Added a few more things

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Vitalik Buterin 2019-10-13 15:52:51 +09:00 committed by Danny Ryan
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@ -15,7 +15,9 @@
- [Helpers](#helpers)
- [Beacon Chain Changes](#beacon-chain-changes)
- [New state variables](#new-state-variables)
- [New block data structures](#new-block-data-structures)
- [Attestation processing](#attestation-processing)
- [Light client signature processing)(#light-client-signature-processing)
- [Epoch transition](#epoch-transition)
- [Fraud proofs](#fraud-proofs)
- [Honest persistent committee member behavior](#honest-persistent-committee-member-behavior)
@ -30,13 +32,15 @@ This document describes the shard transition function (data layer only) and the
### Misc
| Name | Value |
| - | - |
| Name | Value | Unit | Duration |
| - | - | - | - |
| `MAX_SHARDS` | `2**10` (= 1024) |
| `ACTIVE_SHARDS` | `2**6` (= 64) |
| `SHARD_ROOT_HISTORY_LENGTH` | `2**15` (= 32,768) |
| `MAX_CATCHUP` | `2**5` (= 32) |
| `ONLINE_PERIOD` | `2**3` (= 8) |
| `MAX_CATCHUP` | `2**5` (= 32) | slots | 3.2 min |
| `ONLINE_PERIOD` | `2**3` (= 8) | epochs | ~51 min |
| `LIGHT_CLIENT_COMMITTEE_SIZE` | `2**7` (= 128) |
| `LIGHT_CLIENT_COMMITTEE_PERIOD` | `2**8` (= 256) | epochs | ~29 hours |
## Containers
@ -69,6 +73,14 @@ class Attestation(Container):
signature: BLSSignature
```
### `CompactCommittee`
```python
class CompactCommittee(Container):
pubkeys: List[BLSPubkey, MAX_VALIDATORS_PER_COMMITTEE]
compact_validators: List[uint64, MAX_VALIDATORS_PER_COMMITTEE]
```
## Helpers
### `get_online_validators`
@ -86,6 +98,44 @@ def get_shard_state_root(state: BeaconState, shard: Shard) -> Hash:
return state.shard_state_roots[shard][-1]
```
### `pack_compact_validator`
```python
def pack_compact_validator(index: int, slashed: bool, balance_in_increments: int) -> int:
"""
Creates a compact validator object representing index, slashed status, and compressed balance.
Takes as input balance-in-increments (// EFFECTIVE_BALANCE_INCREMENT) to preserve symmetry with
the unpacking function.
"""
return (index << 16) + (slashed << 15) + balance_in_increments
```
### `unpack_compact_validator`
```python
def unpack_compact_validator(compact_validator: int) -> Tuple[int, bool, int]:
"""
Returns validator index, slashed, balance // EFFECTIVE_BALANCE_INCREMENT
"""
return compact_validator >> 16, bool((compact_validator >> 15) % 2), compact_validator & (2**15 - 1)
```
### `committee_to_compact_committee`
```python
def committee_to_compact_committee(state: BeaconState, committee: Sequence[ValidatorIndex]) -> CompactCommittee:
"""
Given a state and a list of validator indices, outputs the CompactCommittee representing them.
"""
validators = [state.validators[i] for i in committee]
compact_validators = [
pack_compact_validator(i, v.slashed, v.effective_balance // EFFECTIVE_BALANCE_INCREMENT)
for i, v in zip(committee, validators)
]
pubkeys = [v.pubkey for v in validators]
return CompactCommittee(pubkeys=pubkeys, compact_validators=compact_validators)
```
## Beacon Chain Changes
### New state variables
@ -94,6 +144,15 @@ def get_shard_state_root(state: BeaconState, shard: Shard) -> Hash:
shard_state_roots: Vector[List[Hash, MAX_CATCHUP], MAX_SHARDS]
shard_next_slot: Vector[Slot, MAX_SHARDS]
online_countdown: Bytes[VALIDATOR_REGISTRY_LIMIT]
current_light_committee: CompactCommittee
next_light_committee: CompactCommittee
```
### New block data structures
```
light_client_signature_bitfield: Bitlist[LIGHT_CLIENT_COMMITTEE_SIZE]
light_client_signature: BLSSignature
```
### Attestation processing
@ -151,12 +210,40 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
state.previous_epoch_attestations.append(pending_attestation)
```
### Light client processing
```python
signer_validators = []
signer_keys = []
for i, bit in enumerate(block.light_client_signature_bitfield):
if bit:
signer_keys.append(state.current_light_committee.pubkeys[i])
index, _, _ = unpack_compact_validator(state.current_light_committee.compact_validators[i])
signer_validators.append(index)
assert bls_verify(
pubkey=bls_aggregate_pubkeys(signer_keys),
message_hash=get_block_root_at_slot(state, state.slot - 1),
signature=block.light_client_signature,
domain=DOMAIN_LIGHT_CLIENT
)
```
### Epoch transition
```python
# Slowly remove validators from the "online" set if they do not show up
for index in range(len(state.validators)):
if state.online_countdown[index] != 0:
state.online_countdown[index] = state.online_countdown[index] - 1
# Update light client committees
if get_current_epoch(state) % LIGHT_CLIENT_COMMITTEE_PERIOD == 0:
state.current_light_committee = state.next_light_committee
seed = get_seed(state, get_current_epoch(state), DOMAIN_LIGHT_CLIENT)
active_indices = get_active_validator_indices(state, get_current_epoch(state))
committee = [active_indices[compute_shuffled_index(ValidatorIndex(i), len(active_indices), seed)] for i in range(LIGHT_CLIENT_COMMITTEE_SIZE)]
state.next_light_committee = committee_to_compact_committee(state, committee)
```
### Fraud proofs