Improve bls::SecretKey privacy (#1164)

* Improve bls::SecretKey privacy

* Add missed file

* Remove more methods from bls::SecretKey

* Add as_bytes() to SecretKey, remove as_raw

* Remove as_raw

* Add back as_raw

* Address review comments

validator_client/src/validator_store.rs

@@ -15,12 +15,31 @@ use types::{
 };
 use validator_dir::{Manager as ValidatorManager, ValidatorDir};
 
-#[derive(PartialEq)]
 struct LocalValidator {
     validator_dir: ValidatorDir,
     voting_keypair: Keypair,
 }
 
+/// We derive our own `PartialEq` to avoid doing equality checks between secret keys.
+///
+/// It's nice to avoid secret key comparisons from a security perspective, but it's also a little
+/// risky when it comes to `HashMap` integrity (that's why we need `PartialEq`).
+///
+/// Currently, we obtain keypairs from keystores where we derive the `PublicKey` from a `SecretKey`
+/// via a hash function. In order to have two equal `PublicKey` with different `SecretKey` we would
+/// need to have either:
+///
+/// - A serious upstream integrity error.
+/// - A hash collision.
+///
+/// It seems reasonable to make these two assumptions in order to avoid the equality checks.
+impl PartialEq for LocalValidator {
+    fn eq(&self, other: &Self) -> bool {
+        self.validator_dir == other.validator_dir
+            && self.voting_keypair.pk == other.voting_keypair.pk
+    }
+}
+
 #[derive(Clone)]
 pub struct ValidatorStore<T, E: EthSpec> {
     validators: Arc<RwLock<HashMap<PublicKey, LocalValidator>>>,