Merge pull request #1470 from ethereum/v09x

v0.9.1 release to master
ethereum · Nov 8, 2019 · 03fb097 · 03fb097
2 parents 0642ff2 + 240b206
commit 03fb097
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diff --git a/README.md b/README.md
@@ -62,7 +62,6 @@ The following are the broad design goals for Ethereum 2.0:
 
 ## For spec contributors
 
-
 Documentation on the different components used during spec writing can be found here:
 * [YAML Test Generators](test_generators/README.md)
 * [Executable Python Spec, with Py-tests](test_libs/pyspec/README.md)

diff --git a/configs/mainnet.yaml b/configs/mainnet.yaml
@@ -23,6 +23,11 @@ MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 65536
 MIN_GENESIS_TIME: 1578009600
 
 
+# Fork Choice
+# ---------------------------------------------------------------
+# 2**3 (= 8)
+SAFE_SLOTS_TO_UPDATE_JUSTIFIED: 8
+
 
 # Deposit contract
 # ---------------------------------------------------------------
@@ -53,7 +58,7 @@ BLS_WITHDRAWAL_PREFIX: 0x00
 # ---------------------------------------------------------------
 # 12 seconds
 SECONDS_PER_SLOT: 12
-# 2**0 (= 1) slots 6 seconds
+# 2**0 (= 1) slots 12 seconds
 MIN_ATTESTATION_INCLUSION_DELAY: 1
 # 2**5 (= 32) slots 6.4 minutes
 SLOTS_PER_EPOCH: 32

diff --git a/configs/minimal.yaml b/configs/minimal.yaml
@@ -21,6 +21,12 @@ MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 64
 # Jan 3, 2020
 MIN_GENESIS_TIME: 1578009600
 
+#
+#
+# Fork Choice
+# ---------------------------------------------------------------
+# 2**1 (= 1)
+SAFE_SLOTS_TO_UPDATE_JUSTIFIED: 2
 
 
 # Deposit contract

diff --git a/scripts/build_spec.py b/scripts/build_spec.py
@@ -24,14 +24,13 @@
     signing_root,
 )
 from eth2spec.utils.ssz.ssz_typing import (
-    bit, boolean, Container, List, Vector, uint64,
+    boolean, Container, List, Vector, uint64,
     Bytes1, Bytes4, Bytes8, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
 )
 from eth2spec.utils.bls import (
     bls_aggregate_signatures,
     bls_aggregate_pubkeys,
     bls_verify,
-    bls_verify_multiple,
     bls_sign,
 )
 

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
@@ -26,7 +26,6 @@
             - [`Checkpoint`](#checkpoint)
             - [`Validator`](#validator)
             - [`AttestationData`](#attestationdata)
-            - [`AttestationDataAndCustodyBit`](#attestationdataandcustodybit)
             - [`IndexedAttestation`](#indexedattestation)
             - [`PendingAttestation`](#pendingattestation)
             - [`Eth1Data`](#eth1data)
@@ -55,7 +54,6 @@
             - [`hash_tree_root`](#hash_tree_root)
             - [`signing_root`](#signing_root)
             - [`bls_verify`](#bls_verify)
-            - [`bls_verify_multiple`](#bls_verify_multiple)
             - [`bls_aggregate_pubkeys`](#bls_aggregate_pubkeys)
         - [Predicates](#predicates)
             - [`is_active_validator`](#is_active_validator)
@@ -204,8 +202,8 @@ The following values are (non-configurable) constants used throughout the specif
 | `SLOTS_PER_EPOCH` | `2**5` (= 32) | slots | 6.4 minutes |
 | `MIN_SEED_LOOKAHEAD` | `2**0` (= 1) | epochs | 6.4 minutes |
 | `MAX_SEED_LOOKAHEAD` | `2**2` (= 4) | epochs | 25.6 minutes |
-| `SLOTS_PER_ETH1_VOTING_PERIOD` | `2**10` (= 1,024) | slots | ~1.7 hours |
-| `SLOTS_PER_HISTORICAL_ROOT` | `2**13` (= 8,192) | slots | ~13 hours |
+| `SLOTS_PER_ETH1_VOTING_PERIOD` | `2**10` (= 1,024) | slots | ~3.4 hours |
+| `SLOTS_PER_HISTORICAL_ROOT` | `2**13` (= 8,192) | slots | ~27 hours |
 | `MIN_VALIDATOR_WITHDRAWABILITY_DELAY` | `2**8` (= 256) | epochs | ~27 hours |
 | `PERSISTENT_COMMITTEE_PERIOD` | `2**11` (= 2,048) | epochs | 9 days |
 | `MIN_EPOCHS_TO_INACTIVITY_PENALTY` | `2**2` (= 4) | epochs | 25.6 minutes |
@@ -308,20 +306,11 @@ class AttestationData(Container):
     target: Checkpoint
 ```
 
-#### `AttestationDataAndCustodyBit`
-
-```python
-class AttestationDataAndCustodyBit(Container):
-    data: AttestationData
-    custody_bit: bit  # Challengeable bit (SSZ-bool, 1 byte) for the custody of shard data
-```
-
 #### `IndexedAttestation`
 
