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source: vbox/trunk/src/libs/openssl-1.1.1f/crypto/bn/bn_exp.c@ 83531

Last change on this file since 83531 was 83531, checked in by vboxsync, 5 years ago

setting svn:sync-process=export for openssl-1.1.1f, all files except tests
File size: 44.3 KB
Line 
1/*
2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include "internal/cryptlib.h"
11#include "internal/constant_time.h"
12#include "bn_local.h"
13
14#include <stdlib.h>
15#ifdef _WIN32
16# include <malloc.h>
17# ifndef alloca
18# define alloca _alloca
19# endif
20#elif defined(__GNUC__)
21# ifndef alloca
22# define alloca(s) __builtin_alloca((s))
23# endif
24#elif defined(__sun)
25# include <alloca.h>
26#endif
27
28#include "rsaz_exp.h"
29
30#undef SPARC_T4_MONT
31#if defined(OPENSSL_BN_ASM_MONT) && (defined(__sparc__) || defined(__sparc))
32# include "sparc_arch.h"
33extern unsigned int OPENSSL_sparcv9cap_P[];
34# define SPARC_T4_MONT
35#endif
36
37/* maximum precomputation table size for *variable* sliding windows */
38#define TABLE_SIZE 32
39
40/* this one works - simple but works */
41int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
42{
43 int i, bits, ret = 0;
44 BIGNUM *v, *rr;
45
46 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
47 || BN_get_flags(a, BN_FLG_CONSTTIME) != 0) {
48 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
49 BNerr(BN_F_BN_EXP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
50 return 0;
51 }
52
53 BN_CTX_start(ctx);
54 rr = ((r == a) || (r == p)) ? BN_CTX_get(ctx) : r;
55 v = BN_CTX_get(ctx);
56 if (rr == NULL || v == NULL)
57 goto err;
58
59 if (BN_copy(v, a) == NULL)
60 goto err;
61 bits = BN_num_bits(p);
62
63 if (BN_is_odd(p)) {
64 if (BN_copy(rr, a) == NULL)
65 goto err;
66 } else {
67 if (!BN_one(rr))
68 goto err;
69 }
70
71 for (i = 1; i < bits; i++) {
72 if (!BN_sqr(v, v, ctx))
73 goto err;
74 if (BN_is_bit_set(p, i)) {
75 if (!BN_mul(rr, rr, v, ctx))
76 goto err;
77 }
78 }
79 if (r != rr && BN_copy(r, rr) == NULL)
80 goto err;
81
82 ret = 1;
83 err:
84 BN_CTX_end(ctx);
85 bn_check_top(r);
86 return ret;
87}
88
89int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
90 BN_CTX *ctx)
91{
92 int ret;
93
94 bn_check_top(a);
95 bn_check_top(p);
96 bn_check_top(m);
97
98 /*-
99 * For even modulus m = 2^k*m_odd, it might make sense to compute
100 * a^p mod m_odd and a^p mod 2^k separately (with Montgomery
101 * exponentiation for the odd part), using appropriate exponent
102 * reductions, and combine the results using the CRT.
103 *
104 * For now, we use Montgomery only if the modulus is odd; otherwise,
105 * exponentiation using the reciprocal-based quick remaindering
106 * algorithm is used.
107 *
108 * (Timing obtained with expspeed.c [computations a^p mod m
109 * where a, p, m are of the same length: 256, 512, 1024, 2048,
110 * 4096, 8192 bits], compared to the running time of the
111 * standard algorithm:
112 *
113 * BN_mod_exp_mont 33 .. 40 % [AMD K6-2, Linux, debug configuration]
114 * 55 .. 77 % [UltraSparc processor, but
115 * debug-solaris-sparcv8-gcc conf.]
116 *
117 * BN_mod_exp_recp 50 .. 70 % [AMD K6-2, Linux, debug configuration]
118 * 62 .. 118 % [UltraSparc, debug-solaris-sparcv8-gcc]
119 *
120 * On the Sparc, BN_mod_exp_recp was faster than BN_mod_exp_mont
121 * at 2048 and more bits, but at 512 and 1024 bits, it was
122 * slower even than the standard algorithm!
123 *
124 * "Real" timings [linux-elf, solaris-sparcv9-gcc configurations]
125 * should be obtained when the new Montgomery reduction code
126 * has been integrated into OpenSSL.)
127 */
128
129#define MONT_MUL_MOD
130#define MONT_EXP_WORD
131#define RECP_MUL_MOD
132
133#ifdef MONT_MUL_MOD
134 if (BN_is_odd(m)) {
135# ifdef MONT_EXP_WORD
136 if (a->top == 1 && !a->neg
137 && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)
138 && (BN_get_flags(a, BN_FLG_CONSTTIME) == 0)
139 && (BN_get_flags(m, BN_FLG_CONSTTIME) == 0)) {
140 BN_ULONG A = a->d[0];
141 ret = BN_mod_exp_mont_word(r, A, p, m, ctx, NULL);
142 } else
143# endif
144 ret = BN_mod_exp_mont(r, a, p, m, ctx, NULL);
145 } else
146#endif
147#ifdef RECP_MUL_MOD
148 {
149 ret = BN_mod_exp_recp(r, a, p, m, ctx);
150 }
151#else
152 {
153 ret = BN_mod_exp_simple(r, a, p, m, ctx);
154 }
155#endif
156
157 bn_check_top(r);
158 return ret;
159}
160
161int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
162 const BIGNUM *m, BN_CTX *ctx)
163{
164 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
165 int start = 1;
166 BIGNUM *aa;
167 /* Table of variables obtained from 'ctx' */
168 BIGNUM *val[TABLE_SIZE];
169 BN_RECP_CTX recp;
170
171 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
172 || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
173 || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
174 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
175 BNerr(BN_F_BN_MOD_EXP_RECP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
176 return 0;
177 }
178
179 bits = BN_num_bits(p);
180 if (bits == 0) {
181 /* x**0 mod 1, or x**0 mod -1 is still zero. */
182 if (BN_abs_is_word(m, 1)) {
183 ret = 1;
184 BN_zero(r);
185 } else {
186 ret = BN_one(r);
187 }
188 return ret;
189 }
190
191 BN_CTX_start(ctx);
192 aa = BN_CTX_get(ctx);
193 val[0] = BN_CTX_get(ctx);
194 if (val[0] == NULL)
195 goto err;
196
197 BN_RECP_CTX_init(&recp);
198 if (m->neg) {
199 /* ignore sign of 'm' */
200 if (!BN_copy(aa, m))
201 goto err;
202 aa->neg = 0;
203 if (BN_RECP_CTX_set(&recp, aa, ctx) <= 0)
204 goto err;
205 } else {
206 if (BN_RECP_CTX_set(&recp, m, ctx) <= 0)
207 goto err;
208 }
209
210 if (!BN_nnmod(val[0], a, m, ctx))
211 goto err; /* 1 */
212 if (BN_is_zero(val[0])) {
213 BN_zero(r);
214 ret = 1;
215 goto err;
216 }
217
218 window = BN_window_bits_for_exponent_size(bits);
219 if (window > 1) {
220 if (!BN_mod_mul_reciprocal(aa, val[0], val[0], &recp, ctx))
