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Major memory management overhaul. Added arena support. Use the secure
[u/mdw/catacomb] / mpbarrett.c
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21a7c4b1 1/* -*-c-*-
2 *
d34decd2 3 * $Id: mpbarrett.c,v 1.4 2000/06/17 11:45:09 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 $
d34decd2 33 * Revision 1.4 2000/06/17 11:45:09 mdw
34 * Major memory management overhaul. Added arena support. Use the secure
35 * arena for secret integers. Replace and improve the MP management macros
36 * (e.g., replace MP_MODIFY by MP_DEST).
37 *
0a5d0bc7 38 * Revision 1.3 1999/12/12 15:08:52 mdw
39 * Don't bother shifting %$q$% in @mpbarrett_reduce@, just skip the least
40 * significant digits.
41 *
ed6d1bd2 42 * Revision 1.2 1999/12/11 01:50:56 mdw
43 * Improve initialization slightly.
44 *
21a7c4b1 45 * Revision 1.1 1999/12/10 23:21:59 mdw
46 * Barrett reduction support: works with even moduli.
47 *
48 */
49
50/*----- Header files ------------------------------------------------------*/
51
52#include "mp.h"
53#include "mpbarrett.h"
54
55/*----- Main code ---------------------------------------------------------*/
56
57/* --- @mpbarrett_create@ --- *
58 *
59 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
60 * @mp *m@ = modulus to work to
61 *
62 *
63 * Returns: ---
64 *
65 * Use: Initializes a Barrett reduction context ready for use.
66 */
67
68void mpbarrett_create(mpbarrett *mb, mp *m)
69{
70 mp *b;
71
72 /* --- Validate the arguments --- */
73
74 assert(((void)"Barrett modulus must be positive", (m->f & MP_NEG) == 0));
75
76 /* --- Compute %$\mu$% --- */
77
78 mp_shrink(m);
79 mb->k = MP_LEN(m);
80 mb->m = MP_COPY(m);
d34decd2 81 b = mp_new(2 * mb->k + 1, 0);
ed6d1bd2 82 MPX_ZERO(b->v, b->vl - 1);
83 b->vl[-1] = 1;
21a7c4b1 84 mp_div(&b, 0, b, m);
85 mb->mu = b;
86}
87
88/* --- @mpbarrett_destroy@ --- *
89 *
90 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
91 *
92 * Returns: ---
93 *
94 * Use: Destroys a Barrett reduction context releasing any resources
95 * claimed.
96 */
97
98void mpbarrett_destroy(mpbarrett *mb)
99{
100 mp_drop(mb->m);
101 mp_drop(mb->mu);
102}
103
104/* --- @mpbarrett_reduce@ --- *
105 *
106 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
107 * @mp *d@ = destination for result
108 * @mp *m@ = number to reduce
109 *
110 * Returns: The residue of @m@ modulo the number in the reduction
111 * context.
112 *
113 * Use: Performs an efficient modular reduction. The argument is
114 * assumed to be positive.
115 */
116
117mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
118{
119 mp *q;
120 size_t k = mb->k;
121
122 /* --- Special case if @m@ is too small --- */
123
124 if (MP_LEN(m) < k) {
125 m = MP_COPY(m);
d34decd2 126 if (d)
127 MP_DROP(d);
21a7c4b1 128 return (m);
129 }
130
131 /* --- First stage --- */
132
133 {
134 mp qq;
135 mp_build(&qq, m->v + (k - 1), m->vl);
136 q = mp_mul(MP_NEW, &qq, mb->mu);
0a5d0bc7 137 if (MP_LEN(q) <= k) {
138 m = MP_COPY(m);
d34decd2 139 if (d)
140 MP_DROP(d);
0a5d0bc7 141 return (m);
142 }
21a7c4b1 143 }
144
145 /* --- Second stage --- */
146
147 {
148 mp *r;
149 mpw *mvl;
150
151 MP_COPY(m);
152 if (MP_LEN(m) <= k + 1)
153 mvl = m->vl;
154 else
155 mvl = m->v + k + 1;
d34decd2 156 r = mp_new(k + 1, (q->f | mb->m->f) & MP_BURN);
0a5d0bc7 157 mpx_umul(r->v, r->vl, q->v + k + 1, q->vl, mb->m->v, mb->m->vl);
d34decd2 158 MP_DEST(d, k + 1, r->f);
21a7c4b1 159 mpx_usub(d->v, d->vl, m->v, mvl, r->v, r->vl);
160 d->f = (m->f | r->f) & MP_BURN;
161 MP_DROP(r);
162 MP_DROP(q);
163 MP_DROP(m);
164 }
165
166 /* --- Final stage --- */
167
168 MP_SHRINK(d);
169 while (MPX_UCMP(d->v, d->vl, >=, mb->m->v, mb->m->vl))
170 mpx_usub(d->v, d->vl, d->v, d->vl, mb->m->v, mb->m->vl);
171
172 MP_SHRINK(d);
173 return (d);
174}
175
176/* --- @mpbarrett_exp@ --- *
177 *
178 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
179 * @mp *d@ = fake destination
180 * @mp *a@ = base
181 * @mp *e@ = exponent
182 *
183 * Returns: Result, %$a^e \bmod m$%.
