Bug Summary

File:src/lib/libcrypto/bn/bn_exp.c
Warning:line 494, column 3
Value stored to 'j' is never read

Annotated Source Code

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clang -cc1 -cc1 -triple amd64-unknown-openbsd7.0 -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name bn_exp.c -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -mrelocation-model pic -pic-level 1 -pic-is-pie -mframe-pointer=all -relaxed-aliasing -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -target-feature +retpoline-indirect-calls -target-feature +retpoline-indirect-branches -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/usr/src/lib/libcrypto/obj -resource-dir /usr/local/lib/clang/13.0.0 -D LIBRESSL_INTERNAL -D LIBRESSL_CRYPTO_INTERNAL -D DSO_DLFCN -D HAVE_DLFCN_H -D HAVE_FUNOPEN -D OPENSSL_NO_HW_PADLOCK -I /usr/src/lib/libcrypto -I /usr/src/lib/libcrypto/asn1 -I /usr/src/lib/libcrypto/bio -I /usr/src/lib/libcrypto/bn -I /usr/src/lib/libcrypto/bytestring -I /usr/src/lib/libcrypto/dh -I /usr/src/lib/libcrypto/dsa -I /usr/src/lib/libcrypto/ec -I /usr/src/lib/libcrypto/ecdh -I /usr/src/lib/libcrypto/ecdsa -I /usr/src/lib/libcrypto/evp -I /usr/src/lib/libcrypto/hmac -I /usr/src/lib/libcrypto/modes -I /usr/src/lib/libcrypto/ocsp -I /usr/src/lib/libcrypto/rsa -I /usr/src/lib/libcrypto/x509 -I /usr/src/lib/libcrypto/obj -D AES_ASM -D BSAES_ASM -D VPAES_ASM -D OPENSSL_IA32_SSE2 -D RSA_ASM -D OPENSSL_BN_ASM_MONT -D OPENSSL_BN_ASM_MONT5 -D OPENSSL_BN_ASM_GF2m -D MD5_ASM -D GHASH_ASM -D RC4_MD5_ASM -D SHA1_ASM -D SHA256_ASM -D SHA512_ASM -D WHIRLPOOL_ASM -D OPENSSL_CPUID_OBJ -internal-isystem /usr/local/lib/clang/13.0.0/include -internal-externc-isystem /usr/include -O2 -fdebug-compilation-dir=/usr/src/lib/libcrypto/obj -ferror-limit 19 -fwrapv -D_RET_PROTECTOR -ret-protector -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -fno-builtin-malloc -fno-builtin-calloc -fno-builtin-realloc -fno-builtin-valloc -fno-builtin-free -fno-builtin-strdup -fno-builtin-strndup -analyzer-output=html -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /home/ben/Projects/vmm/scan-build/2022-01-12-194120-40624-1 -x c /usr/src/lib/libcrypto/bn/bn_exp.c
1/* $OpenBSD: bn_exp.c,v 1.31 2017/05/02 03:59:44 deraadt Exp $ */
2/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
3 * All rights reserved.
4 *
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.
8 *
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).
15 *
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.
22 *
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
25 * are met:
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)"
40 *
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
51 * SUCH DAMAGE.
52 *
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.]
57 */
58/* ====================================================================
59 * Copyright (c) 1998-2005 The OpenSSL Project. All rights reserved.
60 *
61 * Redistribution and use in source and binary forms, with or without
62 * modification, are permitted provided that the following conditions
63 * are met:
64 *
65 * 1. Redistributions of source code must retain the above copyright
66 * notice, this list of conditions and the following disclaimer.
67 *
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
71 * distribution.
72 *
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/)"
77 *
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.
82 *
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.
86 *
87 * 6. Redistributions of any form whatsoever must retain the following
88 * acknowledgment:
89 * "This product includes software developed by the OpenSSL Project
90 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
91 *
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 * ====================================================================
105 *
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).
109 *
110 */
111
112#include <stdlib.h>
113#include <string.h>
114
115#include <openssl/err.h>
116
117#include "bn_lcl.h"
118#include "constant_time_locl.h"
119
120/* maximum precomputation table size for *variable* sliding windows */
121#define TABLE_SIZE32 32
122
123/* this one works - simple but works */
124int
125BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
126{
127 int i, bits, ret = 0;
128 BIGNUM *v, *rr;
129
130 if (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0) {
131 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
132 BNerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED)ERR_put_error(3,(0xfff),((2|64)),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,132);
133 return -1;
134 }
135
136 BN_CTX_start(ctx);
137 if ((r == a) || (r == p))
138 rr = BN_CTX_get(ctx);
139 else
140 rr = r;
141 v = BN_CTX_get(ctx);
142 if (rr == NULL((void *)0) || v == NULL((void *)0))
143 goto err;
144
145 if (BN_copy(v, a) == NULL((void *)0))
146 goto err;
147 bits = BN_num_bits(p);
148
149 if (BN_is_odd(p)) {
150 if (BN_copy(rr, a) == NULL((void *)0))
151 goto err;
152 } else {
153 if (!BN_one(rr)BN_set_word((rr), 1))
154 goto err;
155 }
156
157 for (i = 1; i < bits; i++) {
158 if (!BN_sqr(v, v, ctx))
159 goto err;
160 if (BN_is_bit_set(p, i)) {
161 if (!BN_mul(rr, rr, v, ctx))
162 goto err;
163 }
164 }
165 ret = 1;
166
167err:
168 if (r != rr && rr != NULL((void *)0))
169 BN_copy(r, rr);
170 BN_CTX_end(ctx);
171 bn_check_top(r);
172 return (ret);
173}
174
175static int
176BN_mod_exp_internal(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
177 BN_CTX *ctx, int ct)
178{
179 int ret;
180
181 bn_check_top(a);
182 bn_check_top(p);
183 bn_check_top(m);
184
185 /* For even modulus m = 2^k*m_odd, it might make sense to compute
186 * a^p mod m_odd and a^p mod 2^k separately (with Montgomery
187 * exponentiation for the odd part), using appropriate exponent
188 * reductions, and combine the results using the CRT.
