3 * $Id: g-prime.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
5 * Abstraction for prime groups
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 --------------------------------------------------*
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 ------------------------------------------------------*/
52 /*----- Data structures ---------------------------------------------------*/
60 /*----- Main code ---------------------------------------------------------*/
62 /* --- Group operations --- */
64 static void gdestroygroup(group
*gg
) {
66 mp_drop(g
->gen
); mp_drop(g
->g
.r
); mp_drop(g
->g
.h
);
67 mpmont_destroy(&g
->mm
);
71 static mp
**gcreate(group
*gg
)
72 { mp
**x
= CREATE(mp
*); *x
= MP_COPY(*gg
->i
); return (x
); }
74 static void gcopy(group
*gg
, mp
**d
, mp
**x
)
75 { mp
*t
= MP_COPY(*x
); MP_DROP(*d
); *d
= t
; }
77 static void gburn(group
*gg
, mp
**x
) { (*x
)->f
|= MP_BURN
; }
79 static void gdestroy(group
*gg
, mp
**x
) { MP_DROP(*x
); DESTROY(x
); }
81 static int gsamep(group
*gg
, group
*hh
)
82 { gctx
*g
= (gctx
*)gg
, *h
= (gctx
*)hh
; return (g
->mm
.m
== h
->mm
.m
); }
84 static int geq(group
*gg
, mp
**x
, mp
**y
) { return (MP_EQ(*x
, *y
)); }
86 static const char *gcheck(group
*gg
, grand
*gr
) {
87 gctx
*g
= (gctx
*)gg
; int rc
; mp
*t
;
88 if (!pgen_primep(g
->mm
.m
, gr
)) return ("p is not prime");
89 t
= mp_mul(MP_NEW
, g
->g
.r
, g
->g
.h
); t
= mp_add(t
, t
, MP_ONE
);
90 rc
= MP_EQ(t
, g
->mm
.m
); MP_DROP(t
); if (!rc
) return ("not a subgroup");
91 return (group_stdcheck(gg
, gr
));
94 static void gmul(group
*gg
, mp
**d
, mp
**x
, mp
**y
)
95 { gctx
*g
= (gctx
*)gg
; *d
= mpmont_mul(&g
->mm
, *d
, *x
, *y
); }
97 static void gsqr(group
*gg
, mp
**d
, mp
**x
) {
98 gctx
*g
= (gctx
*)gg
; mp
*r
= mp_sqr(*d
, *x
);
99 *d
= mpmont_reduce(&g
->mm
, r
, r
);
102 static void ginv(group
*gg
, mp
**d
, mp
**x
) {
103 gctx
*g
= (gctx
*)gg
; mp
*r
= mpmont_reduce(&g
->mm
, *d
, *x
);
104 mp_gcd(0, 0, &r
, g
->mm
.m
, r
); *d
= mpmont_mul(&g
->mm
, r
, r
, g
->mm
.r2
);
107 static void gexp(group
*gg
, mp
**d
, mp
**x
, mp
*n
)
108 { gctx
*g
= (gctx
*)gg
; *d
= mpmont_expr(&g
->mm
, *d
, *x
, n
); }
110 static void gmexp(group
*gg
, mp
**d
, const group_expfactor
*f
, size_t n
) {
111 gctx
*g
= (gctx
*)gg
; size_t i
;
112 mp_expfactor
*ff
= xmalloc(n
* sizeof(mp_expfactor
));
113 for (i
= 0; i
< n
; i
++) { ff
[i
].base
= *f
[i
].base
; ff
[i
].exp
= f
[i
].exp
; }
114 *d
= mpmont_mexpr(&g
->mm
, *d
, ff
, n
); xfree(ff
);
117 static int gread(group
*gg
, mp
**d
, const mptext_ops
*ops
, void *p
) {
118 gctx
*g
= (gctx
*)gg
; mp
*t
;
119 if ((t
= mp_read(MP_NEW
, 0, ops
, p
)) == 0) return (-1);
120 mp_drop(*d
); *d
= mpmont_mul(&g
->mm
, t
, t
, g
->mm
.r2
); return (0);
123 static int gwrite(group
*gg
, mp
**x
, const mptext_ops
*ops
, void *p
) {
124 gctx
*g
= (gctx
*)gg
; mp
*t
= mpmont_reduce(&g
->mm
, MP_NEW
, *x
);
125 int rc
= mp_write(t
, 10, ops
, p
); MP_DROP(t
); return (rc
);
128 static mp
*gtoint(group
*gg
, mp
*d
, mp
**x
)
129 { gctx
*g
= (gctx
*)gg
; return (mpmont_reduce(&g
->mm
, d
, *x
)); }
131 static int gfromint(group
*gg
, mp
**d
, mp
*x
) {
132 gctx
*g
= (gctx
*)gg
; mp_div(0, &x
, x
, g
->mm
.m
); mp_drop(*d
);
133 *d
= mpmont_mul(&g
->mm
, x
, x
, g
->mm
.r2
); return (0);
136 static int gtobuf(group
*gg
, buf
*b
, mp
**x
) {
137 gctx
*g
= (gctx
*)gg
; mp
*t
= mpmont_reduce(&g
->mm
, MP_NEW
, *x
);
138 int rc
= buf_putmp(b
, t
); MP_DROP(t
); return (rc
);
141 static int gfrombuf(group
*gg
, buf
*b
, mp
**d
) {
142 gctx
* g
= (gctx
*)gg
; mp
*x
; if ((x
= buf_getmp(b
)) == 0) return (-1);
143 mp_div(0, &x
, x
, g
->mm
.r2
); mp_drop(*d
);
144 *d
= mpmont_mul(&g
->mm
, x
, x
, g
->mm
.r2
); return(0);
147 /* --- @group_prime@ --- *
149 * Arguments: @const gprime_param *gp@ = group parameters
151 * Returns: A pointer to the group.
153 * Use: Constructs an abstract group interface for a subgroup of a
154 * prime field. Group elements are @mp *@ pointers.
157 static const group_ops gops
= {
159 gdestroygroup
, gcreate
, gcopy
, gburn
, gdestroy
,
160 gsamep
, geq
, group_stdidentp
,
162 gmul
, gsqr
, ginv
, group_stddiv
, gexp
, gmexp
,
164 gtoint
, gfromint
, group_stdtoec
, group_stdfromec
, gtobuf
, gfrombuf
167 group
*group_prime(const gprime_param
*gp
)
169 gctx
*g
= CREATE(gctx
);
172 g
->g
.nbits
= mp_bits(gp
->p
);
173 g
->g
.noctets
= (g
->g
.nbits
+ 7) >> 3;
174 mpmont_create(&g
->mm
, gp
->p
);
176 g
->gen
= mpmont_mul(&g
->mm
, MP_NEW
, gp
->g
, g
->mm
.r2
);
178 g
->g
.r
= MP_COPY(gp
->q
);
179 g
->g
.h
= MP_NEW
; mp_div(&g
->g
.h
, 0, gp
->p
, gp
->q
);
183 /*----- That's all, folks -------------------------------------------------*/