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1 | /* -*-c-*- |
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2 | * |
3 | * Standard group operations |
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 "group.h" |
31 | #include "pgen.h" |
32 | |
33 | /*----- Handy functions ---------------------------------------------------*/ |
34 | |
35 | /* --- @group_check@ --- * |
36 | * |
37 | * Arguments: @group *g@ = an abstract group |
38 | * @ge *x@ = a group element |
39 | * |
40 | * Returns: Zero on success, nonzero for failure. |
41 | * |
42 | * Use: Checks that @x@ is a valid group element. This may take a |
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43 | * while, since it checks that %$x \ne 1$% and %$x^r = 1$%. |
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44 | */ |
45 | |
46 | int group_check(group *g, ge *x) |
47 | { |
48 | ge *d = G_CREATE(g); |
49 | int rc; |
50 | |
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51 | G_EXP(g, d, x, g->r); |
52 | rc = (G_IDENTP(g, d) && !G_IDENTP(g, x)); |
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53 | G_DESTROY(g, d); |
54 | if (!rc) return (-1); |
55 | return (0); |
56 | } |
57 | |
58 | /* --- @group_samep@ --- * |
59 | * |
60 | * Arguments: @group *g, *h@ = two abstract groups |
61 | * |
62 | * Returns: Nonzero if the groups are in fact identical (not just |
63 | * isomorphic). |
64 | * |
65 | * Use: Checks to see whether two groups are actually the same. This |
66 | * function does the full check: the group operatrion @samep@ |
67 | * just does the group-specific details. |
68 | */ |
69 | |
70 | int group_samep(group *g, group *h) |
71 | { |
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72 | return (g == h || (g->ops == h->ops && |
73 | MP_EQ(g->r, h->r) && MP_EQ(g->h, h->h) && |
74 | G_EQ(g, g->i, h->i) && G_EQ(g, g->g, h->g) && |
75 | G_SAMEP(g, h))); |
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76 | } |
77 | |
78 | /*----- Standard implementations ------------------------------------------*/ |
79 | |
80 | /* --- @group_stdidentp@ --- * |
81 | * |
82 | * Arguments: @group *g@ = abstract group |
83 | * @ge *x@ = group element |
84 | * |
85 | * Returns: Nonzero if %$x$% is the group identity. |
86 | */ |
87 | |
88 | int group_stdidentp(group *g, ge *x) { return (G_EQ(g, x, g->i)); } |
89 | |
90 | /* --- @group_stdsqr@ --- * |
91 | * |
92 | * Arguments: @group *g@ = abstract group |
93 | * @ge *d@ = destination pointer |
94 | * @ge *x@ = group element |
95 | * |
96 | * Returns: --- |
97 | * |
98 | * Use: Computes %$d = x^2$% as %$d = x x$%. |
99 | */ |
100 | |
101 | void group_stdsqr(group *g, ge *d, ge *x) { G_MUL(g, d, x, x); } |
102 | |
103 | /* --- @group_stddiv@ --- * |
104 | * |
105 | * Arguments: @group *g@ = abstract group |
106 | * @ge *d@ = destination pointer |
107 | * @ge *x@ = dividend |
108 | * @ge *y@ = divisor |
109 | * |
110 | * Returns: --- |
111 | * |
112 | * Use: Computes %$d = x/y$% as %$d = x y^{-1}$%. |
113 | */ |
114 | |
115 | void group_stddiv(group *g, ge *d, ge *x, ge *y) |
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116 | { G_INV(g, d, y); G_MUL(g, d, x, d); } |
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117 | |
118 | /* --- @group_stdtoec@ --- * |
119 | * |
120 | * Arguments: @group *g@ = abstract group |
121 | * @ec *d@ = destination point |
122 | * @ge *x@ = group element |
123 | * |
124 | * Returns: @-1@, indicating failure. |
125 | * |
126 | * Use: Fails to convert a group element to an elliptic curve point. |
127 | */ |
128 | |
129 | int group_stdtoec(group *g, ec *d, ge *x) { return (-1); } |
130 | |
131 | /* --- @group_stdfromec@ --- * |
132 | * |
133 | * Arguments: @group *g@ = abstract group |
134 | * @ge *d@ = destination pointer |
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135 | * @const ec *p@ = elliptic curve point |
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136 | * |
137 | * Returns: Zero for success, @-1@ on failure. |
138 | * |
139 | * Use: Converts %$p$% to a group element by converting its %$x$%- |
140 | * coordinate. |
141 | */ |
142 | |
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143 | int group_stdfromec(group *g, ge *d, const ec *p) |
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144 | { if (EC_ATINF(p)) return (-1); return (G_FROMINT(g, d, p->x)); } |
145 | |
146 | /* --- @group_stdcheck@ --- * |
147 | * |
148 | * Arguments: @group *g@ = abstract group |
149 | * @grand *gr@ = random number source. |
150 | * |
151 | * Returns: Null on success, or a pointer to an error message. |
152 | */ |
153 | |
154 | const char *group_stdcheck(group *g, grand *gr) |
155 | { |
156 | ge *t; |
157 | int rc; |
158 | |
159 | if (!pgen_primep(g->r, gr)) return ("group order not prime"); |
160 | t = G_CREATE(g); G_EXP(g, t, g->g, g->r); |
161 | rc = G_IDENTP(g, t); G_DESTROY(g, t); |
162 | if (!rc) return ("generator not in the group"); |
163 | return (0); |
164 | } |
165 | |
166 | /*----- That's all, folks -------------------------------------------------*/ |