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openssl1.0/crypto/bn/bn_lib.c
Mario Fetka 33f8b6874c Imported Upstream version 1.0.2s
2019-08-09 10:00:55 +02:00

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/* crypto/bn/bn_lib.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
* All rights reserved.
*
* This package is an SSL implementation written
* by Eric Young (eay@cryptsoft.com).
* The implementation was written so as to conform with Netscapes SSL.
*
* This library is free for commercial and non-commercial use as long as
* the following conditions are aheared to. The following conditions
* apply to all code found in this distribution, be it the RC4, RSA,
* lhash, DES, etc., code; not just the SSL code. The SSL documentation
* included with this distribution is covered by the same copyright terms
* except that the holder is Tim Hudson (tjh@cryptsoft.com).
*
* Copyright remains Eric Young's, and as such any Copyright notices in
* the code are not to be removed.
* If this package is used in a product, Eric Young should be given attribution
* as the author of the parts of the library used.
* This can be in the form of a textual message at program startup or
* in documentation (online or textual) provided with the package.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* "This product includes cryptographic software written by
* Eric Young (eay@cryptsoft.com)"
* The word 'cryptographic' can be left out if the rouines from the library
* being used are not cryptographic related :-).
* 4. If you include any Windows specific code (or a derivative thereof) from
* the apps directory (application code) you must include an acknowledgement:
* "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
*
* THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* The licence and distribution terms for any publically available version or
* derivative of this code cannot be changed. i.e. this code cannot simply be
* copied and put under another distribution licence
* [including the GNU Public Licence.]
*/
#ifndef BN_DEBUG
# undef NDEBUG /* avoid conflicting definitions */
# define NDEBUG
#endif
#include <assert.h>
#include <limits.h>
#include <stdio.h>
#include "cryptlib.h"
#include "bn_lcl.h"
const char BN_version[] = "Big Number" OPENSSL_VERSION_PTEXT;
/* This stuff appears to be completely unused, so is deprecated */
#ifndef OPENSSL_NO_DEPRECATED
/*-
* For a 32 bit machine
* 2 - 4 == 128
* 3 - 8 == 256
* 4 - 16 == 512
* 5 - 32 == 1024
* 6 - 64 == 2048
* 7 - 128 == 4096
* 8 - 256 == 8192
*/
static int bn_limit_bits = 0;
static int bn_limit_num = 8; /* (1<<bn_limit_bits) */
static int bn_limit_bits_low = 0;
static int bn_limit_num_low = 8; /* (1<<bn_limit_bits_low) */
static int bn_limit_bits_high = 0;
static int bn_limit_num_high = 8; /* (1<<bn_limit_bits_high) */
static int bn_limit_bits_mont = 0;
static int bn_limit_num_mont = 8; /* (1<<bn_limit_bits_mont) */
void BN_set_params(int mult, int high, int low, int mont)
{
if (mult >= 0) {
if (mult > (int)(sizeof(int) * 8) - 1)
mult = sizeof(int) * 8 - 1;
bn_limit_bits = mult;
bn_limit_num = 1 << mult;
}
if (high >= 0) {
if (high > (int)(sizeof(int) * 8) - 1)
high = sizeof(int) * 8 - 1;
bn_limit_bits_high = high;
bn_limit_num_high = 1 << high;
}
if (low >= 0) {
if (low > (int)(sizeof(int) * 8) - 1)
low = sizeof(int) * 8 - 1;
bn_limit_bits_low = low;
bn_limit_num_low = 1 << low;
}
if (mont >= 0) {
if (mont > (int)(sizeof(int) * 8) - 1)
mont = sizeof(int) * 8 - 1;
bn_limit_bits_mont = mont;