189 *
190 * For now, we use Montgomery only if the modulus is odd; otherwise,
191 * exponentiation using the reciprocal-based quick remaindering
192 * algorithm is used.
193 *
194 * (Timing obtained with expspeed.c [computations a^p mod m
195 * where a, p, m are of the same length: 256, 512, 1024, 2048,
196 * 4096, 8192 bits], compared to the running time of the
197 * standard algorithm:
198 *
199 * BN_mod_exp_mont 33 .. 40 % [AMD K6-2, Linux, debug configuration]
200 * 55 .. 77 % [UltraSparc processor, but
201 * debug-solaris-sparcv8-gcc conf.]
202 *
203 * BN_mod_exp_recp 50 .. 70 % [AMD K6-2, Linux, debug configuration]
204 * 62 .. 118 % [UltraSparc, debug-solaris-sparcv8-gcc]
205 *
206 * On the Sparc, BN_mod_exp_recp was faster than BN_mod_exp_mont
207 * at 2048 and more bits, but at 512 and 1024 bits, it was
208 * slower even than the standard algorithm!
209 *
210 * "Real" timings [linux-elf, solaris-sparcv9-gcc configurations]
211 * should be obtained when the new Montgomery reduction code
212 * has been integrated into OpenSSL.)
213 */
214
215 if (BN_is_odd(m)) {
216 if (a->top == 1 && !a->neg && !ct) {
217 BN_ULONGunsigned long A = a->d[0];
218 ret = BN_mod_exp_mont_word(r, A,p, m,ctx, NULL((void *)0));
219 } else
220 ret = BN_mod_exp_mont_ct(r, a,p, m,ctx, NULL((void *)0));
221 } else {
222 ret = BN_mod_exp_recp(r, a,p, m, ctx);
223 }
224
225 bn_check_top(r);
226 return (ret);
227}
228
229int
230BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
231 BN_CTX *ctx)
232{
233 return BN_mod_exp_internal(r, a, p, m, ctx,
234 (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0));
235}
236
237int
238BN_mod_exp_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
239 BN_CTX *ctx)
240{
241 return BN_mod_exp_internal(r, a, p, m, ctx, 1);
242}
243
244
245int
246BN_mod_exp_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
247 BN_CTX *ctx)
248{
249 return BN_mod_exp_internal(r, a, p, m, ctx, 0);
250}
251
252
253int
254BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
255 BN_CTX *ctx)
256{
257 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
258 int start = 1;
259 BIGNUM *aa;
260 /* Table of variables obtained from 'ctx' */
261 BIGNUM *val[TABLE_SIZE32];
262 BN_RECP_CTX recp;
263
264 if (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0) {
265 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
266 BNerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED)ERR_put_error(3,(0xfff),((2|64)),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,266);
267 return -1;
268 }
269
270 bits = BN_num_bits(p);
271 if (bits == 0) {
272 /* x**0 mod 1 is still zero. */
273 if (BN_is_one(m)) {
274 ret = 1;
275 BN_zero(r)(BN_set_word((r),0));
276 } else
277 ret = BN_one(r)BN_set_word((r), 1);
278 return ret;
279 }
280
281 BN_CTX_start(ctx);
282 if ((aa = BN_CTX_get(ctx)) == NULL((void *)0))
283 goto err;
284 if ((val[0] = BN_CTX_get(ctx)) == NULL((void *)0))
285 goto err;
286
287 BN_RECP_CTX_init(&recp);
288 if (m->neg) {
289 /* ignore sign of 'm' */
290 if (!BN_copy(aa, m))
291 goto err;
292 aa->neg = 0;
293 if (BN_RECP_CTX_set(&recp, aa, ctx) <= 0)
294 goto err;
295 } else {
296 if (BN_RECP_CTX_set(&recp, m, ctx) <= 0)
297 goto err;
298 }
299
300 if (!BN_nnmod(val[0], a, m, ctx))
301 goto err; /* 1 */
302 if (BN_is_zero(val[0])) {
303 BN_zero(r)(BN_set_word((r),0));
304 ret = 1;
305 goto err;
306 }
307
308 window = BN_window_bits_for_exponent_size(bits)((bits) > 671 ? 6 : (bits) > 239 ? 5 : (bits) > 79 ?
