constant_time_internal.h File Reference

#include <stdint.h>
#include <stddef.h>
#include "common.h"
#include "constant_time_impl.h"

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Macros
#define	MBEDTLS_CT_TRUE   ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(SIZE_MAX))
#define	MBEDTLS_CT_FALSE   ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(0))

Typedefs
typedef size_t	mbedtls_ct_condition_t
typedef size_t	mbedtls_ct_uint_t
typedef ptrdiff_t	mbedtls_ct_int_t

Functions
void	mbedtls_ct_memcpy_if (mbedtls_ct_condition_t condition, unsigned char *dest, const unsigned char *src1, const unsigned char *src2, size_t len)
void	mbedtls_ct_memcpy_offset (unsigned char *dest, const unsigned char *src, size_t offset, size_t offset_min, size_t offset_max, size_t len)

Macro Definition Documentation

MBEDTLS_CT_FALSE

#define MBEDTLS_CT_FALSE   ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(0))

MBEDTLS_CT_TRUE

#define MBEDTLS_CT_TRUE   ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(SIZE_MAX))

Typedef Documentation

mbedtls_ct_condition_t

typedef size_t mbedtls_ct_condition_t

Constant-time functions

Copyright The Mbed TLS Contributors SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later

mbedtls_ct_int_t

typedef ptrdiff_t mbedtls_ct_int_t

mbedtls_ct_uint_t

typedef size_t mbedtls_ct_uint_t

Function Documentation

mbedtls_ct_memcpy_if()

void mbedtls_ct_memcpy_if	(	mbedtls_ct_condition_t	condition,
		unsigned char *	dest,
		const unsigned char *	src1,
		const unsigned char *	src2,
		size_t	len
	)

Conditional memcpy.

Functionally equivalent to:

if (condition) { memcpy(dest, src1, len); } else { if (src2 != NULL) memcpy(dest, src2, len); }

It will always read len bytes from src1. If src2 != NULL, it will always read len bytes from src2. If src2 == NULL, it will instead read len bytes from dest (as if src2 == dest).

Parameters

condition	The condition
dest	Secret. Destination pointer.
src1	Secret. Pointer to copy from (if condition == MBEDTLS_CT_TRUE). This may be equal to dest, but may not overlap in other ways.
src2	Secret (contents only - may branch to determine if this parameter is NULL). Pointer to copy from (if condition == MBEDTLS_CT_FALSE and src2 is not NULL). May be NULL. This may be equal to dest, but may not overlap it in other ways. It may overlap with src1.
len	Number of bytes to copy.

mbedtls_ct_memcpy_offset()

void mbedtls_ct_memcpy_offset	(	unsigned char *	dest,
		const unsigned char *	src,
		size_t	offset,
		size_t	offset_min,
		size_t	offset_max,
		size_t	len
	)

Copy data from a secret position.

Functionally equivalent to:

memcpy(dst, src + offset, len)

This function copies len bytes from src + offset to dst, with a code flow and memory access pattern that does not depend on offset, but only on offset_min, offset_max and len.

Note

This function reads from dest, but the value that is read does not influence the result and this function's behavior is well-defined regardless of the contents of the buffers. This may result in false positives from static or dynamic analyzers, especially if dest is not initialized.

Parameters

dest	Secret. The destination buffer. This must point to a writable buffer of at least len bytes.
src	Secret. The base of the source buffer. This must point to a readable buffer of at least offset_max + len bytes. Shouldn't overlap with dest
offset	Secret. The offset in the source buffer from which to copy. This must be no less than offset_min and no greater than offset_max.
offset_min	The minimal value of offset.
offset_max	The maximal value of offset.
len	The number of bytes to copy.