184 */
185
186mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
187{
188 mpscan sc;
189 mp *x = MP_ONE;
190 mp *spare = MP_NEW;
191
192 a = MP_COPY(a);
193 mp_scan(&sc, e);
d34decd2 194 if (e->f & MP_BURN)
195 spare = MP_NEWSEC;
21a7c4b1 196 if (MP_STEP(&sc)) {
197 size_t sq = 0;
198 for (;;) {
199 mp *dd;
200 if (MP_BIT(&sc)) {
201 while (sq) {
202 dd = mp_sqr(spare, a);
203 dd = mpbarrett_reduce(mb, dd, dd);
204 spare = a; a = dd;
205 sq--;
206 }
207 dd = mp_mul(spare, x, a);
208 dd = mpbarrett_reduce(mb, dd, dd);
209 spare = x; x = dd;
210 }
211 sq++;
212 if (!MP_STEP(&sc))
213 break;
214 }
215 }
216
217 MP_DROP(a);
218 if (spare != MP_NEW)
219 MP_DROP(spare);
220 if (d != MP_NEW)
221 MP_DROP(d);
222 return (x);
223}
224
225/*----- Test rig ----------------------------------------------------------*/
226
227#ifdef TEST_RIG
228
229static int vmod(dstr *v)
230{
231 mp *x = *(mp **)v[0].buf;
232 mp *n = *(mp **)v[1].buf;
233 mp *r = *(mp **)v[2].buf;
234 mp *s;
235 mpbarrett mb;
236 int ok = 1;
237
238 mpbarrett_create(&mb, n);
239 s = mpbarrett_reduce(&mb, MP_NEW, x);
240
241 if (MP_CMP(s, !=, r)) {
242 fputs("\n*** barrett reduction failure\n", stderr);
243 fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr);
244 fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr);
245 fputs("r = ", stderr); mp_writefile(r, stderr, 10); fputc('\n', stderr);
246 fputs("s = ", stderr); mp_writefile(s, stderr, 10); fputc('\n', stderr);
247 ok = 0;
248 }
249
250 mpbarrett_destroy(&mb);
251 mp_drop(x);
252 mp_drop(n);
253 mp_drop(r);
254 mp_drop(s);
255 assert(mparena_count(MPARENA_GLOBAL) == 0);
256 return (ok);
257}
258
259static int vexp(dstr *v)
260{
261 mp *m = *(mp **)v[0].buf;
262 mp *a = *(mp **)v[1].buf;
263 mp *b = *(mp **)v[2].buf;
264 mp *r = *(mp **)v[3].buf;
265 mp *mr;
266 int ok = 1;
267
268 mpbarrett mb;
269 mpbarrett_create(&mb, m);
270
271 mr = mpbarrett_exp(&mb, MP_NEW, a, b);
272
273 if (MP_CMP(mr, !=, r)) {
274 fputs("\n*** barrett modexp failed", stderr);
275 fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
276 fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
277 fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
278 fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
279 fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
280 fputc('\n', stderr);
281 ok = 0;
282 }
283
284 mp_drop(m);
285 mp_drop(a);
286 mp_drop(b);
287 mp_drop(r);
288 mp_drop(mr);
289 mpbarrett_destroy(&mb);
290 assert(mparena_count(MPARENA_GLOBAL) == 0);
291 return ok;
292}
293
294static test_chunk tests[] = {
295 { "mpbarrett-reduce", vmod, { &type_mp, &type_mp, &type_mp, 0 } },
296 { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
297 { 0, 0, { 0 } }
298};
299
300int main(int argc, char *argv[])
301{
302 sub_init();
303 test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett");
304 return (0);
305}
306
307#endif
308
309/*----- That's all, folks -------------------------------------------------*/
Catacomb cryptographic library (downstream of http://git.distorted.org.uk/~mdw/catacomb/)