bn_limit_num_mont = 1 << mont;
}
}
int BN_get_params(int which)
{
if (which == 0)
return (bn_limit_bits);
else if (which == 1)
return (bn_limit_bits_high);
else if (which == 2)
return (bn_limit_bits_low);
else if (which == 3)
return (bn_limit_bits_mont);
else
return (0);
}
#endif
const BIGNUM *BN_value_one(void)
{
static const BN_ULONG data_one = 1L;
static const BIGNUM const_one =
{ (BN_ULONG *)&data_one, 1, 1, 0, BN_FLG_STATIC_DATA };
return (&const_one);
}
int BN_num_bits_word(BN_ULONG l)
{
BN_ULONG x, mask;
int bits = (l != 0);
#if BN_BITS2 > 32
x = l >> 32;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 32 & mask;
l ^= (x ^ l) & mask;
#endif
x = l >> 16;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 16 & mask;
l ^= (x ^ l) & mask;
x = l >> 8;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 8 & mask;
l ^= (x ^ l) & mask;
x = l >> 4;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 4 & mask;
l ^= (x ^ l) & mask;
x = l >> 2;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 2 & mask;
l ^= (x ^ l) & mask;
x = l >> 1;
mask = (0 - x) & BN_MASK2;
mask = (0 - (mask >> (BN_BITS2 - 1)));
bits += 1 & mask;
return bits;
}
int BN_num_bits(const BIGNUM *a)
{
int i = a->top - 1;
bn_check_top(a);
if (BN_is_zero(a))
return 0;
return ((i * BN_BITS2) + BN_num_bits_word(a->d[i]));
}
void BN_clear_free(BIGNUM *a)
{
int i;
if (a == NULL)
return;
bn_check_top(a);
if (a->d != NULL) {
OPENSSL_cleanse(a->d, a->dmax * sizeof(a->d[0]));
if (!(BN_get_flags(a, BN_FLG_STATIC_DATA)))
OPENSSL_free(a->d);
}
i = BN_get_flags(a, BN_FLG_MALLOCED);
OPENSSL_cleanse(a, sizeof(BIGNUM));
if (i)
OPENSSL_free(a);
}
void BN_free(BIGNUM *a)
{
if (a == NULL)
return;
bn_check_top(a);
if ((a->d != NULL) && !(BN_get_flags(a, BN_FLG_STATIC_DATA)))
OPENSSL_free(a->d);
if (a->flags & BN_FLG_MALLOCED)
OPENSSL_free(a);
else {
#ifndef OPENSSL_NO_DEPRECATED
a->flags |= BN_FLG_FREE;
#endif
a->d = NULL;
}
}
void BN_init(BIGNUM *a)
{
memset(a, 0, sizeof(BIGNUM));
bn_check_top(a);
}
BIGNUM *BN_new(void)
{
BIGNUM *ret;
if ((ret = (BIGNUM *)OPENSSL_malloc(sizeof(BIGNUM))) == NULL) {
BNerr(BN_F_BN_NEW, ERR_R_MALLOC_FAILURE);
return (NULL);
}
ret->flags = BN_FLG_MALLOCED;
ret->top = 0;
ret->neg = 0;
ret->dmax = 0;
ret->d = NULL;
bn_check_top(ret);
return (ret);
}
/* This is used both by bn_expand2() and bn_dup_expand() */
/* The caller MUST check that words > b->dmax before calling this */
static BN_ULONG *bn_expand_internal(const BIGNUM *b, int words)
{
BN_ULONG *A, *a = NULL;
const BN_ULONG *B;
int i;
if (words > (INT_MAX / (4 * BN_BITS2))) {
BNerr(BN_F_BN_EXPAND_INTERNAL, BN_R_BIGNUM_TOO_LONG);
return NULL;
}
if (BN_get_flags(b, BN_FLG_STATIC_DATA)) {
BNerr(BN_F_BN_EXPAND_INTERNAL, BN_R_EXPAND_ON_STATIC_BIGNUM_DATA);
return (NULL);
}
a = A = (BN_ULONG *)OPENSSL_malloc(sizeof(BN_ULONG) * words);
if (A == NULL) {
BNerr(BN_F_BN_EXPAND_INTERNAL, ERR_R_MALLOC_FAILURE);
return (NULL);
}
#ifdef PURIFY
/*
* Valgrind complains in BN_consttime_swap because we process the whole
* array even if it's not initialised yet. This doesn't matter in that
* function - what's important is constant time operation (we're not
* actually going to use the data)
*/
memset(a, 0, sizeof(BN_ULONG) * words);
#endif
#if 1
B = b->d;
/* Check if the previous number needs to be copied */
if (B != NULL) {
for (i = b->top >> 2; i > 0; i--, A += 4, B += 4) {
/*
* The fact that the loop is unrolled
* 4-wise is a tribute to Intel. It's
* the one that doesn't have enough
* registers to accomodate more data.
