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Merge pull request #6289 from gabor-mezei-arm/6237_Add_conditional_assign_and_swap_for_bignum

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Bignum: Add safe conditional assign and swap for the new MPI types
This commit is contained in:
Gilles Peskine
2022-10-19 15:51:19 +02:00
committed by GitHub
parent 7cd1ebe0bb 4dceede71b
commit db2996357c
7 changed files with 548 additions and 19 deletions
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26
library/constant_time.c
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@@ -30,6 +30,7 @@
#if defined(MBEDTLS_BIGNUM_C)
#include "mbedtls/bignum.h"
#include "bignum_core.h"
#endif
#if defined(MBEDTLS_SSL_TLS_C)
@@ -678,21 +679,19 @@ int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X,
unsigned char assign )
{
int ret = 0;
size_t i;
mbedtls_mpi_uint limb_mask;
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( Y != NULL );
/* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
limb_mask = mbedtls_ct_mpi_uint_mask( assign );;
mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( assign );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
X->s = mbedtls_ct_cond_select_sign( assign, Y->s, X->s );
mbedtls_ct_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
mbedtls_mpi_core_cond_assign( X->p, Y->p, Y->n, assign );
for( i = Y->n; i < X->n; i++ )
for( size_t i = Y->n; i < X->n; i++ )
X->p[i] &= ~limb_mask;
cleanup:
@@ -709,19 +708,14 @@ int mbedtls_mpi_safe_cond_swap( mbedtls_mpi *X,
mbedtls_mpi *Y,
unsigned char swap )
{
int ret, s;
size_t i;
mbedtls_mpi_uint limb_mask;
mbedtls_mpi_uint tmp;
int ret = 0;
int s;
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( Y != NULL );
if( X == Y )
return( 0 );
/* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
limb_mask = mbedtls_ct_mpi_uint_mask( swap );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( Y, X->n ) );
@@ -729,13 +723,7 @@ int mbedtls_mpi_safe_cond_swap( mbedtls_mpi *X,
X->s = mbedtls_ct_cond_select_sign( swap, Y->s, X->s );
Y->s = mbedtls_ct_cond_select_sign( swap, s, Y->s );
for( i = 0; i < X->n; i++ )
{
tmp = X->p[i];
X->p[i] = ( X->p[i] & ~limb_mask ) | ( Y->p[i] & limb_mask );
Y->p[i] = ( Y->p[i] & ~limb_mask ) | ( tmp & limb_mask );
}
mbedtls_mpi_core_cond_swap( X->p, Y->p, X->n, swap );
cleanup:
return( ret );