mirror of
https://github.com/yuzu-emu/mbedtls.git
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139 lines
4.1 KiB
C
139 lines
4.1 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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#include "common.h"
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#include "constant_time.h"
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/* constant-time buffer comparison */
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int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
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{
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size_t i;
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volatile const unsigned char *A = (volatile const unsigned char *) a;
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volatile const unsigned char *B = (volatile const unsigned char *) b;
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volatile unsigned char diff = 0;
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for( i = 0; i < n; i++ )
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{
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/* Read volatile data in order before computing diff.
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* This avoids IAR compiler warning:
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* 'the order of volatile accesses is undefined ..' */
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unsigned char x = A[i], y = B[i];
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diff |= x ^ y;
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}
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return( diff );
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}
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/* Compare the contents of two buffers in constant time.
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* Returns 0 if the contents are bitwise identical, otherwise returns
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* a non-zero value.
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* This is currently only used by GCM and ChaCha20+Poly1305.
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*/
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int mbedtls_constant_time_memcmp( const void *v1, const void *v2,
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size_t len )
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{
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const unsigned char *p1 = (const unsigned char*) v1;
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const unsigned char *p2 = (const unsigned char*) v2;
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size_t i;
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unsigned char diff;
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for( diff = 0, i = 0; i < len; i++ )
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diff |= p1[i] ^ p2[i];
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return( (int)diff );
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}
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/* constant-time buffer comparison */
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unsigned char mbedtls_nist_kw_safer_memcmp( const void *a, const void *b, size_t n )
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{
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size_t i;
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volatile const unsigned char *A = (volatile const unsigned char *) a;
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volatile const unsigned char *B = (volatile const unsigned char *) b;
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volatile unsigned char diff = 0;
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for( i = 0; i < n; i++ )
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{
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/* Read volatile data in order before computing diff.
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* This avoids IAR compiler warning:
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* 'the order of volatile accesses is undefined ..' */
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unsigned char x = A[i], y = B[i];
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diff |= x ^ y;
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}
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return( diff );
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}
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/* constant-time buffer comparison */
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int mbedtls_safer_memcmp( const void *a, const void *b, size_t n )
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{
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size_t i;
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const unsigned char *A = (const unsigned char *) a;
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const unsigned char *B = (const unsigned char *) b;
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unsigned char diff = 0;
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for( i = 0; i < n; i++ )
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diff |= A[i] ^ B[i];
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return( diff );
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}
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/** Turn zero-or-nonzero into zero-or-all-bits-one, without branches.
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*
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* \param value The value to analyze.
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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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{
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/* MSVC has a warning about unary minus on unsigned, but this is
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* well-defined and precisely what we want to do here */
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#if defined(_MSC_VER)
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#pragma warning( push )
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#pragma warning( disable : 4146 )
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#endif
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return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
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#if defined(_MSC_VER)
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#pragma warning( pop )
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#endif
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}
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/*
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* Turn a bit into a mask:
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* - if bit == 1, return the all-bits 1 mask, aka (size_t) -1
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* - if bit == 0, return the all-bits 0 mask, aka 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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* This function is implemented without using comparison operators, as those
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* might be translated to branches by some compilers on some platforms.
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*/
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size_t mbedtls_cf_size_mask( size_t bit )
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{
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/* MSVC has a warning about unary minus on unsigned integer types,
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* but this is well-defined and precisely what we want to do here. */
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#if defined(_MSC_VER)
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#pragma warning( push )
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#pragma warning( disable : 4146 )
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#endif
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return -bit;
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#if defined(_MSC_VER)
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#pragma warning( pop )
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#endif
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}
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