GCC Code Coverage Report
Directory: ./ Exec Total Coverage
File: lib/libcrypto/bn/bn_gcd.c Lines: 78 232 33.6 %
Date: 2017-11-13 Branches: 63 322 19.6 %

Line Branch Exec Source
1
/* $OpenBSD: bn_gcd.c,v 1.15 2017/01/29 17:49:22 beck 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) 1998-2001 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 <openssl/err.h>
113
114
#include "bn_lcl.h"
115
116
static BIGNUM *euclid(BIGNUM *a, BIGNUM *b);
117
static BIGNUM *BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
118
    BN_CTX *ctx);
119
120
int
121
BN_gcd(BIGNUM *r, const BIGNUM *in_a, const BIGNUM *in_b, BN_CTX *ctx)
122
{
123
	BIGNUM *a, *b, *t;
124
	int ret = 0;
125
126
	bn_check_top(in_a);
127
	bn_check_top(in_b);
128
129
	BN_CTX_start(ctx);
130
	if ((a = BN_CTX_get(ctx)) == NULL)
131
		goto err;
132
	if ((b = BN_CTX_get(ctx)) == NULL)
133
		goto err;
134
135
	if (BN_copy(a, in_a) == NULL)
136
		goto err;
137
	if (BN_copy(b, in_b) == NULL)
138
		goto err;
139
	a->neg = 0;
140
	b->neg = 0;
141
142
	if (BN_cmp(a, b) < 0) {
143
		t = a;
144
		a = b;
145
		b = t;
146
	}
147
	t = euclid(a, b);
148
	if (t == NULL)
149
		goto err;
150
151
	if (BN_copy(r, t) == NULL)
152
		goto err;
153
	ret = 1;
154
155
err:
156
	BN_CTX_end(ctx);
157
	bn_check_top(r);
158
	return (ret);
159
}
160
161
int
162
BN_gcd_ct(BIGNUM *r, const BIGNUM *in_a, const BIGNUM *in_b, BN_CTX *ctx)
163
{
164
76
	if (BN_gcd_no_branch(r, in_a, in_b, ctx) == NULL)
165
		return 0;
166
38
	return 1;
167
38
}
168
169
int
170
BN_gcd_nonct(BIGNUM *r, const BIGNUM *in_a, const BIGNUM *in_b, BN_CTX *ctx)
171
{
172
	return BN_gcd(r, in_a, in_b, ctx);
173
}
174
175
176
static BIGNUM *
177
euclid(BIGNUM *a, BIGNUM *b)
178
{
179
	BIGNUM *t;
180
	int shifts = 0;
181
182
	bn_check_top(a);
183
	bn_check_top(b);
184
185
	/* 0 <= b <= a */
186
	while (!BN_is_zero(b)) {
187
		/* 0 < b <= a */
188
189
		if (BN_is_odd(a)) {
190
			if (BN_is_odd(b)) {
191
				if (!BN_sub(a, a, b))
192
					goto err;
193
				if (!BN_rshift1(a, a))
194
					goto err;
195
				if (BN_cmp(a, b) < 0) {
196
					t = a;
197
					a = b;
198
					b = t;
199
				}
200
			}
201
			else		/* a odd - b even */
202
			{
203
				if (!BN_rshift1(b, b))
204
					goto err;
205
				if (BN_cmp(a, b) < 0) {
206
					t = a;
207
					a = b;
208
					b = t;
209
				}
210
			}
211
		}
212
		else			/* a is even */
213
		{
214
			if (BN_is_odd(b)) {
215
				if (!BN_rshift1(a, a))
216
					goto err;
217
				if (BN_cmp(a, b) < 0) {
218
					t = a;
219
					a = b;
220
					b = t;
221
				}
222
			}
