1 /* crypto/bn/bn_exp.c */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
5 * This package is an SSL implementation written
6 * by Eric Young (eay@cryptsoft.com).
7 * The implementation was written so as to conform with Netscapes SSL.
9 * This library is free for commercial and non-commercial use as long as
10 * the following conditions are aheared to. The following conditions
11 * apply to all code found in this distribution, be it the RC4, RSA,
12 * lhash, DES, etc., code; not just the SSL code. The SSL documentation
13 * included with this distribution is covered by the same copyright terms
14 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
16 * Copyright remains Eric Young's, and as such any Copyright notices in
17 * the code are not to be removed.
18 * If this package is used in a product, Eric Young should be given attribution
19 * as the author of the parts of the library used.
20 * This can be in the form of a textual message at program startup or
21 * in documentation (online or textual) provided with the package.
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
26 * 1. Redistributions of source code must retain the copyright
27 * notice, this list of conditions and the following disclaimer.
28 * 2. Redistributions in binary form must reproduce the above copyright
29 * notice, this list of conditions and the following disclaimer in the
30 * documentation and/or other materials provided with the distribution.
31 * 3. All advertising materials mentioning features or use of this software
32 * must display the following acknowledgement:
33 * "This product includes cryptographic software written by
34 * Eric Young (eay@cryptsoft.com)"
35 * The word 'cryptographic' can be left out if the rouines from the library
36 * being used are not cryptographic related :-).
37 * 4. If you include any Windows specific code (or a derivative thereof) from
38 * the apps directory (application code) you must include an acknowledgement:
39 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
44 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
53 * The licence and distribution terms for any publically available version or
54 * derivative of this code cannot be changed. i.e. this code cannot simply be
55 * copied and put under another distribution licence
56 * [including the GNU Public Licence.]
58 /* ====================================================================
59 * Copyright (c) 1998-2005 The OpenSSL Project. All rights reserved.
61 * Redistribution and use in source and binary forms, with or without
62 * modification, are permitted provided that the following conditions
65 * 1. Redistributions of source code must retain the above copyright
66 * notice, this list of conditions and the following disclaimer.
68 * 2. Redistributions in binary form must reproduce the above copyright
69 * notice, this list of conditions and the following disclaimer in
70 * the documentation and/or other materials provided with the
73 * 3. All advertising materials mentioning features or use of this
74 * software must display the following acknowledgment:
75 * "This product includes software developed by the OpenSSL Project
76 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
78 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
79 * endorse or promote products derived from this software without
80 * prior written permission. For written permission, please contact
81 * openssl-core@openssl.org.
83 * 5. Products derived from this software may not be called "OpenSSL"
84 * nor may "OpenSSL" appear in their names without prior written
85 * permission of the OpenSSL Project.
87 * 6. Redistributions of any form whatsoever must retain the following
89 * "This product includes software developed by the OpenSSL Project
90 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
92 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
93 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
94 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
95 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
96 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
97 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
98 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
99 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
100 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
101 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
102 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
103 * OF THE POSSIBILITY OF SUCH DAMAGE.
104 * ====================================================================
106 * This product includes cryptographic software written by Eric Young
107 * (eay@cryptsoft.com). This product includes software written by Tim
108 * Hudson (tjh@cryptsoft.com).
112 #include "cryptlib.h"
113 #include "constant_time_locl.h"
120 # define alloca _alloca
122 #elif defined(__GNUC__)
124 # define alloca(s) __builtin_alloca((s))
128 /* maximum precomputation table size for *variable* sliding windows */
129 #define TABLE_SIZE 32
131 /* this one works - simple but works */
132 int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
134 int i, bits, ret = 0;
137 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
138 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
139 BNerr(BN_F_BN_EXP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
144 if ((r == a) || (r == p))
145 rr = BN_CTX_get(ctx);
149 if (rr == NULL || v == NULL)
152 if (BN_copy(v, a) == NULL)
154 bits = BN_num_bits(p);
157 if (BN_copy(rr, a) == NULL)
164 for (i = 1; i < bits; i++) {
165 if (!BN_sqr(v, v, ctx))
167 if (BN_is_bit_set(p, i)) {
168 if (!BN_mul(rr, rr, v, ctx))
181 int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
191 * For even modulus m = 2^k*m_odd, it might make sense to compute
192 * a^p mod m_odd and a^p mod 2^k separately (with Montgomery
193 * exponentiation for the odd part), using appropriate exponent
194 * reductions, and combine the results using the CRT.