221 goto err; /* 2 */
222 j = 1 << (window - 1);
223 for (i = 1; i < j; i++) {
224 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
225 !BN_mod_mul_reciprocal(val[i], val[i - 1], aa, &recp, ctx))
226 goto err;
227 }
228 }
229
230 start = 1; /* This is used to avoid multiplication etc
231 * when there is only the value '1' in the
232 * buffer. */
233 wvalue = 0; /* The 'value' of the window */
234 wstart = bits - 1; /* The top bit of the window */
235 wend = 0; /* The bottom bit of the window */
236
237 if (!BN_one(r))
238 goto err;
239
240 for (;;) {
241 if (BN_is_bit_set(p, wstart) == 0) {
242 if (!start)
243 if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
244 goto err;
245 if (wstart == 0)
246 break;
247 wstart--;
248 continue;
249 }
250 /*
251 * We now have wstart on a 'set' bit, we now need to work out how bit
252 * a window to do. To do this we need to scan forward until the last
253 * set bit before the end of the window
254 */
255 j = wstart;
256 wvalue = 1;
257 wend = 0;
258 for (i = 1; i < window; i++) {
259 if (wstart - i < 0)
260 break;
261 if (BN_is_bit_set(p, wstart - i)) {
262 wvalue <<= (i - wend);
263 wvalue |= 1;
264 wend = i;
265 }
266 }
267
268 /* wend is the size of the current window */
269 j = wend + 1;
270 /* add the 'bytes above' */
271 if (!start)
272 for (i = 0; i < j; i++) {
273 if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
274 goto err;
275 }
276
277 /* wvalue will be an odd number < 2^window */
278 if (!BN_mod_mul_reciprocal(r, r, val[wvalue >> 1], &recp, ctx))
279 goto err;
280
281 /* move the 'window' down further */
282 wstart -= wend + 1;
283 wvalue = 0;
284 start = 0;
285 if (wstart < 0)
286 break;
287 }
288 ret = 1;
289 err:
290 BN_CTX_end(ctx);
291 BN_RECP_CTX_free(&recp);
292 bn_check_top(r);
293 return ret;
294}
295
296int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
297 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
298{
299 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
300 int start = 1;
301 BIGNUM *d, *r;
302 const BIGNUM *aa;
303 /* Table of variables obtained from 'ctx' */
304 BIGNUM *val[TABLE_SIZE];
305 BN_MONT_CTX *mont = NULL;
306
307 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
308 || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
309 || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
310 return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
311 }
312
313 bn_check_top(a);
314 bn_check_top(p);
315 bn_check_top(m);
316
317 if (!BN_is_odd(m)) {
318 BNerr(BN_F_BN_MOD_EXP_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);
319 return 0;
320 }
321 bits = BN_num_bits(p);
322 if (bits == 0) {
323 /* x**0 mod 1, or x**0 mod -1 is still zero. */
324 if (BN_abs_is_word(m, 1)) {
325 ret = 1;
326 BN_zero(rr);
327 } else {
328 ret = BN_one(rr);
329 }
330 return ret;
331 }
332
333 BN_CTX_start(ctx);
334 d = BN_CTX_get(ctx);
335 r = BN_CTX_get(ctx);
336 val[0] = BN_CTX_get(ctx);
337 if (val[0] == NULL)
338 goto err;
339
340 /*
341 * If this is not done, things will break in the montgomery part
342 */
343
344 if (in_mont != NULL)
345 mont = in_mont;
346 else {
347 if ((mont = BN_MONT_CTX_new()) == NULL)
348 goto err;
349 if (!BN_MONT_CTX_set(mont, m, ctx))
350 goto err;
351 }
352
353 if (a->neg || BN_ucmp(a, m) >= 0) {
354 if (!BN_nnmod(val[0], a, m, ctx))
355 goto err;
356 aa = val[0];
357 } else
358 aa = a;
359 if (!bn_to_mont_fixed_top(val[0], aa, mont, ctx))
360 goto err; /* 1 */
361
362 window = BN_window_bits_for_exponent_size(bits);
363 if (window > 1) {
364 if (!bn_mul_mont_fixed_top(d, val[0], val[0], mont, ctx))
365 goto err; /* 2 */
366 j = 1 << (window - 1);
367 for (i = 1; i < j; i++) {
368 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
369 !bn_mul_mont_fixed_top(val[i], val[i - 1], d, mont, ctx))
370 goto err;
371 }
372 }
373
374 start = 1; /* This is used to avoid multiplication etc
375 * when there is only the value '1' in the
376 * buffer. */
377 wvalue = 0; /* The 'value' of the window */
378 wstart = bits - 1; /* The top bit of the window */
379 wend = 0; /* The bottom bit of the window */
380
381#if 1 /* by Shay Gueron's suggestion */
382 j = m->top; /* borrow j */
383 if (m->d[j - 1] & (((BN_ULONG)1) << (BN_BITS2 - 1))) {
384 if (bn_wexpand(r, j) == NULL)
385 goto err;
386 /* 2^(top*BN_BITS2) - m */
387 r->d[0] = (0 - m->d[0]) & BN_MASK2;
388 for (i = 1; i < j; i++)
389 r->d[i] = (~m->d[i]) & BN_MASK2;
390 r->top = j;
391 r->flags |= BN_FLG_FIXED_TOP;
392 } else
393#endif
394 if (!bn_to_mont_fixed_top(r, BN_value_one(), mont, ctx))
395 goto err;
396 for (;;) {
397 if (BN_is_bit_set(p, wstart) == 0) {
398 if (!start) {
399 if (!bn_mul_mont_fixed_top(r, r, r, mont, ctx))
400 goto err;
401 }
402 if (wstart == 0)
403 break;
404 wstart--;
405 continue;
406 }
407 /*
408 * We now have wstart on a 'set' bit, we now need to work out how bit
409 * a window to do. To do this we need to scan forward until the last
410 * set bit before the end of the window
411 */
412 j = wstart;
413 wvalue = 1;
414 wend = 0;
415 for (i = 1; i < window; i++) {
416 if (wstart - i < 0)
417 break;
418 if (BN_is_bit_set(p, wstart - i)) {
419 wvalue <<= (i - wend);
420 wvalue |= 1;
421 wend = i;
422 }
423 }
424
425 /* wend is the size of the current window */
426 j = wend + 1;
427 /* add the 'bytes above' */
428 if (!start)
429 for (i = 0; i < j; i++) {
430 if (!bn_mul_mont_fixed_top(r, r, r, mont, ctx))
431 goto err;
432 }
433
434 /* wvalue will be an odd number < 2^window */
435 if (!bn_mul_mont_fixed_top(r, r, val[wvalue >> 1], mont, ctx))
436 goto err;
437
438 /* move the 'window' down further */
439 wstart -= wend + 1;
440 wvalue = 0;
441 start = 0;
442 if (wstart < 0)
443 break;
444 }
445 /*
446 * Done with zero-padded intermediate BIGNUMs. Final BN_from_montgomery
447 * removes padding [if any] and makes return value suitable for public
448 * API consumer.
