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Merge pull request #5154 from gabor-mezei-arm/3649_bp2x_move_constant_time_functions_into_separate_module

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[Backport 2.x] Move constant-time functions into a separate module
This commit is contained in:
Gilles Peskine
2021-11-24 19:33:03 +01:00
committed by GitHub
parent 989a4e9388 2dcccbfc19
commit 3107b337e1
19 changed files with 1182 additions and 983 deletions
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45
include/mbedtls/constant_time.h Normal file
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@ -0,0 +1,45 @@
/**
* Constant-time functions
*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef MBEDTLS_CONSTANT_TIME_H
#define MBEDTLS_CONSTANT_TIME_H
#include <stddef.h>
/** Constant-time buffer comparison without branches.
*
* This is equivalent to the standard memcmp function, but is likely to be
* compiled to code using bitwise operation rather than a branch.
*
* This function can be used to write constant-time code by replacing branches
* with bit operations using masks.
*
* \param a Pointer to the first buffer.
* \param b Pointer to the second buffer.
* \param n The number of bytes to compare in the buffer.
*
* \return Zero if the content of the two buffer is the same,
* otherwise non-zero.
*/
int mbedtls_ct_memcmp( const void *a,
const void *b,
size_t n );
#endif /* MBEDTLS_CONSTANT_TIME_H */

20
include/mbedtls/ssl_internal.h
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@ -1212,26 +1212,6 @@ void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
const mbedtls_ssl_session *src );
/* constant-time buffer comparison */
static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
{
size_t i;
volatile const unsigned char *A = (volatile const unsigned char *) a;
volatile const unsigned char *B = (volatile const unsigned char *) b;
volatile unsigned char diff = 0;
for( i = 0; i < n; i++ )
{
/* Read volatile data in order before computing diff.
* This avoids IAR compiler warning:
* 'the order of volatile accesses is undefined ..' */
unsigned char x = A[i], y = B[i];
diff |= x ^ y;
}
return( diff );
}
#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
defined(MBEDTLS_SSL_PROTO_TLS1_1)
int mbedtls_ssl_get_key_exchange_md_ssl_tls( mbedtls_ssl_context *ssl,