223
			else		/* a even - b even */
224
			{
225
				if (!BN_rshift1(a, a))
226
					goto err;
227
				if (!BN_rshift1(b, b))
228
					goto err;
229
				shifts++;
230
			}
231
		}
232
		/* 0 <= b <= a */
233
	}
234
235
	if (shifts) {
236
		if (!BN_lshift(a, a, shifts))
237
			goto err;
238
	}
239
	bn_check_top(a);
240
	return (a);
241
242
err:
243
	return (NULL);
244
}
245
246
247
/* solves ax == 1 (mod n) */
248
static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a,
249
    const BIGNUM *n, BN_CTX *ctx);
250
251
static BIGNUM *
252
BN_mod_inverse_internal(BIGNUM *in, const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx,
253
    int ct)
254
{
255
	BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
256
	BIGNUM *ret = NULL;
257
	int sign;
258
259
85196
	if (ct)
260
42598
		return BN_mod_inverse_no_branch(in, a, n, ctx);
261
262
	bn_check_top(a);
263
	bn_check_top(n);
264
265
	BN_CTX_start(ctx);
266
	if ((A = BN_CTX_get(ctx)) == NULL)
267
		goto err;
268
	if ((B = BN_CTX_get(ctx)) == NULL)
269
		goto err;
270
	if ((X = BN_CTX_get(ctx)) == NULL)
271
		goto err;
272
	if ((D = BN_CTX_get(ctx)) == NULL)
273
		goto err;
274
	if ((M = BN_CTX_get(ctx)) == NULL)
275
		goto err;
276
	if ((Y = BN_CTX_get(ctx)) == NULL)
277
		goto err;
278
	if ((T = BN_CTX_get(ctx)) == NULL)
279
		goto err;
280
281
	if (in == NULL)
282
		R = BN_new();
283
	else
284
		R = in;
285
	if (R == NULL)
286
		goto err;
287
288
	BN_one(X);
289
	BN_zero(Y);
290
	if (BN_copy(B, a) == NULL)
291
		goto err;
292
	if (BN_copy(A, n) == NULL)
293
		goto err;
294
	A->neg = 0;
295
	if (B->neg || (BN_ucmp(B, A) >= 0)) {
296
		if (!BN_nnmod(B, B, A, ctx))
297
			goto err;
298
	}
299
	sign = -1;
300
	/* From  B = a mod |n|,  A = |n|  it follows that
301
	 *
302
	 *      0 <= B < A,
303
	 *     -sign*X*a  ==  B   (mod |n|),
304
	 *      sign*Y*a  ==  A   (mod |n|).
305
	 */
306
307
	if (BN_is_odd(n) && (BN_num_bits(n) <= (BN_BITS <= 32 ? 450 : 2048))) {
308
		/* Binary inversion algorithm; requires odd modulus.
309
		 * This is faster than the general algorithm if the modulus
310
		 * is sufficiently small (about 400 .. 500 bits on 32-bit
311
		 * sytems, but much more on 64-bit systems) */
312
		int shift;
313
314
		while (!BN_is_zero(B)) {
315
			/*
316
			 *      0 < B < |n|,
317
			 *      0 < A <= |n|,
318
			 * (1) -sign*X*a  ==  B   (mod |n|),
319
			 * (2)  sign*Y*a  ==  A   (mod |n|)
320
			 */
321
322
			/* Now divide  B  by the maximum possible power of two in the integers,
323
			 * and divide  X  by the same value mod |n|.