449 */
450#if defined(SPARC_T4_MONT)
451 if (OPENSSL_sparcv9cap_P[0] & (SPARCV9_VIS3 | SPARCV9_PREFER_FPU)) {
452 j = mont->N.top; /* borrow j */
453 val[0]->d[0] = 1; /* borrow val[0] */
454 for (i = 1; i < j; i++)
455 val[0]->d[i] = 0;
456 val[0]->top = j;
457 if (!BN_mod_mul_montgomery(rr, r, val[0], mont, ctx))
458 goto err;
459 } else
460#endif
461 if (!BN_from_montgomery(rr, r, mont, ctx))
462 goto err;
463 ret = 1;
464 err:
465 if (in_mont == NULL)
466 BN_MONT_CTX_free(mont);
467 BN_CTX_end(ctx);
468 bn_check_top(rr);
469 return ret;
470}
471
472static BN_ULONG bn_get_bits(const BIGNUM *a, int bitpos)
473{
474 BN_ULONG ret = 0;
475 int wordpos;
476
477 wordpos = bitpos / BN_BITS2;
478 bitpos %= BN_BITS2;
479 if (wordpos >= 0 && wordpos < a->top) {
480 ret = a->d[wordpos] & BN_MASK2;
481 if (bitpos) {
482 ret >>= bitpos;
483 if (++wordpos < a->top)
484 ret |= a->d[wordpos] << (BN_BITS2 - bitpos);
485 }
486 }
487
488 return ret & BN_MASK2;
489}
490
491/*
492 * BN_mod_exp_mont_consttime() stores the precomputed powers in a specific
493 * layout so that accessing any of these table values shows the same access
494 * pattern as far as cache lines are concerned. The following functions are
495 * used to transfer a BIGNUM from/to that table.
496 */
497
498static int MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top,
499 unsigned char *buf, int idx,
500 int window)
501{
502 int i, j;
503 int width = 1 << window;
504 BN_ULONG *table = (BN_ULONG *)buf;
505
506 if (top > b->top)
507 top = b->top; /* this works because 'buf' is explicitly
508 * zeroed */
509 for (i = 0, j = idx; i < top; i++, j += width) {
510 table[j] = b->d[i];
511 }
512
513 return 1;
514}
515
516static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
517 unsigned char *buf, int idx,
518 int window)
519{
520 int i, j;
521 int width = 1 << window;
522 /*
523 * We declare table 'volatile' in order to discourage compiler
524 * from reordering loads from the table. Concern is that if
525 * reordered in specific manner loads might give away the
526 * information we are trying to conceal. Some would argue that
527 * compiler can reorder them anyway, but it can as well be
528 * argued that doing so would be violation of standard...
529 */
530 volatile BN_ULONG *table = (volatile BN_ULONG *)buf;
531
532 if (bn_wexpand(b, top) == NULL)
533 return 0;
534
535 if (window <= 3) {
536 for (i = 0; i < top; i++, table += width) {
537 BN_ULONG acc = 0;
538
539 for (j = 0; j < width; j++) {
540 acc |= table[j] &
541 ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
542 }
543
544 b->d[i] = acc;
545 }
546 } else {
547 int xstride = 1 << (window - 2);
548 BN_ULONG y0, y1, y2, y3;
549
550 i = idx >> (window - 2); /* equivalent of idx / xstride */
551 idx &= xstride - 1; /* equivalent of idx % xstride */
552
553 y0 = (BN_ULONG)0 - (constant_time_eq_int(i,0)&1);
554 y1 = (BN_ULONG)0 - (constant_time_eq_int(i,1)&1);
555 y2 = (BN_ULONG)0 - (constant_time_eq_int(i,2)&1);
556 y3 = (BN_ULONG)0 - (constant_time_eq_int(i,3)&1);
557
558 for (i = 0; i < top; i++, table += width) {
559 BN_ULONG acc = 0;
560
561 for (j = 0; j < xstride; j++) {
562 acc |= ( (table[j + 0 * xstride] & y0) |
563 (table[j + 1 * xstride] & y1) |
564 (table[j + 2 * xstride] & y2) |
565 (table[j + 3 * xstride] & y3) )
566 & ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
567 }
568
569 b->d[i] = acc;
570 }
571 }
572
573 b->top = top;
574 b->flags |= BN_FLG_FIXED_TOP;
575 return 1;
576}
577
578/*
579 * Given a pointer value, compute the next address that is a cache line
580 * multiple.
