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).
113 #include "cryptlib.h"
116 /* maximum precomputation table size for *variable* sliding windows */
117 #define TABLE_SIZE 32
119 /* this one works - simple but works */
120 int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
125 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0)
127 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
128 BNerr(BN_F_BN_EXP,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
133 if ((r == a) || (r == p))
134 rr = BN_CTX_get(ctx);
137 if ((v = BN_CTX_get(ctx)) == NULL) goto err;
139 if (BN_copy(v,a) == NULL) goto err;
143 { if (BN_copy(rr,a) == NULL) goto err; }
144 else { if (!BN_one(rr)) goto err; }
146 for (i=1; i<bits; i++)
148 if (!BN_sqr(v,v,ctx)) goto err;
149 if (BN_is_bit_set(p,i))
151 if (!BN_mul(rr,rr,v,ctx)) goto err;
156 if (r != rr) BN_copy(r,rr);
163 int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
172 /* For even modulus m = 2^k*m_odd, it might make sense to compute
173 * a^p mod m_odd and a^p mod 2^k separately (with Montgomery
174 * exponentiation for the odd part), using appropriate exponent
175 * reductions, and combine the results using the CRT.
177 * For now, we use Montgomery only if the modulus is odd; otherwise,
178 * exponentiation using the reciprocal-based quick remaindering
181 * (Timing obtained with expspeed.c [computations a^p mod m
182 * where a, p, m are of the same length: 256, 512, 1024, 2048,
183 * 4096, 8192 bits], compared to the running time of the
184 * standard algorithm:
186 * BN_mod_exp_mont 33 .. 40 % [AMD K6-2, Linux, debug configuration]
187 * 55 .. 77 % [UltraSparc processor, but
188 * debug-solaris-sparcv8-gcc conf.]
190 * BN_mod_exp_recp 50 .. 70 % [AMD K6-2, Linux, debug configuration]
191 * 62 .. 118 % [UltraSparc, debug-solaris-sparcv8-gcc]
193 * On the Sparc, BN_mod_exp_recp was faster than BN_mod_exp_mont
194 * at 2048 and more bits, but at 512 and 1024 bits, it was
195 * slower even than the standard algorithm!
197 * "Real" timings [linux-elf, solaris-sparcv9-gcc configurations]
198 * should be obtained when the new Montgomery reduction code
199 * has been integrated into OpenSSL.)
203 #define MONT_EXP_WORD
207 /* I have finally been able to take out this pre-condition of
208 * the top bit being set. It was caused by an error in BN_div
209 * with negatives. There was also another problem when for a^b%m
210 * a >= m. eay 07-May-97 */
211 /* if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */
215 # ifdef MONT_EXP_WORD
216 if (a->top == 1 && !a->neg && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0))
218 BN_ULONG A = a->d[0];
219 ret=BN_mod_exp_mont_word(r,A,p,m,ctx,NULL);
223 ret=BN_mod_exp_mont(r,a,p,m,ctx,NULL);
228 { ret=BN_mod_exp_recp(r,a,p,m,ctx); }
230 { ret=BN_mod_exp_simple(r,a,p,m,ctx); }
238 int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
239 const BIGNUM *m, BN_CTX *ctx)
241 int i,j,bits,ret=0,wstart,wend,window,wvalue;
244 /* Table of variables obtained from 'ctx' */
245 BIGNUM *val[TABLE_SIZE];
248 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0)
250 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
251 BNerr(BN_F_BN_MOD_EXP_RECP,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
264 aa = BN_CTX_get(ctx);
265 val[0] = BN_CTX_get(ctx);
266 if(!aa || !val[0]) goto err;
268 BN_RECP_CTX_init(&recp);
271 /* ignore sign of 'm' */
272 if (!BN_copy(aa, m)) goto err;
274 if (BN_RECP_CTX_set(&recp,aa,ctx) <= 0) goto err;
278 if (BN_RECP_CTX_set(&recp,m,ctx) <= 0) goto err;
281 if (!BN_nnmod(val[0],a,m,ctx)) goto err; /* 1 */
282 if (BN_is_zero(val[0]))
289 window = BN_window_bits_for_exponent_size(bits);
292 if (!BN_mod_mul_reciprocal(aa,val[0],val[0],&recp,ctx))
297 if(((val[i] = BN_CTX_get(ctx)) == NULL) ||
298 !BN_mod_mul_reciprocal(val[i],val[i-1],
304 start=1; /* This is used to avoid multiplication etc
305 * when there is only the value '1' in the
307 wvalue=0; /* The 'value' of the window */
308 wstart=bits-1; /* The top bit of the window */
309 wend=0; /* The bottom bit of the window */
311 if (!BN_one(r)) goto err;
315 if (BN_is_bit_set(p,wstart) == 0)
318 if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))
320 if (wstart == 0) break;
324 /* We now have wstart on a 'set' bit, we now need to work out
325 * how bit a window to do. To do this we need to scan
326 * forward until the last set bit before the end of the
331 for (i=1; i<window; i++)
333 if (wstart-i < 0) break;
334 if (BN_is_bit_set(p,wstart-i))
