3 * $Id: f-prime.c,v 1.3.4.1 2003/06/10 13:43:53 mdw Exp $
5 * Prime fields with Montgomery arithmetic
7 * (c) 2001 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 1.3.4.1 2003/06/10 13:43:53 mdw
34 * Simple (non-projective) curves over prime fields now seem to work.
36 * Revision 1.3 2003/05/15 23:25:59 mdw
37 * Make elliptic curve stuff build.
39 * Revision 1.2 2002/01/13 13:48:44 mdw
42 * Revision 1.1 2001/04/29 18:12:33 mdw
47 /*----- Header files ------------------------------------------------------*/
54 /*----- Data structures ---------------------------------------------------*/
61 /*----- Main code ---------------------------------------------------------*/
63 /* --- Field operations --- */
65 static void fdestroy(field *ff)
68 mpmont_destroy(&f->mm);
72 static mp *fin(field *ff, mp *d, mp *x)
75 mp_div(0, &d, x, f->mm.m);
76 return (mpmont_mul(&f->mm, d, d, f->mm.r2));
79 static mp *fout(field *ff, mp *d, mp *x)
82 return (mpmont_reduce(&f->mm, d, x));
85 static mp *fneg(field *ff, mp *d, mp *x)
88 return (mp_sub(d, f->mm.m, x));
91 static mp *fadd(field *ff, mp *d, mp *x, mp *y)
96 d = mp_add(d, d, f->mm.m);
97 else if (MP_CMP(d, >, f->mm.m))
98 d = mp_sub(d, d, f->mm.m);
102 static mp *fsub(field *ff, mp *d, mp *x, mp *y)
104 fctx *f = (fctx *)ff;
107 d = mp_add(d, d, f->mm.m);
108 else if (MP_CMP(d, >, f->mm.m))
109 d = mp_sub(d, d, f->mm.m);
113 static mp *fmul(field *ff, mp *d, mp *x, mp *y)
115 fctx *f = (fctx *)ff;
116 return (mpmont_mul(&f->mm, d, x, y));
119 static mp *fsqr(field *ff, mp *d, mp *x)
121 fctx *f = (fctx *)ff;
123 return (mpmont_reduce(&f->mm, d, d));
126 static mp *finv(field *ff, mp *d, mp *x)
128 fctx *f = (fctx *)ff;
129 d = mpmont_reduce(&f->mm, d, x);
130 mp_gcd(0, 0, &d, f->mm.m, d);
131 return (mpmont_mul(&f->mm, d, d, f->mm.r2));
134 static mp *freduce(field *ff, mp *d, mp *x)
136 fctx *f = (fctx *)ff;
137 mp_div(0, &d, x, f->mm.m);
141 static mp *fdbl(field *ff, mp *d, mp *x)
143 fctx *f = (fctx *)ff;
145 if (MP_CMP(d, >, f->mm.m))
146 d = mp_sub(d, d, f->mm.m);
150 static mp *ftpl(field *ff, mp *d, mp *x)
152 fctx *f = (fctx *)ff;
153 MP_DEST(d, MP_LEN(x) + 1, x->f);
154 MPX_UMULN(d->v, d->vl, x->v, x->vl, 3);
155 while (MP_CMP(d, >, f->mm.m))
156 d = mp_sub(d, d, f->mm.m);
160 static mp *fsqrt(field *ff, mp *d, mp *x)
162 fctx *f = (fctx *)ff;
163 d = mpmont_reduce(&f->mm, d, x);
164 d = mp_modsqrt(d, d, f->mm.m);
165 return (mpmont_mul(&f->mm, d, d, f->mm.r2));
168 /* --- Field operations table --- */
170 static field_ops fops = {
173 fneg, fadd, fsub, fmul, fsqr, finv, freduce,
177 /* --- @field_prime@ --- *
179 * Arguments: @mp *p@ = the characteristic of the field
181 * Returns: A pointer to the field.
183 * Use: Creates a field structure for a prime field of size %$p$%,
184 * using Montgomery reduction for arithmetic.
187 field *field_prime(mp *p)
189 fctx *f = CREATE(fctx);
191 mpmont_create(&f->mm, p);
197 /*----- That's all, folks -------------------------------------------------*/