From 2fedaf082427503beb346d59e33de83194aee319 Mon Sep 17 00:00:00 2001 From: vbuterin Date: Wed, 31 Oct 2018 03:44:18 -0400 Subject: [PATCH] Chain initialization and main chain block inclusion --- specs/beacon-chain.md | 67 +++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 64 insertions(+), 3 deletions(-) diff --git a/specs/beacon-chain.md b/specs/beacon-chain.md index 6c967a8e4..28c47c56e 100644 --- a/specs/beacon-chain.md +++ b/specs/beacon-chain.md @@ -35,7 +35,7 @@ The primary source of load on the beacon chain are "attestations". Attestations | `MIN_ONLINE_DEPOSIT_SIZE` | 2**4 (= 16) | ETH | | `GWEI_PER_ETH` | 10**9 | Gwei/ETH | | `MIN_COMMITTEE_SIZE` | 2**7 (= 128) | validators | -| `GENESIS_TIME` | **TBD** | seconds | +| `DEPOSIT_CONTRACT_ADDRESS` | **TBD** | - | | `SLOT_DURATION` | 2**4 (= 16) | seconds | | `CYCLE_LENGTH` | 2**6 (= 64) | slots | ~17 minutes | | `MIN_VALIDATOR_SET_CHANGE_INTERVAL` | 2**8 (= 256) | slots | ~1.1 hours | @@ -44,6 +44,7 @@ The primary source of load on the beacon chain are "attestations". Attestations | `WITHDRAWAL_PERIOD` | 2**19 (= 524,288) | slots | ~97 days | | `BASE_REWARD_QUOTIENT` | 2**15 (= 32,768) | — | | `MAX_VALIDATOR_CHURN_QUOTIENT` | 2**5 (= 32) | — | +| `POW_HASH_VOTING_PERIOD` | 2**10 (=1024) | - | | `LOGOUT_MESSAGE` | `"LOGOUT"` | — | | `INITIAL_FORK_VERSION` | 0 | — | @@ -98,7 +99,7 @@ A `BeaconBlock` has the following fields: # Proposer RANDAO reveal 'randao_reveal': 'hash32', # Recent PoW chain reference (block hash) - 'pow_chain_reference': 'hash32', + 'candidate_pow_hash_chain_tip': 'hash32', # Skip list of previous beacon block hashes # i'th item is the most recent ancestor who's slot is a multiple of 2**i for i = 0, ..., 31 'ancestor_hashes': ['hash32'], @@ -209,6 +210,13 @@ The `CrystallizedState` has the following fields: 'deposits_penalized_in_period': ['uint32'], # Hash chain of validator set changes (for light clients to easily track deltas) 'validator_set_delta_hash_chain': 'hash32' + # Genesis time + 'genesis_time': 'hash32', + # PoW chain reference + 'known_pow_hash_chain_tip': 'hash32', + 'processed_pow_hash_chain_tip': 'hash32', + 'candidate_pow_hash_chain_tip': 'hash32', + 'candidate_pow_hash_chain_tip_votes': 'uint64', # Parameters relevant to hard forks / versioning. # Should be updated only by hard forks. 'pre_fork_version': 'uint32', @@ -485,13 +493,51 @@ def int_sqrt(n: int) -> int: return x ``` +### PoW chain contract + +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: + +```python +HashChainValue: event({prev_tip: bytes32, data: bytes[2048], value: wei_value, total_deposit_count: int128}) +ChainStart: event({hash_chain_tip: bytes32, time: timestamp}) + +hash_chain_tip: public(bytes32) +total_deposit_count: int128 + +@payable +@public +def deposit(data: bytes[2048]): + log.HashChainValue(self.hash_chain_tip, data, msg.value, self.total_deposit_count) + self.total_deposit_count += 1 + self.hash_chain_tip = sha3(concat(self.hash_chain_tip, data, as_bytes32(msg.value), as_bytes32(self.total_deposit_count))) + if self.total_deposit_count == 16384: + log.ChainStart(self.hash_chain_tip, block.timestamp) +``` + +The contract is at address `DEPOSIT_CONTRACT_ADDRESS`. When a user wishes to move 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 object of the form: + +```python +{ + 'pubkey': 'int256', + 'proof_of_possession': ['int256'], + 'withdrawal_shard': 'int64', + 'withdrawal_address`: 'bytes20', + 'randao_commitment`: 'hash32', +} +``` + +If they wish to deposit more than 32 ETH, they would need to make multiple calls. When the contract publishes a `ChainStart` log, this initializes the chain, calling `on_startup` with: + +* `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). +* `genesis_time` equal to the `time` value published in the log +* `pow_hash_chain_tip` equal to the `hash_chain_tip` value published in the log ### On startup Run the following code: ```python -def on_startup(initial_validator_entries: List[Any]) -> Tuple[CrystallizedState, ActiveState]: +def on_startup(initial_validator_entries: List[Any], genesis_time: uint64, pow_hash_chain_tip: Hash32) -> Tuple[CrystallizedState, ActiveState]: # Induct validators validators = [] for pubkey, proof_of_possession, withdrawal_shard, withdrawal_address, \ @@ -527,6 +573,11 @@ def on_startup(initial_validator_entries: List[Any]) -> Tuple[CrystallizedState, shard_and_committee_for_slots=x + x, deposits_penalized_in_period=[], validator_set_delta_hash_chain=bytes([0] * 32), # stub + genesis_time=genesis_time, + known_pow_hash_chain_tip=pow_hash_chain_tip, + processed_pow_hash_chain_tip=pow_hash_chain_tip, + candidate_pow_hash_chain_tip=bytes([0] * 32), + candidate_pow_hash_chain_tip_votes=0, pre_fork_version=INITIAL_FORK_VERSION, post_fork_version=INITIAL_FORK_VERSION, fork_slot_number=0 @@ -739,6 +790,16 @@ For each `SpecialRecord` `obj` in `active_state.pending_specials`: * Set `active_state.recent_block_hashes = active_state.recent_block_hashes[CYCLE_LENGTH:]` * Set `shard_and_committee_for_slots[:CYCLE_LENGTH] = shard_and_committee_for_slots[CYCLE_LENGTH:]` +### PoW chain related rules + +If `block.slot % POW_HASH_VOTING_PERIOD == 0`, then: + +* 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` +* Set `crystallized_state.candidate_hash_chain_tip = block.candidate_pow_hash_chain_tip` +* Set `crystallized_state.candidate_hash_chain_tip_votes = 0` + +Otherwise, if `block.candidate_pow_hash_chain_tip = crystallized_state.candidate_pow_hash_chain_tip`, set `crystallized_state.candidate_hash_chain_tip_votes += 1`. + ### Validator set change A validator set change can happen after a state recalculation if all of the following criteria are satisfied: