1 /* $OpenBSD: bn_exp.c,v 1.22 2015/03/21 08:05:20 doug Exp $ */
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).
115 #include <openssl/err.h>
119 /* maximum precomputation table size for *variable* sliding windows */
120 #define TABLE_SIZE 32
122 /* this one works - simple but works */
124 BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
126 int i, bits, ret = 0;
129 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
130 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
131 BNerr(BN_F_BN_EXP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
136 if ((r == a) || (r == p))
137 rr = BN_CTX_get(ctx);
141 if (rr == NULL || v == NULL)
144 if (BN_copy(v, a) == NULL)
146 bits = BN_num_bits(p);
149 if (BN_copy(rr, a) == NULL)
156 for (i = 1; i < bits; i++) {
157 if (!BN_sqr(v, v, ctx))
159 if (BN_is_bit_set(p, i)) {
160 if (!BN_mul(rr, rr, v, ctx))
167 if (r != rr && rr != NULL)
175 BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
184 /* For even modulus m = 2^k*m_odd, it might make sense to compute
185 * a^p mod m_odd and a^p mod 2^k separately (with Montgomery
186 * exponentiation for the odd part), using appropriate exponent
187 * reductions, and combine the results using the CRT.
189 * For now, we use Montgomery only if the modulus is odd; otherwise,
190 * exponentiation using the reciprocal-based quick remaindering
193 * (Timing obtained with expspeed.c [computations a^p mod m
194 * where a, p, m are of the same length: 256, 512, 1024, 2048,
195 * 4096, 8192 bits], compared to the running time of the
196 * standard algorithm:
198 * BN_mod_exp_mont 33 .. 40 % [AMD K6-2, Linux, debug configuration]
199 * 55 .. 77 % [UltraSparc processor, but
200 * debug-solaris-sparcv8-gcc conf.]
202 * BN_mod_exp_recp 50 .. 70 % [AMD K6-2, Linux, debug configuration]
203 * 62 .. 118 % [UltraSparc, debug-solaris-sparcv8-gcc]
205 * On the Sparc, BN_mod_exp_recp was faster than BN_mod_exp_mont
206 * at 2048 and more bits, but at 512 and 1024 bits, it was
207 * slower even than the standard algorithm!
209 * "Real" timings [linux-elf, solaris-sparcv9-gcc configurations]
210 * should be obtained when the new Montgomery reduction code
211 * has been integrated into OpenSSL.)
215 #define MONT_EXP_WORD
219 /* I have finally been able to take out this pre-condition of
220 * the top bit being set. It was caused by an error in BN_div
221 * with negatives. There was also another problem when for a^b%m
222 * a >= m. eay 07-May-97 */
223 /* if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */
226 # ifdef MONT_EXP_WORD
227 if (a->top == 1 && !a->neg &&
228 (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)) {
229 BN_ULONG A = a->d[0];
230 ret = BN_mod_exp_mont_word(r, A,p, m,ctx, NULL);
233 ret = BN_mod_exp_mont(r, a,p, m,ctx, NULL);
238 ret = BN_mod_exp_recp(r, a,p, m, ctx);
242 ret = BN_mod_exp_simple(r, a,p, m, ctx);
251 BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
254 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
257 /* Table of variables obtained from 'ctx' */
258 BIGNUM *val[TABLE_SIZE];
261 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
262 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
263 BNerr(BN_F_BN_MOD_EXP_RECP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
267 bits = BN_num_bits(p);
275 if ((aa = BN_CTX_get(ctx)) == NULL)
277 if ((val[0] = BN_CTX_get(ctx)) == NULL)
280 BN_RECP_CTX_init(&recp);
282 /* ignore sign of 'm' */
286 if (BN_RECP_CTX_set(&recp, aa, ctx) <= 0)
289 if (BN_RECP_CTX_set(&recp, m, ctx) <= 0)
293 if (!BN_nnmod(val[0], a, m, ctx))
295 if (BN_is_zero(val[0])) {
301 window = BN_window_bits_for_exponent_size(bits);
303 if (!BN_mod_mul_reciprocal(aa, val[0], val[0], &recp, ctx))
305 j = 1 << (window - 1);
306 for (i = 1; i < j; i++) {
307 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
308 !BN_mod_mul_reciprocal(val[i], val[i - 1],
314 start = 1; /* This is used to avoid multiplication etc
315 * when there is only the value '1' in the
