Merge pull request #1830 from ethereum/neutral-rewards

Ensure balances remain unchanged for optimal validators during leak

specs/phase0/beacon-chain.md

@@ -1354,6 +1354,25 @@ def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
     return Gwei(effective_balance * BASE_REWARD_FACTOR // integer_squareroot(total_balance) // BASE_REWARDS_PER_EPOCH)
 ```
 
+
+```python
+def get_proposer_reward(state: BeaconState, attesting_index: ValidatorIndex) -> Gwei:
+    return Gwei(get_base_reward(state, attesting_index) // PROPOSER_REWARD_QUOTIENT)
+```
+
+
+```python
+def get_finality_delay(state: BeaconState) -> uint64:
+    return get_previous_epoch(state) - state.finalized_checkpoint.epoch
+```
+
+
+```python
+def is_in_inactivity_leak(state: BeaconState) -> bool:
+    return get_finality_delay(state) > MIN_EPOCHS_TO_INACTIVITY_PENALTY
+```
+
+
 ```python
 def get_eligible_validator_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
     previous_epoch = get_previous_epoch(state)
@@ -1378,8 +1397,13 @@ def get_attestation_component_deltas(state: BeaconState,
     for index in get_eligible_validator_indices(state):
         if index in unslashed_attesting_indices:
             increment = EFFECTIVE_BALANCE_INCREMENT  # Factored out from balance totals to avoid uint64 overflow
-            reward_numerator = get_base_reward(state, index) * (attesting_balance // increment)
-            rewards[index] += reward_numerator // (total_balance // increment)
+            if is_in_inactivity_leak(state):
+                # Since full base reward will be canceled out by inactivity penalty deltas,
+                # optimal participation receives full base reward compensation here.
+                rewards[index] += get_base_reward(state, index)
+            else:
+                reward_numerator = get_base_reward(state, index) * (attesting_balance // increment)
+                rewards[index] += reward_numerator // (total_balance // increment)
         else:
             penalties[index] += get_base_reward(state, index)
     return rewards, penalties
@@ -1426,9 +1450,8 @@ def get_inclusion_delay_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequ
             a for a in matching_source_attestations
             if index in get_attesting_indices(state, a.data, a.aggregation_bits)
         ], key=lambda a: a.inclusion_delay)
-        proposer_reward = Gwei(get_base_reward(state, index) // PROPOSER_REWARD_QUOTIENT)
-        rewards[attestation.proposer_index] += proposer_reward
-        max_attester_reward = get_base_reward(state, index) - proposer_reward
+        rewards[attestation.proposer_index] += get_proposer_reward(state, index)
+        max_attester_reward = get_base_reward(state, index) - get_proposer_reward(state, index)
         rewards[index] += Gwei(max_attester_reward // attestation.inclusion_delay)
 
     # No penalties associated with inclusion delay
@@ -1442,16 +1465,16 @@ def get_inactivity_penalty_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], S
     Return inactivity reward/penalty deltas for each validator.
     """
     penalties = [Gwei(0) for _ in range(len(state.validators))]
-    finality_delay = get_previous_epoch(state) - state.finalized_checkpoint.epoch
-
-    if finality_delay > MIN_EPOCHS_TO_INACTIVITY_PENALTY:
+    if is_in_inactivity_leak(state):
         matching_target_attestations = get_matching_target_attestations(state, get_previous_epoch(state))
         matching_target_attesting_indices = get_unslashed_attesting_indices(state, matching_target_attestations)
         for index in get_eligible_validator_indices(state):
-            penalties[index] += Gwei(BASE_REWARDS_PER_EPOCH * get_base_reward(state, index))
+            # If validator is performing optimally this cancels all rewards for a neutral balance
+            base_reward = get_base_reward(state, index)
+            penalties[index] += Gwei(BASE_REWARDS_PER_EPOCH * base_reward - get_proposer_reward(state, index))
             if index not in matching_target_attesting_indices:
                 effective_balance = state.validators[index].effective_balance
-                penalties[index] += Gwei(effective_balance * finality_delay // INACTIVITY_PENALTY_QUOTIENT)
+                penalties[index] += Gwei(effective_balance * get_finality_delay(state) // INACTIVITY_PENALTY_QUOTIENT)
 