 ```python
 class IndexedAttestation(Container):
-    custody_bit_0_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]  # Indices with custody bit equal to 0
-    custody_bit_1_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]  # Indices with custody bit equal to 1
+    attesting_indices: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]
     data: AttestationData
     signature: BLSSignature
 ```
@@ -399,7 +388,6 @@ class AttesterSlashing(Container):
 class Attestation(Container):
     aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
     data: AttestationData
-    custody_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]
     signature: BLSSignature
 ```
 
@@ -553,10 +541,6 @@ def bytes_to_int(data: bytes) -> uint64:
 
 `bls_verify` is a function for verifying a BLS signature, as defined in the [BLS Signature spec](../bls_signature.md#bls_verify).
 
-#### `bls_verify_multiple`
-
-`bls_verify_multiple` is a function for verifying a BLS signature constructed from multiple messages, as defined in the [BLS Signature spec](../bls_signature.md#bls_verify_multiple).
-
 #### `bls_aggregate_pubkeys`
 
 `bls_aggregate_pubkeys` is a function for aggregating multiple BLS public keys into a single aggregate key, as defined in the [BLS Signature spec](../bls_signature.md#bls_aggregate_pubkeys).
@@ -605,31 +589,18 @@ def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
     """
     Check if ``indexed_attestation`` has valid indices and signature.
     """
-    bit_0_indices = indexed_attestation.custody_bit_0_indices
-    bit_1_indices = indexed_attestation.custody_bit_1_indices
+    indices = indexed_attestation.attesting_indices
 
-    # Verify no index has custody bit equal to 1 [to be removed in phase 1]
-    if not len(bit_1_indices) == 0:  # [to be removed in phase 1]
-        return False                 # [to be removed in phase 1]
     # Verify max number of indices
-    if not len(bit_0_indices) + len(bit_1_indices) <= MAX_VALIDATORS_PER_COMMITTEE:
-        return False
-    # Verify index sets are disjoint
-    if not len(set(bit_0_indices).intersection(bit_1_indices)) == 0:
+    if not len(indices) <= MAX_VALIDATORS_PER_COMMITTEE:
         return False
     # Verify indices are sorted
-    if not (bit_0_indices == sorted(bit_0_indices) and bit_1_indices == sorted(bit_1_indices)):
+    if not indices == sorted(indices):
         return False
     # Verify aggregate signature
-    if not bls_verify_multiple(
-        pubkeys=[
-            bls_aggregate_pubkeys([state.validators[i].pubkey for i in bit_0_indices]),
-            bls_aggregate_pubkeys([state.validators[i].pubkey for i in bit_1_indices]),
-        ],
-        message_hashes=[
-            hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b0)),
-            hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b1)),
-        ],
+    if not bls_verify(
+        pubkey=bls_aggregate_pubkeys([state.validators[i].pubkey for i in indices]),
+        message_hash=hash_tree_root(indexed_attestation.data),
         signature=indexed_attestation.signature,
         domain=get_domain(state, DOMAIN_BEACON_ATTESTER, indexed_attestation.data.target.epoch),
     ):
@@ -922,13 +893,9 @@ def get_indexed_attestation(state: BeaconState, attestation: Attestation) -> Ind
     Return the indexed attestation corresponding to ``attestation``.
     """
     attesting_indices = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
-    custody_bit_1_indices = get_attesting_indices(state, attestation.data, attestation.custody_bits)
-    assert custody_bit_1_indices.issubset(attesting_indices)
-    custody_bit_0_indices = attesting_indices.difference(custody_bit_1_indices)
 