317 wvalue = 0; /* The 'value' of the window */
318 wstart = bits - 1; /* The top bit of the window */
319 wend = 0; /* The bottom bit of the window */
325 if (BN_is_bit_set(p, wstart) == 0) {
327 if (!BN_mod_mul_reciprocal(r, r,r, &recp, ctx))
334 /* We now have wstart on a 'set' bit, we now need to work out
335 * how bit a window to do. To do this we need to scan
336 * forward until the last set bit before the end of the
341 for (i = 1; i < window; i++) {
344 if (BN_is_bit_set(p, wstart - i)) {
345 wvalue <<= (i - wend);
351 /* wend is the size of the current window */
353 /* add the 'bytes above' */
355 for (i = 0; i < j; i++) {
356 if (!BN_mod_mul_reciprocal(r, r,r, &recp, ctx))
360 /* wvalue will be an odd number < 2^window */
361 if (!BN_mod_mul_reciprocal(r, r,val[wvalue >> 1], &recp, ctx))
364 /* move the 'window' down further */
375 BN_RECP_CTX_free(&recp);
381 BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
382 BN_CTX *ctx, BN_MONT_CTX *in_mont)
384 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
388 /* Table of variables obtained from 'ctx' */
389 BIGNUM *val[TABLE_SIZE];
390 BN_MONT_CTX *mont = NULL;
392 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
393 return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
401 BNerr(BN_F_BN_MOD_EXP_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);
404 bits = BN_num_bits(p);
411 if ((d = BN_CTX_get(ctx)) == NULL)
413 if ((r = BN_CTX_get(ctx)) == NULL)
415 if ((val[0] = BN_CTX_get(ctx)) == NULL)
418 /* If this is not done, things will break in the montgomery
424 if ((mont = BN_MONT_CTX_new()) == NULL)
426 if (!BN_MONT_CTX_set(mont, m, ctx))
430 if (a->neg || BN_ucmp(a, m) >= 0) {
431 if (!BN_nnmod(val[0], a,m, ctx))
436 if (BN_is_zero(aa)) {
441 if (!BN_to_montgomery(val[0], aa, mont, ctx))
444 window = BN_window_bits_for_exponent_size(bits);
446 if (!BN_mod_mul_montgomery(d, val[0], val[0], mont, ctx))
448 j = 1 << (window - 1);
449 for (i = 1; i < j; i++) {
450 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
451 !BN_mod_mul_montgomery(val[i], val[i - 1],
457 start = 1; /* This is used to avoid multiplication etc
458 * when there is only the value '1' in the
460 wvalue = 0; /* The 'value' of the window */
461 wstart = bits - 1; /* The top bit of the window */
462 wend = 0; /* The bottom bit of the window */
464 if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
467 if (BN_is_bit_set(p, wstart) == 0) {
469 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
477 /* We now have wstart on a 'set' bit, we now need to work out
478 * how bit a window to do. To do this we need to scan
479 * forward until the last set bit before the end of the
484 for (i = 1; i < window; i++) {
487 if (BN_is_bit_set(p, wstart - i)) {
488 wvalue <<= (i - wend);
494 /* wend is the size of the current window */
496 /* add the 'bytes above' */
498 for (i = 0; i < j; i++) {
499 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
503 /* wvalue will be an odd number < 2^window */
504 if (!BN_mod_mul_montgomery(r, r, val[wvalue >> 1], mont, ctx))
507 /* move the 'window' down further */
514 if (!BN_from_montgomery(rr, r,mont, ctx))
519 if ((in_mont == NULL) && (mont != NULL))
520 BN_MONT_CTX_free(mont);
527 /* BN_mod_exp_mont_consttime() stores the precomputed powers in a specific layout
528 * so that accessing any of these table values shows the same access pattern as far
529 * as cache lines are concerned. The following functions are used to transfer a BIGNUM
530 * from/to that table. */
533 MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top, unsigned char *buf,
539 top = b->top; /* this works because 'buf' is explicitly zeroed */
540 for (i = 0, j = idx; i < top * sizeof b->d[0]; i++, j += width) {
541 buf[j] = ((unsigned char*)b->d)[i];
548 MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx,
553 if (bn_wexpand(b, top) == NULL)
556 for (i = 0, j = idx; i < top * sizeof b->d[0]; i++, j += width) {
