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/* const-time.h - Constant-time functions
* Copyright (C) 2023 g10 Code GmbH
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <https://www.gnu.org/licenses/>.
*/
#ifndef GCRY_CONST_TIME_H
#define GCRY_CONST_TIME_H
#include "types.h"
#define ct_not_memequal _gcry_ct_not_memequal
#define ct_memequal _gcry_ct_memequal
#define ct_memmov_cond _gcry_ct_memmov_cond
#ifndef HAVE_GCC_ASM_VOLATILE_MEMORY
extern volatile unsigned int _gcry_ct_vzero;
extern volatile unsigned int _gcry_ct_vone;
#endif
/*
* Return 0 if A is 0 and return 1 otherwise.
*/
static inline unsigned int
ct_is_not_zero (unsigned int a)
{
/* Sign bit set if A != 0. */
a = a | (-a);
return a >> (sizeof(unsigned int) * 8 - 1);
}
/*
* Return 1 if A is 0 and return 0 otherwise.
*/
static inline unsigned int
ct_is_zero (unsigned int a)
{
/* Sign bit set if A == 0. */
a = ~a & ~(-a);
return a >> (sizeof(unsigned int) * 8 - 1);
}
/*
* Return 1 if it's not same, 0 if same.
*/
static inline unsigned int
ct_not_equal_byte (unsigned char b0, unsigned char b1)
{
unsigned int diff;
diff = b0;
diff ^= b1;
return (0U - diff) >> (sizeof (unsigned int)*8 - 1);
}
/* Compare byte-arrays of length LEN, return 1 if it's not same, 0
otherwise. We use pointer of void *, so that it can be used with
any structure. */
unsigned int _gcry_ct_not_memequal (const void *b1, const void *b2, size_t len);
/* Compare byte-arrays of length LEN, return 0 if it's not same, 1
otherwise. We use pointer of void *, so that it can be used with
any structure. */
unsigned int _gcry_ct_memequal (const void *b1, const void *b2, size_t len);
/*
* Return all bits set if A is 1 and return 0 otherwise.
*/
#ifdef HAVE_GCC_ASM_VOLATILE_MEMORY
# define DEFINE_CT_TYPE_GEN_MASK(name, type) \
static inline type \
ct_##name##_gen_mask (unsigned long op_enable) \
{ \
type mask = -(type)op_enable; \
asm volatile ("\n" : "+r" (mask) :: "memory"); \
return mask; \
}
#else
# define DEFINE_CT_TYPE_GEN_MASK(name, type) \
static inline type \
ct_##name##_gen_mask (unsigned long op_enable) \
{ \
type mask = (type)_gcry_ct_vzero - (type)op_enable; \
return mask; \
}
#endif
DEFINE_CT_TYPE_GEN_MASK(uintptr, uintptr_t)
DEFINE_CT_TYPE_GEN_MASK(ulong, unsigned long)
/*
* Return all bits set if A is 0 and return 1 otherwise.
*/
#ifdef HAVE_GCC_ASM_VOLATILE_MEMORY
# define DEFINE_CT_TYPE_GEN_INV_MASK(name, type) \
static inline type \
ct_##name##_gen_inv_mask (unsigned long op_enable) \
{ \
type mask = (type)op_enable - (type)1; \
asm volatile ("\n" : "+r" (mask) :: "memory"); \
return mask; \
}
#else
# define DEFINE_CT_TYPE_GEN_INV_MASK(name, type) \
static inline type \
ct_##name##_gen_inv_mask (unsigned long op_enable) \
{ \
type mask = (type)op_enable - (type)_gcry_ct_vone; \
return mask; \
}
#endif
DEFINE_CT_TYPE_GEN_INV_MASK(uintptr, uintptr_t)
DEFINE_CT_TYPE_GEN_INV_MASK(ulong, unsigned long)
/*
* Return A when OP_ENABLED=1
* otherwise, return B
*/
#define DEFINE_CT_TYPE_SELECT_FUNC(name, type) \
static inline type \
ct_##name##_select (type a, type b, unsigned long op_enable) \
{ \
type mask_b = ct_##name##_gen_inv_mask(op_enable); \
type mask_a = ct_##name##_gen_mask(op_enable); \
return (mask_a & a) | (mask_b & b); \
}
DEFINE_CT_TYPE_SELECT_FUNC(uintptr, uintptr_t)
DEFINE_CT_TYPE_SELECT_FUNC(ulong, unsigned long)
/*
* Return NULL when OP_ENABLED=1
* otherwise, return W
*/
static inline gcry_sexp_t
sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
{
uintptr_t o = ct_uintptr_select((uintptr_t)NULL, (uintptr_t)w, op_enable);
return (gcry_sexp_t)(void *)o;
}
/*
* Copy LEN bytes from memory area SRC to memory area DST, when
* OP_ENABLED=1. When DST <= SRC, the memory areas may overlap. When
* DST > SRC, the memory areas must not overlap.
*/
void _gcry_ct_memmov_cond (void *dst, const void *src, size_t len,
unsigned long op_enable);
#endif /*GCRY_CONST_TIME_H*/

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