Merge pull request #107 from ethereum/vbuterin-patch-1
Chain initialization and main chain block inclusion
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1f4aa90788
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@ -36,6 +36,7 @@ The primary source of load on the beacon chain are "attestations". Attestations
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| `DEPOSIT_SIZE` | 2**5 (= 32) | ETH |
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| `MIN_ONLINE_DEPOSIT_SIZE` | 2**4 (= 16) | ETH |
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| `GWEI_PER_ETH` | 10**9 | Gwei/ETH |
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| `DEPOSIT_CONTRACT_ADDRESS` | **TBD** | - |
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| `TARGET_COMMITTEE_SIZE` | 2**8 (= 256) | validators |
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| `GENESIS_TIME` | **TBD** | seconds |
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| `SLOT_DURATION` | 2**4 (= 16) | seconds |
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@ -44,11 +45,14 @@ The primary source of load on the beacon chain are "attestations". Attestations
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| `RANDAO_SLOTS_PER_LAYER` | 2**12 (= 4096) | slots | ~18 hours |
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| `SQRT_E_DROP_TIME` | 2**16 (= 65,536) | slots | ~12 days |
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| `WITHDRAWAL_PERIOD` | 2**19 (= 524,288) | slots | ~97 days |
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| `DELETION_PERIOD` | 2**21 (= 2,097,152) | slots | ~1.06 years |
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| `SHARD_PERSISTENT_COMMITTEE_CHANGE_PERIOD` | 2**16 (= 65,536) | slots | ~12 days |
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| `BASE_REWARD_QUOTIENT` | 2**15 (= 32,768) | — |
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| `MAX_VALIDATOR_CHURN_QUOTIENT` | 2**5 (= 32) | — |
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| `MAX_VALIDATOR_CHURN_QUOTIENT` | 2**5 (= 32) | — |
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| `POW_HASH_VOTING_PERIOD` | 2**10 (=1024) | - |
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| `POW_CONTRACT_MERKLE_TREE_DEPTH` | 2**5 (=32) | - |
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| `MAX_SPECIALS_PER_BLOCK` | 2**4 (= 16) | - |
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| `LOGOUT_MESSAGE` | `"LOGOUT"` | — |
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| `LOGOUT_MESSAGE` | `"LOGOUT"` | — |
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| `INITIAL_FORK_VERSION` | 0 | — |
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**Notes**
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@ -101,8 +105,8 @@ A `BeaconBlock` has the following fields:
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'slot': 'uint64',
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# Proposer RANDAO reveal
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'randao_reveal': 'hash32',
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# Recent PoW chain reference (block hash)
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'pow_chain_reference': 'hash32',
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# Recent PoW chain reference (receipt root)
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'candidate_pow_receipt_root': 'hash32',
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# Skip list of previous beacon block hashes
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# i'th item is the most recent ancestor whose slot is a multiple of 2**i for i = 0, ..., 31
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'ancestor_hashes': ['hash32'],
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@ -207,6 +211,12 @@ The `BeaconState` has the following fields:
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'deposits_penalized_in_period': ['uint32'],
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# Hash chain of validator set changes (for light clients to easily track deltas)
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'validator_set_delta_hash_chain': 'hash32'
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# Genesis time
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'genesis_time': 'hash32',
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# PoW chain reference
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'known_pow_receipt_root': 'hash32',
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'candidate_pow_receipt_root': 'hash32',
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'candidate_pow_receipt_root_votes': 'uint32',
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# Parameters relevant to hard forks / versioning.
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# Should be updated only by hard forks.
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'pre_fork_version': 'uint32',
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@ -502,6 +512,130 @@ def int_sqrt(n: int) -> int:
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return x
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```
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### PoW chain contract
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The beacon chain is initialized when a condition is met inside a contract on the existing PoW chain. This contract's code in Vyper is as follows:
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```python
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HashChainValue: event({prev_tip: bytes32, data: bytes[2048], value: wei_value, time: timestamp, total_deposit_count: int128})
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ChainStart: event({hash_chain_tip: bytes32, time: timestamp})
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receipt_tree: bytes32[int128]
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total_deposit_count: int128
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@payable
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@public
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def deposit(data: bytes[2048]):
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log.HashChainValue(self.receipt_tree[1], data, msg.value, block.timestamp, self.total_deposit_count)
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index:int128 = self.total_deposit_count + 2**POW_CONTRACT_MERKLE_TREE_DEPTH
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self.receipt_tree[index] = sha3(concat(data, as_bytes32(msg.value), as_bytes32(block.timestamp))
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for i in range(POW_CONTRACT_MERKLE_TREE_DEPTH):
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index //= 2
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self.receipt_tree[index] = sha3(concat(self.receipt_tree[index * 2], self.receipt_tree[index * 2 + 1]))
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self.total_deposit_count += 1
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if self.total_deposit_count == 16384:
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log.ChainStart(self.receipt_tree[1], block.timestamp)
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@public
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@constant
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def get_receipt_root() -> bytes32:
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return self.receipt_tree[1]
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```
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The contract is at address `DEPOSIT_CONTRACT_ADDRESS`. When a user wishes to become a validator by moving their ETH from the 1.0 chain to the 2.0 chain, they should call the `deposit` function, sending along 32 ETH and providing as `data` a SimpleSerialize'd `DepositParams` object of the form:
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```python
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{
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'pubkey': 'int256',
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'proof_of_possession': ['int256'],
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'withdrawal_shard': 'int64',
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'withdrawal_address`: 'bytes20',
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'randao_commitment`: 'hash32'
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}
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```
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If the user wishes to deposit more than `DEPOSIT_SIZE` ETH, they would need to make multiple calls. When the contract publishes a `ChainStart` log, this initializes the chain, calling `on_startup` with:
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* `initial_validator_entries` equal to the list of data records published as HashChainValue logs so far, in the order in which they were published (oldest to newest).
