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1 | /* -*-c-*- |
2 | * |
3 | * $Id: group-stdops.c,v 1.1 2004/04/01 12:50:09 mdw Exp $ |
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 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: group-stdops.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 "group.h" |
45 | #include "pgen.h" |
46 | |
47 | /*----- Handy functions ---------------------------------------------------*/ |
48 | |
49 | /* --- @group_check@ --- * |
50 | * |
51 | * Arguments: @group *g@ = an abstract group |
52 | * @ge *x@ = a group element |
53 | * |
54 | * Returns: Zero on success, nonzero for failure. |
55 | * |
56 | * Use: Checks that @x@ is a valid group element. This may take a |
57 | * while, since it checks that %$x^h \ne 1$% and %$x^r = 1$%. |
58 | */ |
59 | |
60 | int group_check(group *g, ge *x) |
61 | { |
62 | ge *d = G_CREATE(g); |
63 | int rc; |
64 | |
65 | G_EXP(g, d, x, g->h); rc = !G_IDENTP(g, d); |
66 | if (rc) { G_EXP(g, d, x, g->r); rc = G_IDENTP(g, d); } |
67 | G_DESTROY(g, d); |
68 | if (!rc) return (-1); |
69 | return (0); |
70 | } |
71 | |
72 | /* --- @group_samep@ --- * |
73 | * |
74 | * Arguments: @group *g, *h@ = two abstract groups |
75 | * |
76 | * Returns: Nonzero if the groups are in fact identical (not just |
77 | * isomorphic). |
78 | * |
79 | * Use: Checks to see whether two groups are actually the same. This |
80 | * function does the full check: the group operatrion @samep@ |
81 | * just does the group-specific details. |
82 | */ |
83 | |
84 | int group_samep(group *g, group *h) |
85 | { |
86 | return (g->ops == h->ops && |
87 | MP_EQ(g->r, h->r) && MP_EQ(g->h, h->h) && |
88 | G_EQ(g, g->i, h->i) && G_EQ(g, g->g, h->g) && |
89 | G_SAMEP(g, h)); |
90 | } |
91 | |
92 | /*----- Standard implementations ------------------------------------------*/ |
93 | |
94 | /* --- @group_stdidentp@ --- * |
95 | * |
96 | * Arguments: @group *g@ = abstract group |
97 | * @ge *x@ = group element |
98 | * |
99 | * Returns: Nonzero if %$x$% is the group identity. |
100 | */ |
101 | |
102 | int group_stdidentp(group *g, ge *x) { return (G_EQ(g, x, g->i)); } |
103 | |
104 | /* --- @group_stdsqr@ --- * |
105 | * |
106 | * Arguments: @group *g@ = abstract group |
107 | * @ge *d@ = destination pointer |
108 | * @ge *x@ = group element |
109 | * |
110 | * Returns: --- |
111 | * |
112 | * Use: Computes %$d = x^2$% as %$d = x x$%. |
113 | */ |
114 | |
115 | void group_stdsqr(group *g, ge *d, ge *x) { G_MUL(g, d, x, x); } |
116 | |
117 | /* --- @group_stddiv@ --- * |
118 | * |
119 | * Arguments: @group *g@ = abstract group |
120 | * @ge *d@ = destination pointer |
121 | * @ge *x@ = dividend |
122 | * @ge *y@ = divisor |
123 | * |
124 | * Returns: --- |
125 | * |
126 | * Use: Computes %$d = x/y$% as %$d = x y^{-1}$%. |
127 | */ |
128 | |
129 | void group_stddiv(group *g, ge *d, ge *x, ge *y) |
130 | { |
131 | G_INV(g, d, y); |
132 | G_MUL(g, d, x, d); |
133 | } |
134 | |
135 | /* --- @group_stdtoec@ --- * |
136 | * |
137 | * Arguments: @group *g@ = abstract group |
138 | * @ec *d@ = destination point |
139 | * @ge *x@ = group element |
140 | * |
141 | * Returns: @-1@, indicating failure. |
142 | * |
143 | * Use: Fails to convert a group element to an elliptic curve point. |
144 | */ |
145 | |
146 | int group_stdtoec(group *g, ec *d, ge *x) { return (-1); } |
147 | |
148 | /* --- @group_stdfromec@ --- * |
149 | * |
150 | * Arguments: @group *g@ = abstract group |
151 | * @ge *d@ = destination pointer |
152 | * @ec *p@ = elliptic curve point |
153 | * |
154 | * Returns: Zero for success, @-1@ on failure. |
155 | * |
156 | * Use: Converts %$p$% to a group element by converting its %$x$%- |
157 | * coordinate. |
158 | */ |
159 | |
160 | int group_stdfromec(group *g, ge *d, ec *p) |
161 | { if (EC_ATINF(p)) return (-1); return (G_FROMINT(g, d, p->x)); } |
162 | |
163 | /* --- @group_stdcheck@ --- * |
164 | * |
165 | * Arguments: @group *g@ = abstract group |
166 | * @grand *gr@ = random number source. |
167 | * |
168 | * Returns: Null on success, or a pointer to an error message. |
169 | */ |
170 | |
171 | const char *group_stdcheck(group *g, grand *gr) |
172 | { |
173 | ge *t; |
174 | int rc; |
175 | |
176 | if (!pgen_primep(g->r, gr)) return ("group order not prime"); |
177 | t = G_CREATE(g); G_EXP(g, t, g->g, g->r); |
178 | rc = G_IDENTP(g, t); G_DESTROY(g, t); |
179 | if (!rc) return ("generator not in the group"); |
180 | return (0); |
181 | } |
182 | |
183 | /*----- That's all, folks -------------------------------------------------*/ |