324
			 * When we're done, (1) still holds. */
325
			shift = 0;
326
			while (!BN_is_bit_set(B, shift)) /* note that 0 < B */
327
			{
328
				shift++;
329
330
				if (BN_is_odd(X)) {
331
					if (!BN_uadd(X, X, n))
332
						goto err;
333
				}
334
				/* now X is even, so we can easily divide it by two */
335
				if (!BN_rshift1(X, X))
336
					goto err;
337
			}
338
			if (shift > 0) {
339
				if (!BN_rshift(B, B, shift))
340
					goto err;
341
			}
342
343
344
			/* Same for  A  and  Y.  Afterwards, (2) still holds. */
345
			shift = 0;
346
			while (!BN_is_bit_set(A, shift)) /* note that 0 < A */
347
			{
348
				shift++;
349
350
				if (BN_is_odd(Y)) {
351
					if (!BN_uadd(Y, Y, n))
352
						goto err;
353
				}
354
				/* now Y is even */
355
				if (!BN_rshift1(Y, Y))
356
					goto err;
357
			}
358
			if (shift > 0) {
359
				if (!BN_rshift(A, A, shift))
360
					goto err;
361
			}
362
363
364
			/* We still have (1) and (2).
365
			 * Both  A  and  B  are odd.
366
			 * The following computations ensure that
367
			 *
368
			 *     0 <= B < |n|,
369
			 *      0 < A < |n|,
370
			 * (1) -sign*X*a  ==  B   (mod |n|),
371
			 * (2)  sign*Y*a  ==  A   (mod |n|),
372
			 *
373
			 * and that either  A  or  B  is even in the next iteration.
374
			 */
375
			if (BN_ucmp(B, A) >= 0) {
376
				/* -sign*(X + Y)*a == B - A  (mod |n|) */
377
				if (!BN_uadd(X, X, Y))
378
					goto err;
379
				/* NB: we could use BN_mod_add_quick(X, X, Y, n), but that
380
				 * actually makes the algorithm slower */
381
				if (!BN_usub(B, B, A))
382
					goto err;
383
			} else {
384
				/*  sign*(X + Y)*a == A - B  (mod |n|) */
385
				if (!BN_uadd(Y, Y, X))
386
					goto err;
387
				/* as above, BN_mod_add_quick(Y, Y, X, n) would slow things down */
388
				if (!BN_usub(A, A, B))
389
					goto err;
390
			}
391
		}
392
	} else {
393
		/* general inversion algorithm */
394
395
		while (!BN_is_zero(B)) {
396
			BIGNUM *tmp;
397
398
			/*
399
			 *      0 < B < A,
400
			 * (*) -sign*X*a  ==  B   (mod |n|),
401
			 *      sign*Y*a  ==  A   (mod |n|)
402
			 */
403
404
			/* (D, M) := (A/B, A%B) ... */
405
			if (BN_num_bits(A) == BN_num_bits(B)) {
406
				if (!BN_one(D))
407
					goto err;
408
				if (!BN_sub(M, A, B))
409
					goto err;
410
			} else if (BN_num_bits(A) == BN_num_bits(B) + 1) {
411
				/* A/B is 1, 2, or 3 */
412
				if (!BN_lshift1(T, B))
413
					goto err;
414
				if (BN_ucmp(A, T) < 0) {
415
					/* A < 2*B, so D=1 */
416
					if (!BN_one(D))
417
						goto err;
418
					if (!BN_sub(M, A, B))
419
						goto err;
420
				} else {
421
					/* A >= 2*B, so D=2 or D=3 */
422
					if (!BN_sub(M, A, T))
423
						goto err;
424
					if (!BN_add(D,T,B)) goto err; /* use D (:= 3*B) as temp */
425
						if (BN_ucmp(A, D) < 0) {
426
						/* A < 3*B, so D=2 */
427
						if (!BN_set_word(D, 2))
428
							goto err;
429
						/* M (= A - 2*B) already has the correct value */
430
					} else {
431
						/* only D=3 remains */
432
						if (!BN_set_word(D, 3))
433
							goto err;
434
						/* currently  M = A - 2*B,  but we need  M = A - 3*B */
435
						if (!BN_sub(M, M, B))
436
							goto err;
437
					}
438
				}
439
			} else {
440
				if (!BN_div_nonct(D, M, A, B, ctx))
441
					goto err;
442
			}
443
444
			/* Now
445
			 *      A = D*B + M;
446
			 * thus we have
447
			 * (**)  sign*Y*a  ==  D*B + M   (mod |n|).
