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Unify function parameters

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Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
gabor-mezei-arm 2021-08-10 20:36:09 +02:00 committed by Gabor Mezei
parent 378e7eb5cc
commit 5e4882498e
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GPG Key ID: 106F5A41ECC305BD
2 changed files with 51 additions and 50 deletions
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83
library/constant_time.c
View File

@ -178,19 +178,19 @@ size_t mbedtls_cf_size_bool_eq( size_t x,
/** 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 `x > y`, but is likely to be compiled to
* to code using bitwise operation rather than a branch.
*
* \param size Size to check.
* \param max Maximum desired value for \p size.
* \return \c 0 if `size <= max`.
* \return \c 1 if `size > max`.
* \param x Size to check.
* \param y Maximum desired value for \p size.
* \return \c 0 if `x <= y`.
* \return \c 1 if `x > y`.
*/
unsigned mbedtls_cf_size_gt( size_t size,
size_t max )
unsigned mbedtls_cf_size_gt( size_t x,
size_t y )
{
/* Return the sign bit (1 for negative) of (max - size). */
return( ( max - size ) >> ( sizeof( size_t ) * 8 - 1 ) );
/* Return the sign bit (1 for negative) of (y - x). */
return( ( y - x ) >> ( sizeof( size_t ) * 8 - 1 ) );
}
#if defined(MBEDTLS_BIGNUM_C)
@ -234,57 +234,58 @@ unsigned mbedtls_cf_mpi_uint_lt( const mbedtls_mpi_uint x,
/** Choose between two integer values, without branches.
*
* This is equivalent to `cond ? if1 : if0`, but is likely to be compiled
* This is equivalent to `condition ? if1 : if0`, but is likely to be compiled
* to code using bitwise operation rather than a branch.
*
* \param cond Condition to test.
* \param if1 Value to use if \p cond is nonzero.
* \param if0 Value to use if \p cond is zero.
* \return \c if1 if \p cond is nonzero, otherwise \c if0.
* \param condition Condition to test.
* \param if1 Value to use if \p condition is nonzero.
* \param if0 Value to use if \p condition is zero.
* \return \c if1 if \p condition is nonzero, otherwise \c if0.
*/
unsigned mbedtls_cf_uint_if( unsigned cond,
unsigned mbedtls_cf_uint_if( unsigned condition,
unsigned if1,
unsigned if0 )
{
unsigned mask = mbedtls_cf_uint_mask( cond );
unsigned mask = mbedtls_cf_uint_mask( condition );
return( ( mask & if1 ) | (~mask & if0 ) );
}
size_t mbedtls_cf_size_if( unsigned cond,
size_t mbedtls_cf_size_if( unsigned condition,
size_t if1,
size_t if0 )
{
size_t mask = mbedtls_cf_size_mask( cond );
size_t mask = mbedtls_cf_size_mask( condition );
return( ( mask & if1 ) | (~mask & if0 ) );
}
/**
* Select between two sign values in constant-time.
*
* This is functionally equivalent to second ? a : b but uses only bit
* This is functionally equivalent to condition ? if1 : if0 but uses only bit
* operations in order to avoid branches.
*
* \param[in] a The first sign; must be either +1 or -1.
* \param[in] b The second sign; must be either +1 or -1.
* \param[in] second Must be either 1 (return b) or 0 (return a).
* \param[in] condition Must be either 1 (return \p if1) or 0 (return \pp if0).
* \param[in] if1 The first sign; must be either +1 or -1.
* \param[in] if0 The second sign; must be either +1 or -1.
*
* \return The selected sign value.
* \return \c if1 if \p condition is nonzero, otherwise \c if0.
*/
int mbedtls_cf_cond_select_sign( int a,
int b,
unsigned char second )
int mbedtls_cf_cond_select_sign( unsigned char condition,
int if1,
int if0 )
{
/* In order to avoid questions about what we can reasonnably assume about
* the representations of signed integers, move everything to unsigned
* by taking advantage of the fact that a and b are either +1 or -1. */
unsigned ua = a + 1;
unsigned ub = b + 1;
unsigned uif1 = if1 + 1;
unsigned uif0 = if0 + 1;
/* second was 0 or 1, mask is 0 or 2 as are ua and ub */
const unsigned mask = second << 1;
/* condition was 0 or 1, mask is 0 or 2 as are ua and ub */
const unsigned mask = condition << 1;
/* select ua or ub */
unsigned ur = ( ua & ~mask ) | ( ub & mask );
unsigned ur = ( uif0 & ~mask ) | ( uif1 & mask );
/* ur is now 0 or 2, convert back to -1 or +1 */
return( (int) ur - 1 );
@ -296,12 +297,12 @@ int mbedtls_cf_cond_select_sign( int a,
* Conditionally assign dest = src, without leaking information
* about whether the assignment was made or not.
* dest and src must be arrays of limbs of size n.
* assign must be 0 or 1.
* condition must be 0 or 1.
*/
void mbedtls_cf_mpi_uint_cond_assign( size_t n,
mbedtls_mpi_uint *dest,
const mbedtls_mpi_uint *src,
unsigned char assign )
unsigned char condition )
{
size_t i;
@ -312,8 +313,8 @@ void mbedtls_cf_mpi_uint_cond_assign( size_t n,
#pragma warning( disable : 4146 )
#endif
/* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
const mbedtls_mpi_uint mask = -assign;
/* all-bits 1 if condition is 1, all-bits 0 if condition is 0 */
const mbedtls_mpi_uint mask = -condition;
#if defined(_MSC_VER)
#pragma warning( pop )
@ -375,7 +376,7 @@ void mbedtls_cf_mem_move_to_left( void *start,
* This function is implemented without using comparison operators, as those
* might be translated to branches by some compilers on some platforms.
*/
void mbedtls_cf_memcpy_if_eq( unsigned char *dst,
void mbedtls_cf_memcpy_if_eq( unsigned char *dest,
const unsigned char *src,
size_t len,
size_t c1,
@ -385,9 +386,9 @@ void mbedtls_cf_memcpy_if_eq( unsigned char *dst,
const size_t equal = mbedtls_cf_size_bool_eq( c1, c2 );
const unsigned char mask = (unsigned char) mbedtls_cf_size_mask( equal );
/* dst[i] = c1 == c2 ? src[i] : dst[i] */
/* dest[i] = c1 == c2 ? src[i] : dest[i] */
for( size_t i = 0; i < len; i++ )
dst[i] = ( src[i] & mask ) | ( dst[i] & ~mask );
dest[i] = ( src[i] & mask ) | ( dest[i] & ~mask );
}
/*
@ -543,7 +544,7 @@ int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X,
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
X->s = mbedtls_cf_cond_select_sign( X->s, Y->s, assign );
X->s = mbedtls_cf_cond_select_sign( assign, Y->s, X->s );
mbedtls_cf_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
@ -594,8 +595,8 @@ int mbedtls_mpi_safe_cond_swap( mbedtls_mpi *X,
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( Y, X->n ) );
s = X->s;
X->s = mbedtls_cf_cond_select_sign( X->s, Y->s, swap );
Y->s = mbedtls_cf_cond_select_sign( Y->s, s, swap );
X->s = mbedtls_cf_cond_select_sign( swap, Y->s, X->s );
Y->s = mbedtls_cf_cond_select_sign( swap, s, Y->s );
for( i = 0; i < X->n; i++ )