4 : (bits) > 23 ? 3 : 1);
309 if (window > 1) {
310 if (!BN_mod_mul_reciprocal(aa, val[0], val[0], &recp, ctx))
311 goto err; /* 2 */
312 j = 1 << (window - 1);
313 for (i = 1; i < j; i++) {
314 if (((val[i] = BN_CTX_get(ctx)) == NULL((void *)0)) ||
315 !BN_mod_mul_reciprocal(val[i], val[i - 1],
316 aa, &recp, ctx))
317 goto err;
318 }
319 }
320
321 start = 1; /* This is used to avoid multiplication etc
322 * when there is only the value '1' in the
323 * buffer. */
324 wvalue = 0; /* The 'value' of the window */
325 wstart = bits - 1; /* The top bit of the window */
326 wend = 0; /* The bottom bit of the window */
327
328 if (!BN_one(r)BN_set_word((r), 1))
329 goto err;
330
331 for (;;) {
332 if (BN_is_bit_set(p, wstart) == 0) {
333 if (!start)
334 if (!BN_mod_mul_reciprocal(r, r,r, &recp, ctx))
335 goto err;
336 if (wstart == 0)
337 break;
338 wstart--;
339 continue;
340 }
341 /* We now have wstart on a 'set' bit, we now need to work out
342 * how bit a window to do. To do this we need to scan
343 * forward until the last set bit before the end of the
344 * window */
345 j = wstart;
346 wvalue = 1;
347 wend = 0;
348 for (i = 1; i < window; i++) {
349 if (wstart - i < 0)
350 break;
351 if (BN_is_bit_set(p, wstart - i)) {
352 wvalue <<= (i - wend);
353 wvalue |= 1;
354 wend = i;
355 }
356 }
357
358 /* wend is the size of the current window */
359 j = wend + 1;
360 /* add the 'bytes above' */
361 if (!start)
362 for (i = 0; i < j; i++) {
363 if (!BN_mod_mul_reciprocal(r, r,r, &recp, ctx))
364 goto err;
365 }
366
367 /* wvalue will be an odd number < 2^window */
368 if (!BN_mod_mul_reciprocal(r, r,val[wvalue >> 1], &recp, ctx))
369 goto err;
370
371 /* move the 'window' down further */
372 wstart -= wend + 1;
373 wvalue = 0;
374 start = 0;
375 if (wstart < 0)
376 break;
377 }
378 ret = 1;
379
380err:
381 BN_CTX_end(ctx);
382 BN_RECP_CTX_free(&recp);
383 bn_check_top(r);
384 return (ret);
385}
386
387static int
388BN_mod_exp_mont_internal(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
389 BN_CTX *ctx, BN_MONT_CTX *in_mont, int ct)
390{
391 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
392 int start = 1;
393 BIGNUM *d, *r;
394 const BIGNUM *aa;
395 /* Table of variables obtained from 'ctx' */
396 BIGNUM *val[TABLE_SIZE32];
397 BN_MONT_CTX *mont = NULL((void *)0);
398
399 if (ct) {
400 return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont);
401 }
402
403 bn_check_top(a);
404 bn_check_top(p);
405 bn_check_top(m);
406
407 if (!BN_is_odd(m)) {
408 BNerror(BN_R_CALLED_WITH_EVEN_MODULUS)ERR_put_error(3,(0xfff),(102),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,408);
409 return (0);
410 }
411
412 bits = BN_num_bits(p);
413 if (bits == 0) {
414 /* x**0 mod 1 is still zero. */
415 if (BN_is_one(m)) {
416 ret = 1;
417 BN_zero(rr)(BN_set_word((rr),0));
418 } else
419 ret = BN_one(rr)BN_set_word((rr), 1);
420 return ret;
421 }
422
423 BN_CTX_start(ctx);
424 if ((d = BN_CTX_get(ctx)) == NULL((void *)0))
425 goto err;
426 if ((r = BN_CTX_get(ctx)) == NULL((void *)0))
427 goto err;
428 if ((val[0] = BN_CTX_get(ctx)) == NULL((void *)0))
429 goto err;
430
431 /* If this is not done, things will break in the montgomery
432 * part */
433
434 if (in_mont != NULL((void *)0))
435 mont = in_mont;
436 else {
437 if ((mont = BN_MONT_CTX_new()) == NULL((void *)0))
438 goto err;
439 if (!BN_MONT_CTX_set(mont, m, ctx))
440 goto err;
441 }
442
443 if (a->neg || BN_ucmp(a, m) >= 0) {
444 if (!BN_nnmod(val[0], a,m, ctx))
445 goto err;
446 aa = val[0];
447 } else
448 aa = a;
449 if (BN_is_zero(aa)) {
450 BN_zero(rr)(BN_set_word((rr),0));
451 ret = 1;
452 goto err;
453 }
454 if (!BN_to_montgomery(val[0], aa, mont, ctx))
455 goto err; /* 1 */
456
457 window = BN_window_bits_for_exponent_size(bits)((bits) > 671 ? 6 : (bits) > 239 ? 5 : (bits) > 79 ?