342 /* wend is the size of the current window */
344 /* add the 'bytes above' */
348 if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))
352 /* wvalue will be an odd number < 2^window */
353 if (!BN_mod_mul_reciprocal(r,r,val[wvalue>>1],&recp,ctx))
356 /* move the 'window' down further */
360 if (wstart < 0) break;
365 BN_RECP_CTX_free(&recp);
371 int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
372 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
374 int i,j,bits,ret=0,wstart,wend,window,wvalue;
378 /* Table of variables obtained from 'ctx' */
379 BIGNUM *val[TABLE_SIZE];
380 BN_MONT_CTX *mont=NULL;
382 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0)
384 return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
393 BNerr(BN_F_BN_MOD_EXP_MONT,BN_R_CALLED_WITH_EVEN_MODULUS);
406 val[0] = BN_CTX_get(ctx);
407 if (!d || !r || !val[0]) goto err;
409 /* If this is not done, things will break in the montgomery
416 if ((mont=BN_MONT_CTX_new()) == NULL) goto err;
417 if (!BN_MONT_CTX_set(mont,m,ctx)) goto err;
420 if (a->neg || BN_ucmp(a,m) >= 0)
422 if (!BN_nnmod(val[0],a,m,ctx))
434 if (!BN_to_montgomery(val[0],aa,mont,ctx)) goto err; /* 1 */
436 window = BN_window_bits_for_exponent_size(bits);
439 if (!BN_mod_mul_montgomery(d,val[0],val[0],mont,ctx)) goto err; /* 2 */
443 if(((val[i] = BN_CTX_get(ctx)) == NULL) ||
444 !BN_mod_mul_montgomery(val[i],val[i-1],
450 start=1; /* This is used to avoid multiplication etc
451 * when there is only the value '1' in the
453 wvalue=0; /* The 'value' of the window */
454 wstart=bits-1; /* The top bit of the window */
455 wend=0; /* The bottom bit of the window */
457 if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
460 if (BN_is_bit_set(p,wstart) == 0)
464 if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))
467 if (wstart == 0) break;
471 /* We now have wstart on a 'set' bit, we now need to work out
472 * how bit a window to do. To do this we need to scan
473 * forward until the last set bit before the end of the
478 for (i=1; i<window; i++)
480 if (wstart-i < 0) break;
481 if (BN_is_bit_set(p,wstart-i))
489 /* wend is the size of the current window */
491 /* add the 'bytes above' */
495 if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))
499 /* wvalue will be an odd number < 2^window */
500 if (!BN_mod_mul_montgomery(r,r,val[wvalue>>1],mont,ctx))
503 /* move the 'window' down further */
507 if (wstart < 0) break;
509 if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
512 if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
519 /* BN_mod_exp_mont_consttime() stores the precomputed powers in a specific layout
520 * so that accessing any of these table values shows the same access pattern as far
521 * as cache lines are concerned. The following functions are used to transfer a BIGNUM
522 * from/to that table. */
524 static int MOD_EXP_CTIME_COPY_TO_PREBUF(BIGNUM *b, size_t top,
525 unsigned char *buf, int idx, int width)
529 if (bn_wexpand(b, top) == NULL)
536 for (i = 0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
538 buf[j] = ((unsigned char*)b->d)[i];
545 static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, size_t top,
546 unsigned char *buf, int idx,
551 if (bn_wexpand(b, top) == NULL)
554 for (i=0, j=idx; i < top * sizeof b->d[0]; i++, j+=width)
556 ((unsigned char*)b->d)[i] = buf[j];
564 /* Given a pointer value, compute the next address that is a cache line multiple. */
565 #define MOD_EXP_CTIME_ALIGN(x_) \
566 ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - (((BN_ULONG)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK))))
568 /* This variant of BN_mod_exp_mont() uses fixed windows and the special
569 * precomputation memory layout to limit data-dependency to a minimum
570 * to protect secret exponents (cf. the hyper-threading timing attacks
571 * pointed out by Colin Percival,
572 * http://www.daemonology.net/hyperthreading-considered-harmful/)
574 int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
575 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
577 int i,bits,ret=0,idx,window,wvalue;
581 BN_MONT_CTX *mont=NULL;
584 unsigned char *powerbufFree=NULL;
585 size_t powerbufLen = 0;
586 unsigned char *powerbuf=NULL;
587 BIGNUM *computeTemp=NULL, *am=NULL;
597 BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME,BN_R_CALLED_WITH_EVEN_MODULUS);
607 /* Initialize BIGNUM context and allocate intermediate result */
610 if (r == NULL) goto err;
612 /* Allocate a montgomery context if it was not supplied by the caller.