196 * For now, we use Montgomery only if the modulus is odd; otherwise,
197 * exponentiation using the reciprocal-based quick remaindering
200 * (Timing obtained with expspeed.c [computations a^p mod m
201 * where a, p, m are of the same length: 256, 512, 1024, 2048,
202 * 4096, 8192 bits], compared to the running time of the
203 * standard algorithm:
205 * BN_mod_exp_mont 33 .. 40 % [AMD K6-2, Linux, debug configuration]
206 * 55 .. 77 % [UltraSparc processor, but
207 * debug-solaris-sparcv8-gcc conf.]
209 * BN_mod_exp_recp 50 .. 70 % [AMD K6-2, Linux, debug configuration]
210 * 62 .. 118 % [UltraSparc, debug-solaris-sparcv8-gcc]
212 * On the Sparc, BN_mod_exp_recp was faster than BN_mod_exp_mont
213 * at 2048 and more bits, but at 512 and 1024 bits, it was
214 * slower even than the standard algorithm!
216 * "Real" timings [linux-elf, solaris-sparcv9-gcc configurations]
217 * should be obtained when the new Montgomery reduction code
218 * has been integrated into OpenSSL.)
222 #define MONT_EXP_WORD
227 * I have finally been able to take out this pre-condition of the top bit
228 * being set. It was caused by an error in BN_div with negatives. There
229 * was also another problem when for a^b%m a >= m. eay 07-May-97
231 /* if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */
234 # ifdef MONT_EXP_WORD
235 if (a->top == 1 && !a->neg
236 && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)) {
237 BN_ULONG A = a->d[0];
238 ret = BN_mod_exp_mont_word(r, A, p, m, ctx, NULL);
241 ret = BN_mod_exp_mont(r, a, p, m, ctx, NULL);
246 ret = BN_mod_exp_recp(r, a, p, m, ctx);
250 ret = BN_mod_exp_simple(r, a, p, m, ctx);
258 int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
259 const BIGNUM *m, BN_CTX *ctx)
261 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
264 /* Table of variables obtained from 'ctx' */
265 BIGNUM *val[TABLE_SIZE];
268 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
269 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
270 BNerr(BN_F_BN_MOD_EXP_RECP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
274 bits = BN_num_bits(p);
282 aa = BN_CTX_get(ctx);
283 val[0] = BN_CTX_get(ctx);
287 BN_RECP_CTX_init(&recp);
289 /* ignore sign of 'm' */
293 if (BN_RECP_CTX_set(&recp, aa, ctx) <= 0)
296 if (BN_RECP_CTX_set(&recp, m, ctx) <= 0)
300 if (!BN_nnmod(val[0], a, m, ctx))
302 if (BN_is_zero(val[0])) {
308 window = BN_window_bits_for_exponent_size(bits);
310 if (!BN_mod_mul_reciprocal(aa, val[0], val[0], &recp, ctx))
312 j = 1 << (window - 1);
313 for (i = 1; i < j; i++) {
314 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
315 !BN_mod_mul_reciprocal(val[i], val[i - 1], aa, &recp, ctx))
320 start = 1; /* This is used to avoid multiplication etc
321 * when there is only the value '1' in the
323 wvalue = 0; /* The 'value' of the window */
324 wstart = bits - 1; /* The top bit of the window */
325 wend = 0; /* The bottom bit of the window */
331 if (BN_is_bit_set(p, wstart) == 0) {
333 if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
341 * We now have wstart on a 'set' bit, we now need to work out how bit
342 * a window to do. To do this we need to scan forward until the last
