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Propagate usage of mask generation functions

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Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>
This commit is contained in:
gabor-mezei-arm 2021-08-11 15:07:02 +02:00
parent 396438c57b
commit 9cb55698aa
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GPG Key ID: 106F5A41ECC305BD
3 changed files with 27 additions and 38 deletions
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48
library/constant_time.c
View File

@ -96,6 +96,24 @@ size_t mbedtls_cf_size_mask( size_t value )
#endif
}
#if defined(MBEDTLS_BIGNUM_C)
mbedtls_mpi_uint mbedtls_cf_mpi_uint_mask( mbedtls_mpi_uint 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
}
#endif /* MBEDTLS_BIGNUM_C */
/*
* Constant-flow mask generation for "less than" comparison:
* - if x < y, return all bits 1, that is (size_t) -1
@ -526,21 +544,8 @@ int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X,
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( Y != NULL );
/* MSVC has a warning about unary minus on unsigned integer types,
* 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
/* make sure assign is 0 or 1 in a time-constant manner */
assign = (assign | (unsigned char)-assign) >> (sizeof( assign ) * 8 - 1);
/* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
limb_mask = -assign;
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
limb_mask = mbedtls_cf_mpi_uint_mask( assign );;
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
@ -575,21 +580,8 @@ int mbedtls_mpi_safe_cond_swap( mbedtls_mpi *X,
if( X == Y )
return( 0 );
/* MSVC has a warning about unary minus on unsigned integer types,
* 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
/* make sure swap is 0 or 1 in a time-constant manner */
swap = (swap | (unsigned char)-swap) >> (sizeof( swap ) * 8 - 1);
/* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
limb_mask = -swap;
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
limb_mask = mbedtls_cf_mpi_uint_mask( swap );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( Y, X->n ) );

6
library/constant_time.h
View File

@ -38,6 +38,12 @@ unsigned mbedtls_cf_uint_mask( unsigned value );
size_t mbedtls_cf_size_mask( size_t value );
#if defined(MBEDTLS_BIGNUM_C)
mbedtls_mpi_uint mbedtls_cf_mpi_uint_mask( mbedtls_mpi_uint value );
#endif /* MBEDTLS_BIGNUM_C */
size_t mbedtls_cf_size_mask_lt( size_t x,
size_t y );

11
library/ssl_srv.c
View File

@ -3581,16 +3581,7 @@ static int ssl_parse_encrypted_pms( mbedtls_ssl_context *ssl,
diff |= peer_pms[1] ^ ver[1];
/* mask = diff ? 0xff : 0x00 using bit operations to avoid branches */
/* 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
mask = - ( ( diff | - diff ) >> ( sizeof( unsigned int ) * 8 - 1 ) );
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
mask = mbedtls_cf_uint_mask( diff );
/*
* Protection against Bleichenbacher's attack: invalid PKCS#1 v1.5 padding