476 lines
16 KiB
C
476 lines
16 KiB
C
/**
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* Constant-time functions
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*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef MBEDTLS_CONSTANT_TIME_INTERNAL_H
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#define MBEDTLS_CONSTANT_TIME_INTERNAL_H
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#include <stdint.h>
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#include <stddef.h>
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#include "common.h"
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#if defined(MBEDTLS_BIGNUM_C)
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#include "mbedtls/bignum.h"
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#endif
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/* The constant-time interface provides various operations that are likely
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* to result in constant-time code that does not branch or use conditional
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* instructions for secret data (for secret pointers, this also applies to
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* the data pointed to).
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*
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* It has three main parts:
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*
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* - boolean operations
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* These are all named mbedtls_ct_bool_<operation>, and operate over
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* mbedtls_ct_condition_t.
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* All arguments are considered secret.
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* example: bool x = y | z => x = mbedtls_ct_bool_or(y, z)
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*
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* - conditional data selection
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* These are all named mbedtls_ct_<type>_if and mbedtls_ct_<type>_if0
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* All arguments are considered secret.
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* example: size_t a = x ? b : c => a = mbedtls_ct_size_if(x, b, c)
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* example: unsigned a = x ? b : 0 => a = mbedtls_ct_uint_if0(x, b)
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*
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* - block memory operations
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* Only some arguments are considered secret, as documented for each
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* function.
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* example: if (x) memcpy(...) => mbedtls_ct_memcpy_if(x, ...)
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*
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* mbedtls_ct_condition_t should be treated as opaque and only manipulated
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* via the functions in this header.
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*
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* mbedtls_ct_uint_t is an unsigned integer type over which constant time
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* operations may be performed via the functions in this header. It is as big
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* as the larger of size_t and mbedtls_mpi_uint, i.e. it is safe to cast
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* to/from "unsigned int", "size_t", and "mbedtls_mpi_uint" (and any other
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* not-larger integer types).
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*
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* For Arm (32-bit, 64-bit and Thumb), x86 and x86-64, assembly implementations
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* are used to ensure that the generated code is constant time. For other
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* architectures, a plain C fallback designed to yield constant-time code (this
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* has been observed to be constant-time on latest gcc, clang and MSVC as of
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* May 2023).
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*/
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#if (SIZE_MAX > 0xffffffffffffffffULL)
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/* Pointer size > 64-bit */
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typedef size_t mbedtls_ct_condition_t;
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typedef size_t mbedtls_ct_uint_t;
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typedef ptrdiff_t mbedtls_ct_int_t;
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#define MBEDTLS_CT_TRUE ((mbedtls_ct_condition_t) SIZE_MAX)
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#elif (SIZE_MAX > 0xffffffff) || defined(MBEDTLS_HAVE_INT64)
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/* 32-bit < pointer size <= 64-bit, or 64-bit MPI */
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typedef uint64_t mbedtls_ct_condition_t;
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typedef uint64_t mbedtls_ct_uint_t;
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typedef int64_t mbedtls_ct_int_t;
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#define MBEDTLS_CT_TRUE ((mbedtls_ct_condition_t) UINT64_MAX)
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#else
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/* Pointer size <= 32-bit, and no 64-bit MPIs */
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typedef uint32_t mbedtls_ct_condition_t;
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typedef uint32_t mbedtls_ct_uint_t;
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typedef int32_t mbedtls_ct_int_t;
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#define MBEDTLS_CT_TRUE ((mbedtls_ct_condition_t) UINT32_MAX)
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#endif
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#define MBEDTLS_CT_FALSE ((mbedtls_ct_condition_t) 0)
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/* constant_time_impl.h contains all the static inline implementations,
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* so that constant_time_internal.h is more readable.
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*/
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#include "constant_time_impl.h"
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/* ============================================================================
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* Boolean operations
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*/
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/** Convert a number into a mbedtls_ct_condition_t.
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*
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* \param x Number to convert.
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*
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* \return MBEDTLS_CT_TRUE if \p x != 0, or MBEDTLS_CT_FALSE if \p x == 0
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*
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool(mbedtls_ct_uint_t x);
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/** Boolean "not equal" operation.
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*
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* Functionally equivalent to:
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*
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* \p x != \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x != \p y, otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_ne(mbedtls_ct_uint_t x, mbedtls_ct_uint_t y);
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/** Boolean "equals" operation.
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*
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* Functionally equivalent to:
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*
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* \p x == \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x == \p y, otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_eq(mbedtls_ct_uint_t x,
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mbedtls_ct_uint_t y);
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/** Boolean "less than" operation.
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*
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* Functionally equivalent to:
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*
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* \p x < \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x < \p y, otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_lt(mbedtls_ct_uint_t x, mbedtls_ct_uint_t y);
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/** Boolean "greater than" operation.