* I'd unroll it 8-wise otherwise:-)
*
* <appro@fy.chalmers.se>
*/
BN_ULONG a0, a1, a2, a3;
a0 = B[0];
a1 = B[1];
a2 = B[2];
a3 = B[3];
A[0] = a0;
A[1] = a1;
A[2] = a2;
A[3] = a3;
}
/*
* workaround for ultrix cc: without 'case 0', the optimizer does
* the switch table by doing a=top&3; a--; goto jump_table[a];
* which fails for top== 0
*/
switch (b->top & 3) {
case 3:
A[2] = B[2];
case 2:
A[1] = B[1];
case 1:
A[0] = B[0];
case 0:
;
}
}
#else
memset(A, 0, sizeof(BN_ULONG) * words);
memcpy(A, b->d, sizeof(b->d[0]) * b->top);
#endif
return (a);
}
/*
* This is an internal function that can be used instead of bn_expand2() when
* there is a need to copy BIGNUMs instead of only expanding the data part,
* while still expanding them. Especially useful when needing to expand
* BIGNUMs that are declared 'const' and should therefore not be changed. The
* reason to use this instead of a BN_dup() followed by a bn_expand2() is
* memory allocation overhead. A BN_dup() followed by a bn_expand2() will
* allocate new memory for the BIGNUM data twice, and free it once, while
* bn_dup_expand() makes sure allocation is made only once.
*/
#ifndef OPENSSL_NO_DEPRECATED
BIGNUM *bn_dup_expand(const BIGNUM *b, int words)
{
BIGNUM *r = NULL;
bn_check_top(b);
/*
* This function does not work if words <= b->dmax && top < words because
* BN_dup() does not preserve 'dmax'! (But bn_dup_expand() is not used
* anywhere yet.)
*/
if (words > b->dmax) {
BN_ULONG *a = bn_expand_internal(b, words);
if (a) {
r = BN_new();
if (r) {
r->top = b->top;
r->dmax = words;
r->neg = b->neg;
r->d = a;
} else {
/* r == NULL, BN_new failure */
OPENSSL_free(a);
}
}
/*
* If a == NULL, there was an error in allocation in
* bn_expand_internal(), and NULL should be returned
*/
} else {
r = BN_dup(b);
}
bn_check_top(r);
return r;
}
#endif
/*
* This is an internal function that should not be used in applications. It
* ensures that 'b' has enough room for a 'words' word number and initialises
* any unused part of b->d with leading zeros. It is mostly used by the
* various BIGNUM routines. If there is an error, NULL is returned. If not,
* 'b' is returned.
*/
BIGNUM *bn_expand2(BIGNUM *b, int words)
{
if (words > b->dmax) {
BN_ULONG *a = bn_expand_internal(b, words);
if (!a)
return NULL;
if (b->d)
OPENSSL_free(b->d);
b->d = a;
b->dmax = words;
}
/* None of this should be necessary because of what b->top means! */
#if 0
/*
* NB: bn_wexpand() calls this only if the BIGNUM really has to grow
*/
if (b->top < b->dmax) {
int i;
BN_ULONG *A = &(b->d[b->top]);
for (i = (b->dmax - b->top) >> 3; i > 0; i--, A += 8) {
A[0] = 0;
A[1] = 0;
A[2] = 0;
A[3] = 0;
A[4] = 0;
A[5] = 0;
A[6] = 0;
A[7] = 0;
}
for (i = (b->dmax - b->top) & 7; i > 0; i--, A++)
A[0] = 0;
assert(A == &(b->d[b->dmax]));
}
#endif
return b;
}
BIGNUM *BN_dup(const BIGNUM *a)
{
BIGNUM *t;
if (a == NULL)
return NULL;
bn_check_top(a);
t = BN_new();
if (t == NULL)
return NULL;
if (!BN_copy(t, a)) {
BN_free(t);
return NULL;
}