4 : (bits) > 23 ? 3 : 1);
458 if (window > 1) {
459 if (!BN_mod_mul_montgomery(d, val[0], val[0], mont, ctx))
460 goto err; /* 2 */
461 j = 1 << (window - 1);
462 for (i = 1; i < j; i++) {
463 if (((val[i] = BN_CTX_get(ctx)) == NULL((void *)0)) ||
464 !BN_mod_mul_montgomery(val[i], val[i - 1],
465 d, mont, ctx))
466 goto err;
467 }
468 }
469
470 start = 1; /* This is used to avoid multiplication etc
471 * when there is only the value '1' in the
472 * buffer. */
473 wvalue = 0; /* The 'value' of the window */
474 wstart = bits - 1; /* The top bit of the window */
475 wend = 0; /* The bottom bit of the window */
476
477 if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
478 goto err;
479 for (;;) {
480 if (BN_is_bit_set(p, wstart) == 0) {
481 if (!start) {
482 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
483 goto err;
484 }
485 if (wstart == 0)
486 break;
487 wstart--;
488 continue;
489 }
490 /* We now have wstart on a 'set' bit, we now need to work out
491 * how bit a window to do. To do this we need to scan
492 * forward until the last set bit before the end of the
493 * window */
494 j = wstart;
Value stored to 'j' is never read
495 wvalue = 1;
496 wend = 0;
497 for (i = 1; i < window; i++) {
498 if (wstart - i < 0)
499 break;
500 if (BN_is_bit_set(p, wstart - i)) {
501 wvalue <<= (i - wend);
502 wvalue |= 1;
503 wend = i;
504 }
505 }
506
507 /* wend is the size of the current window */
508 j = wend + 1;
509 /* add the 'bytes above' */
510 if (!start)
511 for (i = 0; i < j; i++) {
512 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
513 goto err;
514 }
515
516 /* wvalue will be an odd number < 2^window */
517 if (!BN_mod_mul_montgomery(r, r, val[wvalue >> 1], mont, ctx))
518 goto err;
519
520 /* move the 'window' down further */
521 wstart -= wend + 1;
522 wvalue = 0;
523 start = 0;
524 if (wstart < 0)
525 break;
526 }
527 if (!BN_from_montgomery(rr, r,mont, ctx))
528 goto err;
529 ret = 1;
530
531err:
532 if ((in_mont == NULL((void *)0)) && (mont != NULL((void *)0)))
533 BN_MONT_CTX_free(mont);
534 BN_CTX_end(ctx);
535 bn_check_top(rr);
536 return (ret);
537}
538
539int
540BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
541 BN_CTX *ctx, BN_MONT_CTX *in_mont)
542{
543 return BN_mod_exp_mont_internal(rr, a, p, m, ctx, in_mont,
544 (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0));
545}
546
547int
548BN_mod_exp_mont_ct(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
549 BN_CTX *ctx, BN_MONT_CTX *in_mont)
550{
551 return BN_mod_exp_mont_internal(rr, a, p, m, ctx, in_mont, 1);
552}
553
554int
555BN_mod_exp_mont_nonct(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
556 BN_CTX *ctx, BN_MONT_CTX *in_mont)
557{
558 return BN_mod_exp_mont_internal(rr, a, p, m, ctx, in_mont, 0);
559}
560
561/* BN_mod_exp_mont_consttime() stores the precomputed powers in a specific layout
562 * so that accessing any of these table values shows the same access pattern as far
563 * as cache lines are concerned. The following functions are used to transfer a BIGNUM
564 * from/to that table. */
565
566static int
567MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top, unsigned char *buf,
568 int idx, int window)
569{
570 int i, j;
571 int width = 1 << window;
572 BN_ULONGunsigned long *table = (BN_ULONGunsigned long *)buf;
573
574 if (top > b->top)
575 top = b->top; /* this works because 'buf' is explicitly zeroed */
576
577 for (i = 0, j = idx; i < top; i++, j += width) {
578 table[j] = b->d[i];
579 }
580
581 return 1;
582}
583
584static int
585MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, unsigned char *buf, int idx,
586 int window)
587{
588 int i, j;
589 int width = 1 << window;
590 volatile BN_ULONGunsigned long *table = (volatile BN_ULONGunsigned long *)buf;
591
592 if (bn_wexpand(b, top)(((top) <= (b)->dmax)?(b):bn_expand2((b),(top))) == NULL((void *)0))
593 return 0;
594
595 if (window <= 3) {
596 for (i = 0; i < top; i++, table += width) {
597 BN_ULONGunsigned long acc = 0;
598
599 for (j = 0; j < width; j++) {
600 acc |= table[j] &
601 ((BN_ULONGunsigned long)0 - (constant_time_eq_int(j,idx)&1));
602 }
603
604 b->d[i] = acc;
605 }
606 } else {
607 int xstride = 1 << (window - 2);
608 BN_ULONGunsigned long y0, y1, y2, y3;
609
610 i = idx >> (window - 2); /* equivalent of idx / xstride */
611 idx &= xstride - 1; /* equivalent of idx % xstride */
612
613 y0 = (BN_ULONGunsigned long)0 - (constant_time_eq_int(i,0)&1);
614 y1 = (BN_ULONGunsigned long)0 - (constant_time_eq_int(i,1)&1);
615 y2 = (BN_ULONGunsigned long)0 - (constant_time_eq_int(i,2)&1);