343 * set bit before the end of the window
348 for (i = 1; i < window; i++) {
351 if (BN_is_bit_set(p, wstart - i)) {
352 wvalue <<= (i - wend);
358 /* wend is the size of the current window */
360 /* add the 'bytes above' */
362 for (i = 0; i < j; i++) {
363 if (!BN_mod_mul_reciprocal(r, r, r, &recp, ctx))
367 /* wvalue will be an odd number < 2^window */
368 if (!BN_mod_mul_reciprocal(r, r, val[wvalue >> 1], &recp, ctx))
371 /* move the 'window' down further */
381 BN_RECP_CTX_free(&recp);
386 int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
387 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
389 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
393 /* Table of variables obtained from 'ctx' */
394 BIGNUM *val[TABLE_SIZE];
395 BN_MONT_CTX *mont = NULL;
397 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
398 return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
406 BNerr(BN_F_BN_MOD_EXP_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);
409 bits = BN_num_bits(p);
418 val[0] = BN_CTX_get(ctx);
419 if (!d || !r || !val[0])
423 * If this is not done, things will break in the montgomery part
429 if ((mont = BN_MONT_CTX_new()) == NULL)
431 if (!BN_MONT_CTX_set(mont, m, ctx))
435 if (a->neg || BN_ucmp(a, m) >= 0) {
436 if (!BN_nnmod(val[0], a, m, ctx))
441 if (BN_is_zero(aa)) {
446 if (!BN_to_montgomery(val[0], aa, mont, ctx))
449 window = BN_window_bits_for_exponent_size(bits);
451 if (!BN_mod_mul_montgomery(d, val[0], val[0], mont, ctx))
453 j = 1 << (window - 1);
454 for (i = 1; i < j; i++) {
455 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
456 !BN_mod_mul_montgomery(val[i], val[i - 1], d, mont, ctx))
461 start = 1; /* This is used to avoid multiplication etc
462 * when there is only the value '1' in the
464 wvalue = 0; /* The 'value' of the window */
465 wstart = bits - 1; /* The top bit of the window */
466 wend = 0; /* The bottom bit of the window */
468 if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
471 if (BN_is_bit_set(p, wstart) == 0) {
473 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
482 * We now have wstart on a 'set' bit, we now need to work out how bit
483 * a window to do. To do this we need to scan forward until the last
484 * set bit before the end of the window
489 for (i = 1; i < window; i++) {
492 if (BN_is_bit_set(p, wstart - i)) {
493 wvalue <<= (i - wend);
499 /* wend is the size of the current window */
501 /* add the 'bytes above' */
503 for (i = 0; i < j; i++) {
504 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
508 /* wvalue will be an odd number < 2^window */
509 if (!BN_mod_mul_montgomery(r, r, val[wvalue >> 1], mont, ctx))
512 /* move the 'window' down further */
519 if (!BN_from_montgomery(rr, r, mont, ctx))
523 if ((in_mont == NULL) && (mont != NULL))
524 BN_MONT_CTX_free(mont);
531 * BN_mod_exp_mont_consttime() stores the precomputed powers in a specific
532 * layout so that accessing any of these table values shows the same access
533 * pattern as far as cache lines are concerned. The following functions are
534 * used to transfer a BIGNUM from/to that table.
