3.5.2 Add more tests to ff-group-tests

The audit recommends checking failure cases for from_bytes,
from_bytes_unechecked, and from_repr. This isn't feasible.

from_bytes is allowed to have non-canonical values. [0xff; 32] may accordingly
be a valid point for non-SEC1-encoded curves.

from_bytes_unchecked doesn't have a defined failure mode, and by name,
unchecked, shouldn't necessarily fail. The audit acknowledges the tests should
test for whatever result is 'appropriate', yet any result which isn't a failure
on a valid element is appropriate.

from_repr must be canonical, yet for a binary field of 2^n where n % 8 == 0, a
[0xff; n / 8] repr would be valid.

crypto/ed448/src/field.rs

@@ -32,5 +32,5 @@ field!(FieldElement, MODULUS, WIDE_MODULUS, 448);
 #[test]
 fn test_field() {
   // TODO: Move to test_prime_field_bits once the impl is finished
-  ff_group_tests::prime_field::test_prime_field::<FieldElement>();
+  ff_group_tests::prime_field::test_prime_field::<_, FieldElement>(&mut rand_core::OsRng);
 }

crypto/ed448/src/point.rs

@@ -323,6 +323,7 @@ fn test_group() {
   test_sub::<Point>();
   test_mul::<Point>();
   test_order::<Point>();
+  test_random::<_, Point>(&mut rand_core::OsRng);
 
   test_encoding::<Point>();
 }

crypto/ed448/src/scalar.rs

@@ -35,5 +35,5 @@ impl Scalar {
 #[test]
 fn test_scalar_field() {
   // TODO: Move to test_prime_field_bits once the impl is finished
-  ff_group_tests::prime_field::test_prime_field::<Scalar>();
+  ff_group_tests::prime_field::test_prime_field::<_, Scalar>(&mut rand_core::OsRng);
 }