Support multiple BLS implementations (#1335)

## Issue Addressed

NA

## Proposed Changes

- Refactor the `bls` crate to support multiple BLS "backends" (e.g., milagro, blst, etc).
- Removes some duplicate, unused code in `common/rest_types/src/validator.rs`.
- Removes the old "upgrade legacy keypairs" functionality (these were unencrypted keys that haven't been supported for a few testnets, no one should be using them anymore).

## Additional Info

Most of the files changed are just inconsequential changes to function names.

## TODO

- [x] Optimization levels
- [x] Infinity point: https://github.com/supranational/blst/issues/11
- [x] Ensure milagro *and* blst are tested via CI
- [x] What to do with unsafe code?
- [x] Test infinity point in signature sets

beacon_node/beacon_chain/src/attestation_verification.rs

@@ -521,7 +521,7 @@ pub fn verify_attestation_signature<T: BeaconChainTypes>(
     let _signature_verification_timer =
         metrics::start_timer(&metrics::ATTESTATION_PROCESSING_SIGNATURE_TIMES);
 
-    if signature_set.is_valid() {
+    if signature_set.verify() {
         Ok(())
     } else {
         Err(Error::InvalidSignature)
@@ -589,7 +589,7 @@ pub fn verify_signed_aggregate_signatures<T: BeaconChainTypes>(
         .map_err(BeaconChainError::SignatureSetError)?,
     ];
 
-    Ok(verify_signature_sets(signature_sets))
+    Ok(verify_signature_sets(signature_sets.iter()))
 }
 
 /// Assists in readability.

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -862,7 +862,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                     root: target_root,
                 },
             },
-            signature: AggregateSignature::empty_signature(),
+            signature: AggregateSignature::empty(),
         })
     }
 
@@ -1654,7 +1654,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 },
             },
             // The block is not signed here, that is the task of a validator client.
-            signature: Signature::empty_signature(),
+            signature: Signature::empty(),
         };
 
         per_block_processing(

beacon_node/beacon_chain/src/builder.rs

@@ -666,7 +666,7 @@ fn genesis_block<T: EthSpec>(
         message: BeaconBlock::empty(&spec),
         // Empty signature, which should NEVER be read. This isn't to-spec, but makes the genesis
         // block consistent with every other block.
-        signature: Signature::empty_signature(),
+        signature: Signature::empty(),
     };
     genesis_block.message.state_root = genesis_state
         .update_tree_hash_cache()

beacon_node/beacon_chain/src/errors.rs

@@ -6,7 +6,6 @@ use crate::observed_attesters::Error as ObservedAttestersError;
 use crate::observed_block_producers::Error as ObservedBlockProducersError;
 use operation_pool::OpPoolError;
 use safe_arith::ArithError;
-use ssz::DecodeError;
 use ssz_types::Error as SszTypesError;
 use state_processing::{
     block_signature_verifier::Error as BlockSignatureVerifierError,
@@ -69,7 +68,7 @@ pub enum BeaconChainError {
     AttestationCacheLockTimeout,
     ValidatorPubkeyCacheLockTimeout,
     IncorrectStateForAttestation(RelativeEpochError),
-    InvalidValidatorPubkeyBytes(DecodeError),
+    InvalidValidatorPubkeyBytes(bls::Error),
     ValidatorPubkeyCacheIncomplete(usize),
     SignatureSetError(SignatureSetError),
     BlockSignatureVerifierError(state_processing::block_signature_verifier::Error),

beacon_node/beacon_chain/src/snapshot_cache.rs

@@ -99,7 +99,7 @@ mod test {
     use super::*;
     use types::{
         test_utils::{generate_deterministic_keypair, TestingBeaconStateBuilder},
-        BeaconBlock, Epoch, MainnetEthSpec, Signature, SignedBeaconBlock, Slot,
+        BeaconBlock, Epoch, MainnetEthSpec, SignedBeaconBlock, Slot,
     };
 
     const CACHE_SIZE: usize = 4;
@@ -115,7 +115,9 @@ mod test {
             beacon_state_root: Hash256::from_low_u64_be(i),
             beacon_block: SignedBeaconBlock {
                 message: BeaconBlock::empty(&spec),
-                signature: Signature::new(&[42], &generate_deterministic_keypair(0).sk),
+                signature: generate_deterministic_keypair(0)
+                    .sk
+                    .sign(Hash256::from_low_u64_be(42)),
             },
             beacon_block_root: Hash256::from_low_u64_be(i),
         }

beacon_node/beacon_chain/src/test_utils.rs

@@ -23,8 +23,8 @@ use tempfile::{tempdir, TempDir};
 use tree_hash::TreeHash;
 use types::{
     AggregateSignature, Attestation, BeaconState, BeaconStateHash, ChainSpec, Domain, EthSpec,
-    Hash256, Keypair, SecretKey, SelectionProof, Signature, SignedAggregateAndProof,
-    SignedBeaconBlock, SignedBeaconBlockHash, SignedRoot, Slot, SubnetId,
+    Hash256, Keypair, SecretKey, SelectionProof, SignedAggregateAndProof, SignedBeaconBlock,
+    SignedBeaconBlockHash, SignedRoot, Slot, SubnetId,
 };
 
 pub use types::test_utils::generate_deterministic_keypairs;
@@ -515,7 +515,7 @@ where
                 self.spec
                     .get_domain(epoch, Domain::Randao, fork, state.genesis_validators_root);
             let message = epoch.signing_root(domain);
-            Signature::new(message.as_bytes(), sk)
+            sk.sign(message)
         };
 
         let (block, state) = self
@@ -586,12 +586,9 @@ where
 
                             let message = attestation.data.signing_root(domain);
 
-                            let mut agg_sig = AggregateSignature::new();
+                            let mut agg_sig = AggregateSignature::infinity();
 
-                            agg_sig.add(&Signature::new(
-                                message.as_bytes(),
-                                self.get_sk(*validator_index),
-                            ));
+                            agg_sig.add_assign(&self.get_sk(*validator_index).sign(message));
 
                             agg_sig
                         };

beacon_node/beacon_chain/src/validator_pubkey_cache.rs

@@ -140,6 +140,7 @@ struct ValidatorPubkeyCacheFile(File);
 enum Error {
     Io(io::Error),
     Ssz(DecodeError),
+    PubkeyDecode(bls::Error),
     /// The file read from disk does not have a contiguous list of validator public keys. The file
     /// has become corrupted.
     InconsistentIndex {
@@ -200,7 +201,7 @@ impl ValidatorPubkeyCacheFile {
             let expected = last.map(|n| n + 1);
             if expected.map_or(true, |expected| index == expected) {
                 last = Some(index);
-                pubkeys.push((&pubkey).try_into().map_err(Error::Ssz)?);
+                pubkeys.push((&pubkey).try_into().map_err(Error::PubkeyDecode)?);
                 indices.insert(pubkey, index);
             } else {
                 return Err(Error::InconsistentIndex {