537 static int MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top,
538 unsigned char *buf, int idx,
542 int width = 1 << window;
543 BN_ULONG *table = (BN_ULONG *)buf;
546 top = b->top; /* this works because 'buf' is explicitly
548 for (i = 0, j = idx; i < top; i++, j += width) {
555 static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
556 unsigned char *buf, int idx,
560 int width = 1 << window;
561 volatile BN_ULONG *table = (volatile BN_ULONG *)buf;
563 if (bn_wexpand(b, top) == NULL)
567 for (i = 0; i < top; i++, table += width) {
570 for (j = 0; j < width; j++) {
572 ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
578 int xstride = 1 << (window - 2);
579 BN_ULONG y0, y1, y2, y3;
581 i = idx >> (window - 2); /* equivalent of idx / xstride */
582 idx &= xstride - 1; /* equivalent of idx % xstride */
584 y0 = (BN_ULONG)0 - (constant_time_eq_int(i,0)&1);
585 y1 = (BN_ULONG)0 - (constant_time_eq_int(i,1)&1);
586 y2 = (BN_ULONG)0 - (constant_time_eq_int(i,2)&1);
587 y3 = (BN_ULONG)0 - (constant_time_eq_int(i,3)&1);
589 for (i = 0; i < top; i++, table += width) {
592 for (j = 0; j < xstride; j++) {
593 acc |= ( (table[j + 0 * xstride] & y0) |
594 (table[j + 1 * xstride] & y1) |
595 (table[j + 2 * xstride] & y2) |
596 (table[j + 3 * xstride] & y3) )
597 & ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
610 * Given a pointer value, compute the next address that is a cache line
613 #define MOD_EXP_CTIME_ALIGN(x_) \
614 ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((size_t)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
617 * This variant of BN_mod_exp_mont() uses fixed windows and the special
618 * precomputation memory layout to limit data-dependency to a minimum to
619 * protect secret exponents (cf. the hyper-threading timing attacks pointed
620 * out by Colin Percival,
621 * http://www.daemong-consideredperthreading-considered-harmful/)
623 int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
624 const BIGNUM *m, BN_CTX *ctx,
625 BN_MONT_CTX *in_mont)
627 int i, bits, ret = 0, window, wvalue;
629 BN_MONT_CTX *mont = NULL;
632 unsigned char *powerbufFree = NULL;
634 unsigned char *powerbuf = NULL;
643 if (!(m->d[0] & 1)) {
644 BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME, BN_R_CALLED_WITH_EVEN_MODULUS);
647 bits = BN_num_bits(p);
656 * Allocate a montgomery context if it was not supplied by the caller. If
657 * this is not done, things will break in the montgomery part.
662 if ((mont = BN_MONT_CTX_new()) == NULL)
664 if (!BN_MONT_CTX_set(mont, m, ctx))
668 /* Get the window size to use with size of p. */
669 window = BN_window_bits_for_ctime_exponent_size(bits);
670 #if defined(OPENSSL_BN_ASM_MONT5)
671 if (window == 6 && bits <= 1024)
672 window = 5; /* ~5% improvement of 2048-bit RSA sign */
676 * Allocate a buffer large enough to hold all of the pre-computed powers
677 * of am, am itself and tmp.
679 numPowers = 1 << window;
680 powerbufLen = sizeof(m->d[0]) * (top * numPowers +
682 numPowers ? (2 * top) : numPowers));
684 if (powerbufLen < 3072)
686 alloca(powerbufLen + MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH);
690 (unsigned char *)OPENSSL_malloc(powerbufLen +
691 MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH))
695 powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
696 memset(powerbuf, 0, powerbufLen);
699 if (powerbufLen < 3072)
703 /* lay down tmp and am right after powers table */
704 tmp.d = (BN_ULONG *)(powerbuf + sizeof(m->d[0]) * top * numPowers);
706 tmp.top = am.top = 0;
707 tmp.dmax = am.dmax = top;
708 tmp.neg = am.neg = 0;
709 tmp.flags = am.flags = BN_FLG_STATIC_DATA;
711 /* prepare a^0 in Montgomery domain */
713 if (!BN_to_montgomery(&tmp, BN_value_one(), mont, ctx))
716 tmp.d[0] = (0 - m->d[0]) & BN_MASK2; /* 2^(top*BN_BITS2) - m */
717 for (i = 1; i < top; i++)
718 tmp.d[i] = (~m->d[i]) & BN_MASK2;
722 /* prepare a^1 in Montgomery domain */
723 if (a->neg || BN_ucmp(a, m) >= 0) {
724 if (!BN_mod(&am, a, m, ctx))
726 if (!BN_to_montgomery(&am, &am, mont, ctx))
728 } else if (!BN_to_montgomery(&am, a, mont, ctx))
731 #if defined(OPENSSL_BN_ASM_MONT5)
732 if (window == 5 && top > 1) {
734 * This optimization uses ideas from http://eprint.iacr.org/2011/239,
735 * specifically optimization of cache-timing attack countermeasures
736 * and pre-computation optimization.
740 * Dedicated window==4 case improves 512-bit RSA sign by ~15%, but as
741 * 512-bit RSA is hardly relevant, we omit it to spare size...