581 */
582#define MOD_EXP_CTIME_ALIGN(x_) \
583 ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((size_t)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
584
585/*
586 * This variant of BN_mod_exp_mont() uses fixed windows and the special
587 * precomputation memory layout to limit data-dependency to a minimum to
588 * protect secret exponents (cf. the hyper-threading timing attacks pointed
589 * out by Colin Percival,
590 * http://www.daemonology.net/hyperthreading-considered-harmful/)
591 */
592int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
593 const BIGNUM *m, BN_CTX *ctx,
594 BN_MONT_CTX *in_mont)
595{
596 int i, bits, ret = 0, window, wvalue, wmask, window0;
597 int top;
598 BN_MONT_CTX *mont = NULL;
599
600 int numPowers;
601 unsigned char *powerbufFree = NULL;
602 int powerbufLen = 0;
603 unsigned char *powerbuf = NULL;
604 BIGNUM tmp, am;
605#if defined(SPARC_T4_MONT)
606 unsigned int t4 = 0;
607#endif
608
609 bn_check_top(a);
610 bn_check_top(p);
611 bn_check_top(m);
612
613 if (!BN_is_odd(m)) {
614 BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME, BN_R_CALLED_WITH_EVEN_MODULUS);
615 return 0;
616 }
617
618 top = m->top;
619
620 /*
621 * Use all bits stored in |p|, rather than |BN_num_bits|, so we do not leak
622 * whether the top bits are zero.
623 */
624 bits = p->top * BN_BITS2;
625 if (bits == 0) {
626 /* x**0 mod 1, or x**0 mod -1 is still zero. */
627 if (BN_abs_is_word(m, 1)) {
628 ret = 1;
629 BN_zero(rr);
630 } else {
631 ret = BN_one(rr);
632 }
633 return ret;
634 }
635
636 BN_CTX_start(ctx);
637
638 /*
639 * Allocate a montgomery context if it was not supplied by the caller. If
640 * this is not done, things will break in the montgomery part.
641 */
642 if (in_mont != NULL)
643 mont = in_mont;
644 else {
645 if ((mont = BN_MONT_CTX_new()) == NULL)
646 goto err;
647 if (!BN_MONT_CTX_set(mont, m, ctx))
648 goto err;
649 }
650
651 if (a->neg || BN_ucmp(a, m) >= 0) {
652 BIGNUM *reduced = BN_CTX_get(ctx);
653 if (reduced == NULL
654 || !BN_nnmod(reduced, a, m, ctx)) {
655 goto err;
656 }
657 a = reduced;
658 }
659
660#ifdef RSAZ_ENABLED
661 /*
662 * If the size of the operands allow it, perform the optimized
663 * RSAZ exponentiation. For further information see
664 * crypto/bn/rsaz_exp.c and accompanying assembly modules.
665 */
666 if ((16 == a->top) && (16 == p->top) && (BN_num_bits(m) == 1024)
667 && rsaz_avx2_eligible()) {
668 if (NULL == bn_wexpand(rr, 16))
669 goto err;
670 RSAZ_1024_mod_exp_avx2(rr->d, a->d, p->d, m->d, mont->RR.d,
671 mont->n0[0]);
672 rr->top = 16;
673 rr->neg = 0;
674 bn_correct_top(rr);
675 ret = 1;
676 goto err;
677 } else if ((8 == a->top) && (8 == p->top) && (BN_num_bits(m) == 512)) {
678 if (NULL == bn_wexpand(rr, 8))
679 goto err;
680 RSAZ_512_mod_exp(rr->d, a->d, p->d, m->d, mont->n0[0], mont->RR.d);
681 rr->top = 8;
682 rr->neg = 0;
683 bn_correct_top(rr);
684 ret = 1;
685 goto err;
686 }
687#endif
688
689 /* Get the window size to use with size of p. */
690 window = BN_window_bits_for_ctime_exponent_size(bits);
691#if defined(SPARC_T4_MONT)
692 if (window >= 5 && (top & 15) == 0 && top <= 64 &&
693 (OPENSSL_sparcv9cap_P[1] & (CFR_MONTMUL | CFR_MONTSQR)) ==
694 (CFR_MONTMUL | CFR_MONTSQR) && (t4 = OPENSSL_sparcv9cap_P[0]))
695 window = 5;
696 else
697#endif
698#if defined(OPENSSL_BN_ASM_MONT5)
699 if (window >= 5) {
700 window = 5; /* ~5% improvement for RSA2048 sign, and even
701 * for RSA4096 */
702 /* reserve space for mont->N.d[] copy */
703 powerbufLen += top * sizeof(mont->N.d[0]);
704 }
705#endif
706 (void)0;
707
708 /*
709 * Allocate a buffer large enough to hold all of the pre-computed powers
710 * of am, am itself and tmp.
