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Updated phase 1: shard block structure

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vbuterin 2019-02-06 20:32:56 -06:00 committed by GitHub
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58
specs/core/1_shard-data-chains.md
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@ -16,10 +16,11 @@ Ethereum 2.0 consists of a central beacon chain along with `SHARD_COUNT` shard c
Phase 1 depends upon all of the constants defined in [Phase 0](0_beacon-chain.md#constants) in addition to the following:
| Constant | Value | Unit | Approximation |
|------------------------|-----------------|-------|---------------|
| `SHARD_CHUNK_SIZE` | 2**5 (= 32) | bytes | |
| `SHARD_BLOCK_SIZE` | 2**14 (= 16384) | bytes | |
| Constant | Value | Unit | Approximation |
|-----------------------------|-----------------|--------|---------------|
| `SHARD_CHUNK_SIZE` | 2**5 (= 32) | bytes | |
| `SHARD_BLOCK_SIZE` | 2**14 (= 16384) | bytes | |
| `PROPOSAL_RESHUFFLE_PERIOD` | 2**11 (= 2048) | epochs | 9 days |
### Flags, domains, etc.
@ -40,12 +41,10 @@ A `ShardBlock` object has the following fields:
'slot': 'uint64',
# What shard is it on
'shard_id': 'uint64',
# Parent block's hash of root
# Parent block's root
'parent_root': 'hash32',
# Beacon chain block
'beacon_chain_ref': 'hash32',
# Depth of the Merkle tree
'data_tree_depth': 'uint8',
# Merkle root of data
'data_root': 'hash32'
# State root (placeholder for now)
@ -67,22 +66,43 @@ For a block on a shard to be processed by a node, the following conditions must
To validate a block header on shard `shard_id`, compute as follows:
* Verify that `beacon_chain_ref` is the hash of a block in the beacon chain with slot less than or equal to `slot`. Verify that `beacon_chain_ref` is equal to or a descendant of the `beacon_chain_ref` specified in the `ShardBlock` pointed to by `parent_root`.
* Let `state` be the state of the beacon chain block referred to by `beacon_chain_ref`. Let `validators` be `[validators[i] for i in state.current_persistent_committees[shard_id]]`.
* Assert `len(participation_bitfield) == ceil_div8(len(validators))`
* Verify that `beacon_chain_ref` is the hash of a block in the (canonical) beacon chain with slot less than or equal to `slot`.
* Verify that `beacon_chain_ref` is equal to or a descendant of the `beacon_chain_ref` specified in the `ShardBlock` pointed to by `parent_root`.
* Let `state` be the state of the beacon chain block referred to by `beacon_chain_ref`. Let `persistent_committee` be `[persistent_committee[i] for i in get_persistent_committee(state, slot, shard_id)`.
* Assert `verify_bitfield(participation_bitfield, len(persistent_committee))`
* Let `proposer_index = hash(state.randao_mix + int_to_bytes8(shard_id) + int_to_bytes8(slot)) % len(validators)`. Let `msg` be the block but with the `block.signature` set to `[0, 0]`. Verify that `BLSVerify(pub=validators[proposer_index].pubkey, msg=hash(msg), sig=block.signature, domain=get_domain(state, slot, SHARD_PROPOSER_DOMAIN))` passes.
* Generate the `group_public_key` by adding the public keys of all the validators for whom the corresponding position in the bitfield is set to 1. Verify that `BLSVerify(pub=group_public_key, msg=parent_root, sig=block.aggregate_signature, domain=get_domain(state, slot, SHARD_ATTESTER_DOMAIN))` passes.
* Let `group_public_key = bls_aggregate_pubkeys([state.validators[index].pubkey for i, index in enumerate(persistent_committee) if get_bitfield_bit(participation_bitfield, i) is True])`. Verify that `bls_verify(pubkey=group_public_key, msg=parent_root, sig=block.aggregate_signature, domain=get_domain(state, slot, SHARD_ATTESTER_DOMAIN))` passes.
### Block Merklization helper
We define the helper `get_proposal_committee` as follows:
```python
def merkle_root(block_body):
assert len(block_body) == SHARD_BLOCK_SIZE
chunks = SHARD_BLOCK_SIZE // SHARD_CHUNK_SIZE
o = [0] * chunks + [block_body[i * SHARD_CHUNK_SIZE: (i+1) * SHARD_CHUNK_SIZE] for i in range(chunks)]
for i in range(chunks-1, 0, -1):
o[i] = hash(o[i*2] + o[i*2+1])
return o[1]
def get_proposal_committee(seed: Bytes32,
validators: List[Validator],
shard: int,
epoch: EpochNumber) -> List[ValidatorIndex]:
earlier_committee_start = epoch - (epoch % PROPOSAL_RESHUFFLE_PERIOD) - PROPOSAL_RESHUFFLE_PERIOD * 2
earlier_committee = split(shuffle(
get_active_validator_indices(validators, earlier_committee_start),
generate_seed(state, earlier_committee_start)
), SHARD_COUNT)[shard]
later_committee_start = epoch - (epoch % PROPOSAL_RESHUFFLE_PERIOD) - PROPOSAL_RESHUFFLE_PERIOD
later_committee = split(shuffle(
get_active_validator_indices(validators, earlier_committee_start),
generate_seed(state, earlier_committee_start)
), SHARD_COUNT)[shard]
def get_switchover_epoch(index):
return (
int.from_bytes(hash(generate_seed(state, earlier_committee_start) + bytes3(index)), 'little') %
PROPOSAL_RESHUFFLE_PERIOD
)
return (
[i for i in earlier_committee if epoch % PROPOSAL_RESHUFFLE_PERIOD < get_switchover_epoch(i)] +
[i for i in later_committee if epoch % PROPOSAL_RESHUFFLE_PERIOD >= get_switchover_epoch(i)]
)
```
### Verifying shard block data