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Implement #459 (light client friendliness) #476

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merged 14 commits into from
Jan 25, 2019
Merged

Implement #459 (light client friendliness) #476

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9e75a76
Implement #459
vbuterin Jan 19, 2019
47170bf
Merge branch 'master' into vbuterin-patch-2
hwwhww Jan 19, 2019
958c338
Update specs/core/0_beacon-chain.md
hwwhww Jan 20, 2019
02725b8
Update specs/core/0_beacon-chain.md
hwwhww Jan 20, 2019
12b217d
Updated as per hww's suggestions
vbuterin Jan 20, 2019
afd9260
Merge branch 'master' into vbuterin-patch-2
hwwhww Jan 22, 2019
697545a
Added entry_exit_effect_slot helper and moved index roots update
vbuterin Jan 23, 2019
f9097bf
Update specs/core/0_beacon-chain.md
djrtwo Jan 23, 2019
ac47c21
Merge branch 'master' into vbuterin-patch-2
vbuterin Jan 24, 2019
f61d364
clean up top language in validator registry section
djrtwo Jan 25, 2019
f96cd87
update ordering of assignments
djrtwo Jan 25, 2019
86faacd
clarify assignments in val reg not change
djrtwo Jan 25, 2019
5603772
add missing period
djrtwo Jan 25, 2019
85d39af
add missing period
djrtwo Jan 25, 2019
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96 changes: 39 additions & 57 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,6 @@
- [Reward and penalty quotients](#reward-and-penalty-quotients)
- [Status flags](#status-flags)
- [Max operations per block](#max-operations-per-block)
- [Validator registry delta flags](#validator-registry-delta-flags)
- [Signature domains](#signature-domains)
- [Data structures](#data-structures)
- [Beacon chain operations](#beacon-chain-operations)
Expand Down Expand Up @@ -47,7 +46,6 @@
- [`Crosslink`](#crosslink)
- [`PendingAttestation`](#pendingattestation)
- [`Fork`](#fork)
- [`ValidatorRegistryDeltaBlock`](#validatorregistrydeltablock)
- [`Eth1Data`](#eth1data)
- [`Eth1DataVote`](#eth1datavote)
- [Ethereum 1.0 deposit contract](#ethereum-10-deposit-contract)
Expand All @@ -73,6 +71,7 @@
- [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot)
- [`get_block_root`](#get_block_root)
- [`get_randao_mix`](#get_randao_mix)
- [`get_active_index_root`](#get_active_index_root)
- [`get_beacon_proposer_index`](#get_beacon_proposer_index)
- [`merkle_root`](#merkle_root)
- [`get_attestation_participants`](#get_attestation_participants)
Expand Down Expand Up @@ -168,6 +167,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
| `MAX_CASPER_VOTES` | `2**10` (= 1,024) | votes |
| `LATEST_BLOCK_ROOTS_LENGTH` | `2**13` (= 8,192) | block roots |
| `LATEST_RANDAO_MIXES_LENGTH` | `2**13` (= 8,192) | randao mixes |
| `LATEST_INDEX_ROOTS_LENGTH` | `2**13` (= 8,192) | index roots |
| `LATEST_PENALIZED_EXIT_LENGTH` | `2**13` (= 8,192) | epochs | ~36 days |
| `MAX_WITHDRAWALS_PER_EPOCH` | `2**2` (= 4) | withdrawals |

Expand Down Expand Up @@ -235,13 +235,6 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
| `MAX_DEPOSITS` | `2**4` (= 16) |
| `MAX_EXITS` | `2**4` (= 16) |

### Validator registry delta flags

| Name | Value |
| - | - |
| `ACTIVATION` | `0` |
| `EXIT` | `1` |

### Signature domains

| Name | Value |
Expand Down Expand Up @@ -478,7 +471,6 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
'validator_balances': ['uint64'],
'validator_registry_update_slot': 'uint64',
'validator_registry_exit_count': 'uint64',
'validator_registry_delta_chain_tip': 'bytes32', # For light clients to track deltas

# Randomness and committees
'latest_randao_mixes': ['bytes32'],
Expand All @@ -487,8 +479,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
'current_epoch_start_shard': 'uint64',
'previous_epoch_calculation_slot': 'uint64',
'current_epoch_calculation_slot': 'uint64',
'previous_epoch_randao_mix': 'bytes32',
'current_epoch_randao_mix': 'bytes32',
'previous_epoch_seed': 'bytes32',
'current_epoch_seed': 'bytes32',

# Custody challenges
'custody_challenges': [CustodyChallenge],
Expand All @@ -502,6 +494,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
# Recent state
'latest_crosslinks': [Crosslink],
'latest_block_roots': ['bytes32'], # Needed to process attestations, older to newer
'latest_index_roots': ['bytes32'],
'latest_penalized_balances': ['uint64'], # Balances penalized at every withdrawal period
'latest_attestations': [PendingAttestation],
'batched_block_roots': ['bytes32'],
Expand Down Expand Up @@ -584,18 +577,6 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be
}
```

#### `ValidatorRegistryDeltaBlock`

