3 * $Id: group-stdops.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
5 * Standard group operations
7 * (c) 2004 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
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.)
42 /*----- Header files ------------------------------------------------------*/
47 /*----- Handy functions ---------------------------------------------------*/
49 /* --- @group_check@ --- *
51 * Arguments: @group *g@ = an abstract group
52 * @ge *x@ = a group element
54 * Returns: Zero on success, nonzero for failure.
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 %$x^r = 1$%.
60 int group_check(group
*g
, ge
*x
)
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
); }
72 /* --- @group_samep@ --- *
74 * Arguments: @group *g, *h@ = two abstract groups
76 * Returns: Nonzero if the groups are in fact identical (not just
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.
84 int group_samep(group
*g
, group
*h
)
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
) &&
92 /*----- Standard implementations ------------------------------------------*/
94 /* --- @group_stdidentp@ --- *
96 * Arguments: @group *g@ = abstract group
97 * @ge *x@ = group element
99 * Returns: Nonzero if %$x$% is the group identity.
102 int group_stdidentp(group
*g
, ge
*x
) { return (G_EQ(g
, x
, g
->i
)); }
104 /* --- @group_stdsqr@ --- *
106 * Arguments: @group *g@ = abstract group
107 * @ge *d@ = destination pointer
108 * @ge *x@ = group element
112 * Use: Computes %$d = x^2$% as %$d = x x$%.
115 void group_stdsqr(group
*g
, ge
*d
, ge
*x
) { G_MUL(g
, d
, x
, x
); }
117 /* --- @group_stddiv@ --- *
119 * Arguments: @group *g@ = abstract group
120 * @ge *d@ = destination pointer
126 * Use: Computes %$d = x/y$% as %$d = x y^{-1}$%.
129 void group_stddiv(group
*g
, ge
*d
, ge
*x
, ge
*y
)
135 /* --- @group_stdtoec@ --- *
137 * Arguments: @group *g@ = abstract group
138 * @ec *d@ = destination point
139 * @ge *x@ = group element
141 * Returns: @-1@, indicating failure.
143 * Use: Fails to convert a group element to an elliptic curve point.
146 int group_stdtoec(group
*g
, ec
*d
, ge
*x
) { return (-1); }
148 /* --- @group_stdfromec@ --- *
150 * Arguments: @group *g@ = abstract group
151 * @ge *d@ = destination pointer
152 * @ec *p@ = elliptic curve point
154 * Returns: Zero for success, @-1@ on failure.
156 * Use: Converts %$p$% to a group element by converting its %$x$%-
160 int group_stdfromec(group
*g
, ge
*d
, ec
*p
)
161 { if (EC_ATINF(p
)) return (-1); return (G_FROMINT(g
, d
, p
->x
)); }
163 /* --- @group_stdcheck@ --- *
165 * Arguments: @group *g@ = abstract group
166 * @grand *gr@ = random number source.
168 * Returns: Null on success, or a pointer to an error message.
171 const char *group_stdcheck(group
*g
, grand
*gr
)
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");
183 /*----- That's all, folks -------------------------------------------------*/