448
			 */
449
			tmp = A; /* keep the BIGNUM object, the value does not matter */
450
451
			/* (A, B) := (B, A mod B) ... */
452
			A = B;
453
			B = M;
454
			/* ... so we have  0 <= B < A  again */
455
456
			/* Since the former  M  is now  B  and the former  B  is now  A,
457
			 * (**) translates into
458
			 *       sign*Y*a  ==  D*A + B    (mod |n|),
459
			 * i.e.
460
			 *       sign*Y*a - D*A  ==  B    (mod |n|).
461
			 * Similarly, (*) translates into
462
			 *      -sign*X*a  ==  A          (mod |n|).
463
			 *
464
			 * Thus,
465
			 *   sign*Y*a + D*sign*X*a  ==  B  (mod |n|),
466
			 * i.e.
467
			 *        sign*(Y + D*X)*a  ==  B  (mod |n|).
468
			 *
469
			 * So if we set  (X, Y, sign) := (Y + D*X, X, -sign),  we arrive back at
470
			 *      -sign*X*a  ==  B   (mod |n|),
471
			 *       sign*Y*a  ==  A   (mod |n|).
472
			 * Note that  X  and  Y  stay non-negative all the time.
473
			 */
474
475
			/* most of the time D is very small, so we can optimize tmp := D*X+Y */
476
			if (BN_is_one(D)) {
477
				if (!BN_add(tmp, X, Y))
478
					goto err;
479
			} else {
480
				if (BN_is_word(D, 2)) {
481
					if (!BN_lshift1(tmp, X))
482
						goto err;
483
				} else if (BN_is_word(D, 4)) {
484
					if (!BN_lshift(tmp, X, 2))
485
						goto err;
486
				} else if (D->top == 1) {
487
					if (!BN_copy(tmp, X))
488
						goto err;
489
					if (!BN_mul_word(tmp, D->d[0]))
490
						goto err;
491
				} else {
492
					if (!BN_mul(tmp, D,X, ctx))
493
						goto err;
494
				}
495
				if (!BN_add(tmp, tmp, Y))
496
					goto err;
497
			}
498
499
			M = Y; /* keep the BIGNUM object, the value does not matter */
500
			Y = X;
501
			X = tmp;
502
			sign = -sign;
503
		}
504
	}
505
506
	/*
507
	 * The while loop (Euclid's algorithm) ends when
508
	 *      A == gcd(a,n);
509
	 * we have
510
	 *       sign*Y*a  ==  A  (mod |n|),
511
	 * where  Y  is non-negative.
512
	 */
513
514
	if (sign < 0) {
515
		if (!BN_sub(Y, n, Y))
516
			goto err;
517
	}
518
	/* Now  Y*a  ==  A  (mod |n|).  */
519
520
	if (BN_is_one(A)) {
521
		/* Y*a == 1  (mod |n|) */
522
		if (!Y->neg && BN_ucmp(Y, n) < 0) {
523
			if (!BN_copy(R, Y))
524
				goto err;
525
		} else {
526
			if (!BN_nnmod(R, Y,n, ctx))
527
				goto err;
528
		}
529
	} else {
530
		BNerror(BN_R_NO_INVERSE);
531
		goto err;
532
	}
533
	ret = R;
534
535
err:
536
	if ((ret == NULL) && (in == NULL))
537
		BN_free(R);
538
	BN_CTX_end(ctx);
539
	bn_check_top(ret);
540
	return (ret);
541
42598
}
542
543
BIGNUM *
544
BN_mod_inverse(BIGNUM *in, const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
545
{
546
	int ct = ((BN_get_flags(a, BN_FLG_CONSTTIME) != 0) ||
547
	    (BN_get_flags(n, BN_FLG_CONSTTIME) != 0));
548
	return BN_mod_inverse_internal(in, a, n, ctx, ct);
549
}
550
551
BIGNUM *
552
BN_mod_inverse_nonct(BIGNUM *in, const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
553
{
554
	return BN_mod_inverse_internal(in, a, n, ctx, 0);
555
}
556
557
BIGNUM *
558
BN_mod_inverse_ct(BIGNUM *in, const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
559
{
560
85196
	return BN_mod_inverse_internal(in, a, n, ctx, 1);
561
}
562
563
/* BN_mod_inverse_no_branch is a special version of BN_mod_inverse.
