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dhm: Fix bias in private key generation and blinding

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Signed-off-by: Ronald Cron <[email protected]>
This commit is contained in:
Ronald Cron
2021-06-10 10:40:34 +02:00
parent 260be63e7d
commit b4367a358f
1 changed files with 7 additions and 7 deletions
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library/dhm.c
+7 -7
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@@ -180,23 +180,23 @@ int mbedtls_dhm_read_params( mbedtls_dhm_context *ctx,
}
/*
* Pick a random R in the range [2, M) for blinding or key generation.
* Pick a random R in the range [2, M-2] 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;
size_t m_size = mbedtls_mpi_size( M );
size_t m_bitlen = mbedtls_mpi_bitlen( M );
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 )
if( count++ > 30 )
return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( R, m_size, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( R, ( m_size * 8 ) - m_bitlen ) );
}
while( dhm_check_range( R, M ) != 0 );