616 y3 = (BN_ULONGunsigned long)0 - (constant_time_eq_int(i,3)&1);
617
618 for (i = 0; i < top; i++, table += width) {
619 BN_ULONGunsigned long acc = 0;
620
621 for (j = 0; j < xstride; j++) {
622 acc |= ( (table[j + 0 * xstride] & y0) |
623 (table[j + 1 * xstride] & y1) |
624 (table[j + 2 * xstride] & y2) |
625 (table[j + 3 * xstride] & y3) )
626 & ((BN_ULONGunsigned long)0 - (constant_time_eq_int(j,idx)&1));
627 }
628
629 b->d[i] = acc;
630 }
631 }
632 b->top = top;
633 bn_correct_top(b){ unsigned long *ftl; int tmp_top = (b)->top; if (tmp_top >
0) { for (ftl= &((b)->d[tmp_top-1]); tmp_top > 0; tmp_top
--) if (*(ftl--)) break; (b)->top = tmp_top; } ; };
634 return 1;
635}
636
637/* Given a pointer value, compute the next address that is a cache line multiple. */
638#define MOD_EXP_CTIME_ALIGN(x_)((unsigned char*)(x_) + (( 64 ) - (((size_t)(x_)) & ((( 64
) - 1))))) \
639 ((unsigned char*)(x_) + (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH( 64 ) - (((size_t)(x_)) & (MOD_EXP_CTIME_MIN_CACHE_LINE_MASK(( 64 ) - 1)))))
640
641/* This variant of BN_mod_exp_mont() uses fixed windows and the special
642 * precomputation memory layout to limit data-dependency to a minimum
643 * to protect secret exponents (cf. the hyper-threading timing attacks
644 * pointed out by Colin Percival,
645 * http://www.daemonology.net/hyperthreading-considered-harmful/)
646 */
647int
648BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
649 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
650{
651 int i, bits, ret = 0, window, wvalue;
652 int top;
653 BN_MONT_CTX *mont = NULL((void *)0);
654 int numPowers;
655 unsigned char *powerbufFree = NULL((void *)0);
656 int powerbufLen = 0;
657 unsigned char *powerbuf = NULL((void *)0);
658 BIGNUM tmp, am;
659
660 bn_check_top(a);
661 bn_check_top(p);
662 bn_check_top(m);
663
664 if (!BN_is_odd(m)) {
665 BNerror(BN_R_CALLED_WITH_EVEN_MODULUS)ERR_put_error(3,(0xfff),(102),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,665);
666 return (0);
667 }
668
669 top = m->top;
670
671 bits = BN_num_bits(p);
672 if (bits == 0) {
673 /* x**0 mod 1 is still zero. */
674 if (BN_is_one(m)) {
675 ret = 1;
676 BN_zero(rr)(BN_set_word((rr),0));
677 } else
678 ret = BN_one(rr)BN_set_word((rr), 1);
679 return ret;
680 }
681
682 BN_CTX_start(ctx);
683
684 /* Allocate a montgomery context if it was not supplied by the caller.
685 * If this is not done, things will break in the montgomery part.
686 */
687 if (in_mont != NULL((void *)0))
688 mont = in_mont;
689 else {
690 if ((mont = BN_MONT_CTX_new()) == NULL((void *)0))
691 goto err;
692 if (!BN_MONT_CTX_set(mont, m, ctx))
693 goto err;
694 }
695
696 /* Get the window size to use with size of p. */
697 window = BN_window_bits_for_ctime_exponent_size(bits)((bits) > 937 ? 6 : (bits) > 306 ? 5 : (bits) > 89 ?
4 : (bits) > 22 ? 3 : 1);
698#if defined(OPENSSL_BN_ASM_MONT51)
699 if (window == 6 && bits <= 1024)
700 window = 5; /* ~5% improvement of 2048-bit RSA sign */
701#endif
702
703 /* Allocate a buffer large enough to hold all of the pre-computed
704 * powers of am, am itself and tmp.
705 */
706 numPowers = 1 << window;
707 powerbufLen = sizeof(m->d[0]) * (top * numPowers +
708 ((2*top) > numPowers ? (2*top) : numPowers));
709 if ((powerbufFree = calloc(powerbufLen +
710 MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH( 64 ), 1)) == NULL((void *)0))
711 goto err;
712 powerbuf = MOD_EXP_CTIME_ALIGN(powerbufFree)((unsigned char*)(powerbufFree) + (( 64 ) - (((size_t)(powerbufFree
)) & ((( 64 ) - 1)))));
713
714 /* lay down tmp and am right after powers table */
715 tmp.d = (BN_ULONGunsigned long *)(powerbuf + sizeof(m->d[0]) * top * numPowers);
716 am.d = tmp.d + top;
717 tmp.top = am.top = 0;
718 tmp.dmax = am.dmax = top;
719 tmp.neg = am.neg = 0;
720 tmp.flags = am.flags = BN_FLG_STATIC_DATA0x02;
721
722 /* prepare a^0 in Montgomery domain */
723#if 1
724 if (!BN_to_montgomery(&tmp, BN_value_one(), mont, ctx))
725 goto err;
726#else
727 tmp.d[0] = (0 - m - >d[0]) & BN_MASK2(0xffffffffffffffffL); /* 2^(top*BN_BITS2) - m */
728 for (i = 1; i < top; i++)
729 tmp.d[i] = (~m->d[i]) & BN_MASK2(0xffffffffffffffffL);
730 tmp.top = top;
731#endif
732
733 /* prepare a^1 in Montgomery domain */
734 if (a->neg || BN_ucmp(a, m) >= 0) {
735 if (!BN_mod_ct(&am, a,m, ctx)BN_div_ct(((void *)0),(&am),(a),(m),(ctx)))
736 goto err;
737 if (!BN_to_montgomery(&am, &am, mont, ctx))
738 goto err;
739 } else if (!BN_to_montgomery(&am, a,mont, ctx))
740 goto err;
741
742#if defined(OPENSSL_BN_ASM_MONT51)
743 /* This optimization uses ideas from http://eprint.iacr.org/2011/239,
