diff --git a/README.md b/README.md index f3aba3f64..c5c88daf9 100644 --- a/README.md +++ b/README.md @@ -16,6 +16,7 @@ Accompanying documents can be found in [specs](specs) and include * [SimpleSerialize (SSZ) spec](specs/simple-serialize.md) * [BLS signature verification](specs/bls_signature.md) * [General test format](specs/test-format.md) +* [Honest validator implementation doc](specs/validator/0_beacon-chain-validator.md) ## Design goals The following are the broad design goals for Ethereum 2.0: diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md index d3ee1b9d5..e39675a15 100644 --- a/specs/core/0_beacon-chain.md +++ b/specs/core/0_beacon-chain.md @@ -15,6 +15,7 @@ - [Deposit contract](#deposit-contract) - [Initial values](#initial-values) - [Time parameters](#time-parameters) + - [State list lengths](#state-list-lengths) - [Reward and penalty quotients](#reward-and-penalty-quotients) - [Status flags](#status-flags) - [Max operations per block](#max-operations-per-block) @@ -23,9 +24,9 @@ - [Beacon chain operations](#beacon-chain-operations) - [Proposer slashings](#proposer-slashings) - [`ProposerSlashing`](#proposerslashing) - - [Casper slashings](#casper-slashings) - - [`CasperSlashing`](#casperslashing) - - [`SlashableVoteData`](#slashablevotedata) + - [Attester slashings](#attester-slashings) + - [`AttesterSlashing`](#attesterslashing) + - [`SlashableVote`](#slashablevote) - [Attestations](#attestations) - [`Attestation`](#attestation) - [`AttestationData`](#attestationdata) @@ -48,76 +49,88 @@ - [`Fork`](#fork) - [`Eth1Data`](#eth1data) - [`Eth1DataVote`](#eth1datavote) + - [Custom Types](#custom-types) + - [Helper functions](#helper-functions) + - [`hash`](#hash) + - [`hash_tree_root`](#hash_tree_root) + - [`slot_to_epoch`](#slot_to_epoch) + - [`get_current_epoch`](#get_current_epoch) + - [`get_epoch_start_slot`](#get_epoch_start_slot) + - [`is_active_validator`](#is_active_validator) + - [`get_active_validator_indices`](#get_active_validator_indices) + - [`shuffle`](#shuffle) + - [`split`](#split) + - [`get_epoch_committee_count`](#get_epoch_committee_count) + - [`get_shuffling`](#get_shuffling) + - [`get_previous_epoch_committee_count`](#get_previous_epoch_committee_count) + - [`get_current_epoch_committee_count`](#get_current_epoch_committee_count) + - [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot) + - [`get_block_root`](#get_block_root) + - [`get_randao_mix`](#get_randao_mix) + - [`get_active_index_root`](#get_active_index_root) + - [`generate_seed`](#generate_seed) + - [`get_beacon_proposer_index`](#get_beacon_proposer_index) + - [`merkle_root`](#merkle_root) + - [`get_attestation_participants`](#get_attestation_participants) + - [`int_to_bytes1`, `int_to_bytes2`, ...](#int_to_bytes1-int_to_bytes2-) + - [`get_effective_balance`](#get_effective_balance) + - [`get_fork_version`](#get_fork_version) + - [`get_domain`](#get_domain) + - [`get_bitfield_bit`](#get_bitfield_bit) + - [`verify_bitfield`](#verify_bitfield) + - [`verify_slashable_vote`](#verify_slashable_vote) + - [`is_double_vote`](#is_double_vote) + - [`is_surround_vote`](#is_surround_vote) + - [`integer_squareroot`](#integer_squareroot) + - [`get_entry_exit_effect_epoch`](#get_entry_exit_effect_epoch) + - [`bls_verify`](#bls_verify) + - [`bls_verify_multiple`](#bls_verify_multiple) + - [`bls_aggregate_pubkeys`](#bls_aggregate_pubkeys) + - [`validate_proof_of_possession`](#validate_proof_of_possession) + - [`process_deposit`](#process_deposit) + - [Routines for updating validator status](#routines-for-updating-validator-status) + - [`activate_validator`](#activate_validator) + - [`initiate_validator_exit`](#initiate_validator_exit) + - [`exit_validator`](#exit_validator) + - [`penalize_validator`](#penalize_validator) + - [`prepare_validator_for_withdrawal`](#prepare_validator_for_withdrawal) - [Ethereum 1.0 deposit contract](#ethereum-10-deposit-contract) - [Deposit arguments](#deposit-arguments) - [Withdrawal credentials](#withdrawal-credentials) - [`Deposit` logs](#deposit-logs) - [`ChainStart` log](#chainstart-log) - [Vyper code](#vyper-code) + - [On startup](#on-startup) - [Beacon chain processing](#beacon-chain-processing) - [Beacon chain fork choice rule](#beacon-chain-fork-choice-rule) - [Beacon chain state transition function](#beacon-chain-state-transition-function) - - [Helper functions](#helper-functions) - - [`hash`](#hash) - - [`hash_tree_root`](#hash_tree_root) - - [`is_active_validator`](#is_active_validator) - - [`get_active_validator_indices`](#get_active_validator_indices) - - [`shuffle`](#shuffle) - - [`split`](#split) - - [`get_committee_count_per_slot`](#get_committee_count_per_slot) - - [`get_shuffling`](#get_shuffling) - - [`get_previous_epoch_committee_count_per_slot`](#get_previous_epoch_committee_count_per_slot) - - [`get_current_epoch_committee_count_per_slot`](#get_current_epoch_committee_count_per_slot) - - [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot) - - [`get_block_root`](#get_block_root) - - [`get_randao_mix`](#get_randao_mix) - - [`get_active_index_root`](#get_active_index_root) - - [`get_beacon_proposer_index`](#get_beacon_proposer_index) - - [`merkle_root`](#merkle_root) - - [`get_attestation_participants`](#get_attestation_participants) - - [`int_to_bytes1`, `int_to_bytes2`, ...](#int_to_bytes1-int_to_bytes2-) - - [`get_effective_balance`](#get_effective_balance) - - [`get_fork_version`](#get_fork_version) - - [`get_domain`](#get_domain) - - [`verify_slashable_vote_data`](#verify_slashable_vote_data) - - [`is_double_vote`](#is_double_vote) - - [`is_surround_vote`](#is_surround_vote) - - [`integer_squareroot`](#integer_squareroot) - - [`entry_exit_effect_slot`](#entry_exit_effect_slot) - - [`bls_verify`](#bls_verify) - - [`bls_verify_multiple`](#bls_verify_multiple) - - [`bls_aggregate_pubkeys`](#bls_aggregate_pubkeys) - - [On startup](#on-startup) - - [Routine for processing deposits](#routine-for-processing-deposits) - - [Routines for updating validator status](#routines-for-updating-validator-status) - - [Per-slot processing](#per-slot-processing) - - [Misc counters](#misc-counters) - - [Block roots](#block-roots) - - [Per-block processing](#per-block-processing) - - [Slot](#slot) - - [Proposer signature](#proposer-signature) - - [RANDAO](#randao) - - [Eth1 data](#eth1-data) - - [Operations](#operations) - - [Proposer slashings](#proposer-slashings-1) - - [Casper slashings](#casper-slashings-1) - - [Attestations](#attestations-1) - - [Deposits](#deposits-1) - - [Exits](#exits-1) - - [Custody](#custody) - - [Per-epoch processing](#per-epoch-processing) - - [Helpers](#helpers) - - [Eth1 data](#eth1-data-1) - - [Justification](#justification) - - [Crosslinks](#crosslinks) - - [Rewards and penalties](#rewards-and-penalties) - - [Justification and finalization](#justification-and-finalization) - - [Attestation inclusion](#attestation-inclusion) - - [Crosslinks](#crosslinks-1) - - [Ejections](#ejections) - - [Validator registry](#validator-registry) - - [Final updates](#final-updates) - - [State root processing](#state-root-processing) + - [Per-slot processing](#per-slot-processing) + - [Slot](#slot) + - [Block roots](#block-roots) + - [Per-block processing](#per-block-processing) + - [Slot](#slot-1) + - [Proposer signature](#proposer-signature) + - [RANDAO](#randao) + - [Eth1 data](#eth1-data) + - [Operations](#operations) + - [Proposer slashings](#proposer-slashings-1) + - [Attester slashings](#attester-slashings-1) + - [Attestations](#attestations-1) + - [Deposits](#deposits-1) + - [Exits](#exits-1) + - [Per-epoch processing](#per-epoch-processing) + - [Helpers](#helpers) + - [Eth1 data](#eth1-data-1) + - [Justification](#justification) + - [Crosslinks](#crosslinks) + - [Rewards and penalties](#rewards-and-penalties) + - [Justification and finalization](#justification-and-finalization) + - [Attestation inclusion](#attestation-inclusion) + - [Crosslinks](#crosslinks-1) + - [Ejections](#ejections) + - [Validator registry and shuffling seed data](#validator-registry-and-shuffling-seed-data) + - [Final updates](#final-updates) + - [State root verification](#state-root-verification) - [References](#references) - [Normative](#normative) - [Informative](#informative) @@ -139,8 +152,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ## Terminology -* **Validator** - a participant in the Casper/sharding consensus system. You can become one by depositing 32 ETH into the Casper mechanism. -* **Active validator** - a [validator](#dfn-validator) currently participating in the protocol which the Casper mechanism looks to produce and attest to blocks, crosslinks and other consensus objects. +* **Validator** - a registered participant in the beacon chain. You can become one by sending Ether into the Ethereum 1.0 deposit contract. +* **Active validator** - an active participant in the Ethereum 2.0 consensus invited to, among other things, propose and attest to blocks and vote for crosslinks. * **Committee** - a (pseudo-) randomly sampled subset of [active validators](#dfn-active-validator). When a committee is referred to collectively, as in "this committee attests to X", this is assumed to mean "some subset of that committee that contains enough [validators](#dfn-validator) that the protocol recognizes it as representing the committee". * **Proposer** - the [validator](#dfn-validator) that creates a beacon chain block * **Attester** - a [validator](#dfn-validator) that is part of a committee that needs to sign off on a beacon chain block while simultaneously creating a link (crosslink) to a recent shard block on a particular shard chain. @@ -165,11 +178,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be | `EJECTION_BALANCE` | `2**4 * 1e9` (= 16,000,000,000) | Gwei | | `MAX_BALANCE_CHURN_QUOTIENT` | `2**5` (= 32) | - | | `BEACON_CHAIN_SHARD_NUMBER` | `2**64 - 1` | - | -| `MAX_CASPER_VOTES` | `2**10` (= 1,024) | votes | -| `LATEST_BLOCK_ROOTS_LENGTH` | `2**13` (= 8,192) | block roots | -| `LATEST_RANDAO_MIXES_LENGTH` | `2**13` (= 8,192) | randao mixes | -| `LATEST_INDEX_ROOTS_LENGTH` | `2**13` (= 8,192) | index roots | -| `LATEST_PENALIZED_EXIT_LENGTH` | `2**13` (= 8,192) | epochs | ~36 days | +| `MAX_INDICES_PER_SLASHABLE_VOTE` | `2**12` (= 4,096) | votes | | `MAX_WITHDRAWALS_PER_EPOCH` | `2**2` (= 4) | withdrawals | * For the safety of crosslinks `TARGET_COMMITTEE_SIZE` exceeds [the recommended minimum committee size of 111](https://vitalik.ca/files/Ithaca201807_Sharding.pdf); with sufficient active validators (at least `EPOCH_LENGTH * TARGET_COMMITTEE_SIZE`), the shuffling algorithm ensures committee sizes at least `TARGET_COMMITTEE_SIZE`. (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.) @@ -188,13 +197,16 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be | Name | Value | | - | - | | `GENESIS_FORK_VERSION` | `0` | -| `GENESIS_SLOT` | `0` | +| `GENESIS_SLOT` | `2**19` | +| `GENESIS_EPOCH` | `slot_to_epoch(GENESIS_SLOT)` | | `GENESIS_START_SHARD` | `0` | -| `FAR_FUTURE_SLOT` | `2**64 - 1` | +| `FAR_FUTURE_EPOCH` | `2**64 - 1` | | `ZERO_HASH` | `int_to_bytes32(0)` | | `EMPTY_SIGNATURE` | `int_to_bytes96(0)` | | `BLS_WITHDRAWAL_PREFIX_BYTE` | `int_to_bytes1(0)` | +* `GENESIS_SLOT` should be at least as large in terms of time as the largest of the time parameters or state list lengths below (ie. it should be at least as large as any value measured in slots, and at least `EPOCH_LENGTH` times as large as any value measured in epochs). + ### Time parameters | Name | Value | Unit | Duration | @@ -202,10 +214,19 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be | `SLOT_DURATION` | `6` | seconds | 6 seconds | | `MIN_ATTESTATION_INCLUSION_DELAY` | `2**2` (= 4) | slots | 24 seconds | | `EPOCH_LENGTH` | `2**6` (= 64) | slots | 6.4 minutes | -| `SEED_LOOKAHEAD` | `2**6` (= 64) | slots | 6.4 minutes | -| `ENTRY_EXIT_DELAY` | `2**8` (= 256) | slots | 25.6 minutes | -| `ETH1_DATA_VOTING_PERIOD` | `2**10` (= 1,024) | slots | ~1.7 hours | -| `MIN_VALIDATOR_WITHDRAWAL_TIME` | `2**14` (= 16,384) | slots | ~27 hours | +| `SEED_LOOKAHEAD` | `2**0` (= 1) | epochs | 6.4 minutes | +| `ENTRY_EXIT_DELAY` | `2**2` (= 4) | epochs | 25.6 minutes | +| `ETH1_DATA_VOTING_PERIOD` | `2**4` (= 16) | epochs | ~1.7 hours | +| `MIN_VALIDATOR_WITHDRAWAL_EPOCHS` | `2**8` (= 256) | epochs | ~27 hours | + +### State list lengths + +| Name | Value | Unit | Duration | +| - | - | :-: | :-: | +| `LATEST_BLOCK_ROOTS_LENGTH` | `2**13` (= 8,192) | slots | ~13 hours | +| `LATEST_RANDAO_MIXES_LENGTH` | `2**13` (= 8,192) | epochs | ~36 days | +| `LATEST_INDEX_ROOTS_LENGTH` | `2**13` (= 8,192) | epochs | ~36 days | +| `LATEST_PENALIZED_EXIT_LENGTH` | `2**13` (= 8,192) | epochs | ~36 days | ### Reward and penalty quotients @@ -231,7 +252,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be | Name | Value | | - | - | | `MAX_PROPOSER_SLASHINGS` | `2**4` (= 16) | -| `MAX_CASPER_SLASHINGS` | `2**4` (= 16) | +| `MAX_ATTESTER_SLASHINGS` | `2**0` (= 1) | | `MAX_ATTESTATIONS` | `2**7` (= 128) | | `MAX_DEPOSITS` | `2**4` (= 16) | | `MAX_EXITS` | `2**4` (= 16) | @@ -248,6 +269,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ## Data structures +The following data structures are defined as [SimpleSerialize (SSZ)](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md) objects. + ### Beacon chain operations #### Proposer slashings @@ -257,7 +280,7 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { # Proposer index - 'proposer_index': 'uint24', + 'proposer_index': 'uint64', # First proposal data 'proposal_data_1': ProposalSignedData, # First proposal signature @@ -269,27 +292,27 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be } ``` -#### Casper slashings +#### Attester slashings -##### `CasperSlashing` +##### `AttesterSlashing` ```python { # First batch of votes - 'slashable_vote_data_1': SlashableVoteData, + 'slashable_vote_1': SlashableVote, # Second batch of votes - 'slashable_vote_data_2': SlashableVoteData, + 'slashable_vote_2': SlashableVote, } ``` -##### `SlashableVoteData` +##### `SlashableVote` ```python { - # Validator indices with custody bit equal to 0 - 'custody_bit_0_indices': ['uint24'], - # Validator indices with custody bit equal to 1 - 'custody_bit_1_indices': ['uint24'], + # Validator indices + 'validator_indices': '[uint64]', + # Custody bitfield + 'custody_bitfield': 'bytes', # Attestation data 'data': AttestationData, # Aggregate signature @@ -330,8 +353,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be 'shard_block_root': 'bytes32', # Last crosslink's hash of root 'latest_crosslink_root': 'bytes32', - # Slot of the last justified beacon block - 'justified_slot': 'uint64', + # Last justified epoch in the beacon state + 'justified_epoch': 'uint64', # Hash of the last justified beacon block 'justified_block_root': 'bytes32', } @@ -342,9 +365,9 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { # Attestation data - data: AttestationData, + 'data': AttestationData, # Custody bit - custody_bit: bool, + 'custody_bit': 'bool', } ``` @@ -395,10 +418,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { - # Minimum slot for processing exit - 'slot': 'uint64', + # Minimum epoch for processing exit + 'epoch': 'uint64', # Index of the exiting validator - 'validator_index': 'uint24', + 'validator_index': 'uint64', # Validator signature 'signature': 'bytes96', } @@ -428,18 +451,13 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { 'proposer_slashings': [ProposerSlashing], - 'casper_slashings': [CasperSlashing], + 'attester_slashings': [AttesterSlashing], 'attestations': [Attestation], - 'custody_reseeds': [CustodyReseed], - 'custody_challenges': [CustodyChallenge], - 'custody_responses': [CustodyResponse], 'deposits': [Deposit], 'exits': [Exit], } ``` -`CustodyReseed`, `CustodyChallenge`, and `CustodyResponse` will be defined in phase 1; for now, put dummy classes as these lists will remain empty throughout phase 0. - #### `ProposalSignedData` ```python @@ -467,31 +485,27 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be # Validator registry 'validator_registry': [Validator], 'validator_balances': ['uint64'], - 'validator_registry_update_slot': 'uint64', + 'validator_registry_update_epoch': 'uint64', 'validator_registry_exit_count': 'uint64', # Randomness and committees 'latest_randao_mixes': ['bytes32'], - 'latest_vdf_outputs': ['bytes32'], 'previous_epoch_start_shard': 'uint64', 'current_epoch_start_shard': 'uint64', - 'previous_epoch_calculation_slot': 'uint64', - 'current_epoch_calculation_slot': 'uint64', + 'previous_calculation_epoch': 'uint64', + 'current_calculation_epoch': 'uint64', 'previous_epoch_seed': 'bytes32', 'current_epoch_seed': 'bytes32', - # Custody challenges - 'custody_challenges': [CustodyChallenge], - # Finality - 'previous_justified_slot': 'uint64', - 'justified_slot': 'uint64', + 'previous_justified_epoch': 'uint64', + 'justified_epoch': 'uint64', 'justification_bitfield': 'uint64', - 'finalized_slot': 'uint64', + 'finalized_epoch': 'uint64', # Recent state 'latest_crosslinks': [Crosslink], - 'latest_block_roots': ['bytes32'], # Needed to process attestations, older to newer + 'latest_block_roots': ['bytes32'], 'latest_index_roots': ['bytes32'], 'latest_penalized_balances': ['uint64'], # Balances penalized at every withdrawal period 'latest_attestations': [PendingAttestation], @@ -511,24 +525,18 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be 'pubkey': 'bytes48', # Withdrawal credentials 'withdrawal_credentials': 'bytes32', - # Number of proposer slots since genesis - 'proposer_slots': 'uint64', - # Slot when validator activated - 'activation_slot': 'uint64', - # Slot when validator exited - 'exit_slot': 'uint64', - # Slot when validator withdrew - 'withdrawal_slot': 'uint64', - # Slot when validator was penalized - 'penalized_slot': 'uint64', + # Epoch when validator activated + 'activation_epoch': 'uint64', + # Epoch when validator exited + 'exit_epoch': 'uint64', + # Epoch when validator withdrew + 'withdrawal_epoch': 'uint64', + # Epoch when validator was penalized + 'penalized_epoch': 'uint64', # Exit counter when validator exited 'exit_count': 'uint64', # Status flags 'status_flags': 'uint64', - # Slot of latest custody reseed - 'latest_custody_reseed_slot': 'uint64', - # Slot of second-latest custody reseed - 'penultimate_custody_reseed_slot': 'uint64', } ``` @@ -536,8 +544,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { - # Slot number - 'slot': 'uint64', + # Epoch number + 'epoch': 'uint64', # Shard block root 'shard_block_root': 'bytes32', } @@ -566,8 +574,8 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be 'previous_version': 'uint64', # Current fork version 'current_version': 'uint64', - # Fork slot number - 'slot': 'uint64', + # Fork epoch number + 'epoch': 'uint64', } ``` @@ -576,9 +584,9 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be ```python { # Root of the deposit tree - 'deposit_root': 'hash32', + 'deposit_root': 'bytes32', # Block hash - 'block_hash': 'hash32', + 'block_hash': 'bytes32', } ``` @@ -593,6 +601,679 @@ Code snippets appearing in `this style` are to be interpreted as Python code. Be } ``` +## Custom Types + +We define the following Python custom types for type hinting and readability: + +| Name | SSZ equivalent | Description | +| - | - | - | +| `SlotNumber` | `uint64` | a slot number | +| `EpochNumber` | `uint64` | an epoch number | +| `ShardNumber` | `uint64` | a shard number | +| `ValidatorIndex` | `uint64` | an index in the validator registry | +| `Gwei` | `uint64` | an amount in Gwei | +| `Bytes32` | `bytes32` | 32 bytes of binary data | +| `BLSPubkey` | `bytes48` | a BLS public key | +| `BLSSignature` | `bytes96` | a BLS signature | + +## Helper functions + +Note: The definitions below are for specification purposes and are not necessarily optimal implementations. + +### `hash` + +The hash function is denoted by `hash`. In Phase 0 the beacon chain is deployed with the same hash function as Ethereum 1.0, i.e. Keccak-256 (also incorrectly known as SHA3). + +Note: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethereum 2.0 deployment phase. + +### `hash_tree_root` + +`def hash_tree_root(object: SSZSerializable) -> Bytes32` is a function for hashing objects into a single root utilizing a hash tree structure. `hash_tree_root` is defined in the [SimpleSerialize spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md#tree-hash). + +### `slot_to_epoch` + +```python +def slot_to_epoch(slot: SlotNumber) -> EpochNumber: + return slot // EPOCH_LENGTH +``` + +### `get_current_epoch` + +```python +def get_current_epoch(state: BeaconState) -> EpochNumber: + return slot_to_epoch(state.slot) +``` + +### `get_epoch_start_slot` + +```python +def get_epoch_start_slot(epoch: EpochNumber) -> SlotNumber: + return epoch * EPOCH_LENGTH +``` + +### `is_active_validator` +```python +def is_active_validator(validator: Validator, epoch: EpochNumber) -> bool: + """ + Checks if ``validator`` is active. + """ + return validator.activation_epoch <= epoch < validator.exit_epoch +``` + +### `get_active_validator_indices` + +```python +def get_active_validator_indices(validators: List[Validator], epoch: EpochNumber) -> List[ValidatorIndex]: + """ + Gets indices of active validators from ``validators``. + """ + return [i for i, v in enumerate(validators) if is_active_validator(v, epoch)] +``` + +### `shuffle` + +```python +def shuffle(values: List[Any], seed: Bytes32) -> List[Any]: + """ + Returns the shuffled ``values`` with ``seed`` as entropy. + """ + values_count = len(values) + + # Entropy is consumed from the seed in 3-byte (24 