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* `genesis_time` equal to the `time` value published in the log
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* `pow_hash_chain_tip` equal to the `hash_chain_tip` value published in the log
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### On startup
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A valid block with slot `0` (the "genesis block") has the following values. Other validity rules (eg. requiring a signature) do not apply.
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```python
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{
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'slot': 0,
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'randao_reveal': bytes32(0),
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'candidate_pow_receipt_root': bytes32(0),
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'ancestor_hashes': [bytes32(0) for i in range(32)],
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'state_root': STARTUP_STATE_ROOT,
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'attestations': [],
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'specials': []
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}
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```
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`STARTUP_STATE_ROOT` is the root of the initial state, computed by running the following code:
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```python
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def on_startup(initial_validator_entries: List[Any], genesis_time: uint64, pow_hash_chain_tip: Hash32) -> BeaconState:
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# Induct validators
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validators = []
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for pubkey, proof_of_possession, withdrawal_shard, withdrawal_address, \
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randao_commitment in initial_validator_entries:
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add_validator(
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validators=validators,
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pubkey=pubkey,
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proof_of_possession=proof_of_possession,
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withdrawal_shard=withdrawal_shard,
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withdrawal_address=withdrawal_address,
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randao_commitment=randao_commitment,
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current_slot=0,
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status=ACTIVE,
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)
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# Setup state
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x = get_new_shuffling(bytes([0] * 32), validators, 0)
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crosslinks = [
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CrosslinkRecord(
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slot=0,
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hash=bytes([0] * 32)
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)
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for i in range(SHARD_COUNT)
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]
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state = BeaconState(
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validator_set_change_slot=0,
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validators=validators,
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crosslinks=crosslinks,
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last_state_recalculation_slot=0,
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last_finalized_slot=0,
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last_justified_slot=0,
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justified_streak=0,
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shard_and_committee_for_slots=x + x,
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persistent_committees=split(shuffle(validators, bytes([0] * 32)), SHARD_COUNT),
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persistent_committee_reassignments=[],
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deposits_penalized_in_period=[],
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next_shuffling_seed=b'\x00'*32,
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validator_set_delta_hash_chain=bytes([0] * 32), # stub
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genesis_time=genesis_time,
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known_pow_hash_chain_tip=pow_hash_chain_tip,
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processed_pow_hash_chain_tip=pow_hash_chain_tip,
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candidate_pow_hash_chain_tip=bytes([0] * 32),
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candidate_pow_hash_chain_tip_votes=0,
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pre_fork_version=INITIAL_FORK_VERSION,
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post_fork_version=INITIAL_FORK_VERSION,
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fork_slot_number=0,
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pending_attestations=[],
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pending_specials=[],
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recent_block_hashes=[bytes([0] * 32) for _ in range(CYCLE_LENGTH * 2)],
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randao_mix=bytes([0] * 32) # stub
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)
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return state
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```
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The `add_validator` routine is defined below.
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### Routine for adding a validator
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This routine should be run for every validator that is inducted as part of a log created on the PoW chain [TODO: explain where to check for these logs]. The status of the validators added after genesis is `PENDING_ACTIVATION`. These logs should be processed in the order in which they are emitted by the PoW chain.
