = an abstract group |
40 | * @ge *x@ = a group element |
41 | * |
42 | * Returns: Zero on success, nonzero for failure. |
43 | * |
44 | * Use: Checks that @x@ is a valid group element. This may take a |
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45 | * while, since it checks that %$x \ne 1$% and %$x^r = 1$%. |
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46 | */ |
47 | |
48 | int group_check(group *g, ge *x) |
49 | { |
50 | ge *d = G_CREATE(g); |
51 | int rc; |
52 | |
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53 | G_EXP(g, d, x, g->r); |
54 | rc = (G_IDENTP(g, d) && !G_IDENTP(g, x)); |
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55 | G_DESTROY(g, d); |
56 | if (!rc) return (-1); |
57 | return (0); |
58 | } |
59 | |
60 | /* --- @group_samep@ --- * |
61 | * |
62 | * Arguments: @group *g, *h@ = two abstract groups |
63 | * |
64 | * Returns: Nonzero if the groups are in fact identical (not just |
65 | * isomorphic). |
66 | * |
67 | * Use: Checks to see whether two groups are actually the same. This |
68 | * function does the full check: the group operatrion @samep@ |
69 | * just does the group-specific details. |
70 | */ |
71 | |
72 | int group_samep(group *g, group *h) |
73 | { |
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74 | return (g == h || (g->ops == h->ops && |
75 | MP_EQ(g->r, h->r) && MP_EQ(g->h, h->h) && |
76 | G_EQ(g, g->i, h->i) && G_EQ(g, g->g, h->g) && |
77 | G_SAMEP(g, h))); |
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78 | } |
79 | |
80 | /*----- Standard implementations ------------------------------------------*/ |
81 | |
82 | /* --- @group_stdidentp@ --- * |
83 | * |
84 | * Arguments: @group *g@ = abstract group |
85 | * @ge *x@ = group element |
86 | * |
87 | * Returns: Nonzero if %$x$% is the group identity. |
88 | */ |
89 | |
90 | int group_stdidentp(group *g, ge *x) { return (G_EQ(g, x, g->i)); } |
91 | |
92 | /* --- @group_stdsqr@ --- * |
93 | * |
94 | * Arguments: @group *g@ = abstract group |
95 | * @ge *d@ = destination pointer |
96 | * @ge *x@ = group element |
97 | * |
98 | * Returns: --- |
99 | * |
100 | * Use: Computes %$d = x^2$% as %$d = x x$%. |
101 | */ |
102 | |
103 | void group_stdsqr(group *g, ge *d, ge *x) { G_MUL(g, d, x, x); } |
104 | |
105 | /* --- @group_stddiv@ --- * |
106 | * |
107 | * Arguments: @group *g@ = abstract group |
108 | * @ge *d@ = destination pointer |
109 | * @ge *x@ = dividend |
110 | * @ge *y@ = divisor |
111 | * |
112 | * Returns: --- |
113 | * |
114 | * Use: Computes %$d = x/y$% as %$d = x y^{-1}$%. |
115 | */ |
116 | |
117 | void group_stddiv(group *g, ge *d, ge *x, ge *y) |
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118 | { G_INV(g, d, y); G_MUL(g, d, x, d); } |
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119 | |
120 | /* --- @group_stdtoec@ --- * |
121 | * |
122 | * Arguments: @group *g@ = abstract group |
123 | * @ec *d@ = destination point |
124 | * @ge *x@ = group element |
125 | * |
126 | * Returns: @-1@, indicating failure. |
127 | * |
128 | * Use: Fails to convert a group element to an elliptic curve point. |
129 | */ |
130 | |
131 | int group_stdtoec(group *g, ec *d, ge *x) { return (-1); } |
132 | |
133 | /* --- @group_stdfromec@ --- * |
134 | * |
135 | * Arguments: @group *g@ = abstract group |
136 | * @ge *d@ = destination pointer |
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137 | * @const ec *p@ = elliptic curve point |
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138 | * |
139 | * Returns: Zero for success, @-1@ on failure. |
140 | * |
141 | * Use: Converts %$p$% to a group element by converting its %$x$%- |
142 | * coordinate. |
143 | */ |
144 | |
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145 | int group_stdfromec(group *g, ge *d, const ec *p) |
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146 | { if (EC_ATINF(p)) return (-1); return (G_FROMINT(g, d, p->x)); } |
147 | |
148 | /* --- @group_stdcheck@ --- * |
149 | * |
150 | * Arguments: @group *g@ = abstract group |
151 | * @grand *gr@ = random number source. |
152 | * |
153 | * Returns: Null on success, or a pointer to an error message. |
154 | */ |
155 | |
156 | const char *group_stdcheck(group *g, grand *gr) |
157 | { |
158 | ge *t; |
159 | int rc; |
160 | |
161 | if (!pgen_primep(g->r, gr)) return ("group order not prime"); |
162 | t = G_CREATE(g); G_EXP(g, t, g->g, g->r); |
163 | rc = G_IDENTP(g, t); G_DESTROY(g, t); |
164 | if (!rc) return ("generator not in the group"); |
165 | return (0); |
166 | } |
167 | |
168 | /*----- That's all, folks -------------------------------------------------*/ |