diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md index 8f1191ded..3ee0a1646 100644 --- a/specs/core/0_beacon-chain.md +++ b/specs/core/0_beacon-chain.md @@ -38,7 +38,6 @@ The primary source of load on the beacon chain are "attestations". Attestations | `GWEI_PER_ETH` | 10**9 | Gwei/ETH | | `DEPOSIT_CONTRACT_ADDRESS` | **TBD** | - | | `TARGET_COMMITTEE_SIZE` | 2**8 (= 256) | validators | -| `GENESIS_TIME` | **TBD** | seconds | | `SLOT_DURATION` | 6 | seconds | | `CYCLE_LENGTH` | 2**6 (= 64) | slots | ~6 minutes | | `MIN_VALIDATOR_SET_CHANGE_INTERVAL` | 2**8 (= 256) | slots | ~25 minutes | @@ -92,6 +91,15 @@ The primary source of load on the beacon chain are "attestations". Attestations | `ENTRY` | `0` | | `EXIT` | `1` | +**Domains for BLS signatures** + +| Name | Value | +| - | :-: | +| `DOMAIN_DEPOSIT` | `0` | +| `DOMAIN_ATTESTATION` | `1` | +| `DOMAIN_PROPOSAL` | `2` | +| `DOMAIN_LOGOUT` | `3` | + ### PoW chain registration contract The initial deployment phases of Ethereum 2.0 are implemented without consensus changes to the PoW chain. A registration contract is added to the PoW chain to deposit ETH. This contract has a `registration` function which takes as arguments `pubkey`, `withdrawal_credentials`, `randao_commitment` as defined in a `ValidatorRecord` below. A BLS `proof_of_possession` of types `bytes` is given as a final argument. @@ -121,7 +129,7 @@ A `BeaconBlock` has the following fields: # Specials (e.g. logouts, penalties) 'specials': [SpecialRecord], # Proposer signature - 'proposer_signature': ['uint256'], + 'proposer_signature': ['uint384'], } ``` @@ -148,7 +156,7 @@ An `AttestationRecord` has the following fields: # Hash of last justified beacon block 'justified_block_hash': 'hash32', # BLS aggregate signature - 'aggregate_sig': ['uint256'] + 'aggregate_sig': ['uint384'] } ``` @@ -156,8 +164,6 @@ A `ProposalSignedData` has the following fields: ```python { - # Fork version - 'fork_version': 'uint64', # Slot number 'slot': 'uint64', # Shard number (or `2**64 - 1` for beacon chain) @@ -171,8 +177,6 @@ An `AttestationSignedData` has the following fields: ```python { - # Fork version - 'fork_version': 'uint64', # Slot number 'slot': 'uint64', # Shard number @@ -195,7 +199,7 @@ A `SpecialRecord` has the following fields: ```python { # Kind - 'kind': 'uint8', + 'kind': 'uint64', # Data 'data': 'bytes' } @@ -258,7 +262,7 @@ A `ValidatorRecord` has the following fields: ```python { # BLS public key - 'pubkey': 'uint256', + 'pubkey': 'uint384', # Withdrawal credentials 'withdrawal_credentials': 'hash32', # RANDAO commitment @@ -268,7 +272,7 @@ A `ValidatorRecord` has the following fields: # Balance in Gwei 'balance': 'uint64', # Status code - 'status': 'uint8', + 'status': 'uint64', # Slot when validator last changed status (or 0) 'last_status_change_slot': 'uint64' # Sequence number when validator exited (or 0) @@ -337,7 +341,7 @@ For a block on the beacon chain to be processed by a node, four conditions have * The parent pointed to by the `ancestor_hashes[0]` has already been processed and accepted * An attestation from the _proposer_ of the block (see later for definition) is included along with the block in the network message object * The PoW chain block pointed to by the `processed_pow_receipt_root` has already been processed and accepted -* The node's local clock time is greater than or equal to the minimum timestamp as computed by `GENESIS_TIME + block.slot * SLOT_DURATION` +* The node's local clock time is greater than or equal to the minimum timestamp as computed by `state.genesis_time + block.slot * SLOT_DURATION` If these conditions are not met, the client should delay processing the beacon block until the conditions are all satisfied. @@ -358,10 +362,13 @@ The beacon chain fork choice rule is a hybrid that combines justification and fi ```python def lmd_ghost(store, start): validators = start.state.validators - active_validators = [validators[i] for i in get_active_validator_indices(validators, start.slot)] - attestation_targets = [get_latest_attestation_target(store, validator) for validator in active_validators] + active_validators = [validators[i] for i in + get_active_validator_indices(validators, start.slot)] + attestation_targets = [get_latest_attestation_target(store, validator) + for validator in active_validators] def get_vote_count(block): - return len([target for target in attestation_targets if get_ancestor(store, target, block.slot) == block]) + return len([target for target in attestation_targets if + get_ancestor(store, target, block.slot) == block]) head = start while 1: @@ -706,7 +713,7 @@ The `add_validator` routine is defined below. 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. -First, a helper function: +First, some helper functions: ```python def min_empty_validator(validators: List[ValidatorRecord], current_slot: int): @@ -716,10 +723,18 @@ def min_empty_validator(validators: List[ValidatorRecord], current_slot: int): return None ``` +```python +def get_fork_version(state: State, slot: int) -> int: + return state.pre_fork_version if slot < state.fork_slot_number else state.post_fork_version + +def get_domain(state: State, slot: int, base_domain: int) -> int: + return get_fork_version(state, slot) * 2**32 + base_domain +``` + Now, to add a validator: ```python -def add_validator(validators: List[ValidatorRecord], +def add_validator(state: State, pubkey: int, proof_of_possession: bytes, withdrawal_credentials: Hash32, @@ -731,9 +746,10 @@ def add_validator(validators: List[ValidatorRecord], signed_message = bytes32(pubkey) + bytes2(withdrawal_shard) + withdrawal_credentials + randao_commitment assert BLSVerify(pub=pubkey, msg=hash(signed_message), - sig=proof_of_possession) + sig=proof_of_possession, + domain=get_domain(state, current_slot, DOMAIN_DEPOSIT)) # Pubkey uniqueness - assert pubkey not in [v.pubkey for v in validators] + assert pubkey not in [v.pubkey for v in state.validators] rec = ValidatorRecord( pubkey=pubkey, withdrawal_credentials=withdrawal_credentials, @@ -744,15 +760,17 @@ def add_validator(validators: List[ValidatorRecord], last_status_change_slot=current_slot, exit_seq=0 ) - index = min_empty_validator(validators) + index = min_empty_validator(state.validators) if index is None: - validators.append(rec) - return len(validators) - 1 + state.validators.append(rec) + return len(state.validators) - 1 else: - validators[index] = rec + state.validators[index] = rec return index ``` +`BLSVerify` is a function for verifying a BLS12-381 signature, defined in the BLS12-381 spec. + ### Routine for removing a validator ```python @@ -814,18 +832,18 @@ Verify that there are at most `MAX_ATTESTATION_COUNT` `AttestationRecord` object * Compute `parent_hashes` = `[get_block_hash(state, block, slot - CYCLE_LENGTH + i) for i in range(1, CYCLE_LENGTH - len(oblique_parent_hashes) + 1)] + oblique_parent_hashes` (eg, if `CYCLE_LENGTH = 4`, `slot = 5`, the actual block hashes starting from slot 0 are `Z A B C D E F G H I J`, and `oblique_parent_hashes = [D', E']` then `parent_hashes = [B, C, D' E']`). Note that when *creating* an attestation for a block, the hash of that block itself won't yet be in the `state`, so you would need to add it explicitly. * Let `attestation_indices` be `get_shards_and_committees_for_slot(state, slot)[x]`, choosing `x` so that `attestation_indices.shard` equals the `shard` value provided to find the set of validators that is creating this attestation record. * Verify that `len(attester_bitfield) == ceil_div8(len(attestation_indices))`, where `ceil_div8 = (x + 7) // 8`. Verify that bits `len(attestation_indices)....