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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: f-prime.c,v 1.12 2004/04/08 01:36:15 mdw Exp $ |
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4 | * |
5 | * Prime fields with Montgomery arithmetic |
6 | * |
7 | * (c) 2001 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 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
32 | #include <mLib/sub.h> |
33 | |
34 | #include "field.h" |
35 | #include "mpmont.h" |
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36 | #include "mprand.h" |
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37 | |
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38 | /*----- Main code ---------------------------------------------------------*/ |
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39 | |
40 | typedef struct fctx { |
41 | field f; |
42 | mpmont mm; |
43 | } fctx; |
44 | |
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45 | /* --- Field operations --- */ |
46 | |
47 | static void fdestroy(field *ff) |
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48 | { fctx *f = (fctx *)ff; mpmont_destroy(&f->mm); DESTROY(f); } |
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49 | |
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50 | static mp *frand(field *ff, mp *d, grand *r) |
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51 | { fctx *f = (fctx *)ff; return (mprand_range(d, f->mm.m, r, 0)); } |
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52 | |
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53 | static mp *fin(field *ff, mp *d, mp *x) { |
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54 | fctx *f = (fctx *)ff; |
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55 | mp_div(0, &d, x, f->mm.m); |
56 | return (mpmont_mul(&f->mm, d, d, f->mm.r2)); |
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57 | } |
58 | |
59 | static mp *fout(field *ff, mp *d, mp *x) |
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60 | { fctx *f = (fctx *)ff; return (mpmont_reduce(&f->mm, d, x)); } |
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61 | |
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62 | static int fzerop(field *ff, mp *x) { return (!MP_LEN(x)); } |
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63 | |
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64 | static mp *fneg(field *ff, mp *d, mp *x) |
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65 | { fctx *f = (fctx *)ff; return (mp_sub(d, f->mm.m, x)); } |
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66 | |
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67 | static mp *fadd(field *ff, mp *d, mp *x, mp *y) { |
68 | fctx *f = (fctx *)ff; d = mp_add(d, x, y); |
69 | if (d->f & MP_NEG) d = mp_add(d, d, f->mm.m); |
70 | else if (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m); |
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71 | return (d); |
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72 | } |
73 | |
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74 | static mp *fsub(field *ff, mp *d, mp *x, mp *y) { |
75 | fctx *f = (fctx *)ff; d = mp_sub(d, x, y); |
76 | if (d->f & MP_NEG) d = mp_add(d, d, f->mm.m); |
77 | else if (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m); |
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78 | return (d); |
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79 | } |
80 | |
81 | static mp *fmul(field *ff, mp *d, mp *x, mp *y) |
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82 | { fctx *f = (fctx *)ff; return (mpmont_mul(&f->mm, d, x, y)); } |
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83 | |
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84 | static mp *fsqr(field *ff, mp *d, mp *x) { |
85 | fctx *f = (fctx *)ff; d = mp_sqr(d, x); |
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86 | return (mpmont_reduce(&f->mm, d, d)); |
87 | } |
88 | |
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89 | static mp *finv(field *ff, mp *d, mp *x) { |
90 | fctx *f = (fctx *)ff; d = mpmont_reduce(&f->mm, d, x); |
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91 | d = mp_modinv(d, d, f->mm.m); return (mpmont_mul(&f->mm, d, d, f->mm.r2)); |
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92 | } |
93 | |
94 | static mp *freduce(field *ff, mp *d, mp *x) |
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95 | { fctx *f = (fctx *)ff; mp_div(0, &d, x, f->mm.m); return (d); } |
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96 | |
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97 | static mp *fsqrt(field *ff, mp *d, mp *x) { |
98 | fctx *f = (fctx *)ff; d = mpmont_reduce(&f->mm, d, x); |
99 | d = mp_modsqrt(d, d, f->mm.m); if (!d) return (d); |
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100 | return (mpmont_mul(&f->mm, d, d, f->mm.r2)); |
101 | } |
102 | |
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103 | static mp *fdbl(field *ff, mp *d, mp *x) { |
104 | fctx *f = (fctx *)ff; d = mp_lsl(d, x, 1); |
105 | if (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m); |
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106 | return (d); |
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107 | } |
108 | |
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109 | static mp *ftpl(field *ff, mp *d, mp *x) { |
110 | fctx *f = (fctx *)ff; MP_DEST(d, MP_LEN(x) + 1, x->f); |
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111 | MPX_UMULN(d->v, d->vl, x->v, x->vl, 3); |
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112 | while (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m); |
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113 | return (d); |
114 | } |
115 | |
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116 | static mp *fqdl(field *ff, mp *d, mp *x) { |
117 | fctx *f = (fctx *)ff; d = mp_lsl(d, x, 2); |
118 | while (MP_CMP(d, >, f->mm.m)) d = mp_sub(d, d, f->mm.m); |
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119 | return (d); |
120 | } |
121 | |
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122 | static mp *fhlv(field *ff, mp *d, mp *x) { |
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123 | fctx *f = (fctx *)ff; |
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124 | if (!MP_LEN(x)) { MP_COPY(x); MP_DROP(d); return (x); } |
125 | if (x->v[0] & 1) { d = mp_add(d, x, f->mm.m); x = d; } |
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126 | return (mp_lsr(d, x, 1)); |
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127 | } |
128 | |
129 | /* --- Field operations table --- */ |
130 | |
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131 | static const field_ops fops = { |
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132 | FTY_PRIME, "prime", |
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133 | fdestroy, frand, field_stdsamep, |
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134 | fin, fout, |
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135 | fzerop, fneg, fadd, fsub, fmul, fsqr, finv, freduce, fsqrt, |
136 | 0, |
137 | fdbl, ftpl, fqdl, fhlv |
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138 | }; |
139 | |
140 | /* --- @field_prime@ --- * |
141 | * |
142 | * Arguments: @mp *p@ = the characteristic of the field |
143 | * |
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144 | * Returns: A pointer to the field or null. |
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145 | * |
146 | * Use: Creates a field structure for a prime field of size %$p$%, |
147 | * using Montgomery reduction for arithmetic. |
148 | */ |
149 | |
150 | field *field_prime(mp *p) |
151 | { |
02d7884d |
152 | fctx *f; |
153 | |
154 | if (!MP_ISPOS(p) || !MP_ISODD(p)) |
155 | return (0); |
156 | f = CREATE(fctx); |
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157 | f->f.ops = &fops; |
158 | mpmont_create(&f->mm, p); |
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159 | f->f.zero = MP_ZERO; |
160 | f->f.one = f->mm.r; |
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161 | f->f.m = f->mm.m; |
162 | f->f.nbits = mp_bits(p); |
163 | f->f.noctets = (f->f.nbits + 7) >> 3; |
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164 | return (&f->f); |
165 | } |
166 | |
167 | /*----- That's all, folks -------------------------------------------------*/ |