298 lines
12 KiB
C
298 lines
12 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 "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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#if defined(MBEDTLS_SSL_TLS_C)
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#include "ssl_misc.h"
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#endif
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#include <stddef.h>
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/** Turn a value into a mask:
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* - if \p value == 0, return the all-bits 0 mask, aka 0
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* - otherwise, return the all-bits 1 mask, aka (unsigned) -1
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*
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* This function can be used to write constant-time code by replacing branches
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* with bit operations using masks.
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*
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* \param value The value to analyze.
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*
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* \return Zero if \p value is zero, otherwise all-bits-one.
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*/
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unsigned mbedtls_cf_uint_mask( unsigned value );
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#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
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/** Turn a value into a mask:
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* - if \p value == 0, return the all-bits 0 mask, aka 0
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* - otherwise, return the all-bits 1 mask, aka (size_t) -1
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*
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* This function can be used to write constant-time code by replacing branches
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* with bit operations using masks.
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*
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* \param value The value to analyze.
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*
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* \return Zero if \p value is zero, otherwise all-bits-one.
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*/
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size_t mbedtls_cf_size_mask( size_t value );
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#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
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#if defined(MBEDTLS_BIGNUM_C)
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/** Turn a value into a mask:
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* - if \p value == 0, return the all-bits 0 mask, aka 0
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* - otherwise, return the all-bits 1 mask, aka (mbedtls_mpi_uint) -1
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*
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* This function can be used to write constant-time code by replacing branches
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* with bit operations using masks.
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*
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* \param value The value to analyze.
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*
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* \return Zero if \p value is zero, otherwise all-bits-one.
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*/
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mbedtls_mpi_uint mbedtls_cf_mpi_uint_mask( mbedtls_mpi_uint value );
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#endif /* MBEDTLS_BIGNUM_C */
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#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
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/** Constant-flow mask generation for "greater or equal" comparison:
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* - if \p x >= \p y, return all-bits 1, that is (size_t) -1
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* - otherwise, return all bits 0, that is 0
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*
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* This function can be used to write constant-time code by replacing branches
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* with bit operations using masks.
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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 All-bits-one if \p x is greater or equal than \p y,
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* otherwise zero.
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*/
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size_t mbedtls_cf_size_mask_ge( size_t x,
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size_t y );
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#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
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/** Constant-flow boolean "equal" comparison:
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* return x == y
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*
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* This is equivalent to \p x == \p y, but is likely to be compiled
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* to code using bitwise operation rather than a branch.
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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 1 if \p x equals to \p y, otherwise 0.
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*/
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unsigned mbedtls_cf_size_bool_eq( size_t x,
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size_t y );
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#if defined(MBEDTLS_BIGNUM_C)
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/** Decide if an integer is less than the other, without branches.
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*
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* This is equivalent to \p x < \p y, but is likely to be compiled
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* to code using bitwise operation rather than a branch.
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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 1 if \p x is less than \p y, otherwise 0.
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*/
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unsigned mbedtls_cf_mpi_uint_lt( const mbedtls_mpi_uint x,
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const mbedtls_mpi_uint y );
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#endif /* MBEDTLS_BIGNUM_C */
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/** Choose between two integer values without branches.
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*
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* This is equivalent to `condition ? if1 : if0`, but is likely to be compiled
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* to code using bitwise operation rather than a branch.
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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 is nonzero.
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* \param if0 Value to use if \p condition is zero.
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*
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* \return \c if1 if \p condition is nonzero, otherwise \c if0.
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*/
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unsigned mbedtls_cf_uint_if( unsigned 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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/** Conditionally assign a value without branches.
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*
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* This is equivalent to `if ( condition ) dest = src`, but is likely
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* to be compiled to code using bitwise operation rather than a branch.
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*
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* \param n \p dest and \p src must be arrays of limbs of size n.
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* \param dest The MPI to conditionally assign to. This must point
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* to an initialized MPI.
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* \param src The MPI to be assigned from. This must point to an
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* initialized MPI.
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* \param condition Condition to test, must be 0 or 1.
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*/
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void mbedtls_cf_mpi_uint_cond_assign( size_t n,
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mbedtls_mpi_uint *dest,
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const mbedtls_mpi_uint *src,
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unsigned char condition );
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#endif /* MBEDTLS_BIGNUM_C */
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#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
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/** Conditional memcpy without branches.