bit) chunks. + rand_bytes = 3 + # The highest possible result of the RNG. + rand_max = 2 ** (rand_bytes * 8) - 1 + + # The range of the RNG places an upper-bound on the size of the list that + # may be shuffled. It is a logic error to supply an oversized list. + assert values_count < rand_max + + output = [x for x in values] + source = seed + index = 0 + while index < values_count - 1: + # Re-hash the `source` to obtain a new pattern of bytes. + source = hash(source) + # Iterate through the `source` bytes in 3-byte chunks. + for position in range(0, 32 - (32 % rand_bytes), rand_bytes): + # Determine the number of indices remaining in `values` and exit + # once the last index is reached. + remaining = values_count - index + if remaining == 1: + break + + # Read 3-bytes of `source` as a 24-bit big-endian integer. + sample_from_source = int.from_bytes(source[position:position + rand_bytes], 'big') + + # Sample values greater than or equal to `sample_max` will cause + # modulo bias when mapped into the `remaining` range. + sample_max = rand_max - rand_max % remaining + + # Perform a swap if the consumed entropy will not cause modulo bias. + if sample_from_source < sample_max: + # Select a replacement index for the current index. + replacement_position = (sample_from_source % remaining) + index + # Swap the current index with the replacement index. + output[index], output[replacement_position] = output[replacement_position], output[index] + index += 1 + else: + # The sample causes modulo bias. A new sample should be read. + pass + + return output +``` + +### `split` + +```python +def split(values: List[Any], split_count: int) -> List[List[Any]]: + """ + Splits ``values`` into ``split_count`` pieces. + """ + list_length = len(values) + return [ + values[(list_length * i // split_count): (list_length * (i + 1) // split_count)] + for i in range(split_count) + ] +``` + +### `get_epoch_committee_count` + +```python +def get_epoch_committee_count(active_validator_count: int) -> int: + return max( + 1, + min( + SHARD_COUNT // EPOCH_LENGTH, + active_validator_count // EPOCH_LENGTH // TARGET_COMMITTEE_SIZE, + ) + ) * EPOCH_LENGTH +``` + +### `get_shuffling` + +```python +def get_shuffling(seed: Bytes32, + validators: List[Validator], + epoch: EpochNumber) -> List[List[ValidatorIndex]] + """ + Shuffles ``validators`` into crosslink committees seeded by ``seed`` and ``epoch``. + Returns a list of ``committees_per_epoch`` committees where each + committee is itself a list of validator indices. + """ + + active_validator_indices = get_active_validator_indices(validators, epoch) + + committees_per_epoch = get_epoch_committee_count(len(active_validator_indices)) + + # Shuffle + seed = xor(seed, int_to_bytes32(epoch)) + shuffled_active_validator_indices = shuffle(active_validator_indices, seed) + + # Split the shuffled list into committees_per_epoch pieces + return split(shuffled_active_validator_indices, committees_per_epoch) +``` + +**Invariant**: if `get_shuffling(seed, validators, epoch)` returns some value `x` for some `epoch <= get_current_epoch(state) + ENTRY_EXIT_DELAY`, it should return the same value `x` for the same `seed` and `epoch` and possible future modifications of `validators` forever in phase 0, and until the ~1 year deletion delay in phase 2 and in the future. + +**Note**: this definition and the next few definitions make heavy use of repetitive computing. Production implementations are expected to appropriately use caching/memoization to avoid redoing work. + +#### `get_previous_epoch_committee_count` + +```python +def get_previous_epoch_committee_count(state: BeaconState) -> int: + previous_active_validators = get_active_validator_indices( + state.validator_registry, + state.previous_calculation_epoch, + ) + return get_epoch_committee_count(len(previous_active_validators)) +``` + +### `get_current_epoch_committee_count` + +```python +def get_current_epoch_committee_count(state: BeaconState) -> int: + current_active_validators = get_active_validator_indices( + state.validator_registry, + state.current_calculation_epoch, + ) + return get_epoch_committee_count(len(current_active_validators)) +``` + +### `get_crosslink_committees_at_slot` + +```python +def get_crosslink_committees_at_slot(state: BeaconState, + slot: SlotNumber) -> List[Tuple[List[ValidatorIndex], ShardNumber]]: + """ + Returns the list of ``(committee, shard)`` tuples for the ``slot``. + """ + epoch = slot_to_epoch(slot) + current_epoch = get_current_epoch(state) + previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else current_epoch + next_epoch = current_epoch + 1 + + assert previous_epoch <= epoch < next_epoch + + if epoch < current_epoch: + committees_per_epoch = get_previous_epoch_committee_count(state) + seed = state.previous_epoch_seed + shuffling_epoch = state.previous_calculation_epoch + shuffling_start_shard = state.previous_epoch_start_shard + else: + committees_per_epoch = get_current_epoch_committee_count(state) + seed = state.current_epoch_seed + shuffling_epoch = state.current_calculation_epoch + shuffling_start_shard = state.current_epoch_start_shard + + shuffling = get_shuffling( + seed, + state.validator_registry, + shuffling_epoch, + ) + offset = slot % EPOCH_LENGTH + committees_per_slot = committees_per_epoch // EPOCH_LENGTH + slot_start_shard = (shuffling_start_shard + committees_per_slot * offset) % SHARD_COUNT + + return [ + ( + shuffling[committees_per_slot * offset + i], + (slot_start_shard + i) % SHARD_COUNT, + ) + for i in range(committees_per_slot) + ] +``` + +**Note**: we plan to replace the shuffling algorithm with a pointwise-evaluable shuffle (see https://github.com/ethereum/eth2.0-specs/issues/323), which will allow calculation of the committees for each slot individually. + +### `get_block_root` + +```python +def get_block_root(state: BeaconState, + slot: SlotNumber) -> Bytes32: + """ + Returns the block root at a recent ``slot``. + """ + assert state.slot <= slot + LATEST_BLOCK_ROOTS_LENGTH + assert slot < state.slot + return state.latest_block_roots[slot % LATEST_BLOCK_ROOTS_LENGTH] +``` + +`get_block_root(_, s)` should always return `hash_tree_root` of the block in the beacon chain at slot `s`, and `get_crosslink_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes. + +### `get_randao_mix` + +```python +def get_randao_mix(state: BeaconState, + epoch: EpochNumber) -> Bytes32: + """ + Returns the randao mix at a recent ``epoch``. + """ + assert get_current_epoch(state) - LATEST_RANDAO_MIXES_LENGTH < epoch <= get_current_epoch(state) + return state.latest_randao_mixes[epoch % LATEST_RANDAO_MIXES_LENGTH] +``` + +### `get_active_index_root` + +```python +def get_active_index_root(state: BeaconState, + epoch: EpochNumber) -> Bytes32: + """ + Returns the index root at a recent ``epoch``. + """ + assert get_current_epoch(state) - LATEST_INDEX_ROOTS_LENGTH < epoch <= get_current_epoch(state) + return state.latest_index_roots[epoch % LATEST_INDEX_ROOTS_LENGTH] +``` + +### `generate_seed` + +```python +def generate_seed(state: BeaconState, + epoch: EpochNumber) -> Bytes32: + """ + Generate a seed for the given ``epoch``. + """ + + return hash( + get_randao_mix(state, epoch - SEED_LOOKAHEAD) + + get_active_index_root(state, epoch) + ) +``` + +### `get_beacon_proposer_index` + +```python +def get_beacon_proposer_index(state: BeaconState, + slot: SlotNumber) -> ValidatorIndex: + """ + Returns the beacon proposer index for the ``slot``. + """ + first_committee, _ = get_crosslink_committees_at_slot(state, slot)[0] + return first_committee[slot % len(first_committee)] +``` + +### `merkle_root` + +```python +def merkle_root(values: List[Bytes32]) -> Bytes32: + """ + Merkleize ``values`` (where ``len(values)`` is a power of two) and return the Merkle root. + """ + o = [0] * len(values) + values + for i in range(len(values) - 1, 0, -1): + o[i] = hash(o[i * 2] + o[i * 2 + 1]) + return o[1] +``` + +### `get_attestation_participants` + +```python +def get_attestation_participants(state: BeaconState, + attestation_data: AttestationData, + bitfield: bytes) -> List[ValidatorIndex]: + """ + Returns the participant indices at for the ``attestation_data`` and ``bitfield``. + """ + # Find the committee in the list with the desired shard + crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot) + + assert attestation_data.shard in [shard for _, shard in crosslink_committees] + crosslink_committee = [committee for committee, shard in crosslink_committees if shard == attestation_data.shard][0] + + assert verify_bitfield(bitfield, len(crosslink_committee)) + + # Find the participating attesters in the committee + participants = [] + for i, validator_index in enumerate(crosslink_committee): + aggregation_bit = get_bitfield_bit(bitfield, i) + if aggregation_bit == 0b1: + participants.append(validator_index) + return participants +``` + +### `int_to_bytes1`, `int_to_bytes2`, ... + +`int_to_bytes1(x): return x.to_bytes(1, 'big')`, `int_to_bytes2(x): return x.to_bytes(2, 'big')`, and so on for all integers, particularly 1, 2, 3, 4, 8, 32, 48, 96. + +### `get_effective_balance` + +```python +def get_effective_balance(state: State, index: ValidatorIndex) -> Gwei: + """ + Returns the effective balance (also known as "balance at stake") for a ``validator`` with the given ``index``. + """ + return min(state.validator_balances[index], MAX_DEPOSIT_AMOUNT) +``` + +### `get_fork_version` + +```python +def get_fork_version(fork: Fork, + epoch: EpochNumber) -> int: + if epoch < fork.epoch: + return fork.previous_version + else: + return fork.current_version +``` + +### `get_domain` + +```python +def get_domain(fork: Fork, + epoch: EpochNumber, + domain_type: int) -> int: + return get_fork_version( + fork, + epoch, + ) * 2**32 + domain_type +``` + +### `get_bitfield_bit` + +```python +def get_bitfield_bit(bitfield: bytes, i: int) -> int: + """ + Extract the bit in ``bitfield`` at position ``i``. + """ + return (bitfield[i // 8] >> (7 - (i % 8))) % 2 +``` + +### `verify_bitfield` + +```python +def verify_bitfield(bitfield: bytes, committee_size: int) -> bool: + """ + Verify ``bitfield`` against the ``committee_size``. + """ + if len(bitfield) != (committee_size + 7) // 8: + return False + + for i in range(committee_size + 1, committee_size - committee_size % 8 + 8): + if get_bitfield_bit(bitfield, i) == 0b1: + return False + + return True +``` + +### `verify_slashable_vote` + +```python +def verify_slashable_vote(state: BeaconState, slashable_vote: SlashableVote) -> bool: + """ + Verify validity of ``slashable_vote`` fields. + """ + if slashable_vote.custody_bitfield != b'\x00' * len(slashable_vote.custody_bitfield): # [TO BE REMOVED IN PHASE 1] + return False + + if len(slashable_vote.validator_indices) == 0: + return False + + for i in