bn_check_top(t);
return t;
}
BIGNUM *BN_copy(BIGNUM *a, const BIGNUM *b)
{
int i;
BN_ULONG *A;
const BN_ULONG *B;
bn_check_top(b);
if (a == b)
return (a);
if (bn_wexpand(a, b->top) == NULL)
return (NULL);
#if 1
A = a->d;
B = b->d;
for (i = b->top >> 2; i > 0; i--, A += 4, B += 4) {
BN_ULONG a0, a1, a2, a3;
a0 = B[0];
a1 = B[1];
a2 = B[2];
a3 = B[3];
A[0] = a0;
A[1] = a1;
A[2] = a2;
A[3] = a3;
}
/* ultrix cc workaround, see comments in bn_expand_internal */
switch (b->top & 3) {
case 3:
A[2] = B[2];
case 2:
A[1] = B[1];
case 1:
A[0] = B[0];
case 0:;
}
#else
memcpy(a->d, b->d, sizeof(b->d[0]) * b->top);
#endif
a->neg = b->neg;
a->top = b->top;
a->flags |= b->flags & BN_FLG_FIXED_TOP;
bn_check_top(a);
return (a);
}
#define FLAGS_DATA(flags) ((flags) & (BN_FLG_STATIC_DATA \
| BN_FLG_CONSTTIME \
| BN_FLG_FIXED_TOP))
#define FLAGS_STRUCT(flags) ((flags) & (BN_FLG_MALLOCED))
void BN_swap(BIGNUM *a, BIGNUM *b)
{
int flags_old_a, flags_old_b;
BN_ULONG *tmp_d;
int tmp_top, tmp_dmax, tmp_neg;
bn_check_top(a);
bn_check_top(b);
flags_old_a = a->flags;
flags_old_b = b->flags;
tmp_d = a->d;
tmp_top = a->top;
tmp_dmax = a->dmax;
tmp_neg = a->neg;
a->d = b->d;
a->top = b->top;
a->dmax = b->dmax;
a->neg = b->neg;
b->d = tmp_d;
b->top = tmp_top;
b->dmax = tmp_dmax;
b->neg = tmp_neg;
a->flags = FLAGS_STRUCT(flags_old_a) | FLAGS_DATA(flags_old_b);
b->flags = FLAGS_STRUCT(flags_old_b) | FLAGS_DATA(flags_old_a);
bn_check_top(a);
bn_check_top(b);
}
void BN_clear(BIGNUM *a)
{
bn_check_top(a);
if (a->d != NULL)
OPENSSL_cleanse(a->d, a->dmax * sizeof(a->d[0]));
a->top = 0;
a->neg = 0;
a->flags &= ~BN_FLG_FIXED_TOP;
}
BN_ULONG BN_get_word(const BIGNUM *a)
{
if (a->top > 1)
return BN_MASK2;
else if (a->top == 1)
return a->d[0];
/* a->top == 0 */
return 0;
}
int BN_set_word(BIGNUM *a, BN_ULONG w)
{
bn_check_top(a);
if (bn_expand(a, (int)sizeof(BN_ULONG) * 8) == NULL)
return (0);
a->neg = 0;
a->d[0] = w;
a->top = (w ? 1 : 0);
a->flags &= ~BN_FLG_FIXED_TOP;
bn_check_top(a);
return (1);
}
BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
{
unsigned int i, m;
unsigned int n;
BN_ULONG l;
BIGNUM *bn = NULL;
if (ret == NULL)
ret = bn = BN_new();
if (ret == NULL)
return (NULL);
bn_check_top(ret);
l = 0;
n = len;
if (n == 0) {
ret->top = 0;
return (ret);
}
i = ((n - 1) / BN_BYTES) + 1;
m = ((n - 1) % (BN_BYTES));
if (bn_wexpand(ret, (int)i) == NULL) {
if (bn)
BN_free(bn);
return NULL;
}
ret->top = i;
ret->neg = 0;
while (n--) {
l = (l << 8L) | *(s++);
if (m-- == 0) {
ret->d[--i] = l;
l = 0;
m = BN_BYTES - 1;
}
}
/*
* need to call this due to clear byte at top if avoiding having the top
* bit set (-ve number)
*/
bn_correct_top(ret);
return (ret);
}
/* ignore negative */
static int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
{
int n;
size_t i, lasti, j, atop, mask;
BN_ULONG l;
/*
* In case |a| is fixed-top, BN_num_bytes can return bogus length,
* but it's assumed that fixed-top inputs ought to be "nominated"
* even for padded output, so it works out...