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*
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* Functionally equivalent to:
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*
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* \p x > \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x > \p y, otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_gt(mbedtls_ct_uint_t x,
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mbedtls_ct_uint_t y);
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/** Boolean "greater or equal" operation.
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*
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* Functionally equivalent to:
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*
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* \p x >= \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x >= \p y,
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* otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_ge(mbedtls_ct_uint_t x,
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mbedtls_ct_uint_t y);
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/** Boolean "less than or equal" operation.
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*
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* Functionally equivalent to:
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*
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* \p x <= \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x <= \p y,
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* otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_le(mbedtls_ct_uint_t x,
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mbedtls_ct_uint_t y);
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/** Boolean "xor" operation.
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*
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* Functionally equivalent to:
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*
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* \p x ^ \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \note This is more efficient than mbedtls_ct_bool_ne if both arguments are
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* mbedtls_ct_condition_t.
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*
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* \return MBEDTLS_CT_TRUE if \p x ^ \p y,
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* otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_xor(mbedtls_ct_condition_t x,
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mbedtls_ct_condition_t y);
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/** Boolean "and" operation.
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*
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* Functionally equivalent to:
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*
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* \p x && \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x && \p y,
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* otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_and(mbedtls_ct_condition_t x,
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mbedtls_ct_condition_t y);
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/** Boolean "or" operation.
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*
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* Functionally equivalent to:
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*
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* \p x || \p y
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*
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* \param x The first value to analyze.
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* \param y The second value to analyze.
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*
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* \return MBEDTLS_CT_TRUE if \p x || \p y,
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* otherwise MBEDTLS_CT_FALSE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_or(mbedtls_ct_condition_t x,
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mbedtls_ct_condition_t y);
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/** Boolean "not" operation.
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*
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* Functionally equivalent to:
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*
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* ! \p x
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*
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* \param x The value to invert
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*
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* \return MBEDTLS_CT_FALSE if \p x, otherwise MBEDTLS_CT_TRUE.
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*/
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static inline mbedtls_ct_condition_t mbedtls_ct_bool_not(mbedtls_ct_condition_t x);
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/* ============================================================================
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* Data selection operations
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*/
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/** Choose between two size_t values.
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*
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* Functionally equivalent to:
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*
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* condition ? if1 : if0.
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*
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* \param condition Condition to test.
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* \param if1 Value to use if \p condition == MBEDTLS_CT_TRUE.
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* \param if0 Value to use if \p condition == MBEDTLS_CT_FALSE.
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*
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* \return \c if1 if \p condition == MBEDTLS_CT_TRUE, otherwise \c if0.
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*/
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static inline size_t mbedtls_ct_size_if(mbedtls_ct_condition_t condition,
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size_t if1,
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size_t if0);
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/** Choose between two unsigned values.
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*
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* Functionally equivalent to:
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*
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* condition ? if1 : if0.
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*
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* \param condition Condition to test.
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* \param if1 Value to use if \p condition == MBEDTLS_CT_TRUE.
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* \param if0 Value to use if \p condition == MBEDTLS_CT_FALSE.
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*
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* \return \c if1 if \p condition == MBEDTLS_CT_TRUE, otherwise \c if0.
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*/
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static inline unsigned mbedtls_ct_uint_if(mbedtls_ct_condition_t condition,
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unsigned if1,
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unsigned if0);
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#if defined(MBEDTLS_BIGNUM_C)
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/** Choose between two mbedtls_mpi_uint values.
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*
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* Functionally equivalent to:
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*
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* condition ? if1 : if0.
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*
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* \param condition Condition to test.
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* \param if1 Value to use if \p condition == MBEDTLS_CT_TRUE.
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* \param if0 Value to use if \p condition == MBEDTLS_CT_FALSE.
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*
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* \return \c if1 if \p condition == MBEDTLS_CT_TRUE, otherwise \c if0.
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*/
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static inline mbedtls_mpi_uint mbedtls_ct_mpi_uint_if(mbedtls_ct_condition_t condition, \
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mbedtls_mpi_uint if1, \
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mbedtls_mpi_uint if0);
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#endif
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/** Choose between an unsigned value and 0.
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*
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* Functionally equivalent to:
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*
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* condition ? if1 : 0.
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*
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* Functionally equivalent tombedtls_ct_uint_if(condition, if1, 0) but
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* results in smaller code size.
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*
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* \param condition Condition to test.
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* \param if1 Value to use if \p condition == MBEDTLS_CT_TRUE.
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*
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* \return \c if1 if \p condition == MBEDTLS_CT_TRUE, otherwise 0.
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*/
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static inline unsigned mbedtls_ct_uint_if0(mbedtls_ct_condition_t condition, unsigned if1);
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#if defined(MBEDTLS_BIGNUM_C)
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/** Choose between an mbedtls_mpi_uint value and 0.
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*
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* Functionally equivalent to:
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*
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* condition ? if1 : 0.