range(len(slashable_vote.validator_indices) - 1): + if slashable_vote.validator_indices[i] >= slashable_vote.validator_indices[i + 1]: + return False + + if not verify_bitfield(slashable_vote.custody_bitfield, len(slashable_vote.validator_indices)): + return False + + if len(slashable_vote.validator_indices) > MAX_INDICES_PER_SLASHABLE_VOTE: + return False + + custody_bit_0_indices = [] + custody_bit_1_indices = [] + for i, validator_index in enumerate(slashable_vote.validator_indices): + if get_bitfield_bit(slashable_vote.custody_bitfield, i) == 0b0: + custody_bit_0_indices.append(validator_index) + else: + custody_bit_1_indices.append(validator_index) + + return bls_verify( + pubkeys=[ + bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_0_indices]), + bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_1_indices]), + ], + messages=[ + hash_tree_root(AttestationDataAndCustodyBit(attestation_data=slashable_vote.data, custody_bit=0b0)), + hash_tree_root(AttestationDataAndCustodyBit(attestation_data=slashable_vote.data, custody_bit=0b1)), + ], + signature=slashable_vote.aggregate_signature, + domain=get_domain( + state.fork, + slot_to_epoch(vote_data.data.slot), + DOMAIN_ATTESTATION, + ), + ) +``` + +### `is_double_vote` + +```python +def is_double_vote(attestation_data_1: AttestationData, + attestation_data_2: AttestationData) -> bool + """ + Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``. + Returns True if the provided ``AttestationData`` are slashable + due to a 'double vote'. + """ + target_epoch_1 = slot_to_epoch(attestation_data_1.slot) + target_epoch_2 = slot_to_epoch(attestation_data_2.slot) + return target_epoch_1 == target_epoch_2 +``` + +### `is_surround_vote` + +```python +def is_surround_vote(attestation_data_1: AttestationData, + attestation_data_2: AttestationData) -> bool: + """ + Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``. + Returns True if the provided ``AttestationData`` are slashable + due to a 'surround vote'. + Note: parameter order matters as this function only checks + that ``attestation_data_1`` surrounds ``attestation_data_2``. + """ + source_epoch_1 = attestation_data_1.justified_epoch + source_epoch_2 = attestation_data_2.justified_epoch + target_epoch_1 = slot_to_epoch(attestation_data_1.slot) + target_epoch_2 = slot_to_epoch(attestation_data_2.slot) + return ( + (source_epoch_1 < source_epoch_2) and + (source_epoch_2 + 1 == target_epoch_2) and + (target_epoch_2 < target_epoch_1) + ) +``` + +### `integer_squareroot` + +```python +def integer_squareroot(n: int) -> int: + """ + The largest integer ``x`` such that ``x**2`` is less than or equal to ``n``. + """ + assert n >= 0 + x = n + y = (x + 1) // 2 + while y < x: + x = y + y = (x + n // x) // 2 + return x +``` + +### `get_entry_exit_effect_epoch` + +```python +def get_entry_exit_effect_epoch(epoch: EpochNumber) -> EpochNumber: + """ + An entry or exit triggered in the ``epoch`` given by the input takes effect at + the epoch given by the output. + """ + return epoch + 1 + ENTRY_EXIT_DELAY +``` + +### `bls_verify` + +`bls_verify` is a function for verifying a BLS signature, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_verify). + +### `bls_verify_multiple` + +`bls_verify_multiple` is a function for verifying a BLS signature constructed from multiple messages, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_verify_multiple). + +### `bls_aggregate_pubkeys` + +`bls_aggregate_pubkeys` is a function for aggregating multiple BLS public keys into a single aggregate key, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_aggregate_pubkeys). + +### `validate_proof_of_possession` + +```python +def validate_proof_of_possession(state: BeaconState, + pubkey: BLSPubkey, + proof_of_possession: BLSSignature, + withdrawal_credentials: Bytes32) -> bool: + proof_of_possession_data = DepositInput( + pubkey=pubkey, + withdrawal_credentials=withdrawal_credentials, + proof_of_possession=EMPTY_SIGNATURE, + ) + + return bls_verify( + pubkey=pubkey, + message=hash_tree_root(proof_of_possession_data), + signature=proof_of_possession, + domain=get_domain( + state.fork, + get_current_epoch(state), + DOMAIN_DEPOSIT, + ) + ) +``` + +### `process_deposit` + +Used to add a [validator](#dfn-validator) or top up an existing [validator](#dfn-validator)'s balance by some `deposit` amount: + +```python +def process_deposit(state: BeaconState, + pubkey: BLSPubkey, + amount: Gwei, + proof_of_possession: BLSSignature, + withdrawal_credentials: Bytes32) -> None: + """ + Process a deposit from Ethereum 1.0. + Note that this function mutates ``state``. + """ + # Validate the given `proof_of_possession` + assert validate_proof_of_possession( + state, + pubkey, + proof_of_possession, + withdrawal_credentials, + ) + + validator_pubkeys = [v.pubkey for v in state.validator_registry] + + if pubkey not in validator_pubkeys: + # Add new validator + validator = Validator( + pubkey=pubkey, + withdrawal_credentials=withdrawal_credentials, + activation_epoch=FAR_FUTURE_EPOCH, + exit_epoch=FAR_FUTURE_EPOCH, + withdrawal_epoch=FAR_FUTURE_EPOCH, + penalized_epoch=FAR_FUTURE_EPOCH, + exit_count=0, + status_flags=0, + ) + + # Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled. + state.validator_registry.append(validator) + state.validator_balances.append(amount) + else: + # Increase balance by deposit amount + index = validator_pubkeys.index(pubkey) + assert state.validator_registry[index].withdrawal_credentials == withdrawal_credentials + + state.validator_balances[index] += amount +``` + +### Routines for updating validator status + +Note: All functions in this section mutate `state`. + +#### `activate_validator` + +```python +def activate_validator(state: BeaconState, index: ValidatorIndex, genesis: bool) -> None: + validator = state.validator_registry[index] + + validator.activation_epoch = GENESIS_EPOCH if genesis else get_entry_exit_effect_epoch(get_current_epoch(state)) +``` + +#### `initiate_validator_exit` + +```python +def initiate_validator_exit(state: BeaconState, index: ValidatorIndex) -> None: + validator = state.validator_registry[index] + validator.status_flags |= INITIATED_EXIT +``` + +#### `exit_validator` + +```python +def exit_validator(state: BeaconState, index: ValidatorIndex) -> None: + validator = state.validator_registry[index] + + # The following updates only occur if not previous exited + if validator.exit_epoch <= get_entry_exit_effect_epoch(get_current_epoch(state)): + return + + validator.exit_epoch = get_entry_exit_effect_epoch(get_current_epoch(state)) + + state.validator_registry_exit_count += 1 + validator.exit_count = state.validator_registry_exit_count +``` + +#### `penalize_validator` + +```python +def penalize_validator(state: BeaconState, index: ValidatorIndex) -> None: + exit_validator(state, index) + validator = state.validator_registry[index] + state.latest_penalized_balances[get_current_epoch(state) % LATEST_PENALIZED_EXIT_LENGTH] += get_effective_balance(state, index) + + whistleblower_index = get_beacon_proposer_index(state, state.slot) + whistleblower_reward = get_effective_balance(state, index) // WHISTLEBLOWER_REWARD_QUOTIENT + state.validator_balances[whistleblower_index] += whistleblower_reward + state.validator_balances[index] -= whistleblower_reward + validator.penalized_epoch = get_current_epoch(state) +``` + +#### `prepare_validator_for_withdrawal` + +```python +def prepare_validator_for_withdrawal(state: BeaconState, index: ValidatorIndex) -> None: + validator = state.validator_registry[index] + validator.status_flags |= WITHDRAWABLE +``` + ## Ethereum 1.0 deposit contract The initial deployment phases of Ethereum 2.0 are implemented without consensus changes to Ethereum 1.0. A deposit contract at address `DEPOSIT_CONTRACT_ADDRESS` is added to Ethereum 1.0 for deposits of ETH to the beacon chain. Validator balances will be withdrawable to the shards in phase 2, i.e. when the EVM2.0 is deployed and the shards have state. @@ -686,508 +1367,7 @@ def get_branch(leaf: uint256) -> bytes32[32]: # size is DEPOSIT_CONTRACT_TREE_DE return branch ``` -## Beacon chain processing - -The beacon chain is the system chain for Ethereum 2.0. The main responsibilities of the beacon chain are: - -* Store and maintain the registry of [validators](#dfn-validator) -* Process crosslinks (see above) -* Process its per-slot consensus, as well as the finality gadget - -Processing the beacon chain is similar to processing the Ethereum 1.0 chain. Clients download and process blocks, and maintain a view of what is the current "canonical chain", terminating at the current "head". However, because of the beacon chain's relationship with Ethereum 1.0, and because it is a proof-of-stake chain, there are differences. - -For a beacon chain block, `block`, to be processed by a node, the following conditions must be met: - -* The parent block with root `block.parent_root` has been processed and accepted. -* The node has processed its `state` up to slot, `block.slot - 1`. -* An Ethereum 1.0 block pointed to by the `state.latest_eth1_data.block_hash` has been processed and accepted. -* The node's local clock time is greater than or equal to `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. - -Beacon block production is significantly different because of the proof of stake mechanism. A client simply checks what it thinks is the canonical chain when it should create a block, and looks up what its slot number is; when the slot arrives, it either proposes or attests to a block as required. Note that this requires each node to have a clock that is roughly (i.e. within `SLOT_DURATION` seconds) synchronized with the other nodes. - -### Beacon chain fork choice rule - -The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time a [validator](#dfn-validator) `v` subjectively calculates the beacon chain head as follows. - -* Let `store` be the set of attestations and blocks that the [validator](#dfn-validator) `v` has observed and verified (in particular, block ancestors must be recursively verified). Attestations not part of any chain are still included in `store`. -* Let `finalized_head` be the finalized block with the highest slot number. (A block `B` is finalized if there is a descendant of `B` in `store` the processing of which sets `B` as finalized.) -* Let `justified_head` be the descendant of `finalized_head` with the highest slot number that has been justified for at least `EPOCH_LENGTH` slots. (A block `B` is justified if there is a descendant of `B` in `store` the processing of which sets `B` as justified.) If no such descendant exists set `justified_head` to `finalized_head`. -* Let `get_ancestor(store, block, slot)` be the ancestor of `block` with slot number `slot`. The `get_ancestor` function can be defined recursively as `def get_ancestor(store, block, slot): return block if block.slot == slot else get_ancestor(store, store.get_parent(block), slot)`. -* Let `get_latest_attestation(store, validator)` be the attestation with the highest slot number in `store` from `validator`. If several such attestations exist, use the one the [validator](#dfn-validator) `v` observed first. -* Let `get_latest_attestation_target(store, validator)` be the target block in the attestation `get_latest_attestation(store, validator)`. -* The head is `lmd_ghost(store, justified_head)` where the function `lmd_ghost` is defined below. Note that the implementation below is suboptimal; there are implementations that compute the head in time logarithmic in slot count. - -```python -def lmd_ghost(store, start): - validators = start.state.validator_registry - active_validators = [validators[i] for i in - get_active_validator_indices(validators, start.state.