*/
n = BN_num_bytes(a);
if (tolen == -1) {
tolen = n;
} else if (tolen < n) { /* uncommon/unlike case */
BIGNUM temp = *a;
bn_correct_top(&temp);
n = BN_num_bytes(&temp);
if (tolen < n)
return -1;
}
/* Swipe through whole available data and don't give away padded zero. */
atop = a->dmax * BN_BYTES;
if (atop == 0) {
OPENSSL_cleanse(to, tolen);
return tolen;
}
lasti = atop - 1;
atop = a->top * BN_BYTES;
for (i = 0, j = 0, to += tolen; j < (size_t)tolen; j++) {
l = a->d[i / BN_BYTES];
mask = 0 - ((j - atop) >> (8 * sizeof(i) - 1));
*--to = (unsigned char)(l >> (8 * (i % BN_BYTES)) & mask);
i += (i - lasti) >> (8 * sizeof(i) - 1); /* stay on last limb */
}
return tolen;
}
int bn_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
{
if (tolen < 0)
return -1;
return bn2binpad(a, to, tolen);
}
int BN_bn2bin(const BIGNUM *a, unsigned char *to)
{
int n, i;
BN_ULONG l;
bn_check_top(a);
n = i = BN_num_bytes(a);
while (i--) {
l = a->d[i / BN_BYTES];
*(to++) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
}
return (n);
}
int BN_ucmp(const BIGNUM *a, const BIGNUM *b)
{
int i;
BN_ULONG t1, t2, *ap, *bp;
bn_check_top(a);
bn_check_top(b);
i = a->top - b->top;
if (i != 0)
return (i);
ap = a->d;
bp = b->d;
for (i = a->top - 1; i >= 0; i--) {
t1 = ap[i];
t2 = bp[i];
if (t1 != t2)
return ((t1 > t2) ? 1 : -1);
}
return (0);
}
int BN_cmp(const BIGNUM *a, const BIGNUM *b)
{
int i;
int gt, lt;
BN_ULONG t1, t2;
if ((a == NULL) || (b == NULL)) {
if (a != NULL)
return (-1);
else if (b != NULL)
return (1);
else
return (0);
}
bn_check_top(a);
bn_check_top(b);
if (a->neg != b->neg) {
if (a->neg)
return (-1);
else
return (1);
}
if (a->neg == 0) {
gt = 1;
lt = -1;
} else {
gt = -1;
lt = 1;
}
if (a->top > b->top)
return (gt);
if (a->top < b->top)
return (lt);
for (i = a->top - 1; i >= 0; i--) {
t1 = a->d[i];
t2 = b->d[i];
if (t1 > t2)
return (gt);
if (t1 < t2)
return (lt);
}
return (0);
}
int BN_set_bit(BIGNUM *a, int n)
{
int i, j, k;
if (n < 0)
return 0;
i = n / BN_BITS2;
j = n % BN_BITS2;
if (a->top <= i) {
if (bn_wexpand(a, i + 1) == NULL)
return (0);
for (k = a->top; k < i + 1; k++)
a->d[k] = 0;
a->top = i + 1;
a->flags &= ~BN_FLG_FIXED_TOP;
}
a->d[i] |= (((BN_ULONG)1) << j);
bn_check_top(a);
return (1);
}
int BN_clear_bit(BIGNUM *a, int n)
{
int i, j;
bn_check_top(a);
if (n < 0)
return 0;
i = n / BN_BITS2;
j = n % BN_BITS2;
if (a->top <= i)
return (0);
a->d[i] &= (~(((BN_ULONG)1) << j));
bn_correct_top(a);
return (1);
}
int BN_is_bit_set(const BIGNUM *a, int n)
{
int i, j;
bn_check_top(a);
if (n < 0)
return 0;
i = n / BN_BITS2;
j = n % BN_BITS2;
if (a->top <= i)
return 0;
return (int)(((a->d[i]) >> j) & ((BN_ULONG)1));
}
int BN_mask_bits(BIGNUM *a, int n)
{
int b, w;
bn_check_top(a);
if (n < 0)
return 0;
w = n / BN_BITS2;
b = n % BN_BITS2;
if (w >= a->top)
return 0;
if (b == 0)
a->top = w;
else {
a->top = w + 1;
a->d[w] &= ~(BN_MASK2 << b);
}
bn_correct_top(a);
return (1);
}
void BN_set_negative(BIGNUM *a, int b)
{
if (b && !BN_is_zero(a))
a->neg = 1;
else
a->neg = 0;
}
int bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n)
{
int i;
BN_ULONG aa, bb;
if (n == 0)
return 0;
aa = a[n - 1];
bb = b[n - 1];
if (aa != bb)
return ((aa > bb) ? 1 : -1);
for (i = n - 2; i >= 0; i--) {
aa = a[i];
bb = b[i];
if (aa != bb)
return ((aa > bb) ? 1 : -1);
}
return (0);
}
/*
* Here follows a specialised variants of bn_cmp_words(). It has the
* property of performing the operation on arrays of different sizes. The
* sizes of those arrays is expressed through cl, which is the common length
* ( basicall, min(len(a),len(b)) ), and dl, which is the delta between the
* two lengths, calculated as len(a)-len(b). All lengths are the number of
* BN_ULONGs...