```python
{
'latest_registry_delta_root': 'bytes32',
'validator_index': 'uint24',
'pubkey': 'bytes48',
'slot': 'uint64',
'flag': 'uint64',
}
```

#### `Eth1Data`

```python
Expand Down Expand Up @@ -954,15 +935,15 @@ def get_crosslink_committees_at_slot(state: BeaconState,
if slot < state_epoch_slot:
committees_per_slot = get_previous_epoch_committee_count_per_slot(state)
shuffling = get_shuffling(
state.previous_epoch_randao_mix,
state.previous_epoch_seed,
state.validator_registry,
state.previous_epoch_calculation_slot,
)
slot_start_shard = (state.previous_epoch_start_shard + committees_per_slot * offset) % SHARD_COUNT
else:
committees_per_slot = get_current_epoch_committee_count_per_slot(state)
shuffling = get_shuffling(
state.current_epoch_randao_mix,
state.current_epoch_seed,
state.validator_registry,
state.current_epoch_calculation_slot,
)
Expand Down Expand Up @@ -1007,6 +988,21 @@ def get_randao_mix(state: BeaconState,
return state.latest_randao_mixes[slot % LATEST_RANDAO_MIXES_LENGTH]
```

#### `get_active_index_root`

```python
def get_active_index_root(state: BeaconState,
slot: int) -> Bytes32:
"""
Returns the index root at a recent ``slot``.
"""
state_epoch = state.slot // EPOCH_LENGTH
given_epoch = slot // EPOCH_LENGTH
assert state_epoch < given_epoch + LATEST_INDEX_ROOTS_LENGTH
assert given_epoch <= state_epoch
return state.latest_index_roots[given_epoch % LATEST_INDEX_ROOTS_LENGTH]
```

#### `get_beacon_proposer_index`

```python
Expand Down Expand Up @@ -1235,7 +1231,6 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
validator_balances=[],
validator_registry_update_slot=GENESIS_SLOT,
validator_registry_exit_count=0,
validator_registry_delta_chain_tip=ZERO_HASH,

# Randomness and committees
latest_randao_mixes=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)],
Expand All @@ -1244,8 +1239,8 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
current_epoch_start_shard=GENESIS_START_SHARD,
previous_epoch_calculation_slot=GENESIS_SLOT,
current_epoch_calculation_slot=GENESIS_SLOT,
previous_epoch_randao_mix=ZERO_HASH,
current_epoch_randao_mix=ZERO_HASH,
previous_epoch_seed=ZERO_HASH,
current_epoch_seed=ZERO_HASH,

# Custody challenges
custody_challenges=[],
Expand All @@ -1259,6 +1254,7 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
# Recent state
latest_crosslinks=[Crosslink(slot=GENESIS_SLOT, shard_block_root=ZERO_HASH) for _ in range(SHARD_COUNT)],
latest_block_roots=[ZERO_HASH for _ in range(LATEST_BLOCK_ROOTS_LENGTH)],
latest_index_roots=[ZERO_HASH for _ in range(LATEST_INDEX_ROOTS_LENGTH)],
latest_penalized_balances=[0 for _ in range(LATEST_PENALIZED_EXIT_LENGTH)],
latest_attestations=[],
batched_block_roots=[],
Expand Down Expand Up @@ -1382,16 +1378,7 @@ Note: All functions in this section mutate `state`.
def activate_validator(state: BeaconState, index: int, genesis: bool) -> None:
validator = state.validator_registry[index]