744 * specifically optimization of cache-timing attack countermeasures
745 * and pre-computation optimization. */
746
747 /* Dedicated window==4 case improves 512-bit RSA sign by ~15%, but as
748 * 512-bit RSA is hardly relevant, we omit it to spare size... */
749 if (window == 5 && top > 1) {
750 void bn_mul_mont_gather5(BN_ULONGunsigned long *rp, const BN_ULONGunsigned long *ap,
751 const void *table, const BN_ULONGunsigned long *np,
752 const BN_ULONGunsigned long *n0, int num, int power);
753 void bn_scatter5(const BN_ULONGunsigned long *inp, size_t num,
754 void *table, size_t power);
755 void bn_gather5(BN_ULONGunsigned long *out, size_t num,
756 void *table, size_t power);
757
758 BN_ULONGunsigned long *np = mont->N.d, *n0 = mont->n0;
759
760 /* BN_to_montgomery can contaminate words above .top
761 * [in BN_DEBUG[_DEBUG] build]... */
762 for (i = am.top; i < top; i++)
763 am.d[i] = 0;
764 for (i = tmp.top; i < top; i++)
765 tmp.d[i] = 0;
766
767 bn_scatter5(tmp.d, top, powerbuf, 0);
768 bn_scatter5(am.d, am.top, powerbuf, 1);
769 bn_mul_mont(tmp.d, am.d, am.d, np, n0, top);
770 bn_scatter5(tmp.d, top, powerbuf, 2);
771
772#if 0
773 for (i = 3; i < 32; i++) {
774 /* Calculate a^i = a^(i-1) * a */
775 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
776 n0, top, i - 1);
777 bn_scatter5(tmp.d, top, powerbuf, i);
778 }
779#else
780 /* same as above, but uses squaring for 1/2 of operations */
781 for (i = 4; i < 32; i*=2) {
782 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
783 bn_scatter5(tmp.d, top, powerbuf, i);
784 }
785 for (i = 3; i < 8; i += 2) {
786 int j;
787 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
788 n0, top, i - 1);
789 bn_scatter5(tmp.d, top, powerbuf, i);
790 for (j = 2 * i; j < 32; j *= 2) {
791 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
792 bn_scatter5(tmp.d, top, powerbuf, j);
793 }
794 }
795 for (; i < 16; i += 2) {
796 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
797 n0, top, i - 1);
798 bn_scatter5(tmp.d, top, powerbuf, i);
799 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
800 bn_scatter5(tmp.d, top, powerbuf, 2*i);
801 }
802 for (; i < 32; i += 2) {
803 bn_mul_mont_gather5(tmp.d, am.d, powerbuf, np,
804 n0, top, i - 1);
805 bn_scatter5(tmp.d, top, powerbuf, i);
806 }
807#endif
808 bits--;
809 for (wvalue = 0, i = bits % 5; i >= 0; i--, bits--)
810 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
811 bn_gather5(tmp.d, top, powerbuf, wvalue);
812
813 /* Scan the exponent one window at a time starting from the most
814 * significant bits.
815 */
816 while (bits >= 0) {
817 for (wvalue = 0, i = 0; i < 5; i++, bits--)
818 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
819
820 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
821 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
822 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
823 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
824 bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top);
825 bn_mul_mont_gather5(tmp.d, tmp.d, powerbuf, np, n0, top, wvalue);
826 }
827
828 tmp.top = top;
829 bn_correct_top(&tmp){ unsigned long *ftl; int tmp_top = (&tmp)->top; if (tmp_top
> 0) { for (ftl= &((&tmp)->d[tmp_top-1]); tmp_top
> 0; tmp_top--) if (*(ftl--)) break; (&tmp)->top =
tmp_top; } ; };
830 } else
831#endif
832 {
833 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0,
834 window))
835 goto err;
836 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1,
837 window))
838 goto err;
839
840 /* If the window size is greater than 1, then calculate
841 * val[i=2..2^winsize-1]. Powers are computed as a*a^(i-1)
842 * (even powers could instead be computed as (a^(i/2))^2
843 * to use the slight performance advantage of sqr over mul).
844 */
845 if (window > 1) {
846 if (!BN_mod_mul_montgomery(&tmp, &am, &am, mont, ctx))
847 goto err;
848 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf,
849 2, window))
850 goto err;
851 for (i = 3; i < numPowers; i++) {
852 /* Calculate a^i = a^(i-1) * a */
853 if (!BN_mod_mul_montgomery(&tmp, &am, &tmp,
854 mont, ctx))
855 goto err;
856 if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top,
857 powerbuf, i, window))
858 goto err;
859 }
860 }
861
862 bits--;
863 for (wvalue = 0, i = bits % window; i >= 0; i--, bits--)
864 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
865 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf,
866 wvalue, window))
867 goto err;
868
869 /* Scan the exponent one window at a time starting from the most
870 * significant bits.