564
 * It does not contain branches that may leak sensitive information.
565
 */
566
static BIGNUM *
567
BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
568
    BN_CTX *ctx)
569
{
570
	BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
571
85196
	BIGNUM local_A, local_B;
572
	BIGNUM *pA, *pB;
573
	BIGNUM *ret = NULL;
574
	int sign;
575
576
	bn_check_top(a);
577
	bn_check_top(n);
578
579
42598
	BN_CTX_start(ctx);
580
42598
	if ((A = BN_CTX_get(ctx)) == NULL)
581
		goto err;
582
42598
	if ((B = BN_CTX_get(ctx)) == NULL)
583
		goto err;
584
42598
	if ((X = BN_CTX_get(ctx)) == NULL)
585
		goto err;
586
42598
	if ((D = BN_CTX_get(ctx)) == NULL)
587
		goto err;
588
42598
	if ((M = BN_CTX_get(ctx)) == NULL)
589
		goto err;
590
42598
	if ((Y = BN_CTX_get(ctx)) == NULL)
591
		goto err;
592
42598
	if ((T = BN_CTX_get(ctx)) == NULL)
593
		goto err;
594
595
42598
	if (in == NULL)
596
8
		R = BN_new();
597
	else
598
		R = in;
599
42598
	if (R == NULL)
600
		goto err;
601
602
42598
	BN_one(X);
603
42598
	BN_zero(Y);
604
42598
	if (BN_copy(B, a) == NULL)
605
		goto err;
606
42598
	if (BN_copy(A, n) == NULL)
607
		goto err;
608
42598
	A->neg = 0;
609
610

85196
	if (B->neg || (BN_ucmp(B, A) >= 0)) {
611
		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
612
	 	 * BN_div_no_branch will be called eventually.
613
	 	 */
614
		pB = &local_B;
615
32265
		BN_with_flags(pB, B, BN_FLG_CONSTTIME);
616
32265
		if (!BN_nnmod(B, pB, A, ctx))
617
			goto err;
618
	}
619
	sign = -1;
620
	/* From  B = a mod |n|,  A = |n|  it follows that
621
	 *
622
	 *      0 <= B < A,
623
	 *     -sign*X*a  ==  B   (mod |n|),
624
	 *      sign*Y*a  ==  A   (mod |n|).
625
	 */
626
627
7292082
	while (!BN_is_zero(B)) {
628
		BIGNUM *tmp;
629
630
		/*
631
		 *      0 < B < A,
632
		 * (*) -sign*X*a  ==  B   (mod |n|),
633
		 *      sign*Y*a  ==  A   (mod |n|)
634
		 */
635
636
		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
637
	 	 * BN_div_no_branch will be called eventually.
638
	 	 */
639
		pA = &local_A;
640
3603446
		BN_with_flags(pA, A, BN_FLG_CONSTTIME);
641
642
		/* (D, M) := (A/B, A%B) ... */
643
3603446
		if (!BN_div_ct(D, M, pA, B, ctx))
644
			goto err;
645
646
		/* Now
647
		 *      A = D*B + M;
648
		 * thus we have
649
		 * (**)  sign*Y*a  ==  D*B + M   (mod |n|).
650
		 */
651
		tmp = A; /* keep the BIGNUM object, the value does not matter */
652
653
		/* (A, B) := (B, A mod B) ... */
654
		A = B;
655
		B = M;
656
		/* ... so we have  0 <= B < A  again */
657
658
		/* Since the former  M  is now  B  and the former  B  is now  A,
659
		 * (**) translates into
660
		 *       sign*Y*a  ==  D*A + B    (mod |n|),
661
		 * i.e.
662
		 *       sign*Y*a - D*A  ==  B    (mod |n|).
663
		 * Similarly, (*) translates into
664
		 *      -sign*X*a  ==  A          (mod |n|).
665
		 *
666
		 * Thus,
667
		 *   sign*Y*a + D*sign*X*a  ==  B  (mod |n|),
668
		 * i.e.
669
		 *        sign*(Y + D*X)*a  ==  B  (mod |n|).
670
		 *
671
		 * So if we set  (X, Y, sign) := (Y + D*X, X, -sign),  we arrive back at
672
		 *      -sign*X*a  ==  B   (mod |n|),
673
		 *       sign*Y*a  ==  A   (mod |n|).
674
		 * Note that  X  and  Y  stay non-negative all the time.
675
		 */
676
677
3603446
		if (!BN_mul(tmp, D, X, ctx))
678
			goto err;
679
3603446
		if (!BN_add(tmp, tmp, Y))
680
			goto err;
681
682
		M = Y; /* keep the BIGNUM object, the value does not matter */
683
		Y = X;
684
		X = tmp;
685
3603446
		sign = -sign;
686
3603446
	}
687
688
	/*
689
	 * The while loop (Euclid's algorithm) ends when
690
	 *      A == gcd(a,n);
691
	 * we have
692
	 *       sign*Y*a  ==  A  (mod |n|),
693
	 * where  Y  is non-negative.
694
	 */
695
696
42595
	if (sign < 0) {
697
20313
		if (!BN_sub(Y, n, Y))
698
			goto err;
699
	}
700
	/* Now  Y*a  ==  A  (mod |n|).  */
701
702

127782
	if (BN_is_one(A)) {
703
		/* Y*a == 1  (mod |n|) */
704

85184
		if (!Y->neg && BN_ucmp(Y, n) < 0) {
705
42528
			if (!BN_copy(R, Y))
706
				goto err;
707
		} else {
708
64
			if (!BN_nnmod(R, Y, n, ctx))
709
				goto err;
710
		}
711
	} else {
712
3
		BNerror(BN_R_NO_INVERSE);
713
3
		goto err;
714
	}
715
42592
	ret = R;
716
717
err:
718
42598
	if ((ret == NULL) && (in == NULL))
719
		BN_free(R);
720
42598
	BN_CTX_end(ctx);
721
	bn_check_top(ret);
722
42598
	return (ret);
723
42598
}
724
725
/*
726
 * BN_gcd_no_branch is a special version of BN_mod_inverse_no_branch.
727
 * that returns the GCD.
728
 */
729
static BIGNUM *
730
BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
731
    BN_CTX *ctx)
732
{
733
	BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
734
76
	BIGNUM local_A, local_B;
735
	BIGNUM *pA, *pB;
736
	BIGNUM *ret = NULL;
737
	int sign;
738
739
38
	if (in == NULL)
740
		goto err;
741
	R = in;
742
743
	bn_check_top(a);
744
	bn_check_top(n);
745
746
38
	BN_CTX_start(ctx);
747
38
	if ((A = BN_CTX_get(ctx)) == NULL)
748
		goto err;
749
38
	if ((B = BN_CTX_get(ctx)) == NULL)
750
		goto err;
751
38
	if ((X = BN_CTX_get(ctx)) == NULL)
752
		goto err;
753
38
	if ((D = BN_CTX_get(ctx)) == NULL)
754
		goto err;
755
38
	if ((M = BN_CTX_get(ctx)) == NULL)
756
		goto err;
757
38
	if ((Y = BN_CTX_get(ctx)) == NULL)
758
		goto err;
759
38
	if ((T = BN_CTX_get(ctx)) == NULL)
760
		goto err;
761
762
38
	BN_one(X);
763
38
	BN_zero(Y);
764
38
	if (BN_copy(B, a) == NULL)
765
		goto err;
766
38
	if (BN_copy(A, n) == NULL)
767
		goto err;
768
38
	A->neg = 0;
769
770

76
	if (B->neg || (BN_ucmp(B, A) >= 0)) {
771
		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
772
	 	 * BN_div_no_branch will be called eventually.