557 ((unsigned char*)b->d)[i] = buf[j];
565 /* Given a pointer value, compute the next address that is a cache line multiple. */
566 #define MOD_EXP_CTIME_ALIGN(x_) \
567 ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((size_t)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
569 /* This variant of BN_mod_exp_mont() uses fixed windows and the special
570 * precomputation memory layout to limit data-dependency to a minimum
571 * to protect secret exponents (cf. the hyper-threading timing attacks
572 * pointed out by Colin Percival,
573 * http://www.daemonology.net/hyperthreading-considered-harmful/)
576 BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
577 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
579 int i, bits, ret = 0, window, wvalue;
581 BN_MONT_CTX *mont = NULL;
583 unsigned char *powerbufFree = NULL;
585 unsigned char *powerbuf = NULL;
594 if (!(m->d[0] & 1)) {
595 BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME,
596 BN_R_CALLED_WITH_EVEN_MODULUS);
599 bits = BN_num_bits(p);
607 /* Allocate a montgomery context if it was not supplied by the caller.
608 * If this is not done, things will break in the montgomery part.
613 if ((mont = BN_MONT_CTX_new()) == NULL)
615 if (!BN_MONT_CTX_set(mont, m, ctx))
619 /* Get the window size to use with size of p. */
620 window = BN_window_bits_for_ctime_exponent_size(bits);
621 #if defined(OPENSSL_BN_ASM_MONT5)
622 if (window == 6 && bits <= 1024)
623 window = 5; /* ~5% improvement of 2048-bit RSA sign */
626 /* Allocate a buffer large enough to hold all of the pre-computed
627 * powers of am, am itself and tmp.
629 numPowers = 1 << window;
630 powerbufLen = sizeof(m->d[0]) * (top * numPowers +
631 ((2*top) > numPowers ? (2*top) : numPowers));
632 if ((powerbufFree = malloc(powerbufLen +
633 MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH)) == NULL)
636 powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
637 memset(powerbuf, 0, powerbufLen);
639 /* lay down tmp and am right after powers table */
640 tmp.d = (BN_ULONG *)(powerbuf + sizeof(m->d[0]) * top * numPowers);
642 tmp.top = am.top = 0;
643 tmp.dmax = am.dmax = top;
644 tmp.neg = am.neg = 0;
645 tmp.flags = am.flags = BN_FLG_STATIC_DATA;
647 /* prepare a^0 in Montgomery domain */
649 if (!BN_to_montgomery(&tmp, BN_value_one(), mont, ctx))
652 tmp.d[0] = (0 - m - >d[0]) & BN_MASK2; /* 2^(top*BN_BITS2) - m */
653 for (i = 1; i < top; i++)
654 tmp.d[i] = (~m->d[i]) & BN_MASK2;
658 /* prepare a^1 in Montgomery domain */
659 if (a->neg || BN_ucmp(a, m) >= 0) {
660 if (!BN_mod(&am, a,m, ctx))
662 if (!BN_to_montgomery(&am, &am, mont, ctx))
664 } else if (!BN_to_montgomery(&am, a,mont, ctx))
667 #if defined(OPENSSL_BN_ASM_MONT5)
668 /* This optimization uses ideas from http://eprint.iacr.org/2011/239,
669 * specifically optimization of cache-timing attack countermeasures
670 * and pre-computation optimization. */
672 /* Dedicated window==4 case improves 512-bit RSA sign by ~15%, but as
673 * 512-bit RSA is hardly relevant, we omit it to spare size... */
674 if (window == 5 && top > 1) {
675 void bn_mul_mont_gather5(BN_ULONG *rp, const BN_ULONG *ap,
676 const void *table, const BN_ULONG *np,
677 const BN_ULONG *n0, int num, int power);
678 void bn_scatter5(const BN_ULONG *inp, size_t num,
679 void *table, size_t power);
680 void bn_gather5(BN_ULONG *out, size_t num,
681 void *table, size_t power);
683 BN_ULONG *np = mont->N.d, *n0 = mont->n0;
685 /* BN_to_montgomery can contaminate words above .top
686 * [in BN_DEBUG[_DEBUG] build]... */
687 for (i = am.top; i < top; i++)
689 for (i = tmp.top; i < top; i++)
692 bn_scatter5(tmp.d, top, powerbuf, 0);
693 bn_scatter5(am.d, am.top, powerbuf, 1);
694 bn_mul_mont(tmp.d, am.d, am.d, np, n0, top);
695 bn_scatter5(tmp.d, top, powerbuf, 2);
698 for (i = 3; i < 32; i++) {
699 /* Calculate a^i = a^(i-1) * a */
700 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
702 bn_scatter5(tmp.d, top, powerbuf, i);
705 /* same as above, but uses squaring for 1/2 of operations */
706 for (i = 4; i < 32; i*=2) {
707 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
708 bn_scatter5(tmp.d, top, powerbuf, i);
710 for (i = 3; i < 8; i += 2) {
712 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
714 bn_scatter5(tmp.d, top, powerbuf, i);
715 for (j = 2 * i; j < 32; j *= 2) {
716 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
717 bn_scatter5(tmp.d, top, powerbuf, j);
720 for (; i < 16; i += 2) {
721 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
723 bn_scatter5(tmp.d, top, powerbuf, i);
724 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
725 bn_scatter5(tmp.d, top, powerbuf, 2*i);
727 for (; i < 32; i += 2) {
728 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
730 bn_scatter5(tmp.d, top, powerbuf, i);
734 for (wvalue = 0, i = bits % 5; i >= 0; i--, bits--)
735 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
736 bn_gather5(tmp.d, top, powerbuf, wvalue);
738 /* Scan the exponent one window at a time starting from the most
742 for (wvalue = 0, i = 0; i < 5; i++, bits--)
743 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
745 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
746 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
747 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
748 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
749 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
750 bn_mul_mont_gather5(tmp.d, tmp.d, powerbuf, np, n0, top, wvalue);
754 bn_correct_top(&tmp);
758 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0,
761 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1,
765 /* If the window size is greater than 1, then calculate
766 * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1)
767 * (even powers could instead be computed as (a^(i/2))^2
768 * to use the slight performance advantage of sqr over mul).
771 if (!BN_mod_mul_montgomery(&tmp, &am, &am, mont, ctx))
773 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf,
776 for (i = 3; i < numPowers; i++) {
777 /* Calculate a^i = a^(i-1) * a */
778 if (!BN_mod_mul_montgomery(&tmp, &am, &tmp,
781 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top,
782 powerbuf, i, numPowers))
788 for (wvalue = 0, i = bits % window; i >= 0; i--, bits--)
789 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
790 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf,
794 /* Scan the exponent one window at a time starting from the most
798 wvalue = 0; /* The 'value' of the window */
800 /* Scan the window, squaring the result as we go */
801 for (i = 0; i < window; i++, bits--) {
802 if (!BN_mod_mul_montgomery(&tmp, &tmp, &tmp,
805 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
808 /* Fetch the appropriate pre-computed value from the pre-buf */
809 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf,
813 /* Multiply the result into the intermediate result */
814 if (!BN_mod_mul_montgomery(&tmp, &tmp, &am, mont, ctx))
819 /* Convert the final result from montgomery to standard format */
820 if (!BN_from_montgomery(rr, &tmp, mont, ctx))
825 if ((in_mont == NULL) && (mont != NULL))
826 BN_MONT_CTX_free(mont);
827 if (powerbuf != NULL) {
828 explicit_bzero(powerbuf, powerbufLen);
836 BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, const BIGNUM *m,
837 BN_CTX *ctx, BN_MONT_CTX *in_mont)
839 BN_MONT_CTX *mont = NULL;
840 int b, bits, ret = 0;
846 #define BN_MOD_MUL_WORD(r, w, m) \
847 (BN_mul_word(r, (w)) && \
848 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/ \
849 (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
850 /* BN_MOD_MUL_WORD is only used with 'w' large,
851 * so the BN_ucmp test is probably more overhead
852 * than always using BN_mod (which uses BN_copy if
853 * a similar test returns true). */
854 /* We can use BN_mod and do not need BN_nnmod because our
855 * accumulator is never negative (the result of BN_mod does
856 * not depend on the sign of the modulus).