613 * If this is not done, things will break in the montgomery part.
619 if ((mont=BN_MONT_CTX_new()) == NULL) goto err;
620 if (!BN_MONT_CTX_set(mont,m,ctx)) goto err;
623 /* Get the window size to use with size of p. */
624 window = BN_window_bits_for_ctime_exponent_size(bits);
626 /* Allocate a buffer large enough to hold all of the pre-computed
629 numPowers = 1 << window;
630 powerbufLen = sizeof(m->d[0])*top*numPowers;
631 if ((powerbufFree=OPENSSL_malloc(powerbufLen+MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH)) == NULL)
634 powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree);
635 memset(powerbuf, 0, powerbufLen);
637 /* Initialize the intermediate result. Do this early to save double conversion,
638 * once each for a^0 and intermediate result.
640 if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
641 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(r, top, powerbuf, 0, numPowers)) goto err;
643 /* Initialize computeTemp as a^1 with montgomery precalcs */
644 computeTemp = BN_CTX_get(ctx);
645 am = BN_CTX_get(ctx);
646 if (computeTemp==NULL || am==NULL) goto err;
648 if (a->neg || BN_ucmp(a,m) >= 0)
650 if (!BN_mod(am,a,m,ctx))
656 if (!BN_to_montgomery(am,aa,mont,ctx)) goto err;
657 if (!BN_copy(computeTemp, am)) goto err;
658 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(am, top, powerbuf, 1, numPowers)) goto err;
660 /* If the window size is greater than 1, then calculate
661 * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1)
662 * (even powers could instead be computed as (a^(i/2))^2
663 * to use the slight performance advantage of sqr over mul).
667 for (i=2; i<numPowers; i++)
669 /* Calculate a^i = a^(i-1) * a */
670 if (!BN_mod_mul_montgomery(computeTemp,am,computeTemp,mont,ctx))
672 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(computeTemp, top, powerbuf, i, numPowers)) goto err;
676 /* Adjust the number of bits up to a multiple of the window size.
677 * If the exponent length is not a multiple of the window size, then
678 * this pads the most significant bits with zeros to normalize the
679 * scanning loop to there's no special cases.
681 * * NOTE: Making the window size a power of two less than the native
682 * * word size ensures that the padded bits won't go past the last
683 * * word in the internal BIGNUM structure. Going past the end will
684 * * still produce the correct result, but causes a different branch
685 * * to be taken in the BN_is_bit_set function.
687 bits = ((bits+window-1)/window)*window;
688 idx=bits-1; /* The top bit of the window */
690 /* Scan the exponent one window at a time starting from the most
695 wvalue=0; /* The 'value' of the window */
697 /* Scan the window, squaring the result as we go */
698 for (i=0; i<window; i++,idx--)
700 if (!BN_mod_mul_montgomery(r,r,r,mont,ctx)) goto err;
701 wvalue = (wvalue<<1)+BN_is_bit_set(p,idx);
704 /* Fetch the appropriate pre-computed value from the pre-buf */
705 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(computeTemp, top, powerbuf, wvalue, numPowers)) goto err;
707 /* Multiply the result into the intermediate result */
708 if (!BN_mod_mul_montgomery(r,r,computeTemp,mont,ctx)) goto err;
711 /* Convert the final result from montgomery to standard format */
712 if (!BN_from_montgomery(rr,r,mont,ctx)) goto err;
715 if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
718 OPENSSL_cleanse(powerbuf,powerbufLen);
719 OPENSSL_free(powerbufFree);
721 if (am!=NULL) BN_clear(am);
722 if (computeTemp!=NULL) BN_clear(computeTemp);
727 int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
728 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
730 BN_MONT_CTX *mont = NULL;
736 #define BN_MOD_MUL_WORD(r, w, m) \
737 (BN_mul_word(r, (w)) && \
738 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/ \
739 (BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
740 /* BN_MOD_MUL_WORD is only used with 'w' large,
741 * so the BN_ucmp test is probably more overhead
742 * than always using BN_mod (which uses BN_copy if
743 * a similar test returns true). */
744 /* We can use BN_mod and do not need BN_nnmod because our
745 * accumulator is never negative (the result of BN_mod does
746 * not depend on the sign of the modulus).
