Trait for weak keys

[baloo]

It would be great to get a trait to test for weak keys.

For example there are 64 known weak keys for DES (https://en.wikipedia.org/wiki/Weak_key#Weak_keys_in_DES), or an AES key with zeros on the upper half.

The purpose is the rejection of weak keys as specified in the TPM spec section 11.4.10.4:
https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=82

[newpavlov]

Sounds interesting. Do you imagine something like this?

trait WeakKeyTest: KeySizeUser {
    fn weak_key_test(key: &Key<Self>) -> Result<(), WeakKeyError>;
}

One open question is whether we should have a default impl which returns Ok(()). If yes, then it may make sense to move the test method to KeySizeUser or KeyInit trait.

[baloo]

Something along those lines, and a:

impl<T> for Key<T> where T: WeakKeyTest {
    fn is_weak(&self) -> Result<(), WeakKeyError> {
        T:weak_key_test(self)
    }
}

To make it a bit more convenient to use.

I guess KeySizeUser with a default implementation would work.