Update /validator/subscribe (#969)

* Add progress on duties refactor

* Add simple is_aggregator bool to val subscription

* Remove unused function

eth2/types/src/aggregate_and_proof.rs

@@ -1,5 +1,6 @@
 use super::{
-    Attestation, ChainSpec, Domain, EthSpec, Fork, PublicKey, SecretKey, Signature, SignedRoot,
+    Attestation, ChainSpec, Domain, EthSpec, Fork, PublicKey, SecretKey, SelectionProof, Signature,
+    SignedRoot,
 };
 use crate::test_utils::TestRandom;
 use serde_derive::{Deserialize, Serialize};
@@ -32,20 +33,13 @@ impl<T: EthSpec> AggregateAndProof<T> {
         fork: &Fork,
         spec: &ChainSpec,
     ) -> Self {
-        let slot = aggregate.data.slot;
-
-        let domain = spec.get_domain(
-            slot.epoch(T::slots_per_epoch()),
-            Domain::SelectionProof,
-            fork,
-        );
-
-        let message = slot.signing_root(domain);
+        let selection_proof =
+            SelectionProof::new::<T>(aggregate.data.slot, secret_key, fork, spec).into();
 
         Self {
             aggregator_index,
             aggregate,
-            selection_proof: Signature::new(message.as_bytes(), secret_key),
+            selection_proof,
         }
     }
 

eth2/types/src/lib.rs

@@ -32,6 +32,7 @@ pub mod indexed_attestation;
 pub mod pending_attestation;
 pub mod proposer_slashing;
 pub mod relative_epoch;
+pub mod selection_proof;
 pub mod signed_aggregate_and_proof;
 pub mod signed_beacon_block;
 pub mod signed_beacon_block_header;
@@ -72,6 +73,7 @@ pub use crate::indexed_attestation::IndexedAttestation;
 pub use crate::pending_attestation::PendingAttestation;
 pub use crate::proposer_slashing::ProposerSlashing;
 pub use crate::relative_epoch::{Error as RelativeEpochError, RelativeEpoch};
+pub use crate::selection_proof::SelectionProof;
 pub use crate::signed_aggregate_and_proof::SignedAggregateAndProof;
 pub use crate::signed_beacon_block::SignedBeaconBlock;
 pub use crate::signed_beacon_block_header::SignedBeaconBlockHeader;

eth2/types/src/selection_proof.rs

@@ -0,0 +1,42 @@
+use crate::{ChainSpec, Domain, EthSpec, Fork, SecretKey, Signature, SignedRoot, Slot};
+use std::convert::TryInto;
+use tree_hash::TreeHash;
+
+#[derive(PartialEq, Debug, Clone)]
+pub struct SelectionProof(Signature);
+
+impl SelectionProof {
+    pub fn new<T: EthSpec>(
+        slot: Slot,
+        secret_key: &SecretKey,
+        fork: &Fork,
+        spec: &ChainSpec,
+    ) -> Self {
+        let domain = spec.get_domain(
+            slot.epoch(T::slots_per_epoch()),
+            Domain::SelectionProof,
+            fork,
+        );
+        let message = slot.signing_root(domain);
+
+        Self(Signature::new(message.as_bytes(), secret_key))
+    }
+
+    pub fn is_aggregator(&self, modulo: u64) -> bool {
+        let signature_hash = self.0.tree_hash_root();
+        let signature_hash_int = u64::from_le_bytes(
+            signature_hash[0..8]
+                .as_ref()
+                .try_into()
+                .expect("first 8 bytes of signature should always convert to fixed array"),
+        );
+
+        signature_hash_int % modulo == 0
+    }
+}
+
+impl Into<Signature> for SelectionProof {
+    fn into(self) -> Signature {
+        self.0
+    }
+}