743 void bn_mul_mont_gather5(BN_ULONG *rp, const BN_ULONG *ap,
744 const void *table, const BN_ULONG *np,
745 const BN_ULONG *n0, int num, int power);
746 void bn_scatter5(const BN_ULONG *inp, size_t num,
747 void *table, size_t power);
748 void bn_gather5(BN_ULONG *out, size_t num, void *table, size_t power);
750 BN_ULONG *np = mont->N.d, *n0 = mont->n0;
753 * BN_to_montgomery can contaminate words above .top [in
754 * BN_DEBUG[_DEBUG] build]...
756 for (i = am.top; i < top; i++)
758 for (i = tmp.top; i < top; i++)
761 bn_scatter5(tmp.d, top, powerbuf, 0);
762 bn_scatter5(am.d, am.top, powerbuf, 1);
763 bn_mul_mont(tmp.d, am.d, am.d, np, n0, top);
764 bn_scatter5(tmp.d, top, powerbuf, 2);
767 for (i = 3; i < 32; i++) {
768 /* Calculate a^i = a^(i-1) * a */
769 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
770 bn_scatter5(tmp.d, top, powerbuf, i);
773 /* same as above, but uses squaring for 1/2 of operations */
774 for (i = 4; i < 32; i *= 2) {
775 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
776 bn_scatter5(tmp.d, top, powerbuf, i);
778 for (i = 3; i < 8; i += 2) {
780 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
781 bn_scatter5(tmp.d, top, powerbuf, i);
782 for (j = 2 * i; j < 32; j *= 2) {
783 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
784 bn_scatter5(tmp.d, top, powerbuf, j);
787 for (; i < 16; i += 2) {
788 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
789 bn_scatter5(tmp.d, top, powerbuf, i);
790 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
791 bn_scatter5(tmp.d, top, powerbuf, 2 * i);
793 for (; i < 32; i += 2) {
794 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np, n0, top, i - 1);
795 bn_scatter5(tmp.d, top, powerbuf, i);
799 for (wvalue = 0, i = bits % 5; i >= 0; i--, bits--)
800 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
801 bn_gather5(tmp.d, top, powerbuf, wvalue);
804 * Scan the exponent one window at a time starting from the most
808 for (wvalue = 0, i = 0; i < 5; i++, bits--)
809 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
811 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
812 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
813 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
814 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
815 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
816 bn_mul_mont_gather5(tmp.d, tmp.d, powerbuf, np, n0, top, wvalue);
820 bn_correct_top(&tmp);
824 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0, window))
826 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1, window))
830 * If the window size is greater than 1, then calculate
831 * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1) (even
832 * powers could instead be computed as (a^(i/2))^2 to use the slight
833 * performance advantage of sqr over mul).
836 if (!BN_mod_mul_montgomery(&tmp, &am, &am, mont, ctx))
838 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 2,
841 for (i = 3; i < numPowers; i++) {
842 /* Calculate a^i = a^(i-1) * a */
843 if (!BN_mod_mul_montgomery(&tmp, &am, &tmp, mont, ctx))
845 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, i,
852 for (wvalue = 0, i = bits % window; i >= 0; i--, bits--)
853 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
854 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf, wvalue,
859 * Scan the exponent one window at a time starting from the most
863 wvalue = 0; /* The 'value' of the window */
865 /* Scan the window, squaring the result as we go */
866 for (i = 0; i < window; i++, bits--) {
867 if (!BN_mod_mul_montgomery(&tmp, &tmp, &tmp, mont, ctx))
869 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
873 * Fetch the appropriate pre-computed value from the pre-buf
875 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf, wvalue,
879 /* Multiply the result into the intermediate result */
880 if (!BN_mod_mul_montgomery(&tmp, &tmp, &am, mont, ctx))
885 /* Convert the final result from montgomery to standard format */
886 if (!BN_from_montgomery(rr, &tmp, mont, ctx))
890 if ((in_mont == NULL) && (mont != NULL))
891 BN_MONT_CTX_free(mont);
892 if (powerbuf != NULL) {
893 OPENSSL_cleanse(powerbuf, powerbufLen);
895 OPENSSL_free(powerbufFree);
901 int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
902 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
904 BN_MONT_CTX *mont = NULL;
905 int b, bits, ret = 0;
910 #define BN_MOD_MUL_WORD(r, w, m) \
911 (BN_mul_word(r, (w)) && \
912 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/ \
913 (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
915 * BN_MOD_MUL_WORD is only used with 'w' large, so the BN_ucmp test is
916 * probably more overhead than always using BN_mod (which uses BN_copy if
917 * a similar test returns true).
