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Move mbedtls_cf_uint_mask function to the constant-time module

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Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>
This commit is contained in:
gabor-mezei-arm 2021-09-27 11:40:03 +02:00
parent db9a38c672
commit 340948e4a5
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GPG key ID: 106F5A41ECC305BD
3 changed files with 22 additions and 19 deletions
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19
library/constant_time.c
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@ -92,3 +92,22 @@ int mbedtls_safer_memcmp( const void *a, const void *b, size_t n )
return( diff ); return( diff );
} }
/** Turn zero-or-nonzero into zero-or-all-bits-one, without branches.
*
* \param value The value to analyze.
* \return Zero if \p value is zero, otherwise all-bits-one.
*/
unsigned mbedtls_cf_uint_mask( unsigned value )
{
/* MSVC has a warning about unary minus on unsigned, but this is
* well-defined and precisely what we want to do here */
#if defined(_MSC_VER)
#pragma warning( push )
#pragma warning( disable : 4146 )
#endif
return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
}

3
library/constant_time.h
View file

@ -28,3 +28,6 @@ int mbedtls_constant_time_memcmp( const void *v1, const void *v2, size_t len );
unsigned char mbedtls_nist_kw_safer_memcmp( const void *a, const void *b, size_t n ); unsigned char mbedtls_nist_kw_safer_memcmp( const void *a, const void *b, size_t n );
int mbedtls_safer_memcmp( const void *a, const void *b, size_t n ); int mbedtls_safer_memcmp( const void *a, const void *b, size_t n );
unsigned mbedtls_cf_uint_mask( unsigned value );

19
library/rsa.c
View file

@ -1458,25 +1458,6 @@ cleanup:
#endif /* MBEDTLS_PKCS1_V21 */ #endif /* MBEDTLS_PKCS1_V21 */
#if defined(MBEDTLS_PKCS1_V15) #if defined(MBEDTLS_PKCS1_V15)
/** Turn zero-or-nonzero into zero-or-all-bits-one, without branches.
*
* \param value The value to analyze.
* \return Zero if \p value is zero, otherwise all-bits-one.
*/
static unsigned mbedtls_cf_uint_mask( unsigned value )
{
/* MSVC has a warning about unary minus on unsigned, but this is
* well-defined and precisely what we want to do here */
#if defined(_MSC_VER)
#pragma warning( push )
#pragma warning( disable : 4146 )
#endif
return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
}
/** Check whether a size is out of bounds, without branches. /** Check whether a size is out of bounds, without branches.
* *
* This is equivalent to `size > max`, but is likely to be compiled to * This is equivalent to `size > max`, but is likely to be compiled to