871 */
872 while (bits >= 0) {
873 wvalue = 0; /* The 'value' of the window */
874
875 /* Scan the window, squaring the result as we go */
876 for (i = 0; i < window; i++, bits--) {
877 if (!BN_mod_mul_montgomery(&tmp, &tmp, &tmp,
878 mont, ctx))
879 goto err;
880 wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
881 }
882
883 /* Fetch the appropriate pre-computed value from the pre-buf */
884 if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf,
885 wvalue, window))
886 goto err;
887
888 /* Multiply the result into the intermediate result */
889 if (!BN_mod_mul_montgomery(&tmp, &tmp, &am, mont, ctx))
890 goto err;
891 }
892 }
893
894 /* Convert the final result from montgomery to standard format */
895 if (!BN_from_montgomery(rr, &tmp, mont, ctx))
896 goto err;
897 ret = 1;
898
899err:
900 if ((in_mont == NULL((void *)0)) && (mont != NULL((void *)0)))
901 BN_MONT_CTX_free(mont);
902 freezero(powerbufFree, powerbufLen + MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH( 64 ));
903 BN_CTX_end(ctx);
904 return (ret);
905}
906
907int
908BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONGunsigned long a, const BIGNUM *p, const BIGNUM *m,
909 BN_CTX *ctx, BN_MONT_CTX *in_mont)
910{
911 BN_MONT_CTX *mont = NULL((void *)0);
912 int b, bits, ret = 0;
913 int r_is_one;
914 BN_ULONGunsigned long w, next_w;
915 BIGNUM *d, *r, *t;
916 BIGNUM *swap_tmp;
917
918#define BN_MOD_MUL_WORD(r, w, m)(BN_mul_word(r, (w)) && ( (BN_div_ct(((void *)0),(t),
(r),(m),(ctx)) && (swap_tmp = r, r = t, t = swap_tmp,
1)))) \
919 (BN_mul_word(r, (w)) && \
920 (/* BN_ucmp(r, (m)) < 0 ? 1 :*/ \
921 (BN_mod_ct(t, r, m, ctx)BN_div_ct(((void *)0),(t),(r),(m),(ctx)) && (swap_tmp = r, r = t, t = swap_tmp, 1))))
922 /* BN_MOD_MUL_WORD is only used with 'w' large,
923 * so the BN_ucmp test is probably more overhead
924 * than always using BN_mod (which uses BN_copy if
925 * a similar test returns true). */
926 /* We can use BN_mod and do not need BN_nnmod because our
927 * accumulator is never negative (the result of BN_mod does
928 * not depend on the sign of the modulus).
929 */
930#define BN_TO_MONTGOMERY_WORD(r, w, mont)(BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont)
, ctx)) \
931 (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx))
932
933 if (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0) {
934 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
935 BNerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED)ERR_put_error(3,(0xfff),((2|64)),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,935);
936 return -1;
937 }
938
939 bn_check_top(p);
940 bn_check_top(m);
941
942 if (!BN_is_odd(m)) {
943 BNerror(BN_R_CALLED_WITH_EVEN_MODULUS)ERR_put_error(3,(0xfff),(102),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,943);
944 return (0);
945 }
946 if (m->top == 1)
947 a %= m->d[0]; /* make sure that 'a' is reduced */
948
949 bits = BN_num_bits(p);
950 if (bits == 0) {
951 /* x**0 mod 1 is still zero. */
952 if (BN_is_one(m)) {
953 ret = 1;
954 BN_zero(rr)(BN_set_word((rr),0));
955 } else
956 ret = BN_one(rr)BN_set_word((rr), 1);
957 return ret;
958 }
959 if (a == 0) {
960 BN_zero(rr)(BN_set_word((rr),0));
961 ret = 1;
962 return ret;
963 }
964
965 BN_CTX_start(ctx);
966 if ((d = BN_CTX_get(ctx)) == NULL((void *)0))
967 goto err;
968 if ((r = BN_CTX_get(ctx)) == NULL((void *)0))
969 goto err;
970 if ((t = BN_CTX_get(ctx)) == NULL((void *)0))
971 goto err;
972
973 if (in_mont != NULL((void *)0))
974 mont = in_mont;
975 else {
976 if ((mont = BN_MONT_CTX_new()) == NULL((void *)0))
977 goto err;
978 if (!BN_MONT_CTX_set(mont, m, ctx))
979 goto err;
980 }
981
982 r_is_one = 1; /* except for Montgomery factor */
983
984 /* bits-1 >= 0 */
985
986 /* The result is accumulated in the product r*w. */
987 w = a; /* bit 'bits-1' of 'p' is always set */
988 for (b = bits - 2; b >= 0; b--) {
989 /* First, square r*w. */
990 next_w = w * w;
991 if ((next_w / w) != w) /* overflow */
992 {
993 if (r_is_one) {
994 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)(BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont)
, ctx)))
995 goto err;
996 r_is_one = 0;
997 } else {
998 if (!BN_MOD_MUL_WORD(r, w, m)(BN_mul_word(r, (w)) && ( (BN_div_ct(((void *)0),(t),
(r),(m),(ctx)) && (swap_tmp = r, r = t, t = swap_tmp,
1)))))
999 goto err;
1000 }
1001 next_w = 1;
1002 }
1003 w = next_w;
1004 if (!r_is_one) {
1005 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
1006 goto err;
1007 }
1008
1009 /* Second, multiply r*w by 'a' if exponent bit is set. */