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@ -509,9 +643,9 @@ This routine should be run for every validator that is inducted as part of a log
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First, a helper function:
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```python
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def min_empty_validator(validators: List[ValidatorRecord]):
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def min_empty_validator(validators: List[ValidatorRecord], current_slot: int):
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for i, v in enumerate(validators):
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if v.status == WITHDRAWN:
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if v.status == WITHDRAWN and v.exit_slot <= current_slot - DELETION_PERIOD:
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return i
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return None
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```
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@ -529,9 +663,12 @@ def add_validator(validators: List[ValidatorRecord],
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current_slot: int) -> int:
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# if following assert fails, validator induction failed
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# move on to next validator registration log
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signed_message = as_bytes32(pubkey) + as_bytes2(withdrawal_shard) + withdrawal_address + randao_commitment
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assert BLSVerify(pub=pubkey,
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msg=hash(pubkey),
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msg=hash(signed_message),
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sig=proof_of_possession)
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# Pubkey uniqueness
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assert pubkey not in [v.pubkey for v in validators]
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rec = ValidatorRecord(
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pubkey=pubkey,
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withdrawal_shard=withdrawal_shard,
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@ -676,6 +813,8 @@ Additionally, verify and update the RANDAO reveal. This is done as follows:
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* Verify that `repeat_hash(block.randao_reveal, (block.slot - V.randao_last_change) // RANDAO_SLOTS_PER_LAYER + 1) == V.randao_commitment`
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* Set `state.randao_mix = xor(state.randao_mix, block.randao_reveal)`, `V.randao_commitment = block.randao_reveal`, `V.randao_last_change = block.slot`
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Finally, if `block.candidate_pow_hash_chain_tip = crystallized_state.candidate_pow_hash_chain_tip`, set `crystallized_state.candidate_hash_chain_tip_votes += 1`.
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### Process penalties, logouts and other special objects
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Verify that there are at most `MAX_SPECIALS_PER_BLOCK` objects in `block.specials`.
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@ -719,6 +858,39 @@ Perform the following checks:
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For each validator index `v` in `intersection`, if `state.validators[v].status` does not equal `PENALIZED`, then run `exit_validator(v, state, penalize=True, current_slot=block.slot)`
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#### DEPOSIT_PROOF
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```python
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{
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'merkle_branch': '[hash32]',
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'merkle_tree_index': 'uint64',
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'deposit_data': {
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'params': DepositParams,
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'msg_value': 'uint256',
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'timestamp': 'uint256'
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}
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}
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```
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Note that `deposit_data` in serialized form should be the `DepositParams` followed by 32 bytes for the `msg.value` and 32 bytes for the `timestamp`, or exactly the data the hash of which was placed into the Merkle tree in the PoW contract.
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Use the following procedure to verify the `merkle_branch`, setting `leaf=serialized_deposit_data`, `depth=POW_CONTRACT_MERKLE_TREE_DEPTH` and `root=state.known_pow_receipt_root`:
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```python
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def verify_merkle_branch(leaf: Hash32, branch: [Hash32], depth: int, index: int, root: Hash32) -> bool:
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value = leaf
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for i in range(depth):
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if index % 2:
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value = hash(branch[i], value)
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else:
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value = hash(value, branch[i])
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return value == root
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```
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Verify that `msg.value == DEPOSIT_SIZE` and `block.slot - (timestamp - state.genesis_time) // SLOT_DURATION < DELETION_PERIOD`.
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Run `add_validator(validators, deposit_data.params.pubkey, deposit_data.params.proof_of_possession, deposit_data.params.withdrawal_shard, data.withdrawal_address, deposit_data.params.randao_commitment, PENDING_ACTIVATION, block.slot)`.
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## State recalculations (every `CYCLE_LENGTH` slots)
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Repeat while `slot - last_state_recalculation_slot >= CYCLE_LENGTH`:
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@ -773,6 +945,14 @@ For every shard number `shard` for which a crosslink committee exists in the cyc
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* Adjust balances as follows:
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* Participating validators gain `B // reward_quotient * (2 * total_balance_of_v_participating - total_balance_of_v) // total_balance_of_v`.
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* Non-participating validators lose `B // reward_quotient`.
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#### PoW chain related rules
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If `last_state_recalculation_slot % POW_HASH_VOTING_PERIOD == 0`, then:
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* If `crystallized_state.candidate_hash_chain_tip_votes * 3 >= POW_HASH_VOTING_PERIOD * 2`, set `crystallized_state.hash_chain_tip = crystallized_state.candidate_hash_chain_tip`
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* Set `crystallized_state.candidate_hash_chain_tip = block.candidate_pow_hash_chain_tip`
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* Set `crystallized_state.candidate_hash_chain_tip_votes = 0`
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### Validator set change
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@ -785,7 +965,7 @@ A validator set change can happen after a state recalculation if all of the foll
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Then, run the following algorithm to update the validator set:
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```python
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def change_validators(validators: List[ValidatorRecord]) -> None:
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def change_validators(validators: List[ValidatorRecord], current_slot: int) -> None:
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# The active validator set
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active_validators = get_active_validator_indices(validators)
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# The total balance of active validators
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@ -834,10 +1014,12 @@ def change_validators(validators: List[ValidatorRecord]) -> None:
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if validators[i].status == PENALIZED:
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validators[i].balance -= validators[i].balance * min(total_penalties * 3, total_balance) // total_balance
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validators[i].status = WITHDRAWN
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validators[i].exit_slot = current_slot
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withdraw_amount = validators[i].balance
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...
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# STUB: withdraw to shard chain
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```
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* Set `state.validator_set_change_slot = state.last_state_recalculation_slot`
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