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]) - - head = start - while 1: - children = get_children(head) - if len(children) == 0: - return head - head = max(children, key=get_vote_count) -``` - -## Beacon chain state transition function - -We now define the state transition function. At a high level the state transition is made up of two parts: - -1. The per-slot transitions, which happens every slot, and only affects a parts of the `state`. -2. The per-epoch transitions, which happens at every epoch boundary (i.e. `state.slot % EPOCH_LENGTH == 0`), and affects the entire `state`. - -The per-slot transitions generally focus on verifying aggregate signatures and saving temporary records relating to the per-slot activity in the `BeaconState`. The per-epoch transitions focus on the [validator](#dfn-validator) registry, including adjusting balances and activating and exiting [validators](#dfn-validator), as well as processing crosslinks and managing block justification/finalization. - -### Helper functions - -Note: The definitions below are for specification purposes and are not necessarily optimal implementations. - -#### `hash` - -The hash function is denoted by `hash`. In Phase 0 the beacon chain is deployed with the same hash function as Ethereum 1.0, i.e. Keccak-256 (also incorrectly known as SHA3). - -Note: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethereum 2.0 deployment phase. - -#### `hash_tree_root` - -`hash_tree_root` is a function for hashing objects into a single root utilizing a hash tree structure. `hash_tree_root` is defined in the [SimpleSerialize spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md#tree-hash). - -#### `is_active_validator` -```python -def is_active_validator(validator: Validator, slot: int) -> bool: - """ - Checks if ``validator`` is active. - """ - return validator.activation_slot <= slot < validator.exit_slot -``` - -#### `get_active_validator_indices` - -```python -def get_active_validator_indices(validators: [Validator], slot: int) -> List[int]: - """ - Gets indices of active validators from ``validators``. - """ - return [i for i, v in enumerate(validators) if is_active_validator(v, slot)] -``` - -#### `shuffle` - -```python -def shuffle(values: List[Any], seed: Bytes32) -> List[Any]: - """ - Returns the shuffled ``values`` with ``seed`` as entropy. - """ - values_count = len(values) - - # Entropy is consumed from the seed in 3-byte (24 bit) chunks. - rand_bytes = 3 - # The highest possible result of the RNG. - rand_max = 2 ** (rand_bytes * 8) - 1 - - # The range of the RNG places an upper-bound on the size of the list that - # may be shuffled. It is a logic error to supply an oversized list. - assert values_count < rand_max - - output = [x for x in values] - source = seed - index = 0 - while index < values_count - 1: - # Re-hash the `source` to obtain a new pattern of bytes. - source = hash(source) - # Iterate through the `source` bytes in 3-byte chunks. - for position in range(0, 32 - (32 % rand_bytes), rand_bytes): - # Determine the number of indices remaining in `values` and exit - # once the last index is reached. - remaining = values_count - index - if remaining == 1: - break - - # Read 3-bytes of `source` as a 24-bit big-endian integer. - sample_from_source = int.from_bytes(source[position:position + rand_bytes], 'big') - - # Sample values greater than or equal to `sample_max` will cause - # modulo bias when mapped into the `remaining` range. - sample_max = rand_max - rand_max % remaining - - # Perform a swap if the consumed entropy will not cause modulo bias. - if sample_from_source < sample_max: - # Select a replacement index for the current index. - replacement_position = (sample_from_source % remaining) + index - # Swap the current index with the replacement index. - output[index], output[replacement_position] = output[replacement_position], output[index] - index += 1 - else: - # The sample causes modulo bias. A new sample should be read. - pass - - return output -``` - -#### `split` - -```python -def split(values: List[Any], split_count: int) -> List[List[Any]]: - """ - Splits ``values`` into ``split_count`` pieces. - """ - list_length = len(values) - return [ - values[(list_length * i // split_count): (list_length * (i + 1) // split_count)] - for i in range(split_count) - ] -``` - -#### `get_committee_count_per_slot` - -```python -def get_committee_count_per_slot(active_validator_count: int) -> int: - return max( - 1, - min( - SHARD_COUNT // EPOCH_LENGTH, - active_validator_count // EPOCH_LENGTH // TARGET_COMMITTEE_SIZE, - ) - ) -``` - -#### `get_shuffling` - -```python -def get_shuffling(seed: Bytes32, - validators: List[Validator], - slot: int) -> List[List[int]] - """ - Shuffles ``validators`` into crosslink committees seeded by ``seed`` and ``slot``. - Returns a list of ``EPOCH_LENGTH * committees_per_slot`` committees where each - committee is itself a list of validator indices. - """ - - # Normalizes slot to start of epoch boundary - slot -= slot % EPOCH_LENGTH - - active_validator_indices = get_active_validator_indices(validators, slot) - - committees_per_slot = get_committee_count_per_slot(len(active_validator_indices)) - - # Shuffle - seed = xor(seed, int_to_bytes32(slot)) - shuffled_active_validator_indices = shuffle(active_validator_indices, seed) - - # Split the shuffled list into epoch_length * committees_per_slot pieces - return split(shuffled_active_validator_indices, committees_per_slot * EPOCH_LENGTH) -``` - -**Invariant**: if `get_shuffling(seed, validators, slot)` returns some value `x` for some `slot <= state.slot + ENTRY_EXIT_DELAY`, it should return the same value `x` for the same `seed` and `slot` and possible future modifications of `validators` forever in phase 0, and until the ~1 year deletion delay in phase 2 and in the future. - -**Note**: this definition and the next few definitions make heavy use of repetitive computing. Production implementations are expected to appropriately use caching/memoization to avoid redoing work. - -#### `get_previous_epoch_committee_count_per_slot` - -```python -def get_previous_epoch_committee_count_per_slot(state: BeaconState) -> int: - previous_active_validators = get_active_validator_indices( - state.validator_registry, - state.previous_epoch_calculation_slot, - ) - return get_committee_count_per_slot(len(previous_active_validators)) -``` - -#### `get_current_epoch_committee_count_per_slot` - -```python -def get_current_epoch_committee_count_per_slot(state: BeaconState) -> int: - current_active_validators = get_active_validator_indices( - state.validator_registry, - state.current_epoch_calculation_slot, - ) - return get_committee_count_per_slot(len(current_active_validators)) -``` - -#### `get_crosslink_committees_at_slot` - -```python -def get_crosslink_committees_at_slot(state: BeaconState, - slot: int) -> List[Tuple[List[int], int]]: - """ - Returns the list of ``(committee, shard)`` tuples for the ``slot``. - """ - state_epoch_slot = state.slot - (state.slot % EPOCH_LENGTH) - assert state_epoch_slot <= slot + EPOCH_LENGTH - assert slot < state_epoch_slot + EPOCH_LENGTH - offset = slot % EPOCH_LENGTH - - if slot < state_epoch_slot: - committees_per_slot = get_previous_epoch_committee_count_per_slot(state) - shuffling = get_shuffling( - state.previous_epoch_seed, - state.validator_registry, - state.previous_epoch_calculation_slot, - ) - slot_start_shard = (state.previous_epoch_start_shard + committees_per_slot * offset) % SHARD_COUNT - else: - committees_per_slot = get_current_epoch_committee_count_per_slot(state) - shuffling = get_shuffling( - state.current_epoch_seed, - state.validator_registry, - state.current_epoch_calculation_slot, - ) - slot_start_shard = (state.current_epoch_start_shard + committees_per_slot * offset) % SHARD_COUNT - - return [ - ( - shuffling[committees_per_slot * offset + i], - (slot_start_shard + i) % SHARD_COUNT, - ) - for i in range(committees_per_slot) - ] -``` - -**Note**: we plan to replace the shuffling algorithm with a pointwise-evaluable shuffle (see https://github.com/ethereum/eth2.0-specs/issues/323), which will allow calculation of the committees for each slot individually. - -#### `get_block_root` - -```python -def get_block_root(state: BeaconState, - slot: int) -> Bytes32: - """ - Returns the block root at a recent ``slot``. - """ - assert state.slot <= slot + LATEST_BLOCK_ROOTS_LENGTH - assert slot < state.slot - return state.latest_block_roots[slot % LATEST_BLOCK_ROOTS_LENGTH] -``` - -`get_block_root(_, s)` should always return `hash_tree_root` of the block in the beacon chain at slot `s`, and `get_crosslink_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes. - -#### `get_randao_mix` - -```python -def get_randao_mix(state: BeaconState, - slot: int) -> Bytes32: - """ - Returns the randao mix at a recent ``slot``. - """ - assert state.slot < slot + LATEST_RANDAO_MIXES_LENGTH - assert slot <= state.slot - return state.latest_randao_mixes[slot % LATEST_RANDAO_MIXES_LENGTH] -``` - -#### `get_active_index_root` - -```python -def get_active_index_root(state: BeaconState, - slot: int) -> Bytes32: - """ - Returns the index root at a recent ``slot``. - """ - state_epoch = state.slot // EPOCH_LENGTH - given_epoch = slot // EPOCH_LENGTH - assert state_epoch < given_epoch + LATEST_INDEX_ROOTS_LENGTH - assert given_epoch <= state_epoch - return state.latest_index_roots[given_epoch % LATEST_INDEX_ROOTS_LENGTH] -``` - -#### `get_beacon_proposer_index` - -```python -def get_beacon_proposer_index(state: BeaconState, - slot: int) -> int: - """ - Returns the beacon proposer index for the ``slot``. - """ - first_committee, _ = get_crosslink_committees_at_slot(state, slot)[0] - return first_committee[slot % len(first_committee)] -``` - -#### `merkle_root` - -```python -def merkle_root(values: List[Bytes32]) -> Bytes32: - """ - Merkleize ``values`` (where ``len(values)`` is