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A few more cleanups

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vbuterin 2019-02-08 03:54:02 -06:00 committed by GitHub
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specs/core/1_shard-data-chains.md
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@ -29,52 +29,9 @@ Phase 1 depends upon all of the constants defined in [Phase 0](0_beacon-chain.md
| `SHARD_PROPOSER_DOMAIN`| 129 |
| `SHARD_ATTESTER_DOMAIN`| 130 |
## Data Structures
## Helper functions
### Shard chain blocks
A `ShardBlock` object has the following fields:
```python
{
# Slot number
'slot': 'uint64',
# What shard is it on
'shard_id': 'uint64',
# Parent block's root
'parent_root': 'bytes32',
# Beacon chain block
'beacon_chain_ref': 'bytes32',
# Merkle root of data
'data_root': 'bytes32'
# State root (placeholder for now)
'state_root': 'bytes32',
# Block signature
'signature': 'bytes96',
# Attestation
'participation_bitfield': 'bytes',
'aggregate_signature': 'bytes96',
}
```
## Shard block processing
For a block on a shard to be processed by a node, the following conditions must be met:
* The `ShardBlock` pointed to by `parent_root` has already been processed and accepted
* The signature for the block from the _proposer_ (see below for definition) of that block is included along with the block in the network message object
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 (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.
* 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, message_hash=parent_root, sig=block.aggregate_signature, domain=get_domain(state, slot, SHARD_ATTESTER_DOMAIN))` passes.
We define the helper `get_persistent_committee` as follows:
#### get_persistent_committee
```python
def get_persistent_commmitee(seed: Bytes32,
@ -106,6 +63,52 @@ def get_persistent_commmitee(seed: Bytes32,
)
```
## Data Structures
### Shard chain blocks
A `ShardBlock` object has the following fields:
```python
{
# Slot number
'slot': 'uint64',
# What shard is it on
'shard_id': 'uint64',
# Parent block's root
'parent_root': 'bytes32',
# Beacon chain block
'beacon_chain_ref': 'bytes32',
# Merkle root of data
'data_root': 'bytes32'
# State root (placeholder for now)
'state_root': 'bytes32',
# Block signature
'signature': 'bytes96',
# Attestation
'participation_bitfield': 'bytes',
'aggregate_signature': 'bytes96',
}
```
## Shard block processing
For a `shard_block` on a shard to be processed by a node, the following conditions must be met:
* The `ShardBlock` pointed to by `shard_block.parent_root` has already been processed and accepted
* The signature for the block from the _proposer_ (see below for definition) of that block is included along with the block in the network message object
To validate a block header on shard `shard_block.shard_id`, compute as follows:
* Verify that `shard_block.beacon_chain_ref` is the hash of a block in the (canonical) beacon chain with slot less than or equal to `slot`.
* Verify that `shard_block.beacon_chain_ref` is equal to or a descendant of the `shard_block.beacon_chain_ref` specified in the `ShardBlock` pointed to by `shard_block.parent_root`.
* Let `state` be the state of the beacon chain block referred to by `shard_block.beacon_chain_ref`.
* Let `persistent_committee` be `[persistent_committee[i] for i in get_persistent_committee(state, shard_block.slot, shard_block.shard_id)`.
* Assert `verify_bitfield(shard_block.participation_bitfield, len(persistent_committee))`
* Let `proposer_index = hash(state.randao_mix + int_to_bytes8(shard_block.shard_id) + int_to_bytes8(shard_block.slot)) % len(validators)`. Let `msg` be the `shard_block` but with `shard_block.signature` set to `[0, 0]`. Verify that `bls_verify(pubkey=validators[proposer_index].pubkey, message_hash=hash(msg), signature=shard_block.signature, domain=get_domain(state, shard_block.slot, SHARD_PROPOSER_DOMAIN))` passes.
* Let `group_public_key = bls_aggregate_pubkeys([state.validators[index].pubkey for i, index in enumerate(persistent_committee) if get_bitfield_bit(shard_block.participation_bitfield, i) is True])`. Verify that `bls_verify(pubkey=group_public_key, message_hash=shard_block.parent_root, sig=shard_block.aggregate_signature, domain=get_domain(state, slot, SHARD_ATTESTER_DOMAIN))` passes.
### Verifying shard block data
At network layer, we expect a shard block header to be broadcast along with its `block_body`.