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Make `shard_state_transition` more like beacon state_transition function

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Hsiao-Wei Wang 2020-04-02 10:53:46 +08:00
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specs/phase1/fraud-proofs.md
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@ -45,14 +45,30 @@ The proof verifies that one of the two conditions is false:
## Shard state transition function
```python
def shard_state_transition(shard: Shard,
def shard_state_transition(beacon_state: BeaconState,
shard: Shard,
slot: Slot,
pre_state: Root,
previous_beacon_root: Root,
proposer_pubkey: BLSPubkey,
block_data: ByteList[MAX_SHARD_BLOCK_SIZE]) -> Root:
proposer_index: ValidatorIndex,
signed_block: SignedShardBlock,
validate_result: bool=True) -> Root:
# We will add something more substantive in phase 2
return hash(pre_state + hash_tree_root(previous_beacon_root) + hash_tree_root(block_data))
# Verify the proposer_index and signature
assert proposer_index == signed_block.message.proposer_index
if validate_result:
assert verify_shard_block_signature(beacon_state, signed_block)
return hash(pre_state + hash_tree_root(previous_beacon_root) + hash_tree_root(signed_block.message.data))
```
```python
def verify_shard_block_signature(beacon_state: BeaconState,
signed_block: SignedShardBlock) -> bool:
proposer = beacon_state.validators[signed_block.message.proposer_index]
signing_root = compute_signing_root(signed_block.message, get_domain(beacon_state, DOMAIN_SHARD_PROPOSAL))
return bls.Verify(proposer.pubkey, signing_root, signed_block.signature)
```
## Honest committee member behavior
@ -61,10 +77,10 @@ Suppose you are a committee member on shard `shard` at slot `current_slot`. Let
* Initialize `proposals = []`, `shard_states = []`, `shard_state = state.shard_states[shard][-1]`, `start_slot = shard_state.slot`.
* For `slot in get_offset_slots(state, start_slot)`, do the following:
* Look for all valid proposals for `slot`; that is, a Bytes `proposal` where `shard_state_transition(shard, slot, shard_state, get_block_root_at_slot(state, state.slot - 1), get_shard_proposer_index(state, shard, slot), proposal)` returns a result and does not throw an exception. Let `choices` be the set of non-empty valid proposals you discover.
* Look for all valid proposals for `slot`; that is, a SignedShardBlock `proposal` where `shard_state_transition(shard, slot, shard_state, get_block_root_at_slot(state, state.slot - 1), get_shard_proposer_index(state, slot, shard), proposal)` returns a result and does not throw an exception. Let `choices` be the set of non-empty valid proposals you discover.
* If `len(choices) == 0`, do `proposals.append(make_empty_proposal(shard_state, slot))`
* If `len(choices) == 1`, do `proposals.append(choices[0])`
* If `len(choices) > 1`, let `winning_proposal` be the proposal with the largest number of total attestations from slots in `state.shard_next_slots[shard]....slot-1` supporting it or any of its descendants, breaking ties by choosing the first proposal locally seen. Do `proposals.append(winning_proposal)`.
* If `proposals[-1]` is NOT an empty proposal, set `shard_state = shard_state_transition(shard, slot, shard_state, get_block_root_at_slot(state, state.slot - 1), get_shard_proposer_index(state, shard, slot), proposals[-1])` and do `shard_states.append(shard_state)`. If it is an empty proposal, leave `shard_state` unchanged.
* If `proposals.message.data[-1]` is NOT an empty proposal, set `shard_state = shard_state_transition(shard, slot, shard_state, get_block_root_at_slot(state, state.slot - 1), get_shard_proposer_index(state, slot, shard), proposals[-1])` and do `shard_states.append(shard_state)`. If it is an empty proposal, leave `shard_state` unchanged.
Make an attestation using `shard_data_roots = [hash_tree_root(proposal) for proposal in proposals]` and `shard_state_roots = shard_states`.
Make an attestation using `shard_data_roots = [hash_tree_root(proposal.message.data) for proposal in proposals]` and `shard_state_roots = shard_states`.