858 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
859 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
861 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
862 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
863 BNerr(BN_F_BN_MOD_EXP_MONT_WORD,
864 ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
872 BNerr(BN_F_BN_MOD_EXP_MONT_WORD, BN_R_CALLED_WITH_EVEN_MODULUS);
876 a %= m->d[0]; /* make sure that 'a' is reduced */
878 bits = BN_num_bits(p);
890 if ((d = BN_CTX_get(ctx)) == NULL)
892 if ((r = BN_CTX_get(ctx)) == NULL)
894 if ((t = BN_CTX_get(ctx)) == NULL)
900 if ((mont = BN_MONT_CTX_new()) == NULL)
902 if (!BN_MONT_CTX_set(mont, m, ctx))
906 r_is_one = 1; /* except for Montgomery factor */
910 /* The result is accumulated in the product r*w. */
911 w = a; /* bit 'bits-1' of 'p' is always set */
912 for (b = bits - 2; b >= 0; b--) {
913 /* First, square r*w. */
915 if ((next_w / w) != w) /* overflow */
918 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
922 if (!BN_MOD_MUL_WORD(r, w, m))
929 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
933 /* Second, multiply r*w by 'a' if exponent bit is set. */
934 if (BN_is_bit_set(p, b)) {
936 if ((next_w / a) != w) /* overflow */
939 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
943 if (!BN_MOD_MUL_WORD(r, w, m))
952 /* Finally, set r:=r*w. */
955 if (!BN_TO_MONTGOMERY_WORD(r, w, mont))
959 if (!BN_MOD_MUL_WORD(r, w, m))
964 if (r_is_one) /* can happen only if a == 1*/
969 if (!BN_from_montgomery(rr, r, mont, ctx))
975 if ((in_mont == NULL) && (mont != NULL))
976 BN_MONT_CTX_free(mont);
983 /* The old fallback, simple version :-) */
985 BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
988 int i, j,bits, ret = 0, wstart, wend, window, wvalue;
991 /* Table of variables obtained from 'ctx' */
992 BIGNUM *val[TABLE_SIZE];
994 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) {
995 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
996 BNerr(BN_F_BN_MOD_EXP_SIMPLE,
997 ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
1001 bits = BN_num_bits(p);
1009 if ((d = BN_CTX_get(ctx)) == NULL)
1011 if ((val[0] = BN_CTX_get(ctx)) == NULL)
1014 if (!BN_nnmod(val[0],a,m,ctx))
1016 if (BN_is_zero(val[0])) {
1022 window = BN_window_bits_for_exponent_size(bits);
1024 if (!BN_mod_mul(d, val[0], val[0], m, ctx))
1026 j = 1 << (window - 1);
1027 for (i = 1; i < j; i++) {
1028 if (((val[i] = BN_CTX_get(ctx)) == NULL) ||
1029 !BN_mod_mul(val[i], val[i - 1], d,m, ctx))
1034 start = 1; /* This is used to avoid multiplication etc
1035 * when there is only the value '1' in the
1037 wvalue = 0; /* The 'value' of the window */
1038 wstart = bits - 1; /* The top bit of the window */
1039 wend = 0; /* The bottom bit of the window */
1045 if (BN_is_bit_set(p, wstart) == 0) {
1047 if (!BN_mod_mul(r, r, r, m, ctx))
1054 /* We now have wstart on a 'set' bit, we now need to work out
1055 * how bit a window to do. To do this we need to scan
1056 * forward until the last set bit before the end of the
1061 for (i = 1; i < window; i++) {
1064 if (BN_is_bit_set(p, wstart - i)) {
1065 wvalue <<= (i - wend);
1071 /* wend is the size of the current window */
1073 /* add the 'bytes above' */
1075 for (i = 0; i < j; i++) {
1076 if (!BN_mod_mul(r, r, r, m, ctx))
1080 /* wvalue will be an odd number < 2^window */
1081 if (!BN_mod_mul(r, r, val[wvalue >> 1], m, ctx))
1084 /* move the 'window' down further */