a power of two) and return the Merkle root. - """ - o = [0] * len(values) + values - for i in range(len(values) - 1, 0, -1): - o[i] = hash(o[i * 2] + o[i * 2 + 1]) - return o[1] -``` - -#### `get_attestation_participants` - -```python -def get_attestation_participants(state: BeaconState, - attestation_data: AttestationData, - aggregation_bitfield: bytes) -> List[int]: - """ - Returns the participant indices at for the ``attestation_data`` and ``aggregation_bitfield``. - """ - - # Find the committee in the list with the desired shard - crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot) - - assert attestation_data.shard in [shard for _, shard in crosslink_committees] - crosslink_committee = [committee for committee, shard in crosslink_committees if shard == attestation_data.shard][0] - assert len(aggregation_bitfield) == (len(crosslink_committee) + 7) // 8 - - # Find the participating attesters in the committee - participants = [] - for i, validator_index in enumerate(crosslink_committee): - aggregation_bit = (aggregation_bitfield[i // 8] >> (7 - (i % 8))) % 2 - if aggregation_bit == 1: - participants.append(validator_index) - return participants -``` - -#### `int_to_bytes1`, `int_to_bytes2`, ... - -`int_to_bytes1(x): return x.to_bytes(1, 'big')`, `int_to_bytes2(x): return x.to_bytes(2, 'big')`, and so on for all integers, particularly 1, 2, 3, 4, 8, 32, 48, 96. - -#### `get_effective_balance` - -```python -def get_effective_balance(state: State, index: int) -> int: - """ - Returns the effective balance (also known as "balance at stake") for a ``validator`` with the given ``index``. - """ - return min(state.validator_balances[index], MAX_DEPOSIT_AMOUNT) -``` - -#### `get_fork_version` - -```python -def get_fork_version(fork: Fork, - slot: int) -> int: - if slot < fork.slot: - return fork.previous_version - else: - return fork.current_version -``` - -#### `get_domain` - -```python -def get_domain(fork: Fork, - slot: int, - domain_type: int) -> int: - return get_fork_version( - fork, - slot - ) * 2**32 + domain_type -``` - -#### `verify_slashable_vote_data` - -```python -def verify_slashable_vote_data(state: BeaconState, vote_data: SlashableVoteData) -> bool: - if len(vote_data.custody_bit_0_indices) + len(vote_data.custody_bit_1_indices) > MAX_CASPER_VOTES: - return False - - return bls_verify_multiple( - pubkeys=[ - bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in vote_data.custody_bit_0_indices]), - bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in vote_data.custody_bit_1_indices]), - ], - messages=[ - hash_tree_root(AttestationDataAndCustodyBit(vote_data.data, False)), - hash_tree_root(AttestationDataAndCustodyBit(vote_data.data, True)), - ], - signature=vote_data.aggregate_signature, - domain=get_domain( - state.fork, - vote_data.data.slot, - DOMAIN_ATTESTATION, - ), - ) -``` - -#### `is_double_vote` - -```python -def is_double_vote(attestation_data_1: AttestationData, - attestation_data_2: AttestationData) -> bool - """ - Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``. - Returns True if the provided ``AttestationData`` are slashable - due to a 'double vote'. - """ - target_epoch_1 = attestation_data_1.slot // EPOCH_LENGTH - target_epoch_2 = attestation_data_2.slot // EPOCH_LENGTH - return target_epoch_1 == target_epoch_2 -``` - -#### `is_surround_vote` - -```python -def is_surround_vote(attestation_data_1: AttestationData, - attestation_data_2: AttestationData) -> bool: - """ - Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``. - Returns True if the provided ``AttestationData`` are slashable - due to a 'surround vote'. - Note: parameter order matters as this function only checks - that ``attestation_data_1`` surrounds ``attestation_data_2``. - """ - source_epoch_1 = attestation_data_1.justified_slot // EPOCH_LENGTH - source_epoch_2 = attestation_data_2.justified_slot // EPOCH_LENGTH - target_epoch_1 = attestation_data_1.slot // EPOCH_LENGTH - target_epoch_2 = attestation_data_2.slot // EPOCH_LENGTH - return ( - (source_epoch_1 < source_epoch_2) and - (source_epoch_2 + 1 == target_epoch_2) and - (target_epoch_2 < target_epoch_1) - ) -``` - -#### `integer_squareroot` - -```python -def integer_squareroot(n: int) -> int: - """ - The largest integer ``x`` such that ``x**2`` is less than or equal to ``n``. - """ - assert n >= 0 - x = n - y = (x + 1) // 2 - while y < x: - x = y - y = (x + n // x) // 2 - return x -``` - -#### `entry_exit_effect_slot` - -```python -def entry_exit_effect_slot(n: int) -> int: - """ - An entry or exit triggered in the slot given by the input takes effect at - the slot given by the output. - """ - return (n - n % EPOCH_LENGTH) + EPOCH_LENGTH + ENTRY_EXIT_DELAY -``` - -#### `bls_verify` - -`bls_verify` is a function for verifying a BLS signature, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_verify). - -#### `bls_verify_multiple` - -`bls_verify_multiple` is a function for verifying a BLS signature constructed from multiple messages, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_verify_multiple). - -#### `bls_aggregate_pubkeys` - -`bls_aggregate_pubkeys` is a function for aggregating multiple BLS public keys into a single aggregate key, defined in the [BLS Signature spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/bls_signature.md#bls_aggregate_pubkeys). - -### On startup +## On startup A valid block with slot `GENESIS_SLOT` (a "genesis block") has the following values. Other validity rules (e.g. requiring a signature) do not apply. @@ -1204,11 +1384,8 @@ A valid block with slot `GENESIS_SLOT` (a "genesis block") has the following val signature=EMPTY_SIGNATURE, body=BeaconBlockBody( proposer_slashings=[], - casper_slashings=[], + attester_slashings=[], attestations=[], - custody_reseeds=[], - custody_challenges=[], - custody_responses=[], deposits=[], exits=[], ), @@ -1228,13 +1405,13 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit], fork=Fork( previous_version=GENESIS_FORK_VERSION, current_version=GENESIS_FORK_VERSION, - slot=GENESIS_SLOT, + epoch=GENESIS_EPOCH, ), # Validator registry validator_registry=[], validator_balances=[], - validator_registry_update_slot=GENESIS_SLOT, + validator_registry_update_epoch=GENESIS_EPOCH, validator_registry_exit_count=0, # Randomness and committees @@ -1242,22 +1419,19 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit], latest_vdf_outputs=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH // EPOCH_LENGTH)], previous_epoch_start_shard=GENESIS_START_SHARD, current_epoch_start_shard=GENESIS_START_SHARD, - previous_epoch_calculation_slot=GENESIS_SLOT, - current_epoch_calculation_slot=GENESIS_SLOT, + previous_calculation_epoch=GENESIS_EPOCH, + current_calculation_epoch=GENESIS_EPOCH, previous_epoch_seed=ZERO_HASH, current_epoch_seed=ZERO_HASH, - # Custody challenges - custody_challenges=[], - # Finality - previous_justified_slot=GENESIS_SLOT, - justified_slot=GENESIS_SLOT, + previous_justified_epoch=GENESIS_EPOCH, + justified_epoch=GENESIS_EPOCH, justification_bitfield=0, - finalized_slot=GENESIS_SLOT, + finalized_epoch=GENESIS_EPOCH, # Recent state - latest_crosslinks=[Crosslink(slot=GENESIS_SLOT, shard_block_root=ZERO_HASH) for _ in range(SHARD_COUNT)], + latest_crosslinks=[Crosslink(epoch=GENESIS_EPOCH, shard_block_root=ZERO_HASH) for _ in range(SHARD_COUNT)], latest_block_roots=[ZERO_HASH for _ in range(LATEST_BLOCK_ROOTS_LENGTH)], latest_index_roots=[ZERO_HASH for _ in range(LATEST_INDEX_ROOTS_LENGTH)], latest_penalized_balances=[0 for _ in range(LATEST_PENALIZED_EXIT_LENGTH)], @@ -1284,179 +1458,127 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit], if get_effective_balance(state, validator_index) >= MAX_DEPOSIT_AMOUNT: activate_validator(state, validator_index, True) + state.latest_index_roots[GENESIS_EPOCH % LATEST_INDEX_ROOTS_LENGTH] = hash_tree_root(get_active_validator_indices(state, GENESIS_EPOCH)) + state.current_epoch_seed = generate_seed(state, GENESIS_EPOCH) + return state ``` -### Routine for processing deposits +## Beacon chain processing -First, a helper function: +The beacon chain is the system chain for Ethereum 2.0. The main responsibilities of the beacon chain are: + +* Store and maintain the registry of [validators](#dfn-validator) +* Process crosslinks (see above) +* Process its per-block consensus, as well as the finality gadget + +Processing the beacon chain is similar to processing the Ethereum 1.0 chain. Clients download and process blocks, and maintain a view of what is the current "canonical chain", terminating at the current "head". However, because of the beacon chain's relationship with Ethereum 1.0, and because it is a proof-of-stake chain, there are differences. + +For a beacon chain block, `block`, to be processed by a node, the following conditions must be met: + +* The parent block with root `block.parent_root` has been processed and accepted. +* An Ethereum 1.0 block pointed to by the `state.latest_eth1_data.block_hash` has been processed and accepted. +* The node's local clock time is greater than or equal to `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. + +Beacon block production is significantly different because of the proof of stake mechanism. A client simply checks what it thinks is the canonical chain when it should create a block, and looks up what its slot number is; when the slot arrives, it either proposes or attests to a block as required. Note that this requires each node to have a clock that is roughly (i.e. within `SLOT_DURATION` seconds) synchronized with the other nodes. + +### Beacon chain fork choice rule + +The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time a [validator](#dfn-validator) `v` subjectively calculates the beacon chain head as follows. + +* Abstractly define `Store` as the type of storage object for the chain data and `store` be the set of attestations and blocks that the [validator](#dfn-validator) `v` has observed and verified (in particular, block ancestors must be recursively verified). Attestations not yet included in any chain are still included in `store`. +* Let `finalized_head` be the finalized block with the highest epoch. (A block `B` is finalized if there is a descendant of `B` in `store` the processing of which sets `B` as finalized.) +* Let `justified_head` be the descendant of `finalized_head` with the highest epoch that has been justified for at least 1 epoch. (A block `B` is justified if there is a descendant of `B` in `store` the processing of which sets `B` as justified.) If no such descendant exists set `justified_head` to `finalized_head`. +* Let `get_ancestor(store: Store, block: BeaconBlock, slot: SlotNumber) -> BeaconBlock` be the ancestor of `block` with slot number `slot`. The `get_ancestor` function can be defined recursively as `def get_ancestor(store: Store, block: BeaconBlock, slot: SlotNumber) -> BeaconBlock: return block if block.slot == slot else get_ancestor(store, store.get_parent(block), slot)`. +* Let `get_latest_attestation(store: Store, validator: Validator) -> Attestation` be the attestation with the highest slot number in `store` from `validator`. If several such attestations exist, use the one the [validator](#dfn-validator) `v` observed first. +* Let `get_latest_attestation_target(store: Store, validator: Validator) -> BeaconBlock` be the target block in the attestation `get_latest_attestation(store, validator)`. +* Let `get_children(store: Store, block: BeaconBlock) -> List[BeaconBlock]` returns the child blocks of the given `block`. +* Let `justified_head_state` be the resulting `BeaconState` object from processing the chain up to the `justified_head`. +* The `head` is `lmd_ghost(store, justified_head_state, justified_head)` where the function `lmd_ghost` is defined below. Note that the implementation below is suboptimal; there are implementations that compute the head in time logarithmic in slot count. ```python -def validate_proof_of_possession(state: BeaconState, - pubkey: Bytes48, - proof_of_possession: Bytes96, - withdrawal_credentials: Bytes32) -> bool: - proof_of_possession_data = DepositInput( - pubkey=pubkey, - withdrawal_credentials=withdrawal_credentials, - proof_of_possession=EMPTY_SIGNATURE, - ) +def lmd_ghost(store: Store, start_state: BeaconState, start_block: BeaconBlock) -> BeaconBlock: + validators = start_state.validator_registry + active_validators = [ + validators[i] + for i in get_active_validator_indices(validators, start_state.slot) + ] + attestation_targets = [ + get_latest_attestation_target(store, validator) + for validator in active_validators + ] - return bls_verify( - pubkey=pubkey, - message=hash_tree_root(proof_of_possession_data), - signature=proof_of_possession, - domain=get_domain( - state.fork, - state.slot, - DOMAIN_DEPOSIT, - ) - ) + def get_vote_count(block: BeaconBlock) -> int: + return len([ + target + for target in attestation_targets + if get_ancestor(store, target, block.slot) == block + ]) + + head = start_block + while 1: + children = get_children(store, head) + if len(children) == 0: + return head + head = max(children, key=get_vote_count) ``` -Now, to add a [validator](#dfn-validator) or top up an existing [validator](#dfn-validator)'s balance by some `deposit` amount: +## Beacon chain state transition function -```python -def process_deposit(state: BeaconState, - pubkey: Bytes48, - amount: int, - proof_of_possession: Bytes96, - withdrawal_credentials: Bytes32) -> None: - """ - Process a deposit from Ethereum 1.0. - Note that this function mutates ``state``. - """ - # Validate the given `proof_of_possession` - assert validate_proof_of_possession( - state, - pubkey, - proof_of_possession, - withdrawal_credentials, - ) +We now define the state transition function. At a high level the state transition is made up of three parts: - validator_pubkeys = [v.pubkey for v in state.validator_registry] +1. The per-slot transitions, which happens at the start of every slot. +2. The per-block transitions, which happens at every block. +3. The per-epoch transitions, which happens at the end of the last slot of every epoch (i.e. `(state.slot + 1) % EPOCH_LENGTH == 0`). - if pubkey not in validator_pubkeys: - # Add new validator - validator = Validator( - pubkey=pubkey, - withdrawal_credentials=withdrawal_credentials, - proposer_slots=0, - activation_slot=FAR_FUTURE_SLOT, - exit_slot=FAR_FUTURE_SLOT, - withdrawal_slot=FAR_FUTURE_SLOT, - penalized_slot=FAR_FUTURE_SLOT, - exit_count=0, - status_flags=0, - latest_custody_reseed_slot=GENESIS_SLOT, - penultimate_custody_reseed_slot=GENESIS_SLOT, - ) +The per-slot transitions focus on the slot counter and block roots records updates; the per-block transitions generally focus on verifying aggregate signatures and saving temporary records relating to the per-block activity in the `BeaconState`; the per-epoch transitions focus on the [validator](#dfn-validator) registry, including adjusting balances and activating and exiting [validators](#dfn-validator), as well as processing crosslinks and managing block justification/finalization. - # Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled. - state.validator_registry.append(validator) - state.validator_balances.append(amount) - else: - # Increase balance by deposit amount - index = validator_pubkeys.index(pubkey) - assert state.validator_registry[index].withdrawal_credentials == withdrawal_credentials +_Note_: If there are skipped slots between a block and its parent block, run the steps in the [per-slot](#per-slot-processing) and [per-epoch](#per-epoch-processing) sections once for each skipped slot and then once for the slot containing the new block. - state.validator_balances[index] += amount -``` - -### Routines for updating validator status - -Note: All functions in this section mutate `state`. - -```python -def activate_validator(state: BeaconState, index: int, genesis: bool) -> None: - validator = state.validator_registry[index] - - validator.activation_slot = GENESIS_SLOT if genesis else entry_exit_effect_slot(state.slot) -``` - -```python -def initiate_validator_exit(state: BeaconState, index: int) -> None: - validator = state.validator_registry[index] - validator.status_flags |= INITIATED_EXIT -``` - -```python -def exit_validator(state: BeaconState, index: int) -> None: - validator = state.validator_registry[index] - - # The following updates only occur if not previous exited - if validator.exit_slot <= entry_exit_effect_slot(state.slot): - return - - validator.exit_slot = entry_exit_effect_slot(state.slot) - - state.validator_registry_exit_count += 1 - validator.exit_count = state.validator_registry_exit_count -``` - -```python -def penalize_validator(state: BeaconState, index: int) -> None: - exit_validator(state, index) - validator = state.validator_registry[index] - state.latest_penalized_balances[(state.slot // EPOCH_LENGTH) % LATEST_PENALIZED_EXIT_LENGTH] += get_effective_balance(state, index) - - whistleblower_index = get_beacon_proposer_index(state, state.slot) - whistleblower_reward = get_effective_balance(state, index) // WHISTLEBLOWER_REWARD_QUOTIENT - state.validator_balances[whistleblower_index] += whistleblower_reward - state.validator_balances[index] -= whistleblower_reward - validator.penalized_slot = state.slot -``` - -```python -def prepare_validator_for_withdrawal(state: BeaconState, index: int) -> None: - validator = state.validator_registry[index] - validator.status_flags |= WITHDRAWABLE -``` - -## Per-slot processing +### Per-slot processing Below are the processing steps that happen at every slot. -### Misc counters +#### Slot * Set `state.slot += 1`. -* Set `state.validator_registry[get_beacon_proposer_index(state, state.slot)].proposer_slots += 1`. -* Set `state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] = state.latest_randao_mixes[(state.slot - 1) % LATEST_RANDAO_MIXES_LENGTH]` -### Block roots +#### Block roots * Let `previous_block_root` be the `tree_hash_root` of the previous beacon block processed in the chain. * Set `state.latest_block_roots[(state.slot - 1) % LATEST_BLOCK_ROOTS_LENGTH] = previous_block_root`. * If `state.slot % LATEST_BLOCK_ROOTS_LENGTH == 0` append `merkle_root(state.latest_block_roots)` to `state.batched_block_roots`. -## Per-block processing +### Per-block processing Below are the processing steps that happen at every `block`. -### Slot +#### Slot * Verify that `block.slot == state.slot`. -### Proposer signature +#### Proposer signature * Let `block_without_signature_root` be the `hash_tree_root` of `block` where `block.signature` is set to `EMPTY_SIGNATURE`. * Let `proposal_root = hash_tree_root(ProposalSignedData(state.slot, BEACON_CHAIN_SHARD_NUMBER, block_without_signature_root))`. -* Verify that `bls_verify(pubkey=state.validator_registry[get_beacon_proposer_index(state, state.slot)].pubkey, message=proposal_root, signature=block.signature, domain=get_domain(state.fork, state.slot, DOMAIN_PROPOSAL))`. +* Verify that `bls_verify(pubkey=state.validator_registry[get_beacon_proposer_index(state, state.slot)].pubkey, message=proposal_root, signature=block.signature, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_PROPOSAL))`. -### RANDAO +#### RANDAO * Let `proposer = state.validator_registry[get_beacon_proposer_index(state, state.slot)]`. -* Verify that `bls_verify(pubkey=proposer.pubkey, message=int_to_bytes32(proposer.proposer_slots), signature=block.randao_reveal, domain=get_domain(state.fork, state.slot, DOMAIN_RANDAO))`. -* Set `state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] = hash(state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] + block.randao_reveal)`. +* Verify that `bls_verify(pubkey=proposer.pubkey, message=int_to_bytes32(get_current_epoch(state)), signature=block.randao_reveal, domain=get_domain(state.fork, get_current_epoch(state), DOMAIN_RANDAO))`. +* Set `state.latest_randao_mixes[get_current_epoch(state) % LATEST_RANDAO_MIXES_LENGTH] = xor(get_randao_mix(state, get_current_epoch(state)), hash(block.randao_reveal))`. -### Eth1 data +#### Eth1 data * If `block.eth1_data` equals `eth1_data_vote.eth1_data` for some `eth1_data_vote` in `state.eth1_data_votes`, set `eth1_data_vote.vote_count += 1`. * Otherwise, append to `state.eth1_data_votes` a new `Eth1DataVote(eth1_data=block.eth1_data, vote_count=1)`. -### Operations +#### Operations -#### Proposer slashings +##### Proposer slashings Verify that `len(block.body.proposer_slashings) <= MAX_PROPOSER_SLASHINGS`. @@ -1466,29 +1588,28 @@ For each `proposer_slashing` in `block.body.proposer_slashings`: * Verify that `proposer_slashing.proposal_data_1.slot == proposer_slashing.proposal_data_2.slot`. * Verify that `proposer_slashing.proposal_data_1.shard == proposer_slashing.proposal_data_2.shard`. * Verify that `proposer_slashing.proposal_data_1.block_root != proposer_slashing.proposal_data_2.block_root`. -* Verify that `proposer.penalized_slot > state.slot`. -* Verify that `bls_verify(pubkey=proposer.pubkey, message=hash_tree_root(proposer_slashing.proposal_data_1), signature=proposer_slashing.proposal_signature_1, domain=get_domain(state.fork, proposer_slashing.proposal_data_1.slot, DOMAIN_PROPOSAL))`. -* Verify that `bls_verify(pubkey=proposer.pubkey, message=hash_tree_root(proposer_slashing.proposal_data_2), signature=proposer_slashing.proposal_signature_2, domain=get_domain(state.fork, proposer_slashing.proposal_data_2.slot, DOMAIN_PROPOSAL))`. +* Verify that `proposer.penalized_epoch > get_current_epoch(state)`. +* Verify that `bls_verify(pubkey=proposer.pubkey, message=hash_tree_root(proposer_slashing.proposal_data_1), signature=proposer_slashing.proposal_signature_1, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_data_1.slot), DOMAIN_PROPOSAL))`. +* Verify