1010 if (BN_is_bit_set(p, b)) {
1011 next_w = w * a;
1012 if ((next_w / a) != w) /* overflow */
1013 {
1014 if (r_is_one) {
1015 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)(BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont)
, ctx)))
1016 goto err;
1017 r_is_one = 0;
1018 } else {
1019 if (!BN_MOD_MUL_WORD(r, w, m)(BN_mul_word(r, (w)) && ( (BN_div_ct(((void *)0),(t),
(r),(m),(ctx)) && (swap_tmp = r, r = t, t = swap_tmp,
1)))))
1020 goto err;
1021 }
1022 next_w = a;
1023 }
1024 w = next_w;
1025 }
1026 }
1027
1028 /* Finally, set r:=r*w. */
1029 if (w != 1) {
1030 if (r_is_one) {
1031 if (!BN_TO_MONTGOMERY_WORD(r, w, mont)(BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont)
, ctx)))
1032 goto err;
1033 r_is_one = 0;
1034 } else {
1035 if (!BN_MOD_MUL_WORD(r, w, m)(BN_mul_word(r, (w)) && ( (BN_div_ct(((void *)0),(t),
(r),(m),(ctx)) && (swap_tmp = r, r = t, t = swap_tmp,
1)))))
1036 goto err;
1037 }
1038 }
1039
1040 if (r_is_one) /* can happen only if a == 1*/
1041 {
1042 if (!BN_one(rr)BN_set_word((rr), 1))
1043 goto err;
1044 } else {
1045 if (!BN_from_montgomery(rr, r, mont, ctx))
1046 goto err;
1047 }
1048 ret = 1;
1049
1050err:
1051 if ((in_mont == NULL((void *)0)) && (mont != NULL((void *)0)))
1052 BN_MONT_CTX_free(mont);
1053 BN_CTX_end(ctx);
1054 bn_check_top(rr);
1055 return (ret);
1056}
1057
1058
1059/* The old fallback, simple version :-) */
1060int
1061BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
1062 BN_CTX *ctx)
1063{
1064 int i, j, bits, ret = 0, wstart, wend, window, wvalue;
1065 int start = 1;
1066 BIGNUM *d;
1067 /* Table of variables obtained from 'ctx' */
1068 BIGNUM *val[TABLE_SIZE32];
1069
1070 if (BN_get_flags(p, BN_FLG_CONSTTIME0x04) != 0) {
1071 /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */
1072 BNerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED)ERR_put_error(3,(0xfff),((2|64)),"/usr/src/lib/libcrypto/bn/bn_exp.c"
,1072);
1073 return -1;
1074 }
1075
1076 bits = BN_num_bits(p);
1077 if (bits == 0) {
1078 /* x**0 mod 1 is still zero. */
1079 if (BN_is_one(m)) {
1080 ret = 1;
1081 BN_zero(r)(BN_set_word((r),0));
1082 } else
1083 ret = BN_one(r)BN_set_word((r), 1);
1084 return ret;
1085 }
1086
1087 BN_CTX_start(ctx);
1088 if ((d = BN_CTX_get(ctx)) == NULL((void *)0))
1089 goto err;
1090 if ((val[0] = BN_CTX_get(ctx)) == NULL((void *)0))
1091 goto err;
1092
1093 if (!BN_nnmod(val[0],a,m,ctx))
1094 goto err; /* 1 */
1095 if (BN_is_zero(val[0])) {
1096 BN_zero(r)(BN_set_word((r),0));
1097 ret = 1;
1098 goto err;
1099 }
1100
1101 window = BN_window_bits_for_exponent_size(bits)((bits) > 671 ? 6 : (bits) > 239 ? 5 : (bits) > 79 ?
4 : (bits) > 23 ? 3 : 1);
1102 if (window > 1) {
1103 if (!BN_mod_mul(d, val[0], val[0], m, ctx))
1104 goto err; /* 2 */
1105 j = 1 << (window - 1);
1106 for (i = 1; i < j; i++) {
1107 if (((val[i] = BN_CTX_get(ctx)) == NULL((void *)0)) ||
1108 !BN_mod_mul(val[i], val[i - 1], d,m, ctx))
1109 goto err;
1110 }
1111 }
1112
1113 start = 1; /* This is used to avoid multiplication etc
1114 * when there is only the value '1' in the
1115 * buffer. */
1116 wvalue = 0; /* The 'value' of the window */
1117 wstart = bits - 1; /* The top bit of the window */
1118 wend = 0; /* The bottom bit of the window */
1119
1120 if (!BN_one(r)BN_set_word((r), 1))
1121 goto err;
1122
1123 for (;;) {
1124 if (BN_is_bit_set(p, wstart) == 0) {
1125 if (!start)
1126 if (!BN_mod_mul(r, r, r, m, ctx))
1127 goto err;
1128 if (wstart == 0)
1129 break;
1130 wstart--;
1131 continue;
1132 }
1133 /* We now have wstart on a 'set' bit, we now need to work out
1134 * how bit a window to do. To do this we need to scan
1135 * forward until the last set bit before the end of the
1136 * window */
1137 j = wstart;
1138 wvalue = 1;
1139 wend = 0;
1140 for (i = 1; i < window; i++) {
1141 if (wstart - i < 0)
1142 break;
1143 if (BN_is_bit_set(p, wstart - i)) {
1144 wvalue <<= (i - wend);
1145 wvalue |= 1;
1146 wend = i;
1147 }
1148 }
1149
1150 /* wend is the size of the current window */
1151 j = wend + 1;
1152 /* add the 'bytes above' */
1153 if (!start)
1154 for (i = 0; i < j; i++) {
1155 if (!BN_mod_mul(r, r, r, m, ctx))
1156 goto err;
1157 }
1158
1159 /* wvalue will be an odd number < 2^window */
1160 if (!BN_mod_mul(r, r, val[wvalue >> 1], m, ctx))
1161 goto err;
1162
1163 /* move the 'window' down further */
1164 wstart -= wend + 1;
1165 wvalue = 0;
1166 start = 0;
1167 if (wstart < 0)
1168 break;
1169 }
1170 ret = 1;
1171
1172err:
1173 BN_CTX_end(ctx);
1174 bn_check_top(r);
1175 return (ret);
1176}