711 */
712 numPowers = 1 << window;
713 powerbufLen += sizeof(m->d[0]) * (top * numPowers +
714 ((2 * top) >
715 numPowers ? (2 * top) : numPowers));
716#ifdef alloca
717 if (powerbufLen < 3072)
718 powerbufFree =
719 alloca(powerbufLen + MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH);
720 else
721#endif
722 if ((powerbufFree =
723 OPENSSL_malloc(powerbufLen + MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH))
724 == NULL)
725 goto err;
726
727 powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
728 memset(powerbuf, 0, powerbufLen);
729
730#ifdef alloca
731 if (powerbufLen < 3072)
732 powerbufFree = NULL;
733#endif
734
735 /* lay down tmp and am right after powers table */
736 tmp.d = (BN_ULONG *)(powerbuf + sizeof(m->d[0]) * top * numPowers);
737 am.d = tmp.d + top;
738 tmp.top = am.top = 0;
739 tmp.dmax = am.dmax = top;
740 tmp.neg = am.neg = 0;
741 tmp.flags = am.flags = BN_FLG_STATIC_DATA;
742
743 /* prepare a^0 in Montgomery domain */
744#if 1 /* by Shay Gueron's suggestion */
745 if (m->d[top - 1] & (((BN_ULONG)1) << (BN_BITS2 - 1))) {
746 /* 2^(top*BN_BITS2) - m */
747 tmp.d[0] = (0 - m->d[0]) & BN_MASK2;
748 for (i = 1; i < top; i++)
749 tmp.d[i] = (~m->d[i]) & BN_MASK2;
750 tmp.top = top;
751 } else
752#endif
753 if (!bn_to_mont_fixed_top(&tmp, BN_value_one(), mont, ctx))
754 goto err;
755
756 /* prepare a^1 in Montgomery domain */
757 if (!bn_to_mont_fixed_top(&am, a, mont, ctx))
758 goto err;
759
760#if defined(SPARC_T4_MONT)
761 if (t4) {
762 typedef int (*bn_pwr5_mont_f) (BN_ULONG *tp, const BN_ULONG *np,
763 const BN_ULONG *n0, const void *table,
764 int power, int bits);
765 int bn_pwr5_mont_t4_8(BN_ULONG *tp, const BN_ULONG *np,
766 const BN_ULONG *n0, const void *table,
767 int power, int bits);
768 int bn_pwr5_mont_t4_16(BN_ULONG *tp, const BN_ULONG *np,
769 const BN_ULONG *n0, const void *table,
770 int power, int bits);
771 int bn_pwr5_mont_t4_24(BN_ULONG *tp, const BN_ULONG *np,
772 const BN_ULONG *n0, const void *table,
773 int power, int bits);
774 int bn_pwr5_mont_t4_32(BN_ULONG *tp, const BN_ULONG *np,
775 const BN_ULONG *n0, const void *table,
776 int power, int bits);
777 static const bn_pwr5_mont_f pwr5_funcs[4] = {
778 bn_pwr5_mont_t4_8, bn_pwr5_mont_t4_16,
779 bn_pwr5_mont_t4_24, bn_pwr5_mont_t4_32
780 };
781 bn_pwr5_mont_f pwr5_worker = pwr5_funcs[top / 16 - 1];
782
783 typedef int (*bn_mul_mont_f) (BN_ULONG *rp, const BN_ULONG *ap,
784 const void *bp, const BN_ULONG *np,
785 const BN_ULONG *n0);
786 int bn_mul_mont_t4_8(BN_ULONG *rp, const BN_ULONG *ap, const void *bp,
787 const BN_ULONG *np, const BN_ULONG *n0);
788 int bn_mul_mont_t4_16(BN_ULONG *rp, const BN_ULONG *ap,
789 const void *bp, const BN_ULONG *np,
790 const BN_ULONG *n0);
791 int bn_mul_mont_t4_24(BN_ULONG *rp, const BN_ULONG *ap,
792 const void *bp, const BN_ULONG *np,
793 const BN_ULONG *n0);
794 int bn_mul_mont_t4_32(BN_ULONG *rp, const BN_ULONG *ap,
795 const void *bp, const BN_ULONG *np,
796 const BN_ULONG *n0);
797 static const bn_mul_mont_f mul_funcs[4] = {
798 bn_mul_mont_t4_8, bn_mul_mont_t4_16,
799 bn_mul_mont_t4_24, bn_mul_mont_t4_32
800 };
801 bn_mul_mont_f mul_worker = mul_funcs[top / 16 - 1];
802
803 void bn_mul_mont_vis3(BN_ULONG *rp, const BN_ULONG *ap,
804 const void *bp, const BN_ULONG *np,
805 const BN_ULONG *n0, int num);
806 void bn_mul_mont_t4(BN_ULONG *rp, const BN_ULONG *ap,
807 const void *bp, const BN_ULONG *np,
808 const BN_ULONG *n0, int num);
809 void bn_mul_mont_gather5_t4(BN_ULONG *rp, const BN_ULONG *ap,
810 const void *table, const BN_ULONG *np,
811 const BN_ULONG *n0, int num, int power);
812 void bn_flip_n_scatter5_t4(const BN_ULONG *inp, size_t num,
813 void *table, size_t power);
814 void bn_gather5_t4(BN_ULONG *out, size_t num,
815 void *table, size_t power);
816 void bn_flip_t4(BN_ULONG *dst, BN_ULONG *src, size_t num);
817
818 BN_ULONG *np = mont->N.d, *n0 = mont->n0;
819 int stride = 5 * (6 - (top / 16 - 1)); /* multiple of 5, but less
820 * than 32 */
821
822 /*
823 * BN_to_montgomery can contaminate words above .top [in
824 * BN_DEBUG[_DEBUG] build]...
825 */
826 for (i = am.top; i < top; i++)
827 am.d[i] = 0;
828 for (i = tmp.top; i < top; i++)
829 tmp.d[i] = 0;
830
831 bn_flip_n_scatter5_t4(tmp.d, top, powerbuf, 0);
832 bn_flip_n_scatter5_t4(am.d, top, powerbuf, 1);
833 if (!(*mul_worker) (tmp.d, am.d, am.d, np, n0) &&
834 !(*mul_worker) (tmp.d, am.d, am.d, np, n0))
835 bn_mul_mont_vis3(tmp.d, am.d, am.d, np, n0, top);
836 bn_flip_n_scatter5_t4(tmp.d, top, powerbuf, 2);
837
838 for (i = 3; i < 32; i++) {
839 /* Calculate a^i = a^(i-1) * a */
840 if (!(*mul_worker) (tmp.d, tmp.d, am.d, np, n0) &&
841 !(*mul_worker) (tmp.d, tmp.d, am.d, np, n0))
842 bn_mul_mont_vis3(tmp.d, tmp.d, am.d, np, n0, top);
843 bn_flip_n_scatter5_t4(tmp.d, top, powerbuf, i);
844 }
845
846 /* switch to 64-bit domain */
847 np = alloca(top * sizeof(BN_ULONG));
848 top /= 2;
849 bn_flip_t4(np, mont->N.d, top);
850
851 /*
852 * The exponent may not have a whole number of fixed-size windows.
853 * To simplify the main loop, the initial window has between 1 and
854 * full-window-size bits such that what remains is always a whole
855 * number of windows
856 */
857 window0 = (bits - 1) % 5 + 1;
858 wmask = (1 << window0) - 1;
859 bits -= window0;
860 wvalue = bn_get_bits(p, bits) & wmask;
861 bn_gather5_t4(tmp.d, top, powerbuf, wvalue);
862
863 /*
864 * Scan the exponent one window at a time starting from the most
865 * significant bits.