     return IndexedAttestation(
-        custody_bit_0_indices=sorted(custody_bit_0_indices),
-        custody_bit_1_indices=sorted(custody_bit_1_indices),
+        attesting_indices=sorted(attesting_indices),
         data=attestation.data,
         signature=attestation.signature,
     )
@@ -1026,7 +993,7 @@ Before the Ethereum 2.0 genesis has been triggered, and for every Ethereum 1.0 b
 
 - `eth1_block_hash` is the hash of the Ethereum 1.0 block
 - `eth1_timestamp` is the Unix timestamp corresponding to `eth1_block_hash`
-- `deposits` is the sequence of all deposits, ordered chronologically, up to the block with hash `eth1_block_hash`
+- `deposits` is the sequence of all deposits, ordered chronologically, up to (and including) the block with hash `eth1_block_hash`
 
 ```python
 def initialize_beacon_state_from_eth1(eth1_block_hash: Hash,
@@ -1460,9 +1427,8 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
     assert is_valid_indexed_attestation(state, attestation_2)
 
     slashed_any = False
-    attesting_indices_1 = attestation_1.custody_bit_0_indices + attestation_1.custody_bit_1_indices
-    attesting_indices_2 = attestation_2.custody_bit_0_indices + attestation_2.custody_bit_1_indices
-    for index in sorted(set(attesting_indices_1).intersection(attesting_indices_2)):
+    indices = set(attestation_1.attesting_indices).intersection(attestation_2.attesting_indices)
+    for index in sorted(indices):
         if is_slashable_validator(state.validators[index], get_current_epoch(state)):
             slash_validator(state, index)
             slashed_any = True
@@ -1479,7 +1445,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH
 
     committee = get_beacon_committee(state, data.slot, data.index)
-    assert len(attestation.aggregation_bits) == len(attestation.custody_bits) == len(committee)
+    assert len(attestation.aggregation_bits) == len(committee)
 
     pending_attestation = PendingAttestation(
         data=data,

diff --git a/specs/core/0_fork-choice.md b/specs/core/0_fork-choice.md
@@ -43,6 +43,12 @@ The head block root associated with a `store` is defined as `get_head(store)`. A
 4) **Manual forks**: Manual forks may arbitrarily change the fork choice rule but are expected to be enacted at epoch transitions, with the fork details reflected in `state.fork`.
 5) **Implementation**: The implementation found in this specification is constructed for ease of understanding rather than for optimization in computation, space, or any other resource. A number of optimized alternatives can be found [here](https://github.com/protolambda/lmd-ghost).
 
+### Configuration
+
+| Name | Value | Unit | Duration |
+| - | - | :-: | :-: |
+| `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` | `2**3` (= 8) | slots | 96 seconds |
+
 ### Helpers
 
 #### `LatestMessage`
@@ -60,8 +66,10 @@ class LatestMessage(object):
 @dataclass
 class Store(object):
     time: uint64
+    genesis_time: uint64
     justified_checkpoint: Checkpoint
     finalized_checkpoint: Checkpoint
+    best_justified_checkpoint: Checkpoint
     blocks: Dict[Hash, BeaconBlock] = field(default_factory=dict)
     block_states: Dict[Hash, BeaconState] = field(default_factory=dict)
     checkpoint_states: Dict[Checkpoint, BeaconState] = field(default_factory=dict)
@@ -78,14 +86,30 @@ def get_genesis_store(genesis_state: BeaconState) -> Store:
     finalized_checkpoint = Checkpoint(epoch=GENESIS_EPOCH, root=root)
     return Store(
         time=genesis_state.genesis_time,
+        genesis_time=genesis_state.genesis_time,
         justified_checkpoint=justified_checkpoint,
         finalized_checkpoint=finalized_checkpoint,
+        best_justified_checkpoint=justified_checkpoint,
         blocks={root: genesis_block},
         block_states={root: genesis_state.copy()},
         checkpoint_states={justified_checkpoint: genesis_state.copy()},
     )
 ```
 
