3 * $Id: mpbarrett.c,v 1.5 2000/07/29 17:04:33 mdw Exp $
5 * Barrett modular reduction
7 * (c) 1999 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 --------------------------------------------------*
32 * $Log: mpbarrett.c,v $
33 * Revision 1.5 2000/07/29 17:04:33 mdw
34 * Change to use left-to-right bitwise exponentiation. This will improve
35 * performance when the base is small.
37 * Revision 1.4 2000/06/17 11:45:09 mdw
38 * Major memory management overhaul. Added arena support. Use the secure
39 * arena for secret integers. Replace and improve the MP management macros
40 * (e.g., replace MP_MODIFY by MP_DEST).
42 * Revision 1.3 1999/12/12 15:08:52 mdw
43 * Don't bother shifting %$q$% in @mpbarrett_reduce@, just skip the least
46 * Revision 1.2 1999/12/11 01:50:56 mdw
47 * Improve initialization slightly.
49 * Revision 1.1 1999/12/10 23:21:59 mdw
50 * Barrett reduction support: works with even moduli.
54 /*----- Header files ------------------------------------------------------*/
57 #include "mpbarrett.h"
59 /*----- Main code ---------------------------------------------------------*/
61 /* --- @mpbarrett_create@ --- *
63 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
64 * @mp *m@ = modulus to work to
69 * Use: Initializes a Barrett reduction context ready for use.
72 void mpbarrett_create(mpbarrett
*mb
, mp
*m
)
76 /* --- Validate the arguments --- */
78 assert(((void)"Barrett modulus must be positive", (m
->f
& MP_NEG
) == 0));
80 /* --- Compute %$\mu$% --- */
85 b
= mp_new(2 * mb
->k
+ 1, 0);
86 MPX_ZERO(b
->v
, b
->vl
- 1);
92 /* --- @mpbarrett_destroy@ --- *
94 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
98 * Use: Destroys a Barrett reduction context releasing any resources
102 void mpbarrett_destroy(mpbarrett
*mb
)
108 /* --- @mpbarrett_reduce@ --- *
110 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
111 * @mp *d@ = destination for result
112 * @mp *m@ = number to reduce
114 * Returns: The residue of @m@ modulo the number in the reduction
117 * Use: Performs an efficient modular reduction. The argument is
118 * assumed to be positive.
121 mp
*mpbarrett_reduce(mpbarrett
*mb
, mp
*d
, mp
*m
)
126 /* --- Special case if @m@ is too small --- */
135 /* --- First stage --- */
139 mp_build(&qq
, m
->v
+ (k
- 1), m
->vl
);
140 q
= mp_mul(MP_NEW
, &qq
, mb
->mu
);
141 if (MP_LEN(q
) <= k
) {
149 /* --- Second stage --- */
156 if (MP_LEN(m
) <= k
+ 1)
160 r
= mp_new(k
+ 1, (q
->f
| mb
->m
->f
) & MP_BURN
);
161 mpx_umul(r
->v
, r
->vl
, q
->v
+ k
+ 1, q
->vl
, mb
->m
->v
, mb
->m
->vl
);
162 MP_DEST(d
, k
+ 1, r
->f
);
163 mpx_usub(d
->v
, d
->vl
, m
->v
, mvl
, r
->v
, r
->vl
);
164 d
->f
= (m
->f
| r
->f
) & MP_BURN
;
170 /* --- Final stage --- */
173 while (MPX_UCMP(d
->v
, d
->vl
, >=, mb
->m
->v
, mb
->m
->vl
))
174 mpx_usub(d
->v
, d
->vl
, d
->v
, d
->vl
, mb
->m
->v
, mb
->m
->vl
);
180 /* --- @mpbarrett_exp@ --- *
182 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
183 * @mp *d@ = fake destination
187 * Returns: Result, %$a^e \bmod m$%.
190 mp
*mpbarrett_exp(mpbarrett
*mb
, mp
*d
, mp
*a
, mp
*e
)
194 mp
*spare
= (e
->f
& MP_BURN
) ? MP_NEWSEC
: MP_NEW
;
201 while (!MP_RBIT(&sc
))
204 /* --- Do the main body of the work --- */
210 y
= mp_sqr(spare
, x
);
211 y
= mpbarrett_reduce(mb
, y
, y
);
216 mp
*y
= mp_mul(spare
, x
, a
);
217 y
= mpbarrett_reduce(mb
, y
, y
);
229 /* --- Do a final round of squaring --- */
234 y
= mp_sqr(spare
, x
);
235 y
= mpbarrett_reduce(mb
, y
, y
);
249 /*----- Test rig ----------------------------------------------------------*/
253 static int vmod(dstr
*v
)
255 mp
*x
= *(mp
**)v
[0].buf
;
256 mp
*n
= *(mp
**)v
[1].buf
;
257 mp
*r
= *(mp
**)v
[2].buf
;
262 mpbarrett_create(&mb
, n
);
263 s
= mpbarrett_reduce(&mb
, MP_NEW
, x
);
265 if (MP_CMP(s
, !=, r
)) {
266 fputs("\n*** barrett reduction failure\n", stderr
);
267 fputs("x = ", stderr
); mp_writefile(x
, stderr
, 10); fputc('\n', stderr
);
268 fputs("n = ", stderr
); mp_writefile(n
, stderr
, 10); fputc('\n', stderr
);
269 fputs("r = ", stderr
); mp_writefile(r
, stderr
, 10); fputc('\n', stderr
);
270 fputs("s = ", stderr
); mp_writefile(s
, stderr
, 10); fputc('\n', stderr
);
274 mpbarrett_destroy(&mb
);
279 assert(mparena_count(MPARENA_GLOBAL
) == 0);
283 static int vexp(dstr
*v
)
285 mp
*m
= *(mp
**)v
[0].buf
;
286 mp
*a
= *(mp
**)v
[1].buf
;
287 mp
*b
= *(mp
**)v
[2].buf
;
288 mp
*r
= *(mp
**)v
[3].buf
;
293 mpbarrett_create(&mb
, m
);
295 mr
= mpbarrett_exp(&mb
, MP_NEW
, a
, b
);
297 if (MP_CMP(mr
, !=, r
)) {
298 fputs("\n*** barrett modexp failed", stderr
);
299 fputs("\n m = ", stderr
); mp_writefile(m
, stderr
, 10);
300 fputs("\n a = ", stderr
); mp_writefile(a
, stderr
, 10);
301 fputs("\n e = ", stderr
); mp_writefile(b
, stderr
, 10);
302 fputs("\n r = ", stderr
); mp_writefile(r
, stderr
, 10);
303 fputs("\nmr = ", stderr
); mp_writefile(mr
, stderr
, 10);
313 mpbarrett_destroy(&mb
);
314 assert(mparena_count(MPARENA_GLOBAL
) == 0);
318 static test_chunk tests
[] = {
319 { "mpbarrett-reduce", vmod
, { &type_mp
, &type_mp
, &type_mp
, 0 } },
320 { "mpbarrett-exp", vexp
, { &type_mp
, &type_mp
, &type_mp
, &type_mp
, 0 } },
324 int main(int argc
, char *argv
[])
327 test_run(argc
, argv
, tests
, SRCDIR
"/tests/mpbarrett");
333 /*----- That's all, folks -------------------------------------------------*/