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Fix mbedtls_mpi_random when N has leading zeros

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mbedtls_mpi_random() uses mbedtls_mpi_cmp_mpi_ct(), which requires its
two arguments to have the same storage size. This was not the case
when the upper bound passed to mbedtls_mpi_random() had leading zero
limbs.

Fix this by forcing the result MPI to the desired size. Since this is
not what mbedtls_mpi_fill_random() does, don't call it from
mbedtls_mpi_random(), but instead call a new auxiliary function.

Add tests to cover this and other conditions with varying sizes for
the two arguments.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-04-01 15:57:18 +02:00
parent be4b5dd8c1
commit 8f45470515
3 changed files with 88 additions and 8 deletions
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23
tests/suites/test_suite_mpi.function
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@ -1537,6 +1537,29 @@ exit:
}
/* END_CASE */
/* BEGIN_CASE */
void mpi_random_grown( int min, data_t *bound_bytes, int nlimbs )
{
mbedtls_mpi upper_bound;
mbedtls_mpi result;
mbedtls_mpi_init( &upper_bound );
mbedtls_mpi_init( &result );
TEST_EQUAL( 0, mbedtls_mpi_grow( &result, nlimbs ) );
TEST_EQUAL( 0, mbedtls_mpi_read_binary( &upper_bound,
bound_bytes->x, bound_bytes->len ) );
TEST_EQUAL( 0, mbedtls_mpi_random( &result, min, &upper_bound,
mbedtls_test_rnd_std_rand, NULL ) );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &result, &upper_bound ) < 0 );
TEST_ASSERT( mbedtls_mpi_cmp_int( &result, min ) >= 0 );
exit:
mbedtls_mpi_free( &upper_bound );
mbedtls_mpi_free( &result );
}
/* END_CASE */
/* BEGIN_CASE */
void mpi_random_fail( int min, data_t *bound_bytes, int expected_ret )
{