773
	 	 */
774
		pB = &local_B;
775
38
		BN_with_flags(pB, B, BN_FLG_CONSTTIME);
776
38
		if (!BN_nnmod(B, pB, A, ctx))
777
			goto err;
778
	}
779
	sign = -1;
780
	/* From  B = a mod |n|,  A = |n|  it follows that
781
	 *
782
	 *      0 <= B < A,
783
	 *     -sign*X*a  ==  B   (mod |n|),
784
	 *      sign*Y*a  ==  A   (mod |n|).
785
	 */
786
787
3052
	while (!BN_is_zero(B)) {
788
		BIGNUM *tmp;
789
790
		/*
791
		 *      0 < B < A,
792
		 * (*) -sign*X*a  ==  B   (mod |n|),
793
		 *      sign*Y*a  ==  A   (mod |n|)
794
		 */
795
796
		/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
797
	 	 * BN_div_no_branch will be called eventually.
798
	 	 */
799
		pA = &local_A;
800
1488
		BN_with_flags(pA, A, BN_FLG_CONSTTIME);
801
802
		/* (D, M) := (A/B, A%B) ... */
803
1488
		if (!BN_div_ct(D, M, pA, B, ctx))
804
			goto err;
805
806
		/* Now
807
		 *      A = D*B + M;
808
		 * thus we have
809
		 * (**)  sign*Y*a  ==  D*B + M   (mod |n|).
810
		 */
811
		tmp = A; /* keep the BIGNUM object, the value does not matter */
812
813
		/* (A, B) := (B, A mod B) ... */
814
		A = B;
815
		B = M;
816
		/* ... so we have  0 <= B < A  again */
817
818
		/* Since the former  M  is now  B  and the former  B  is now  A,
819
		 * (**) translates into
820
		 *       sign*Y*a  ==  D*A + B    (mod |n|),
821
		 * i.e.
822
		 *       sign*Y*a - D*A  ==  B    (mod |n|).
823
		 * Similarly, (*) translates into
824
		 *      -sign*X*a  ==  A          (mod |n|).
825
		 *
826
		 * Thus,
827
		 *   sign*Y*a + D*sign*X*a  ==  B  (mod |n|),
828
		 * i.e.
829
		 *        sign*(Y + D*X)*a  ==  B  (mod |n|).
830
		 *
831
		 * So if we set  (X, Y, sign) := (Y + D*X, X, -sign),  we arrive back at
832
		 *      -sign*X*a  ==  B   (mod |n|),
833
		 *       sign*Y*a  ==  A   (mod |n|).
834
		 * Note that  X  and  Y  stay non-negative all the time.
835
		 */
836
837
1488
		if (!BN_mul(tmp, D, X, ctx))
838
			goto err;
839
1488
		if (!BN_add(tmp, tmp, Y))
840
			goto err;
841
842
		M = Y; /* keep the BIGNUM object, the value does not matter */
843
		Y = X;
844
		X = tmp;
845
1488
		sign = -sign;
846
1488
	}
847
848
	/*
849
	 * The while loop (Euclid's algorithm) ends when
850
	 *      A == gcd(a,n);
851
	 */
852
853
38
	if (!BN_copy(R, A))
854
		goto err;
855
38
	ret = R;
856
err:
857
38
	if ((ret == NULL) && (in == NULL))
858
		BN_free(R);
859
38
	BN_CTX_end(ctx);
860
	bn_check_top(ret);
861
38
	return (ret);
862
38
}