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Move mbedtls_mpi_safe_cond_assign function to the constant-time module

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Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
gabor-mezei-arm 2021-09-27 15:33:35 +02:00 committed by Gabor Mezei
parent 6e4ace6b40
commit b8caeeed5c
2 changed files with 49 additions and 42 deletions
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42
library/bignum.c
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@ -269,48 +269,6 @@ void mbedtls_mpi_swap( mbedtls_mpi *X, mbedtls_mpi *Y )
memcpy( Y, &T, sizeof( mbedtls_mpi ) );
}
/*
* Conditionally assign X = Y, without leaking information
* about whether the assignment was made or not.
* (Leaking information about the respective sizes of X and Y is ok however.)
*/
int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X, const mbedtls_mpi *Y, unsigned char assign )
{
int ret = 0;
size_t i;
mbedtls_mpi_uint limb_mask;
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
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
X->s = mbedtls_cf_cond_select_sign( X->s, Y->s, assign );
mbedtls_cf_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
for( i = Y->n; i < X->n; i++ )
X->p[i] &= ~limb_mask;
cleanup:
return( ret );
}
/*
* Conditionally swap X and Y, without leaking information
* about whether the swap was made or not.

49
library/constant_time.c
View File

@ -536,3 +536,52 @@ cleanup:
}
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
#if defined(MBEDTLS_BIGNUM_C)
#define MPI_VALIDATE_RET( cond ) \
MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
/*
* Conditionally assign X = Y, without leaking information
* about whether the assignment was made or not.
* (Leaking information about the respective sizes of X and Y is ok however.)
*/
int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X, const mbedtls_mpi *Y, unsigned char assign )
{
int ret = 0;
size_t i;
mbedtls_mpi_uint limb_mask;
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
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
X->s = mbedtls_cf_cond_select_sign( X->s, Y->s, assign );
mbedtls_cf_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
for( i = Y->n; i < X->n; i++ )
X->p[i] &= ~limb_mask;
cleanup:
return( ret );
}
#endif /* MBEDTLS_BIGNUM_C */