866 */
867 while (bits > 0) {
868 if (bits < stride)
869 stride = bits;
870 bits -= stride;
871 wvalue = bn_get_bits(p, bits);
872
873 if ((*pwr5_worker) (tmp.d, np, n0, powerbuf, wvalue, stride))
874 continue;
875 /* retry once and fall back */
876 if ((*pwr5_worker) (tmp.d, np, n0, powerbuf, wvalue, stride))
877 continue;
878
879 bits += stride - 5;
880 wvalue >>= stride - 5;
881 wvalue &= 31;
882 bn_mul_mont_t4(tmp.d, tmp.d, tmp.d, np, n0, top);
883 bn_mul_mont_t4(tmp.d, tmp.d, tmp.d, np, n0, top);
884 bn_mul_mont_t4(tmp.d, tmp.d, tmp.d, np, n0, top);
885 bn_mul_mont_t4(tmp.d, tmp.d, tmp.d, np, n0, top);
886 bn_mul_mont_t4(tmp.d, tmp.d, tmp.d, np, n0, top);
887 bn_mul_mont_gather5_t4(tmp.d, tmp.d, powerbuf, np, n0, top,
888 wvalue);
889 }
890
891 bn_flip_t4(tmp.d, tmp.d, top);
892 top *= 2;
893 /* back to 32-bit domain */
894 tmp.top = top;
895 bn_correct_top(&tmp);
896 OPENSSL_cleanse(np, top * sizeof(BN_ULONG));
897 } else
898#endif
899#if defined(OPENSSL_BN_ASM_MONT5)
900 if (window == 5 && top > 1) {
901 /*
902 * This optimization uses ideas from http://eprint.iacr.org/2011/239,
903 * specifically optimization of cache-timing attack countermeasures
904 * and pre-computation optimization.
905 */
906
907 /*
908 * Dedicated window==4 case improves 512-bit RSA sign by ~15%, but as
909 * 512-bit RSA is hardly relevant, we omit it to spare size...
910 */
911 void bn_mul_mont_gather5(BN_ULONG *rp, const BN_ULONG *ap,
912 const void *table, const BN_ULONG *np,
913 const BN_ULONG *n0, int num, int power);
914 void bn_scatter5(const BN_ULONG *inp, size_t num,
915 void *table, size_t power);
916 void bn_gather5(BN_ULONG *out, size_t num, void *table, size_t power);
917 void bn_power5(BN_ULONG *rp, const BN_ULONG *ap,
918 const void *table, const BN_ULONG *np,
919 const BN_ULONG *n0, int num, int power);
920 int bn_get_bits5(const BN_ULONG *ap, int off);
921 int bn_from_montgomery(BN_ULONG *rp, const BN_ULONG *ap,
922 const BN_ULONG *not_used, const BN_ULONG *np,
923 const BN_ULONG *n0, int num);
924
925 BN_ULONG *n0 = mont->n0, *np;
926
927 /*
928 * BN_to_montgomery can contaminate words above .top [in
929 * BN_DEBUG[_DEBUG] build]...
930 */
931 for (i = am.top; i < top; i++)
932 am.d[i] = 0;
933 for (i = tmp.top; i < top; i++)
934 tmp.d[i] = 0;
935
936 /*
937 * copy mont->N.d[] to improve cache locality
938 */
939 for (np = am.d + top, i = 0; i < top; i++)
940 np[i] = mont->N.d[i];
941
942 bn_scatter5(tmp.d, top, powerbuf, 0);
943 bn_scatter5(am.d, am.top, powerbuf, 1);
944 bn_mul_mont(tmp.d, am.d, am.d, np, n0, top);
945 bn_scatter5(tmp.d, top, powerbuf, 2);
946
947# if 0
948 for (i = 3; i < 32; i++) {
949 /* Calculate a^i = a^(i-1) * a */
950 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
951 bn_scatter5(tmp.d, top, powerbuf, i);
952 }
953# else
954 /* same as above, but uses squaring for 1/2 of operations */
955 for (i = 4; i < 32; i *= 2) {
956 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
957 bn_scatter5(tmp.d, top, powerbuf, i);
958 }
959 for (i = 3; i < 8; i += 2) {
960 int j;
961 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
962 bn_scatter5(tmp.d, top, powerbuf, i);
963 for (j = 2 * i; j < 32; j *= 2) {
964 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
965 bn_scatter5(tmp.d, top, powerbuf, j);
966 }
967 }
968 for (; i < 16; i += 2) {
969 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
970 bn_scatter5(tmp.d, top, powerbuf, i);
971 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
972 bn_scatter5(tmp.d, top, powerbuf, 2 * i);
973 }
974 for (; i < 32; i += 2) {
975 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
976 bn_scatter5(tmp.d, top, powerbuf, i);
977 }
978# endif
979 /*
980 * The exponent may not have a whole number of fixed-size windows.
981 * To simplify the main loop, the initial window has between 1 and
982 * full-window-size bits such that what remains is always a whole
983 * number of windows
984 */
985 window0 = (bits - 1) % 5 + 1;
986 wmask = (1 << window0) - 1;
987 bits -= window0;
988 wvalue = bn_get_bits(p, bits) & wmask;
989 bn_gather5(tmp.d, top, powerbuf, wvalue);
990
991 /*
992 * Scan the exponent one window at a time starting from the most
993 * significant bits.
994 */
995 if (top & 7) {
996 while (bits > 0) {
997 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
998 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
999 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
1000 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
1001 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
1002 bn_mul_mont_gather5(tmp.d, tmp.d, powerbuf, np, n0, top,
1003 bn_get_bits5(p->d, bits -= 5));
1004 }
1005 } else {
1006 while (bits > 0) {
1007 bn_power5(tmp.d, tmp.d, powerbuf, np, n0, top,
1008 bn_get_bits5(p->d, bits -= 5));
1009 }
1010 }
1011
1012 ret = bn_from_montgomery(tmp.d, tmp.d, NULL, np, n0, top);
1013 tmp.top = top;
1014 bn_correct_top(&tmp);
1015 if (ret) {
1016 if (!BN_copy(rr, &tmp))
1017 ret = 0;
1018 goto err; /* non-zero ret means it's not error */
1019 }
1020 } else
1021#endif
1022 {
1023 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0, window))
1024 goto err;
1025 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1, window))
1026 goto err;
1027
1028 /*
1029 * If the window size is greater than 1, then calculate
1030 * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1) (even
1031 * powers could instead be computed as (a^(i/2))^2 to use the slight
1032 * performance advantage of sqr over mul).