` and higher, if present (i.e. `len(attestation_indices)` is not a multiple of 8), are all zero. -* Derive a group public key by adding the public keys of all of the attesters in `attestation_indices` for whom the corresponding bit in `attester_bitfield` (the ith bit is `(attester_bitfield[i // 8] >> (7 - (i %8))) % 2`) equals 1. -* Let `fork_version = pre_fork_version if slot < fork_slot_number else post_fork_version`. -* Verify that `aggregate_sig` verifies using the group pubkey generated and the serialized form of `AttestationSignedData(fork_version, slot, shard, parent_hashes, shard_block_hash, last_crosslinked_hash, shard_block_combined_data_root, justified_slot)` as the message. -* [TO BE REMOVED IN PHASE 1] Verify that `shard_block_hash == bytes([0] * 32)` +* Derive a `group_public_key` by adding the public keys of all of the attesters in `attestation_indices` for whom the corresponding bit in `attester_bitfield` (the ith bit is `(attester_bitfield[i // 8] >> (7 - (i % 8))) % 2`) equals 1. +* Let `data = AttestationSignedData(slot, shard, parent_hashes, shard_block_hash, last_crosslinked_hash, shard_block_combined_data_root, justified_slot)`. +* Check `BLSVerify(pubkey=group_public_key, msg=data, sig=aggregate_sig, domain=get_domain(state, slot, DOMAIN_ATTESTATION))`. +* [TO BE REMOVED IN PHASE 1] Verify that `shard_block_hash == bytes([0] * 32)`. Extend the list of `AttestationRecord` objects in the `state` with those included in the block, ordering the new additions in the same order as they came in the block. ### Verify proposer signature -Let `proposal_hash = hash(ProposalSignedData(fork_version, block.slot, 2**64 - 1, block_hash_without_sig))` where `block_hash_without_sig` is the hash of the block except setting `proposer_signature` to `[0, 0]`. +Let `proposal_hash = hash(ProposalSignedData(block.slot, 2**64 - 1, block_hash_without_sig))` where `block_hash_without_sig` is the hash of the block except setting `proposer_signature` to `[0, 0]`. -Verify that `BLSVerify(pubkey=get_beacon_proposer(state, block.slot).pubkey, data=proposal_hash, sig=block.proposer_signature)` passes. +Verify that `BLSVerify(pubkey=get_beacon_proposer(state, block.slot).pubkey, data=proposal_hash, sig=block.proposer_signature, domain=get_domain(state, block.slot, DOMAIN_PROPOSAL))` passes. ### Verify and process RANDAO reveal @@ -859,12 +877,12 @@ For each `SpecialRecord` `obj` in `block.specials`, verify that its `kind` is on ```python { 'validator_index': 'uint64', - 'signature': '[uint256]' + 'signature': '[uint384]' } ``` Perform the following checks: -* Let `fork_version = pre_fork_version if block.slot < fork_slot_number else post_fork_version`. Verify that `BLSVerify(pubkey=validators[data.validator_index].pubkey, msg=hash(LOGOUT_MESSAGE + bytes8(fork_version)), sig=data.signature)` +* Verify that `BLSVerify(pubkey=validators[data.validator_index].pubkey, msg=bytes([0] * 32), sig=data.signature, domain=get_domain(state, current_slot, DOMAIN_LOGOUT))` * Verify that `validators[validator_index].status == ACTIVE`. * Verify that `block.slot >= last_status_change_slot + SHARD_PERSISTENT_COMMITTEE_CHANGE_PERIOD` @@ -876,16 +894,16 @@ Run `exit_validator(data.validator_index, state, block, penalize=False, current_ { 'vote1_aggregate_sig_indices': '[uint24]', 'vote1_data': AttestationSignedData, - 'vote1_aggregate_sig': '[uint256]', + 'vote1_aggregate_sig': '[uint384]', 'vote2_aggregate_sig_indices': '[uint24]', 'vote2_data': AttestationSignedData, - 'vote2_aggregate_sig': '[uint256]', + 'vote2_aggregate_sig': '[uint384]', } ``` Perform the following checks: -* For each `aggregate_sig`, verify that `BLSVerify(pubkey=aggregate_pubkey([validators[i].pubkey for i in aggregate_sig_indices]), msg=vote_data, sig=aggsig)` passes. +* For each `vote`, verify that `BLSVerify(pubkey=aggregate_pubkey([validators[i].pubkey for i in vote_aggregate_sig_indices]), msg=vote_data, sig=vote_aggregate_sig, domain=get_domain(state, vote_data.slot, DOMAIN_ATTESTATION))` passes. * Verify that `vote1_data != vote2_data`. * Let `intersection = [x for x in vote1_aggregate_sig_indices if x in vote2_aggregate_sig_indices]`. Verify that `len(intersection) >= 1`. * Verify that `vote1_data.justified_slot < vote2_data.justified_slot < vote2_data.slot <= vote1_data.slot`. @@ -898,12 +916,12 @@ For each validator index `v` in `intersection`, if `state.validators[v].status` { 'proposer_index': 'uint24', 