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/*
* Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <assert.h>
#include "internal/cryptlib.h"
#include "bn_local.h"
int BN_lshift1(BIGNUM *r, const BIGNUM *a)
{
register BN_ULONG *ap, *rp, t, c;
int i;
bn_check_top(r);
bn_check_top(a);
if (r != a) {
r->neg = a->neg;
if (bn_wexpand(r, a->top + 1) == NULL)
return 0;
r->top = a->top;
} else {
if (bn_wexpand(r, a->top + 1) == NULL)
return 0;
}
ap = a->d;
rp = r->d;
c = 0;
for (i = 0; i < a->top; i++) {
t = *(ap++);
*(rp++) = ((t << 1) | c) & BN_MASK2;
c = t >> (BN_BITS2 - 1);
}
*rp = c;
r->top += c;
bn_check_top(r);
return 1;
}
int BN_rshift1(BIGNUM *r, const BIGNUM *a)
{
BN_ULONG *ap, *rp, t, c;
int i;
bn_check_top(r);
bn_check_top(a);
if (BN_is_zero(a)) {
BN_zero(r);
return 1;
}
i = a->top;
ap = a->d;
if (a != r) {
if (bn_wexpand(r, i) == NULL)
return 0;
r->neg = a->neg;
}
rp = r->d;
r->top = i;
t = ap[--i];
rp[i] = t >> 1;
c = t << (BN_BITS2 - 1);
r->top -= (t == 1);
while (i > 0) {
t = ap[--i];
rp[i] = ((t >> 1) & BN_MASK2) | c;
c = t << (BN_BITS2 - 1);
}
if (!r->top)
r->neg = 0; /* don't allow negative zero */
bn_check_top(r);
return 1;
}
int BN_lshift(BIGNUM *r, const BIGNUM *a, int n)
{
int ret;
if (n < 0) {
BNerr(BN_F_BN_LSHIFT, BN_R_INVALID_SHIFT);
return 0;
}
ret = bn_lshift_fixed_top(r, a, n);
bn_correct_top(r);
bn_check_top(r);
return ret;
}
/*
* In respect to shift factor the execution time is invariant of
* |n % BN_BITS2|, but not |n / BN_BITS2|. Or in other words pre-condition
* for constant-time-ness is |n < BN_BITS2| or |n / BN_BITS2| being
* non-secret.
*/
int bn_lshift_fixed_top(BIGNUM *r, const BIGNUM *a, int n)
{
int i, nw;
unsigned int lb, rb;
BN_ULONG *t, *f;
BN_ULONG l, m, rmask = 0;
assert(n >= 0);
bn_check_top(r);
bn_check_top(a);
nw = n / BN_BITS2;
if (bn_wexpand(r, a->top + nw + 1) == NULL)
return 0;
if (a->top != 0) {
lb = (unsigned int)n % BN_BITS2;
rb = BN_BITS2 - lb;
rb %= BN_BITS2; /* say no to undefined behaviour */
rmask = (BN_ULONG)0 - rb; /* rmask = 0 - (rb != 0) */
rmask |= rmask >> 8;
f = &(a->d[0]);
t = &(r->d[nw]);
l = f[a->top - 1];
t[a->top] = (l >> rb) & rmask;
for (i = a->top - 1; i > 0; i--) {
m = l << lb;
l = f[i - 1];
t[i] = (m | ((l >> rb) & rmask)) & BN_MASK2;
}
t[0] = (l << lb) & BN_MASK2;
} else {
/* shouldn't happen, but formally required */
r->d[nw] = 0;
}
if (nw != 0)
memset(r->d, 0, sizeof(*t) * nw);
r->neg = a->neg;
r->top = a->top + nw + 1;
r->flags |= BN_FLG_FIXED_TOP;
return 1;
}
int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
{
int ret = 0;
if (n < 0) {
BNerr(BN_F_BN_RSHIFT, BN_R_INVALID_SHIFT);
return 0;
}
ret = bn_rshift_fixed_top(r, a, n);
bn_correct_top(r);
bn_check_top(r);
return ret;
}
/*
* In respect to shift factor the execution time is invariant of
* |n % BN_BITS2|, but not |n / BN_BITS2|. Or in other words pre-condition
* for constant-time-ness for sufficiently[!] zero-padded inputs is
* |n < BN_BITS2| or |n / BN_BITS2| being non-secret.
*/
int bn_rshift_fixed_top(BIGNUM *r, const BIGNUM *a, int n)
{
int i, top, nw;
unsigned int lb, rb;
BN_ULONG *t, *f;
BN_ULONG l, m, mask;
bn_check_top(r);
bn_check_top(a);
assert(n >= 0);
nw = n / BN_BITS2;
if (nw >= a->top) {
/* shouldn't happen, but formally required */
BN_zero(r);
return 1;
}
rb = (unsigned int)n % BN_BITS2;
lb = BN_BITS2 - rb;
lb %= BN_BITS2; /* say no to undefined behaviour */
mask = (BN_ULONG)0 - lb; /* mask = 0 - (lb != 0) */
mask |= mask >> 8;
top = a->top - nw;
if (r != a && bn_wexpand(r, top) == NULL)
return 0;
t = &(r->d[0]);
f = &(a->d[nw]);
l = f[0];
for (i = 0; i < top - 1; i++) {
m = f[i + 1];
t[i] = (l >> rb) | ((m << lb) & mask);
l = m;
}
t[i] = l >> rb;
r->neg = a->neg;
r->top = top;
r->flags |= BN_FLG_FIXED_TOP;
return 1;
}
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