1033 */
1034 if (window > 1) {
1035 if (!bn_mul_mont_fixed_top(&tmp, &am, &am, mont, ctx))
1036 goto err;
1037 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 2,
1038 window))
1039 goto err;
1040 for (i = 3; i < numPowers; i++) {
1041 /* Calculate a^i = a^(i-1) * a */
1042 if (!bn_mul_mont_fixed_top(&tmp, &am, &tmp, mont, ctx))
1043 goto err;
1044 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, i,
1045 window))
1046 goto err;
1047 }
1048 }
1049
1050 /*
1051 * The exponent may not have a whole number of fixed-size windows.
1052 * To simplify the main loop, the initial window has between 1 and
1053 * full-window-size bits such that what remains is always a whole
1054 * number of windows
1055 */
1056 window0 = (bits - 1) % window + 1;
1057 wmask = (1 << window0) - 1;
1058 bits -= window0;
1059 wvalue = bn_get_bits(p, bits) & wmask;
1060 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf, wvalue,
1061 window))
1062 goto err;
1063
1064 wmask = (1 << window) - 1;
1065 /*
1066 * Scan the exponent one window at a time starting from the most
1067 * significant bits.
1068 */
1069 while (bits > 0) {
1070
1071 /* Square the result window-size times */
1072 for (i = 0; i < window; i++)
1073 if (!bn_mul_mont_fixed_top(&tmp, &tmp, &tmp, mont, ctx))
1074 goto err;
1075
1076 /*
1077 * Get a window's worth of bits from the exponent
1078 * This avoids calling BN_is_bit_set for each bit, which
1079 * is not only slower but also makes each bit vulnerable to
1080 * EM (and likely other) side-channel attacks like One&Done
1081 * (for details see "One&Done: A Single-Decryption EM-Based
1082 * Attack on OpenSSL's Constant-Time Blinded RSA" by M. Alam,
1083 * H. Khan, M. Dey, N. Sinha, R. Callan, A. Zajic, and
1084 * M. Prvulovic, in USENIX Security'18)
1085 */
1086 bits -= window;
1087 wvalue = bn_get_bits(p, bits) & wmask;
1088 /*
1089 * Fetch the appropriate pre-computed value from the pre-buf
1090 */
1091 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf, wvalue,
1092 window))
1093 goto err;
1094
1095 /* Multiply the result into the intermediate result */
1096 if (!bn_mul_mont_fixed_top(&tmp, &tmp, &am, mont, ctx))
1097 goto err;
1098 }
1099 }
1100
1101 /*
1102 * Done with zero-padded intermediate BIGNUMs. Final BN_from_montgomery
1103 * removes padding [if any] and makes return value suitable for public
1104 * API consumer.
1105 */
1106#if defined(SPARC_T4_MONT)
1107 if (OPENSSL_sparcv9cap_P[0] & (SPARCV9_VIS3 | SPARCV9_PREFER_FPU)) {
1108 am.d[0] = 1; /* borrow am */
1109 for (i = 1; i < top; i++)
1110 am.d[i] = 0;
1111 if (!BN_mod_mul_montgomery(rr, &tmp, &am, mont, ctx))
1112 goto err;
1113 } else
1114#endif
1115 if (!BN_from_montgomery(rr, &tmp, mont, ctx))
1116 goto err;
1117 ret = 1;
1118 err:
1119 if (in_mont == NULL)
1120 BN_MONT_CTX_free(mont);
1121 if (powerbuf != NULL) {
1122 OPENSSL_cleanse(powerbuf, powerbufLen);
1123 OPENSSL_free(powerbufFree);
1124 }
1125 BN_CTX_end(ctx);
1126 return ret;
1127}
1128
1129int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
1130 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
1131{
1132 BN_MONT_CTX *mont = NULL;
1133 int b, bits, ret = 0;
1134 int r_is_one;
1135 BN_ULONG w, next_w;
1136 BIGNUM *r, *t;
1137 BIGNUM *swap_tmp;
1138#define BN_MOD_MUL_WORD(r, w, m) \
1139 (BN_mul_word(r, (w)) && \
1140 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/ \
1141 (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
1142 /*
1143 * BN_MOD_MUL_WORD is only used with 'w' large, so the BN_ucmp test is
1144 * probably more overhead than always using BN_mod (which uses BN_copy if
1145 * a similar test returns true).
1146 */
1147 /*
1148 * We can use BN_mod and do not need BN_nnmod because our accumulator is
1149 * never negative (the result of BN_mod does not depend on the sign of
1150 * the modulus).