748 #define BN_TO_MONTGOMERY_WORD(r, w, mont) \
749 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
751 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0)
753 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
754 BNerr(BN_F_BN_MOD_EXP_MONT_WORD,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
763 BNerr(BN_F_BN_MOD_EXP_MONT_WORD,BN_R_CALLED_WITH_EVEN_MODULUS);
767 a %= m->d[0]; /* make sure that 'a' is reduced */
769 bits = BN_num_bits(p);
786 if (d == NULL || r == NULL || t == NULL) goto err;
792 if ((mont = BN_MONT_CTX_new()) == NULL) goto err;
793 if (!BN_MONT_CTX_set(mont, m, ctx)) goto err;
796 r_is_one = 1; /* except for Montgomery factor */
800 /* The result is accumulated in the product r*w. */
801 w = a; /* bit 'bits-1' of 'p' is always set */
802 for (b = bits-2; b >= 0; b--)
804 /* First, square r*w. */
806 if ((next_w/w) != w) /* overflow */
810 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
815 if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
822 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) goto err;
825 /* Second, multiply r*w by 'a' if exponent bit is set. */
826 if (BN_is_bit_set(p, b))
829 if ((next_w/a) != w) /* overflow */
833 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
838 if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
846 /* Finally, set r:=r*w. */
851 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)) goto err;
856 if (!BN_MOD_MUL_WORD(r, w, m)) goto err;
860 if (r_is_one) /* can happen only if a == 1*/
862 if (!BN_one(rr)) goto err;
866 if (!BN_from_montgomery(rr, r, mont, ctx)) goto err;
870 if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
877 /* The old fallback, simple version :-) */
878 int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
879 const BIGNUM *m, BN_CTX *ctx)
881 int i,j,bits,ret=0,wstart,wend,window,wvalue;
884 /* Table of variables obtained from 'ctx' */
885 BIGNUM *val[TABLE_SIZE];
887 if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0)
889 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
890 BNerr(BN_F_BN_MOD_EXP_SIMPLE,ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
904 val[0] = BN_CTX_get(ctx);
905 if(!d || !val[0]) goto err;
907 if (!BN_nnmod(val[0],a,m,ctx)) goto err; /* 1 */
908 if (BN_is_zero(val[0]))
915 window = BN_window_bits_for_exponent_size(bits);
918 if (!BN_mod_mul(d,val[0],val[0],m,ctx))
923 if(((val[i] = BN_CTX_get(ctx)) == NULL) ||
924 !BN_mod_mul(val[i],val[i-1],d,m,ctx))
929 start=1; /* This is used to avoid multiplication etc
930 * when there is only the value '1' in the
932 wvalue=0; /* The 'value' of the window */
933 wstart=bits-1; /* The top bit of the window */
934 wend=0; /* The bottom bit of the window */
936 if (!BN_one(r)) goto err;
940 if (BN_is_bit_set(p,wstart) == 0)
943 if (!BN_mod_mul(r,r,r,m,ctx))
945 if (wstart == 0) break;
949 /* We now have wstart on a 'set' bit, we now need to work out
950 * how bit a window to do. To do this we need to scan
951 * forward until the last set bit before the end of the
956 for (i=1; i<window; i++)
958 if (wstart-i < 0) break;
959 if (BN_is_bit_set(p,wstart-i))
967 /* wend is the size of the current window */
969 /* add the 'bytes above' */
973 if (!BN_mod_mul(r,r,r,m,ctx))
977 /* wvalue will be an odd number < 2^window */
978 if (!BN_mod_mul(r,r,val[wvalue>>1],m,ctx))
981 /* move the 'window' down further */
985 if (wstart < 0) break;