Fix mbedtls_mpi_random when N has leading zeros
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>
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index fb2c553..3488854 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -1132,6 +1132,33 @@
MPI random in range: 3..4
mpi_random_many:1:"04":1000
+MPI random in range: smaller result
+mpi_random_grown:1:"aaaaaaaaaaaaaaaabbbbbbbbbbbbbbbb":1
+
+MPI random in range: same size result (32-bit limbs)
+mpi_random_grown:1:"aaaaaaaaaaaaaaaa":2
+
+MPI random in range: same size result (64-bit limbs)
+mpi_random_grown:1:"aaaaaaaaaaaaaaaa":1
+
+MPI random in range: larger result
+mpi_random_grown:1:"aaaaaaaaaaaaaaaa":3
+
+MPI random in range: leading 0 limb in upper bound #0
+mpi_random_grown:1:"00aaaaaaaaaaaaaaaa":0
+
+MPI random in range: leading 0 limb in upper bound #1
+mpi_random_grown:1:"00aaaaaaaaaaaaaaaa":1
+
+MPI random in range: leading 0 limb in upper bound #2
+mpi_random_grown:1:"00aaaaaaaaaaaaaaaa":2
+
+MPI random in range: leading 0 limb in upper bound #3
+mpi_random_grown:1:"00aaaaaaaaaaaaaaaa":3
+
+MPI random in range: leading 0 limb in upper bound #4
+mpi_random_grown:1:"00aaaaaaaaaaaaaaaa":4
+
MPI random bad arguments: min < 0
mpi_random_fail:-1:"04":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 0ca6b64..f3c9107 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1538,6 +1538,29 @@
/* 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 )
{
mbedtls_mpi upper_bound;