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*
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* Functionally equivalent tombedtls_ct_mpi_uint_if(condition, if1, 0) but
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* results in smaller code size.
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*
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* \param condition Condition to test.
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* \param if1 Value to use if \p condition == MBEDTLS_CT_TRUE.
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*
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* \return \c if1 if \p condition == MBEDTLS_CT_TRUE, otherwise 0.
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*/
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static inline mbedtls_mpi_uint mbedtls_ct_mpi_uint_if0(mbedtls_ct_condition_t condition,
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mbedtls_mpi_uint if1);
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#endif
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/** Constant-flow char selection
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*
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* \param low Secret. Bottom of range
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* \param high Secret. Top of range
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* \param c Secret. Value to compare to range
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* \param t Secret. Value to return, if in range
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*
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* \return \p t if \p low <= \p c <= \p high, 0 otherwise.
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*/
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static inline unsigned char mbedtls_ct_uchar_in_range_if(unsigned char low,
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unsigned char high,
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unsigned char c,
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unsigned char t);
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/* ============================================================================
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* Block memory operations
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*/
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#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
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/** Conditionally set a block of memory to zero.
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*
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* Regardless of the condition, every byte will be read once and written to
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* once.
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*
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* \param condition Secret. Condition to test.
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* \param buf Secret. Pointer to the start of the buffer.
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* \param len Number of bytes to set to zero.
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*
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* \warning Unlike mbedtls_platform_zeroize, this does not have the same guarantees
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* about not being optimised away if the memory is never read again.
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*/
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void mbedtls_ct_zeroize_if(mbedtls_ct_condition_t condition, void *buf, size_t len);
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/** Shift some data towards the left inside a buffer.
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*
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* Functionally equivalent to:
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*
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* memmove(start, start + offset, total - offset);
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* memset(start + (total - offset), 0, offset);
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*
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* Timing independence comes at the expense of performance.
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*
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* \param start Secret. Pointer to the start of the buffer.
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* \param total Total size of the buffer.
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* \param offset Secret. Offset from which to copy \p total - \p offset bytes.
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*/
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void mbedtls_ct_memmove_left(void *start,
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size_t total,
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size_t offset);
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#endif /* defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) */
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/** Conditional memcpy.
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*
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* Functionally equivalent to:
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*
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* if (condition) {
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* memcpy(dest, src1, len);
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* } else {
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* if (src2 != NULL)
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* memcpy(dest, src2, len);
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* }
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*
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* It will always read len bytes from src1.
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* If src2 != NULL, it will always read len bytes from src2.
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* If src2 == NULL, it will instead read len bytes from dest (as if src2 == dest).
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*
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* \param condition The condition
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* \param dest Secret. Destination pointer.
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* \param src1 Secret. Pointer to copy from (if \p condition == MBEDTLS_CT_TRUE).
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* This may be equal to \p dest, but may not overlap in other ways.
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* \param src2 Secret (contents only - may branch to test if src2 == NULL).
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* Pointer to copy from (if \p condition == MBEDTLS_CT_FALSE and \p src2 is not NULL). May be NULL.
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* This may be equal to \p dest, but may not overlap it in other ways. It may overlap with \p src1.
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* \param len Number of bytes to copy.
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*/
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void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition,
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unsigned char *dest,
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const unsigned char *src1,
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const unsigned char *src2,
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size_t len
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);
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/** Copy data from a secret position.
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*
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* Functionally equivalent to:
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*
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* memcpy(dst, src + offset, len)
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*
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* This function copies \p len bytes from \p src_base + \p offset to \p
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* dst, with a code flow and memory access pattern that does not depend on
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* \p offset, but only on \p offset_min, \p offset_max and \p len.
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*
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* \note This function reads from \p dest, but the value that
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* is read does not influence the result and this
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* function's behavior is well-defined regardless of the
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* contents of the buffers. This may result in false
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* positives from static or dynamic analyzers, especially
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* if \p dest is not initialized.
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*
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* \param dest Secret. The destination buffer. This must point to a writable
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* buffer of at least \p len bytes.
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* \param src Secret. The base of the source buffer. This must point to a
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* readable buffer of at least \p offset_max + \p len
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* bytes. Shouldn't overlap with \p dest
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* \param offset Secret. The offset in the source buffer from which to copy.
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* This must be no less than \p offset_min and no greater
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* than \p offset_max.
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* \param offset_min The minimal value of \p offset.
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* \param offset_max The maximal value of \p offset.
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* \param len The number of bytes to copy.
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*/
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void mbedtls_ct_memcpy_offset(unsigned char *dest,
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const unsigned char *src,
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size_t offset,
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size_t offset_min,
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size_t offset_max,
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size_t len);
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/* Documented in include/mbedtls/constant_time.h. a and b are secret. */
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int mbedtls_ct_memcmp(const void *a,
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const void *b,
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size_t n);
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#endif /* MBEDTLS_CONSTANT_TIME_INTERNAL_H */
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