     # No rewards associated with inactivity penalties
     rewards = [Gwei(0) for _ in range(len(state.validators))]

tests/core/pyspec/eth2spec/test/helpers/rewards.py

@@ -1,4 +1,5 @@
 from random import Random
+from lru import LRU
 
 from eth2spec.phase0 import spec as spec_phase0
 from eth2spec.test.helpers.attestations import cached_prepare_state_with_attestations
@@ -150,16 +151,16 @@ def run_get_inactivity_penalty_deltas(spec, state):
     matching_attestations = spec.get_matching_target_attestations(state, spec.get_previous_epoch(state))
     matching_attesting_indices = spec.get_unslashed_attesting_indices(state, matching_attestations)
 
-    finality_delay = spec.get_previous_epoch(state) - state.finalized_checkpoint.epoch
     eligible_indices = spec.get_eligible_validator_indices(state)
     for index in range(len(state.validators)):
         assert rewards[index] == 0
         if index not in eligible_indices:
             assert penalties[index] == 0
             continue
 
-        if finality_delay > spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY:
-            base_penalty = spec.BASE_REWARDS_PER_EPOCH * spec.get_base_reward(state, index)
+        if spec.is_in_inactivity_leak(state):
+            base_reward = spec.get_base_reward(state, index)
+            base_penalty = spec.BASE_REWARDS_PER_EPOCH * base_reward - spec.get_proposer_reward(state, index)
             if not has_enough_for_reward(spec, state, index):
                 assert penalties[index] == 0
             elif index in matching_attesting_indices:
@@ -170,6 +171,39 @@ def run_get_inactivity_penalty_deltas(spec, state):
             assert penalties[index] == 0
 
 
+def transition_state_to_leak(spec, state, epochs=None):
+    if epochs is None:
+        epochs = spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY
+    assert epochs >= spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY
+
+    for _ in range(epochs):
+        next_epoch(spec, state)
+
+
+_cache_dict = LRU(size=10)
+
+
+def leaking(epochs=None):
+
+    def deco(fn):
+        def entry(*args, spec, state, **kw):
+            # If the pre-state is not already known in the LRU, then take it,
+            # transition it to leak, and put it in the LRU.
+            # The input state is likely already cached, so the hash-tree-root does not affect speed.
+            key = (state.hash_tree_root(), spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY, spec.SLOTS_PER_EPOCH, epochs)
+            global _cache_dict
+            if key not in _cache_dict:
+                transition_state_to_leak(spec, state, epochs=epochs)
+                _cache_dict[key] = state.get_backing()  # cache the tree structure, not the view wrapping it.
+
+            # Take an entry out of the LRU.
+            # No copy is necessary, as we wrap the immutable backing with a new view.
+            state = spec.BeaconState(backing=_cache_dict[key])
+            return fn(*args, spec=spec, state=state, **kw)
+        return entry
+    return deco
+
+
 def set_some_new_deposits(spec, state, rng):
     num_validators = len(state.validators)
     # Set ~1/10 to just recently deposited

tests/core/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_rewards_and_penalties.py

@@ -14,6 +14,7 @@
     get_valid_attestation,
     prepare_state_with_attestations,
 )
+from eth2spec.test.helpers.rewards import leaking
 from eth2spec.test.helpers.attester_slashings import get_indexed_attestation_participants
 from eth2spec.test.phase_0.epoch_processing.run_epoch_process_base import run_epoch_processing_with
 from random import Random
@@ -62,24 +63,6 @@ def test_genesis_epoch_full_attestations_no_rewards(spec, state):
         assert state.balances[index] == pre_state.balances[index]
 
 
-@with_all_phases
-@spec_state_test
-def test_full_attestations(spec, state):
-    attestations = prepare_state_with_attestations(spec, state)
-
-    pre_state = state.copy()
-
-    yield from run_process_rewards_and_penalties(spec, state)
-
-    attesting_indices = spec.get_unslashed_attesting_indices(state, attestations)
-    assert len(attesting_indices) == len(pre_state.validators)
-    for index in range(len(pre_state.validators)):
-        if index in attesting_indices:
-            assert state.balances[index] > pre_state.balances[index]
-        else:
-            assert state.balances[index] < pre_state.balances[index]
-
-
 @with_all_phases
 @spec_state_test
 def test_full_attestations_random_incorrect_fields(spec, state):
@@ -173,6 +156,7 @@ def participation_tracker(slot, comm_index, comm):
         return att_participants
 
     attestations = prepare_state_with_attestations(spec, state, participation_fn=participation_tracker)
+    proposer_indices = [a.proposer_index for a in state.previous_epoch_attestations]
 
     pre_state = state.copy()
 
@@ -182,10 +166,20 @@ def participation_tracker(slot, comm_index, comm):
     assert len(attesting_indices) == len(participated)
 
     for index in range(len(pre_state.validators)):
-        if index in participated:
-            assert state.balances[index] > pre_state.balances[index]
+        if spec.is_in_inactivity_leak(state):
+            # Proposers can still make money during a leak
+            if index in proposer_indices and index in participated:
+                assert state.balances[index] > pre_state.balances[index]
+            # If not proposer but participated optimally, should have exactly neutral balance
+            elif index in attesting_indices:
+                assert state.balances[index] == pre_state.balances[index]
+            else:
+                assert state.balances[index] < pre_state.balances[index]
         else:
-            assert state.balances[index] < pre_state.balances[index]
+            if index in participated:
+                assert state.balances[index] > pre_state.balances[index]
+            else:
+                assert state.balances[index] < pre_state.balances[index]
 
 
 @with_all_phases
@@ -195,26 +189,57 @@ def test_almost_empty_attestations(spec, state):
     yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, 1))
 
 
+@with_all_phases
+@spec_state_test
+@leaking()
+def test_almost_empty_attestations_with_leak(spec, state):
+    rng = Random(1234)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, 1))
+
+
 @with_all_phases
 @spec_state_test
 def test_random_fill_attestations(spec, state):
     rng = Random(4567)
     yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) // 3))
 
 
+@with_all_phases
+@spec_state_test
+@leaking()
+def test_random_fill_attestations_with_leak(spec, state):
+    rng = Random(4567)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) // 3))
+
+
 @with_all_phases
 @spec_state_test
 def test_almost_full_attestations(spec, state):
     rng = Random(8901)
     yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) - 1))
 
 
+@with_all_phases
+@spec_state_test
+@leaking()
+def test_almost_full_attestations_with_leak(spec, state):
+    rng = Random(8901)
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: rng.sample(comm, len(comm) - 1))
+
+
 @with_all_phases
 @spec_state_test
 def test_full_attestation_participation(spec, state):
     yield from run_with_participation(spec, state, lambda slot, comm_index, comm: comm)
 
 
+@with_all_phases
+@spec_state_test
+@leaking()
+def test_full_attestation_participation_with_leak(spec, state):
+    yield from run_with_participation(spec, state, lambda slot, comm_index, comm: comm)
+
+
 @with_all_phases
 @spec_state_test
 def test_duplicate_attestation(spec, state):

tests/core/pyspec/eth2spec/test/phase_0/rewards/test_leak.py

@@ -1,40 +1,6 @@
 from eth2spec.test.context import with_all_phases, spec_state_test
-from eth2spec.test.helpers.state import next_epoch
+from eth2spec.test.helpers.rewards import leaking
 import eth2spec.test.helpers.rewards as rewards_helpers
-from lru import LRU
-
-
-def transition_state_to_leak(spec, state, epochs=None):
-    if epochs is None:
-        epochs = spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY
-    assert epochs >= spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY
-
-    for _ in range(epochs):
-        next_epoch(spec, state)
-
-
-_cache_dict = LRU(size=10)
-
-
-def leaking(epochs=None):
-
-    def deco(fn):
-        def entry(*args, spec, state, **kw):
-            # If the pre-state is not already known in the LRU, then take it,
-            # transition it to leak, and put it in the LRU.
-            # The input state is likely already cached, so the hash-tree-root does not affect speed.
-            key = (state.hash_tree_root(), spec.MIN_EPOCHS_TO_INACTIVITY_PENALTY, spec.SLOTS_PER_EPOCH, epochs)
-            global _cache_dict
-            if key not in _cache_dict:
-                transition_state_to_leak(spec, state, epochs=epochs)
-                _cache_dict[key] = state.get_backing()  # cache the tree structure, not the view wrapping it.
-
-            # Take an entry out of the LRU.
-            # No copy is necessary, as we wrap the immutable backing with a new view.
-            state = spec.BeaconState(backing=_cache_dict[key])
-            return fn(*args, spec=spec, state=state, **kw)
-        return entry
-    return deco
 
 
 @with_all_phases