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*
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* This is equivalent to `if ( c1 == c2 ) memcpy(dst, src, len)`, but is likely
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* to be compiled to code using bitwise operation rather than a branch.
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*
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* \param dest The pointer to conditionally copy to.
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* \param src The pointer to copy from. Shouldn't overlap with \p dest.
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* \param len The number of bytes to copy.
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* \param c1 The first value to analyze in the condition.
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* \param c2 The second value to analyze in the condition.
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*/
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void mbedtls_cf_memcpy_if_eq( unsigned char *dest,
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const unsigned char *src,
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size_t len,
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size_t c1, size_t c2 );
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/** Copy data from a secret position with constant flow.
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*
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* This function copies \p len bytes from \p src_base + \p offset_secret to \p
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* dst, with a code flow and memory access pattern that does not depend on \p
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* offset_secret, but only on \p offset_min, \p offset_max and \p len.
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* Functionally equivalent to `memcpy(dst, src + offset_secret, len)`.
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*
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* \param dest 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 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 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_cf_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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/** Compute the HMAC of variable-length data with constant flow.
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*
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* This function computes the HMAC of the concatenation of \p add_data and \p
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* data, and does with a code flow and memory access pattern that does not
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* depend on \p data_len_secret, but only on \p min_data_len and \p
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* max_data_len. In particular, this function always reads exactly \p
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* max_data_len bytes from \p data.
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*
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* \param ctx The HMAC context. It must have keys configured
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* with mbedtls_md_hmac_starts() and use one of the
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* following hashes: SHA-384, SHA-256, SHA-1 or MD-5.
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* It is reset using mbedtls_md_hmac_reset() after
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* the computation is complete to prepare for the
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* next computation.
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* \param add_data The first part of the message whose HMAC is being
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* calculated. This must point to a readable buffer
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* of \p add_data_len bytes.
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* \param add_data_len The length of \p add_data in bytes.
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* \param data The buffer containing the second part of the
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* message. This must point to a readable buffer
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* of \p max_data_len bytes.
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* \param data_len_secret The length of the data to process in \p data.
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* This must be no less than \p min_data_len and no
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* greater than \p max_data_len.
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* \param min_data_len The minimal length of the second part of the
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* message, read from /p data.
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* \param max_data_len The maximal length of the second part of the
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* message, read from /p data.
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* \param output The HMAC will be written here. This must point to
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* a writable buffer of sufficient size to hold the
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* HMAC value.
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*
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* \retval 0 on success.
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* \retval #MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED
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* The hardware accelerator failed.
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*/
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int mbedtls_cf_hmac( mbedtls_md_context_t *ctx,
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const unsigned char *add_data,
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size_t add_data_len,
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const unsigned char *data,
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size_t data_len_secret,
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size_t min_data_len,
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size_t max_data_len,
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unsigned char *output );
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#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
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#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
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/** This function performs the unpadding part of a PKCS#1 v1.5 decryption
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* operation (EME-PKCS1-v1_5 decoding).
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*
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* \note The return value from this function is a sensitive value
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* (this is unusual). #MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE shouldn't happen
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* in a well-written application, but 0 vs #MBEDTLS_ERR_RSA_INVALID_PADDING
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* is often a situation that an attacker can provoke and leaking which
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* one is the result is precisely the information the attacker wants.
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*
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* \param input The input buffer which is the payload inside PKCS#1v1.5
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* encryption padding, called the "encoded message EM"
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* by the terminology.
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* \param ilen The length of the payload in the \p input buffer.
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* \param output The buffer for the payload, called "message M" by the
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* PKCS#1 terminology. This must be a writable buffer of
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* length \p output_max_len bytes.
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* \param olen The address at which to store the length of
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* the payload. This must not be \c NULL.
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* \param output_max_len The length in bytes of the output buffer \p output.
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*
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE
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* The output buffer is too small for the unpadded payload.
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* \return #MBEDTLS_ERR_RSA_INVALID_PADDING
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* The input doesn't contain properly formatted padding.
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*/
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int mbedtls_cf_rsaes_pkcs1_v15_unpadding( unsigned char *input,
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size_t ilen,
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unsigned char *output,
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size_t output_max_len,
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size_t *olen );
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#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */
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#endif /* MBEDTLS_CONSTANT_TIME_INTERNAL_H */
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