+#### `get_current_slot`
+
+```python
+def get_current_slot(store: Store) -> Slot:
+    return Slot((store.time - store.genesis_time) // SECONDS_PER_SLOT)
+```
+
+#### `compute_slots_since_epoch_start`
+
+```python
+def compute_slots_since_epoch_start(slot: Slot) -> int:
+    return slot - compute_start_slot_at_epoch(compute_epoch_at_slot(slot))
+```
+
 #### `get_ancestor`
 
 ```python
@@ -130,13 +154,50 @@ def get_head(store: Store) -> Hash:
         head = max(children, key=lambda root: (get_latest_attesting_balance(store, root), root))
 ```
 
+#### `should_update_justified_checkpoint`
+
+```python
+def should_update_justified_checkpoint(store: Store, new_justified_checkpoint: Checkpoint) -> bool:
+    """
+    To address the bouncing attack, only update conflicting justified
+    checkpoints in the fork choice if in the early slots of the epoch.
+    Otherwise, delay incorporation of new justified checkpoint until next epoch boundary.
+
+    See https://ethresear.ch/t/prevention-of-bouncing-attack-on-ffg/6114 for more detailed analysis and discussion.
+    """
+    if compute_slots_since_epoch_start(get_current_slot(store)) < SAFE_SLOTS_TO_UPDATE_JUSTIFIED:
+        return True
+
+    new_justified_block = store.blocks[new_justified_checkpoint.root]
+    if new_justified_block.slot <= compute_start_slot_at_epoch(store.justified_checkpoint.epoch):
+        return False
+    if not (
+        get_ancestor(store, new_justified_checkpoint.root, store.blocks[store.justified_checkpoint.root].slot) ==
+        store.justified_checkpoint.root
+    ):
+        return False
+
+    return True
+```
+
 ### Handlers
 
 #### `on_tick`
 
 ```python
 def on_tick(store: Store, time: uint64) -> None:
+    previous_slot = get_current_slot(store)
+
+    # update store time
     store.time = time
+
+    current_slot = get_current_slot(store)
+    # Not a new epoch, return
+    if not (current_slot > previous_slot and compute_slots_since_epoch_start(current_slot) == 0):
+        return
+    # Update store.justified_checkpoint if a better checkpoint is known
+    if store.best_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
+        store.justified_checkpoint = store.best_justified_checkpoint
 ```
 
 #### `on_block`
@@ -164,7 +225,9 @@ def on_block(store: Store, block: BeaconBlock) -> None:
 
     # Update justified checkpoint
     if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
-        store.justified_checkpoint = state.current_justified_checkpoint
+        store.best_justified_checkpoint = state.current_justified_checkpoint
+        if should_update_justified_checkpoint(store, state.current_justified_checkpoint):
+            store.justified_checkpoint = state.current_justified_checkpoint
 
     # Update finalized checkpoint
     if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch:
@@ -177,6 +240,11 @@ def on_block(store: Store, block: BeaconBlock) -> None:
 def on_attestation(store: Store, attestation: Attestation) -> None:
     target = attestation.data.target
 
+    # Attestations must be from the current or previous epoch 
+    current_epoch = compute_epoch_at_slot(get_current_slot(store))
+    # Use GENESIS_EPOCH for previous when genesis to avoid underflow
+    previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else GENESIS_EPOCH
+    assert target.epoch in [current_epoch, previous_epoch]
     # Cannot calculate the current shuffling if have not seen the target
     assert target.root in store.blocks
 
@@ -199,7 +267,7 @@ def on_attestation(store: Store, attestation: Attestation) -> None:
     assert is_valid_indexed_attestation(target_state, indexed_attestation)
 
     # Update latest messages
-    for i in indexed_attestation.custody_bit_0_indices + indexed_attestation.custody_bit_1_indices:
+    for i in indexed_attestation.attesting_indices:
         if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
             store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=attestation.data.beacon_block_root)
 ```