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DHM refactoring: use dhm_random_below in dhm_make_common

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dhm_make_common includes a piece of code that is identical to
dhm_random_below except for returning a different error code in one
case. Call dhm_random_below instead of repeating the code.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-31 22:48:14 +02:00
parent b4e815f638
commit 87fdb1f872
1 changed files with 38 additions and 37 deletions
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75
library/dhm.c
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@ -150,29 +150,55 @@ int mbedtls_dhm_read_params( mbedtls_dhm_context *ctx,
return( 0 );
}
/*
* Pick a random R in the range [2, M) for blinding or key generation.
*/
static int dhm_random_below( mbedtls_mpi *R, const mbedtls_mpi *M,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, count;
count = 0;
do
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( R, mbedtls_mpi_size( M ), f_rng, p_rng ) );
while( mbedtls_mpi_cmp_mpi( R, M ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( R, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
}
while( dhm_check_range( R, M ) != 0 );
cleanup:
return( ret );
}
static int dhm_make_common( mbedtls_dhm_context *ctx, int x_size,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret, count = 0;
int ret = 0;
if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
if( x_size < 0 )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
/*
* Generate X as large as possible ( < P )
*/
do
if( (unsigned) x_size < mbedtls_mpi_size( &ctx->P ) )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng ) );
while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED );
}
while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
else
{
/* Generate X as large as possible ( <= P - 2 ) */
ret = dhm_random_below( &ctx->X, &ctx->P, f_rng, p_rng );
if( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED );
if( ret != 0 )
return( ret );
}
/*
* Calculate GX = G^X mod P
@ -310,31 +336,6 @@ cleanup:
return( ret );
}
/*
* Pick a random R in the range [2, M) for blinding purposes
*/
static int dhm_random_below( mbedtls_mpi *R, const mbedtls_mpi *M,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, count;
count = 0;
do
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( R, mbedtls_mpi_size( M ), f_rng, p_rng ) );
while( mbedtls_mpi_cmp_mpi( R, M ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( R, 1 ) );
if( count++ > 10 )
return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
}
while( dhm_check_range( R, M ) != 0 );
cleanup:
return( ret );
}
/*
* Use the blinding method and optimisation suggested in section 10 of: