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Fix bug in test rig link flags. Add Karatsuba squaring.
[u/mdw/catacomb] / mpbarrett.c
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21a7c4b1 1/* -*-c-*-
2 *
ed6d1bd2 3 * $Id: mpbarrett.c,v 1.2 1999/12/11 01:50:56 mdw Exp $
21a7c4b1 4 *
5 * Barrett modular reduction
6 *
7 * (c) 1999 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: mpbarrett.c,v $
ed6d1bd2 33 * Revision 1.2 1999/12/11 01:50:56 mdw
34 * Improve initialization slightly.
35 *
21a7c4b1 36 * Revision 1.1 1999/12/10 23:21:59 mdw
37 * Barrett reduction support: works with even moduli.
38 *
39 */
40
41/*----- Header files ------------------------------------------------------*/
42
43#include "mp.h"
44#include "mpbarrett.h"
45
46/*----- Main code ---------------------------------------------------------*/
47
48/* --- @mpbarrett_create@ --- *
49 *
50 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
51 * @mp *m@ = modulus to work to
52 *
53 *
54 * Returns: ---
55 *
56 * Use: Initializes a Barrett reduction context ready for use.
57 */
58
59void mpbarrett_create(mpbarrett *mb, mp *m)
60{
61 mp *b;
62
63 /* --- Validate the arguments --- */
64
65 assert(((void)"Barrett modulus must be positive", (m->f & MP_NEG) == 0));
66
67 /* --- Compute %$\mu$% --- */
68
69 mp_shrink(m);
70 mb->k = MP_LEN(m);
71 mb->m = MP_COPY(m);
ed6d1bd2 72 b = mp_create(2 * mb->k + 1);
73 MPX_ZERO(b->v, b->vl - 1);
74 b->vl[-1] = 1;
21a7c4b1 75 mp_div(&b, 0, b, m);
76 mb->mu = b;
77}
78
79/* --- @mpbarrett_destroy@ --- *
80 *
81 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
82 *
83 * Returns: ---
84 *
85 * Use: Destroys a Barrett reduction context releasing any resources
86 * claimed.
87 */
88
89void mpbarrett_destroy(mpbarrett *mb)
90{
91 mp_drop(mb->m);
92 mp_drop(mb->mu);
93}
94
95/* --- @mpbarrett_reduce@ --- *
96 *
97 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
98 * @mp *d@ = destination for result
99 * @mp *m@ = number to reduce
100 *
101 * Returns: The residue of @m@ modulo the number in the reduction
102 * context.
103 *
104 * Use: Performs an efficient modular reduction. The argument is
105 * assumed to be positive.
106 */
107
108mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
109{
110 mp *q;
111 size_t k = mb->k;
112
113 /* --- Special case if @m@ is too small --- */
114
115 if (MP_LEN(m) < k) {
116 m = MP_COPY(m);
117 MP_DROP(d);
118 return (m);
119 }
120
121 /* --- First stage --- */
122
123 {
124 mp qq;
125 mp_build(&qq, m->v + (k - 1), m->vl);
126 q = mp_mul(MP_NEW, &qq, mb->mu);
127 q = mp_lsr(q, q, MPW_BITS * (k + 1));
128 }
129
130 /* --- Second stage --- */
131
132 {
133 mp *r;
134 mpw *mvl;
135
136 MP_COPY(m);
137 if (MP_LEN(m) <= k + 1)
138 mvl = m->vl;
139 else
140 mvl = m->v + k + 1;
141 r = mp_create(k + 1);
142 mpx_umul(r->v, r->vl, q->v, q->vl, mb->m->v, mb->m->vl);
143 r->f = (q->f | mb->m->f) & MP_BURN;
144 MP_MODIFY(d, k + 1);
145 mpx_usub(d->v, d->vl, m->v, mvl, r->v, r->vl);
146 d->f = (m->f | r->f) & MP_BURN;
147 MP_DROP(r);
148 MP_DROP(q);
149 MP_DROP(m);
150 }
151
152 /* --- Final stage --- */
153
154 MP_SHRINK(d);
155 while (MPX_UCMP(d->v, d->vl, >=, mb->m->v, mb->m->vl))
156 mpx_usub(d->v, d->vl, d->v, d->vl, mb->m->v, mb->m->vl);
157
158 MP_SHRINK(d);
159 return (d);
160}
161
162/* --- @mpbarrett_exp@ --- *
163 *
164 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
165 * @mp *d@ = fake destination
166 * @mp *a@ = base
167 * @mp *e@ = exponent
168 *
169 * Returns: Result, %$a^e \bmod m$%.