validator.activation_slot = GENESIS_SLOT if genesis else (state.slot + ENTRY_EXIT_DELAY)
state.validator_registry_delta_chain_tip = hash_tree_root(
ValidatorRegistryDeltaBlock(
latest_registry_delta_root=state.validator_registry_delta_chain_tip,
validator_index=index,
pubkey=validator.pubkey,
slot=validator.activation_slot,
flag=ACTIVATION,
)
)
validator.activation_slot = GENESIS_SLOT if genesis else (state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY)
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```

```python
Expand All @@ -1405,22 +1392,13 @@ def exit_validator(state: BeaconState, index: int) -> None:
validator = state.validator_registry[index]

# The following updates only occur if not previous exited
if validator.exit_slot <= state.slot + ENTRY_EXIT_DELAY:
if validator.exit_slot <= state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY:
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return

validator.exit_slot = state.slot + ENTRY_EXIT_DELAY
validator.exit_slot = state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY

state.validator_registry_exit_count += 1
validator.exit_count = state.validator_registry_exit_count
state.validator_registry_delta_chain_tip = hash_tree_root(
ValidatorRegistryDeltaBlock(
latest_registry_delta_root=state.validator_registry_delta_chain_tip,
validator_index=index,
pubkey=validator.pubkey,
slot=validator.exit_slot,
flag=EXIT,
)
)
```

```python
Expand Down Expand Up @@ -1582,7 +1560,7 @@ Verify that `len(block.body.exits) <= MAX_EXITS`.
For each `exit` in `block.body.exits`:

* Let `validator = state.validator_registry[exit.validator_index]`.
* Verify that `validator.exit_slot > state.slot + ENTRY_EXIT_DELAY`.
* Verify that `validator.exit_slot > state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY`.
* Verify that `state.slot >= exit.slot`.
* Let `exit_message = hash_tree_root(Exit(slot=exit.slot, validator_index=exit.validator_index, signature=EMPTY_SIGNATURE))`.
* Verify that `bls_verify(pubkey=validator.pubkey, message=exit_message, signature=exit.signature, domain=get_domain(state.fork, exit.slot, DOMAIN_EXIT))`.
Expand Down Expand Up @@ -1767,7 +1745,7 @@ def update_validator_registry(state: BeaconState) -> None:
# Activate validators within the allowable balance churn
balance_churn = 0
for index, validator in enumerate(state.validator_registry):
if validator.activation_slot > state.slot + ENTRY_EXIT_DELAY and state.validator_balances[index] >= MAX_DEPOSIT_AMOUNT:
if validator.activation_slot > state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY and state.validator_balances[index] >= MAX_DEPOSIT_AMOUNT:
# Check the balance churn would be within the allowance
balance_churn += get_effective_balance(state, index)
if balance_churn > max_balance_churn:
Expand All @@ -1779,7 +1757,7 @@ def update_validator_registry(state: BeaconState) -> None:
# Exit validators within the allowable balance churn
balance_churn = 0
for index, validator in enumerate(state.validator_registry):
if validator.exit_slot > state.slot + ENTRY_EXIT_DELAY and validator.status_flags & INITIATED_EXIT:
if validator.exit_slot > state.slot - state.slot % EPOCH_LENGTH + ENTRY_EXIT_DELAY and validator.status_flags & INITIATED_EXIT:
# Check the balance churn would be within the allowance
balance_churn += get_effective_balance(state, index)
if balance_churn > max_balance_churn:
Expand All @@ -1793,15 +1771,17 @@ def update_validator_registry(state: BeaconState) -> None:

and perform the following updates:

* Set `state.previous_epoch_randao_mix = state.current_epoch_randao_mix`
* Set `state.previous_epoch_seed = state.current_epoch_seed`
* Set `state.current_epoch_calculation_slot = state.slot`
* Set `state.current_epoch_start_shard = (state.current_epoch_start_shard + get_current_epoch_committee_count_per_slot(state) * EPOCH_LENGTH) % SHARD_COUNT`
* Set `state.current_epoch_randao_mix = get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD)`
* Set `state.current_epoch_seed = hash(get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD) + get_active_index_root(state, state.current_epoch_calculation_slot))`
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If a validator registry update does _not_ happen do the following:

* Let `epochs_since_last_registry_change = (state.slot - state.validator_registry_update_slot) // EPOCH_LENGTH`.
* If `epochs_since_last_registry_change` is an exact power of 2, set `state.current_epoch_calculation_slot = state.slot` and `state.current_epoch_randao_mix = state.latest_randao_mixes[(state.current_epoch_calculation_slot - SEED_LOOKAHEAD) % LATEST_RANDAO_MIXES_LENGTH]`. Note that `state.current_epoch_start_shard` is left unchanged.
* If `epochs_since_last_registry_change` is an exact power of 2, set `state.current_epoch_calculation_slot = state.slot` and `state.current_epoch_seed = hash(get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD) + get_active_index_root(state, state.current_epoch_calculation_slot))`. Note that `state.current_epoch_start_shard` is left unchanged.
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**Invariant**: the active index root that is hashed into the shuffling seed actually is the `hash_tree_root` of the validator set that is used for that epoch.

Regardless of whether or not a validator set change happens, run the following:

Expand Down Expand Up @@ -1842,8 +1822,10 @@ def process_penalties_and_exits(state: BeaconState) -> None:

### Final updates

* Let `e = state.slot // EPOCH_LENGTH`. Set `state.latest_penalized_balances[(e+1) % LATEST_PENALIZED_EXIT_LENGTH] = state.latest_penalized_balances[e % LATEST_PENALIZED_EXIT_LENGTH]`
* Let `epoch = state.slot // EPOCH_LENGTH`.
* Set `state.latest_penalized_balances[(epoch+1) % LATEST_PENALIZED_EXIT_LENGTH] = state.latest_penalized_balances[epoch % LATEST_PENALIZED_EXIT_LENGTH]`
* Remove any `attestation` in `state.latest_attestations` such that `attestation.data.slot < state.slot - EPOCH_LENGTH`.
* Set `state.latest_index_roots[epoch % LATEST_INDEX_ROOTS_LENGTH] = hash_tree_root(get_active_validator_indices(state, state.slot))`

## State root processing

Expand Down