18
library/constant_time.h
View File

@ -47,8 +47,8 @@ size_t mbedtls_cf_size_mask_ge( size_t x,
size_t mbedtls_cf_size_bool_eq( size_t x,
size_t y );
unsigned mbedtls_cf_size_gt( size_t size,
size_t max );
unsigned mbedtls_cf_size_gt( size_t x,
size_t y );
#if defined(MBEDTLS_BIGNUM_C)
@ -57,24 +57,24 @@ unsigned mbedtls_cf_mpi_uint_lt( const mbedtls_mpi_uint x,
#endif /* MBEDTLS_BIGNUM_C */
unsigned mbedtls_cf_uint_if( unsigned cond,
unsigned mbedtls_cf_uint_if( unsigned condition,
unsigned if1,
unsigned if0 );
size_t mbedtls_cf_size_if( unsigned cond,
size_t mbedtls_cf_size_if( unsigned condition,
size_t if1,
size_t if0 );
int mbedtls_cf_cond_select_sign( int a,
int b,
unsigned char second );
int mbedtls_cf_cond_select_sign( unsigned char condition,
int if1,
int if0 );
#if defined(MBEDTLS_BIGNUM_C)
void mbedtls_cf_mpi_uint_cond_assign( size_t n,
mbedtls_mpi_uint *dest,
const mbedtls_mpi_uint *src,
unsigned char assign );
unsigned char condition );
#endif /* MBEDTLS_BIGNUM_C */
@ -82,7 +82,7 @@ void mbedtls_cf_mem_move_to_left( void *start,
size_t total,
size_t offset );
void mbedtls_cf_memcpy_if_eq( unsigned char *dst,
void mbedtls_cf_memcpy_if_eq( unsigned char *dest,
const unsigned char *src,
size_t len,
size_t c1, size_t c2 );