1151 */
1152#define BN_TO_MONTGOMERY_WORD(r, w, mont) \
1153 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
1154
1155 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
1156 || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
1157 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
1158 BNerr(BN_F_BN_MOD_EXP_MONT_WORD, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
1159 return 0;
1160 }
1161
1162 bn_check_top(p);
1163 bn_check_top(m);
1164
1165 if (!BN_is_odd(m)) {
1166 BNerr(BN_F_BN_MOD_EXP_MONT_WORD, BN_R_CALLED_WITH_EVEN_MODULUS);
1167 return 0;
1168 }
1169 if (m->top == 1)
1170 a %= m->d[0]; /* make sure that 'a' is reduced */
1171
1172 bits = BN_num_bits(p);
1173 if (bits == 0) {
1174 /* x**0 mod 1, or x**0 mod -1 is still zero. */
1175 if (BN_abs_is_word(m, 1)) {
1176 ret = 1;
1177 BN_zero(rr);
1178 } else {
1179 ret = BN_one(rr);
1180 }
1181 return ret;
1182 }
1183 if (a == 0) {
1184 BN_zero(rr);
1185 ret = 1;
1186 return ret;
1187 }
1188
1189 BN_CTX_start(ctx);
1190 r = BN_CTX_get(ctx);
1191 t = BN_CTX_get(ctx);
1192 if (t == NULL)
1193 goto err;
1194
1195 if (in_mont != NULL)
1196 mont = in_mont;
1197 else {
1198 if ((mont = BN_MONT_CTX_new()) == NULL)
1199 goto err;
1200 if (!BN_MONT_CTX_set(mont, m, ctx))
1201 goto err;
1202 }
1203
1204 r_is_one = 1; /* except for Montgomery factor */
1205
1206 /* bits-1 >= 0 */
1207
1208 /* The result is accumulated in the product r*w. */
1209 w = a; /* bit 'bits-1' of 'p' is always set */
1210 for (b = bits - 2; b >= 0; b--) {
1211 /* First, square r*w. */
1212 next_w = w * w;
1213 if ((next_w / w) != w) { /* overflow */
1214 if (r_is_one) {
1215 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
1216 goto err;
1217 r_is_one = 0;
1218 } else {
1219 if (!BN_MOD_MUL_WORD(r, w, m))
1220 goto err;
1221 }
1222 next_w = 1;
1223 }
1224 w = next_w;
1225 if (!r_is_one) {
1226 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
1227 goto err;
1228 }
1229
1230 /* Second, multiply r*w by 'a' if exponent bit is set. */
1231 if (BN_is_bit_set(p, b)) {
1232 next_w = w * a;
1233 if ((next_w / a) != w) { /* overflow */
1234 if (r_is_one) {
1235 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
1236 goto err;
1237 r_is_one = 0;
1238 } else {
1239 if (!BN_MOD_MUL_WORD(r, w, m))
1240 goto err;
1241 }
1242 next_w = a;
1243 }
1244 w = next_w;
1245 }
1246 }
1247
1248 /* Finally, set r:=r*w. */
1249 if (w != 1) {
1250 if (r_is_one) {
1251 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
1252 goto err;
1253 r_is_one = 0;
1254 } else {
1255 if (!BN_MOD_MUL_WORD(r, w, m))
1256 goto err;
1257 }
1258 }
1259
1260 if (r_is_one) { /* can happen only if a == 1 */
1261 if (!BN_one(rr))
1262 goto err;
1263 } else {
1264 if (!BN_from_montgomery(rr, r, mont, ctx))
1265 goto err;
1266 }
1267 ret = 1;
1268 err:
1269 if (in_mont == NULL)
1270 BN_MONT_CTX_free(mont);
1271 BN_CTX_end(ctx);
1272 bn_check_top(rr);
1273 return ret;
1274}
1275
1276/* The old fallback, simple version :-) */
1277int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
1278 const BIGNUM *m, BN_CTX *ctx)
1279{
1280 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
1281 int start = 1;
1282 BIGNUM *d;
1283 /* Table of variables obtained from 'ctx' */
1284 BIGNUM *val[TABLE_SIZE];
1285
1286 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0
1287 || BN_get_flags(a, BN_FLG_CONSTTIME) != 0
1288 || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) {
1289 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
1290 BNerr(BN_F_BN_MOD_EXP_SIMPLE, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
1291 return 0;
1292 }
1293
1294 bits = BN_num_bits(p);
1295 if (bits == 0) {
1296 /* x**0 mod 1, or x**0 mod -1 is still zero. */
1297 if (BN_abs_is_word(m, 1)) {
1298 ret = 1;
1299 BN_zero(r);
1300 } else {
1301 ret = BN_one(r);
1302 }
1303 return ret;
1304 }
1305
1306 BN_CTX_start(ctx);
1307 d = BN_CTX_get(ctx);
1308 val[0] = BN_CTX_get(ctx);
1309 if (val[0] == NULL)
1310 goto err;
1311
1312 if (!BN_nnmod(val[0], a, m, ctx))
1313 goto err; /* 1 */
1314 if (BN_is_zero(val[0])) {
1315 BN_zero(r);
1316 ret = 1;
1317 goto err;
1318 }
1319
1320 window = BN_window_bits_for_exponent_size(bits);
1321 if (window > 1) {
1322 if (!BN_mod_mul(d, val[0], val[0], m, ctx))
1323 goto err; /* 2 */
1324 j = 1 << (window - 1);
1325 for (i = 1; i < j; i++) {
1326 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
1327 !BN_mod_mul(val[i], val[i - 1], d, m, ctx))
1328 goto err;
1329 }
1330 }
1331
1332 start = 1; /* This is used to avoid multiplication etc
1333 * when there is only the value '1' in the
1334 * buffer. */
1335 wvalue = 0; /* The 'value' of the window */
1336 wstart = bits - 1; /* The top bit of the window */
1337 wend = 0; /* The bottom bit of the window */
1338
1339 if (!BN_one(r))
1340 goto err;
1341
1342 for (;;) {
1343 if (BN_is_bit_set(p, wstart) == 0) {
1344 if (!start)
1345 if (!BN_mod_mul(r, r, r, m, ctx))
1346 goto err;
1347 if (wstart == 0)
1348 break;
1349 wstart--;
1350 continue;
1351 }
1352 /*
1353 * We now have wstart on a 'set' bit, we now need to work out how bit
1354 * a window to do. To do this we need to scan forward until the last
1355 * set bit before the end of the window
1356 */
1357 j = wstart;
1358 wvalue = 1;
1359 wend = 0;
1360 for (i = 1; i < window; i++) {
1361 if (wstart - i < 0)
1362 break;
1363 if (BN_is_bit_set(p, wstart - i)) {
1364 wvalue <<= (i - wend);
1365 wvalue |= 1;
1366 wend = i;
1367 }
1368 }
1369
1370 /* wend is the size of the current window */
1371 j = wend + 1;
1372 /* add the 'bytes above' */
1373 if (!start)
1374 for (i = 0; i < j; i++) {
1375 if (!BN_mod_mul(r, r, r, m, ctx))
1376 goto err;
1377 }
1378
1379 /* wvalue will be an odd number < 2^window */
1380 if (!BN_mod_mul(r, r, val[wvalue >> 1], m, ctx))
1381 goto err;
1382
1383 /* move the 'window' down further */
1384 wstart -= wend + 1;
1385 wvalue = 0;
1386 start = 0;
1387 if (wstart < 0)
1388 break;
1389 }
1390 ret = 1;
1391 err:
1392 BN_CTX_end(ctx);
1393 bn_check_top(r);
1394 return ret;
1395}
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