*/
int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b, int cl, int dl)
{
int n, i;
n = cl - 1;
if (dl < 0) {
for (i = dl; i < 0; i++) {
if (b[n - i] != 0)
return -1; /* a < b */
}
}
if (dl > 0) {
for (i = dl; i > 0; i--) {
if (a[n + i] != 0)
return 1; /* a > b */
}
}
return bn_cmp_words(a, b, cl);
}
/*
* Constant-time conditional swap of a and b.
* a and b are swapped if condition is not 0. The code assumes that at most one bit of condition is set.
* nwords is the number of words to swap. The code assumes that at least nwords are allocated in both a and b,
* and that no more than nwords are used by either a or b.
* a and b cannot be the same number
*/
void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
{
BN_ULONG t;
int i;
bn_wcheck_size(a, nwords);
bn_wcheck_size(b, nwords);
assert(a != b);
assert((condition & (condition - 1)) == 0);
assert(sizeof(BN_ULONG) >= sizeof(int));
condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;
t = (a->top ^ b->top) & condition;
a->top ^= t;
b->top ^= t;
t = (a->neg ^ b->neg) & condition;
a->neg ^= t;
b->neg ^= t;
/*-
* BN_FLG_STATIC_DATA: indicates that data may not be written to. Intention
* is actually to treat it as it's read-only data, and some (if not most)
* of it does reside in read-only segment. In other words observation of
* BN_FLG_STATIC_DATA in BN_consttime_swap should be treated as fatal
* condition. It would either cause SEGV or effectively cause data
* corruption.
*
* BN_FLG_MALLOCED: refers to BN structure itself, and hence must be
* preserved.
*
* BN_FLG_SECURE: must be preserved, because it determines how x->d was
* allocated and hence how to free it.
*
* BN_FLG_CONSTTIME: sufficient to mask and swap
*
* BN_FLG_FIXED_TOP: indicates that we haven't called bn_correct_top() on
* the data, so the d array may be padded with additional 0 values (i.e.
* top could be greater than the minimal value that it could be). We should
* be swapping it
*/
#define BN_CONSTTIME_SWAP_FLAGS (BN_FLG_CONSTTIME | BN_FLG_FIXED_TOP)
t = ((a->flags ^ b->flags) & BN_CONSTTIME_SWAP_FLAGS) & condition;
a->flags ^= t;
b->flags ^= t;
#define BN_CONSTTIME_SWAP(ind) \
do { \
t = (a->d[ind] ^ b->d[ind]) & condition; \
a->d[ind] ^= t; \
b->d[ind] ^= t; \
} while (0)
switch (nwords) {
default:
for (i = 10; i < nwords; i++)
BN_CONSTTIME_SWAP(i);
/* Fallthrough */
case 10:
BN_CONSTTIME_SWAP(9); /* Fallthrough */
case 9:
BN_CONSTTIME_SWAP(8); /* Fallthrough */
case 8:
BN_CONSTTIME_SWAP(7); /* Fallthrough */
case 7:
BN_CONSTTIME_SWAP(6); /* Fallthrough */
case 6:
BN_CONSTTIME_SWAP(5); /* Fallthrough */
case 5:
BN_CONSTTIME_SWAP(4); /* Fallthrough */
case 4:
BN_CONSTTIME_SWAP(3); /* Fallthrough */
case 3:
BN_CONSTTIME_SWAP(2); /* Fallthrough */
case 2:
BN_CONSTTIME_SWAP(1); /* Fallthrough */
case 1:
BN_CONSTTIME_SWAP(0);
}
#undef BN_CONSTTIME_SWAP
}
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