'proposal1_data': ProposalSignedData, - 'proposal1_signature': '[uint256]', + 'proposal1_signature': '[uint384]', 'proposal2_data': ProposalSignedData, - 'proposal1_signature': '[uint256]', + 'proposal1_signature': '[uint384]', } ``` -For each `proposal_signature`, verify that `BLSVerify(pubkey=validators[proposer_index].pubkey, msg=hash(proposal_data), sig=proposal_signature)` passes. Verify that `proposal1_data.slot == proposal2_data.slot` but `proposal1 != proposal2`. If `state.validators[proposer_index].status` does not equal `PENALIZED`, then run `exit_validator(proposer_index, state, penalize=True, current_slot=block.slot)` +For each `proposal_signature`, verify that `BLSVerify(pubkey=validators[proposer_index].pubkey, msg=hash(proposal_data), sig=proposal_signature, domain=get_domain(state, proposal_data.slot, DOMAIN_PROPOSAL))` passes. Verify that `proposal1_data.slot == proposal2_data.slot` but `proposal1 != proposal2`. If `state.validators[proposer_index].status` does not equal `PENALIZED`, then run `exit_validator(proposer_index, state, penalize=True, current_slot=block.slot)` #### DEPOSIT_PROOF diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md index c01c6e98f..59a6f6c1a 100644 --- a/specs/core/1_shard-data-chains.md +++ b/specs/core/1_shard-data-chains.md @@ -19,7 +19,14 @@ Phase 1 depends upon all of the constants defined in [Phase 0](0_beacon-chain.md | Constant | Value | Unit | Approximation | |------------------------|-----------------|-------|---------------| | `CHUNK_SIZE` | 2**8 (= 256) | bytes | | -| `MAX_SHARD_BLOCK_SIZE` | 2**15 (= 32768) | bytes | | +| `SHARD_BLOCK_SIZE` | 2**14 (= 16384) | bytes | | + +### Flags, domains, etc. + +| Constant | Value | +|------------------------|-----------------| +| `SHARD_PROPOSER_DOMAIN`| 129 | +| `SHARD_ATTESTER_DOMAIN`| 130 | ## Data Structures @@ -43,7 +50,9 @@ A `ShardBlock` object has the following fields: 'data_root': 'hash32' # State root (placeholder for now) 'state_root': 'hash32', - # Attestation (including block signature) + # Block signature + 'signature': ['uint256'], + # Attestation 'attester_bitfield': 'bytes', 'aggregate_sig': ['uint256'], } @@ -61,31 +70,27 @@ 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_hash`. * 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(attester_bitfield) == ceil_div8(len(validators))` -* Let `curblock_proposer_index = hash(state.randao_mix + bytes8(shard_id) + bytes8(slot)) % len(validators)`. Let `parent_proposer_index` be the same value calculated for the parent block. -* Make sure that the `parent_proposer_index`'th bit in the `attester_bitfield` is set to 1. -* 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 the `aggregate_sig` using this as the pubkey and the `parent_hash` as the message. +* Let `proposer_index = hash(state.randao_mix + bytes8(shard_id) + 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_hash, sig=block.aggregate_sig, domain=get_domain(state, slot, SHARD_ATTESTER_DOMAIN))` passes. + +### Block Merklization helper + +```python +def merkle_root(block_body): + assert len(block_body) == SHARD_BLOCK_SIZE + chunks = SHARD_BLOCK_SIZE // CHUNK_SIZE + o = [0] * chunks + [block_body[i * CHUNK_SIZE: (i+1) * 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] +``` ### Verifying shard block data -At network layer, we expect a shard block header to be broadcast along with its `block_body`. First, we define a helper function that takes as input beacon chain state and outputs the max block size in bytes: +At network layer, we expect a shard block header to be broadcast along with its `block_body`. -```python -def shard_block_maxbytes(state): - max_grains = MAX_SHARD_BLOCK_SIZE // CHUNK_SIZE - validators_at_target_committee_size = SHARD_COUNT * TARGET_COMMITTEE_SIZE - - # number of grains per block is proportional to the number of validators - # up until `validators_at_target_committee_size` - grains = min( - len(get_active_validator_indices(state.validators)) * max_grains // validators_at_target_committee_size, - max_grains - ) - - return CHUNK_SIZE * grains -``` - -* Verify that `len(block_body) == shard_block_maxbytes(state)` -* Define `filler_bytes = next_power_of_2(len(block_body)) - len(block_body)`. Compute a simple binary Merkle tree of `block_body + bytes([0] * filler_bytes)` and verify that the root equals the `data_root` in the header. +* Verify that `len(block_body) == SHARD_BLOCK_SIZE` +* Verify that `merkle_root(block_body)` equals the `data_root` in the header. ### Verifying a crosslink @@ -93,23 +98,13 @@ A node should sign a crosslink only if the following conditions hold. **If a nod First, the conditions must recursively apply to the crosslink referenced in `last_crosslink_hash` for the same shard (unless `last_crosslink_hash` equals zero, in which case we are at the genesis). -Second, we verify the `shard_block_combined_data_root`. Let `h` be the slot _immediately after_ the slot of the shard block included by the last crosslink, and `h+n-1` be the slot number of the block directly referenced by the current `shard_block_hash`. Let `B[i]` be the block at slot `h+i` in the shard chain. Let `bodies[0] .... bodies[n-1]` be the bodies of these blocks and `roots[0] ... roots[n-1]` the data roots. If there is a missing slot in the shard chain at position `h+i`, then `bodies[i] == b'\x00' * shard_block_maxbytes(state[i])` and `roots[i]` be the Merkle root of the empty data. Define `compute_merkle_root` be a simple Merkle root calculating function that takes as input a list of objects, where the list's length must be an exact power of two. Let `state[i]` be the beacon chain state at height `h+i` (if the beacon chain is missing a block at some slot, the state is unchanged), and `depths[i]` be equal to `log2(next_power_of_2(shard_block_maxbytes(state[i]) // CHUNK_SIZE))` (ie. the expected depth of the i'th data tree). We define the function for computing the combined data root as follows: +Second, we verify the `shard_block_combined_data_root`. Let `h` be the slot _immediately after_ the slot of the shard block included by the last crosslink, and `h+n-1` be the slot number of the block directly referenced by the current `shard_block_hash`. Let `B[i]` be the block at slot `h+i` in the shard chain. Let `bodies[0] .... bodies[n-1]` be the bodies of these blocks and `roots[0] ... roots[n-1]` the data roots. If there is a missing slot in the shard chain at position `h+i`, then `bodies[i] == b'\x00' * shard_block_maxbytes(state[i])` and `roots[i]` be the Merkle root of the empty data. Define `compute_merkle_root` be a simple Merkle root calculating function that takes as input a list of objects, where the list's length must be an exact power of two. We define the function for computing the combined data root as follows: ```python -def get_zeroroot_at_depth(n): - o = b'\x00' * CHUNK_SIZE - for i in range(n): - o = hash(o + o) - return o +ZERO_ROOT = merkle_root(bytes([0] * SHARD_BLOCK_SIZE)) -def mk_combined_data_root(depths, roots): - default_value = get_zeroroot_at_depth(max(depths)) - data = [default_value for _ in range(next_power_of_2(len(roots)))] - for i, (depth, root) in enumerate(zip(depths, roots)): - value = root - for j in range(depth, max(depths)): - value = hash(value, get_zeroroot_at_depth(depth + j)) - data[i] = value +def mk_combined_data_root(roots): + data = roots + [ZERO_ROOT for _ in range(len(roots), next_power_of_2(len(roots)))] return compute_merkle_root(data) ``` @@ -117,12 +112,7 @@ This outputs the root of a tree of the data roots, with the data roots all adjus ```python def mk_combined_data_root(depths, bodies): - default_value = get_zeroroot_at_depth(max(depths)) - padded_body_length = max([CHUNK_SIZE * 2**d for d in depths]) - data = b'' - for body in bodies: - padded_body = body + bytes([0] * (padded_body_length - len(body))) - data += padded_body + data = b''.join(bodies) data += bytes([0] * (next_power_of_2(len(data)) - len(data)) return compute_merkle_root([data[pos:pos+CHUNK_SIZE] for pos in range(0, len(data), CHUNK_SIZE)]) ```