920 * We can use BN_mod and do not need BN_nnmod because our accumulator is
921 * never negative (the result of BN_mod does not depend on the sign of
924 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
925 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
927 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
928 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
929 BNerr(BN_F_BN_MOD_EXP_MONT_WORD, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
937 BNerr(BN_F_BN_MOD_EXP_MONT_WORD, BN_R_CALLED_WITH_EVEN_MODULUS);
941 a %= m->d[0]; /* make sure that 'a' is reduced */
943 bits = BN_num_bits(p);
945 /* x**0 mod 1 is still zero. */
963 if (d == NULL || r == NULL || t == NULL)
969 if ((mont = BN_MONT_CTX_new()) == NULL)
971 if (!BN_MONT_CTX_set(mont, m, ctx))
975 r_is_one = 1; /* except for Montgomery factor */
979 /* The result is accumulated in the product r*w. */
980 w = a; /* bit 'bits-1' of 'p' is always set */
981 for (b = bits - 2; b >= 0; b--) {
982 /* First, square r*w. */
984 if ((next_w / w) != w) { /* overflow */
986 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
990 if (!BN_MOD_MUL_WORD(r, w, m))
997 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
1001 /* Second, multiply r*w by 'a' if exponent bit is set. */
1002 if (BN_is_bit_set(p, b)) {
1004 if ((next_w / a) != w) { /* overflow */
1006 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
1010 if (!BN_MOD_MUL_WORD(r, w, m))
1019 /* Finally, set r:=r*w. */
1022 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
1026 if (!BN_MOD_MUL_WORD(r, w, m))
1031 if (r_is_one) { /* can happen only if a == 1 */
1035 if (!BN_from_montgomery(rr, r, mont, ctx))
1040 if ((in_mont == NULL) && (mont != NULL))
1041 BN_MONT_CTX_free(mont);
1047 /* The old fallback, simple version :-) */
1048 int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
1049 const BIGNUM *m, BN_CTX *ctx)
1051 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
1054 /* Table of variables obtained from 'ctx' */
1055 BIGNUM *val[TABLE_SIZE];
1057 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
1058 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
1059 BNerr(BN_F_BN_MOD_EXP_SIMPLE, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
1063 bits = BN_num_bits(p);
1071 d = BN_CTX_get(ctx);
1072 val[0] = BN_CTX_get(ctx);
1076 if (!BN_nnmod(val[0], a, m, ctx))
1078 if (BN_is_zero(val[0])) {
1084 window = BN_window_bits_for_exponent_size(bits);
1086 if (!BN_mod_mul(d, val[0], val[0], m, ctx))
1088 j = 1 << (window - 1);
1089 for (i = 1; i < j; i++) {
1090 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
1091 !BN_mod_mul(val[i], val[i - 1], d, m, ctx))
1096 start = 1; /* This is used to avoid multiplication etc
1097 * when there is only the value '1' in the
1099 wvalue = 0; /* The 'value' of the window */
1100 wstart = bits - 1; /* The top bit of the window */
1101 wend = 0; /* The bottom bit of the window */
1107 if (BN_is_bit_set(p, wstart) == 0) {
1109 if (!BN_mod_mul(r, r, r, m, ctx))
1117 * We now have wstart on a 'set' bit, we now need to work out how bit
1118 * a window to do. To do this we need to scan forward until the last
1119 * set bit before the end of the window
1124 for (i = 1; i < window; i++) {
1127 if (BN_is_bit_set(p, wstart - i)) {
1128 wvalue <<= (i - wend);
1134 /* wend is the size of the current window */
1136 /* add the 'bytes above' */
1138 for (i = 0; i < j; i++) {
1139 if (!BN_mod_mul(r, r, r, m, ctx))
1143 /* wvalue will be an odd number < 2^window */
1144 if (!BN_mod_mul(r, r, val[wvalue >> 1], m, ctx))
1147 /* move the 'window' down further */