170 */
171
172mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
173{
174 mpscan sc;
175 mp *x = MP_ONE;
176 mp *spare = MP_NEW;
177
178 a = MP_COPY(a);
179 mp_scan(&sc, e);
180 if (MP_STEP(&sc)) {
181 size_t sq = 0;
182 for (;;) {
183 mp *dd;
184 if (MP_BIT(&sc)) {
185 while (sq) {
186 dd = mp_sqr(spare, a);
187 dd = mpbarrett_reduce(mb, dd, dd);
188 spare = a; a = dd;
189 sq--;
190 }
191 dd = mp_mul(spare, x, a);
192 dd = mpbarrett_reduce(mb, dd, dd);
193 spare = x; x = dd;
194 }
195 sq++;
196 if (!MP_STEP(&sc))
197 break;
198 }
199 }
200
201 MP_DROP(a);
202 if (spare != MP_NEW)
203 MP_DROP(spare);
204 if (d != MP_NEW)
205 MP_DROP(d);
206 return (x);
207}
208
209/*----- Test rig ----------------------------------------------------------*/
210
211#ifdef TEST_RIG
212
213static int vmod(dstr *v)
214{
215 mp *x = *(mp **)v[0].buf;
216 mp *n = *(mp **)v[1].buf;
217 mp *r = *(mp **)v[2].buf;
218 mp *s;
219 mpbarrett mb;
220 int ok = 1;
221
222 mpbarrett_create(&mb, n);
223 s = mpbarrett_reduce(&mb, MP_NEW, x);
224
225 if (MP_CMP(s, !=, r)) {
226 fputs("\n*** barrett reduction failure\n", stderr);
227 fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr);
228 fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr);
229 fputs("r = ", stderr); mp_writefile(r, stderr, 10); fputc('\n', stderr);
230 fputs("s = ", stderr); mp_writefile(s, stderr, 10); fputc('\n', stderr);
231 ok = 0;
232 }
233
234 mpbarrett_destroy(&mb);
235 mp_drop(x);
236 mp_drop(n);
237 mp_drop(r);
238 mp_drop(s);
239 assert(mparena_count(MPARENA_GLOBAL) == 0);
240 return (ok);
241}
242
243static int vexp(dstr *v)
244{
245 mp *m = *(mp **)v[0].buf;
246 mp *a = *(mp **)v[1].buf;
247 mp *b = *(mp **)v[2].buf;
248 mp *r = *(mp **)v[3].buf;
249 mp *mr;
250 int ok = 1;
251
252 mpbarrett mb;
253 mpbarrett_create(&mb, m);
254
255 mr = mpbarrett_exp(&mb, MP_NEW, a, b);
256
257 if (MP_CMP(mr, !=, r)) {
258 fputs("\n*** barrett modexp failed", stderr);
259 fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
260 fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
261 fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
262 fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
263 fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
264 fputc('\n', stderr);
265 ok = 0;
266 }
267
268 mp_drop(m);
269 mp_drop(a);
270 mp_drop(b);
271 mp_drop(r);
272 mp_drop(mr);
273 mpbarrett_destroy(&mb);
274 assert(mparena_count(MPARENA_GLOBAL) == 0);
275 return ok;
276}
277
278static test_chunk tests[] = {
279 { "mpbarrett-reduce", vmod, { &type_mp, &type_mp, &type_mp, 0 } },
280 { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
281 { 0, 0, { 0 } }
282};
283
284int main(int argc, char *argv[])
285{
286 sub_init();
287 test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett");
288 return (0);
289}
290
291#endif
292
293/*----- That's all, folks -------------------------------------------------*/
Catacomb cryptographic library (downstream of http://git.distorted.org.uk/~mdw/catacomb/)