that `bls_verify(pubkey=proposer.pubkey, message=hash_tree_root(proposer_slashing.proposal_data_2), signature=proposer_slashing.proposal_signature_2, domain=get_domain(state.fork, slot_to_epoch(proposer_slashing.proposal_data_2.slot), DOMAIN_PROPOSAL))`. * Run `penalize_validator(state, proposer_slashing.proposer_index)`. -#### Casper slashings +##### Attester slashings -Verify that `len(block.body.casper_slashings) <= MAX_CASPER_SLASHINGS`. +Verify that `len(block.body.attester_slashings) <= MAX_ATTESTER_SLASHINGS`. -For each `casper_slashing` in `block.body.casper_slashings`: +For each `attester_slashing` in `block.body.attester_slashings`: -* Let `slashable_vote_data_1 = casper_slashing.slashable_vote_data_1`. -* Let `slashable_vote_data_2 = casper_slashing.slashable_vote_data_2`. -* Let `indices(slashable_vote_data) = slashable_vote_data.custody_bit_0_indices + slashable_vote_data.custody_bit_1_indices`. -* Let `intersection = [x for x in indices(slashable_vote_data_1) if x in indices(slashable_vote_data_2)]`. +* Let `slashable_vote_1 = attester_slashing.slashable_vote_1`. +* Let `slashable_vote_2 = attester_slashing.slashable_vote_2`. +* Let `intersection = [x for x in slashable_vote_1.validator_indices if x in slashable_vote_2.validator_indices]`. * Verify that `len(intersection) >= 1`. -* Verify that `slashable_vote_data_1.data != slashable_vote_data_2.data`. -* Verify that `is_double_vote(slashable_vote_data_1.data, slashable_vote_data_2.data)` or `is_surround_vote(slashable_vote_data_1.data, slashable_vote_data_2.data)`. -* Verify that `verify_slashable_vote_data(state, slashable_vote_data_1)`. -* Verify that `verify_slashable_vote_data(state, slashable_vote_data_2)`. -* For each [validator](#dfn-validator) index `i` in `intersection` run `penalize_validator(state, i)` if `state.validator_registry[i].penalized_slot > state.slot`. +* Verify that `slashable_vote_1.data != slashable_vote_2.data`. +* Verify that `is_double_vote(slashable_vote_1.data, slashable_vote_2.data)` or `is_surround_vote(slashable_vote_1.data, slashable_vote_2.data)`. +* Verify that `verify_slashable_vote(state, slashable_vote_1)`. +* Verify that `verify_slashable_vote(state, slashable_vote_2)`. +* For each [validator](#dfn-validator) index `i` in `intersection` run `penalize_validator(state, i)` if `state.validator_registry[i].penalized_epoch > get_current_epoch(state)`. -#### Attestations +##### Attestations Verify that `len(block.body.attestations) <= MAX_ATTESTATIONS`. @@ -1496,17 +1617,41 @@ For each `attestation` in `block.body.attestations`: * Verify that `attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot`. * Verify that `attestation.data.slot + EPOCH_LENGTH >= state.slot`. -* Verify that `attestation.data.justified_slot` is equal to `state.justified_slot if attestation.data.slot >= state.slot - (state.slot % EPOCH_LENGTH) else state.previous_justified_slot`. -* Verify that `attestation.data.justified_block_root` is equal to `get_block_root(state, attestation.data.justified_slot)`. +* Verify that `attestation.data.justified_epoch` is equal to `state.justified_epoch if attestation.data.slot >= get_epoch_start_slot(get_current_epoch(state)) else state.previous_justified_epoch`. +* Verify that `attestation.data.justified_block_root` is equal to `get_block_root(state, get_epoch_start_slot(attestation.data.justified_epoch))`. * Verify that either `attestation.data.latest_crosslink_root` or `attestation.data.shard_block_root` equals `state.latest_crosslinks[shard].shard_block_root`. -* `aggregate_signature` verification: - * Let `participants = get_attestation_participants(state, attestation.data, attestation.aggregation_bitfield)`. - * Let `group_public_key = bls_aggregate_pubkeys([state.validator_registry[v].pubkey for v in participants])`. - * Verify that `bls_verify(pubkey=group_public_key, message=hash_tree_root(AttestationDataAndCustodyBit(attestation.data, False)), signature=attestation.aggregate_signature, domain=get_domain(state.fork, attestation.data.slot, DOMAIN_ATTESTATION))`. +* Verify bitfields and aggregate signature: + +```python + assert attestation.custody_bitfield == b'\x00' * len(attestation.custody_bitfield) # [TO BE REMOVED IN PHASE 1] + assert attestation.aggregation_bitfield != b'\x00' * len(attestation.aggregation_bitfield) + + for i in range(len(crosslink_committee)): + if get_bitfield_bit(attestation.aggregation_bitfield) == 0b0: + assert get_bitfield_bit(attestation.custody_bitfield) == 0b0 + + participants = get_attestation_participants(state, attestation.data, attestation.aggregation_bitfield) + custody_bit_1_participants = get_attestation_participants(state, attestation.data, attestation.custody_bitfield) + custody_bit_0_participants = [i in participants for i not in custody_bit_1_participants] + + assert bls_verify_multiple( + pubkeys=[ + bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_0_participants]), + bls_aggregate_pubkeys([state.validator_registry[i].pubkey for i in custody_bit_1_participants]), + ], + messages=[ + hash_tree_root(AttestationDataAndCustodyBit(data=attestation.data, custody_bit=0b0)), + hash_tree_root(AttestationDataAndCustodyBit(data=attestation.data, custody_bit=0b1)), + ], + signature=attestation.aggregate_signature, + domain=get_domain(state.fork, slot_to_epoch(attestation.data.slot), DOMAIN_ATTESTATION), + ) +``` + * [TO BE REMOVED IN PHASE 1] Verify that `attestation.data.shard_block_root == ZERO_HASH`. * Append `PendingAttestation(data=attestation.data, aggregation_bitfield=attestation.aggregation_bitfield, custody_bitfield=attestation.custody_bitfield, slot_included=state.slot)` to `state.latest_attestations`. -#### Deposits +##### Deposits Verify that `len(block.body.deposits) <= MAX_DEPOSITS`. @@ -1519,7 +1664,7 @@ For each `deposit` in `block.body.deposits`: * Verify that `verify_merkle_branch(hash(serialized_deposit_data), deposit.branch, DEPOSIT_CONTRACT_TREE_DEPTH, deposit.index, state.latest_eth1_data.deposit_root)` is `True`. ```python -def verify_merkle_branch(leaf: Bytes32, branch: [Bytes32], depth: int, index: int, root: Bytes32) -> bool: +def verify_merkle_branch(leaf: Bytes32, branch: List[Bytes32], depth: int, index: int, root: Bytes32) -> bool: value = leaf for i in range(depth): if index // (2**i) % 2: @@ -1541,53 +1686,50 @@ process_deposit( ) ``` -#### Exits +##### Exits Verify that `len(block.body.exits) <= MAX_EXITS`. For each `exit` in `block.body.exits`: * Let `validator = state.validator_registry[exit.validator_index]`. -* Verify that `validator.exit_slot > entry_exit_effect_slot(state.slot)`. -* Verify that `state.slot >= exit.slot`. -* Let `exit_message = hash_tree_root(Exit(slot=exit.slot, validator_index=exit.validator_index, signature=EMPTY_SIGNATURE))`. -* Verify that `bls_verify(pubkey=validator.pubkey, message=exit_message, signature=exit.signature, domain=get_domain(state.fork, exit.slot, DOMAIN_EXIT))`. +* Verify that `validator.exit_epoch > get_entry_exit_effect_epoch(get_current_epoch(state))`. +* Verify that `get_current_epoch(state) >= exit.epoch`. +* Let `exit_message = hash_tree_root(Exit(epoch=exit.epoch, validator_index=exit.validator_index, signature=EMPTY_SIGNATURE))`. +* Verify that `bls_verify(pubkey=validator.pubkey, message=exit_message, signature=exit.signature, domain=get_domain(state.fork, exit.epoch, DOMAIN_EXIT))`. * Run `initiate_validator_exit(state, exit.validator_index)`. -#### Custody +### Per-epoch processing -[TO BE REMOVED IN PHASE 1] Verify that `len(block.body.custody_reseeds) == len(block.body.custody_challenges) == len(block.body.custody_responses) == 0`. +The steps below happen when `(state.slot + 1) % EPOCH_LENGTH == 0`. -## Per-epoch processing +#### Helpers -The steps below happen when `state.slot % EPOCH_LENGTH == 0`. - -### Helpers - -All [validators](#dfn-validator): - -* Let `active_validator_indices = get_active_validator_indices(state.validator_registry, state.slot)`. -* Let `total_balance = sum([get_effective_balance(state, i) for i in active_validator_indices])`. +* Let `current_epoch = get_current_epoch(state)`. +* Let `previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else current_epoch`. +* Let `next_epoch = current_epoch + 1`. [Validators](#dfn-Validator) attesting during the current epoch: -* Let `current_epoch_attestations = [a for a in state.latest_attestations if state.slot - EPOCH_LENGTH <= a.data.slot < state.slot]`. (Note: this is the set of attestations of slots in the epoch `state.slot-EPOCH_LENGTH...state.slot-1`, _not_ attestations that got included in the chain during the epoch `state.slot-EPOCH_LENGTH...state.slot-1`.) +* Let `current_total_balance = sum([get_effective_balance(state, i) for i in get_active_validator_indices(state.validator_registry, current_epoch)])`. +* Let `current_epoch_attestations = [a for a in state.latest_attestations if current_epoch == slot_to_epoch(a.data.slot)]`. (Note: this is the set of attestations of slots in the epoch `current_epoch`, _not_ attestations that got included in the chain during the epoch `current_epoch`.) * Validators justifying the epoch boundary block at the start of the current epoch: - * Let `current_epoch_boundary_attestations = [a for a in current_epoch_attestations if a.data.epoch_boundary_root == get_block_root(state, state.slot-EPOCH_LENGTH) and a.data.justified_slot == state.justified_slot]`. + * Let `current_epoch_boundary_attestations = [a for a in current_epoch_attestations if a.data.epoch_boundary_root == get_block_root(state, get_epoch_start_slot(current_epoch)) and a.data.justified_epoch == state.justified_epoch]`. * Let `current_epoch_boundary_attester_indices` be the union of the [validator](#dfn-validator) index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in current_epoch_boundary_attestations]`. * Let `current_epoch_boundary_attesting_balance = sum([get_effective_balance(state, i) for i in current_epoch_boundary_attester_indices])`. [Validators](#dfn-Validator) attesting during the previous epoch: +* Let `previous_total_balance = sum([get_effective_balance(state, i) for i in get_active_validator_indices(state.validator_registry, previous_epoch)])`. * Validators that made an attestation during the previous epoch: - * Let `previous_epoch_attestations = [a for a in state.latest_attestations if state.slot - 2 * EPOCH_LENGTH <= a.data.slot < state.slot - EPOCH_LENGTH]`. + * Let `previous_epoch_attestations = [a for a in state.latest_attestations if previous_epoch == slot_to_epoch(a.data.slot)]`. * Let `previous_epoch_attester_indices` be the union of the validator index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in previous_epoch_attestations]`. * Validators targeting the previous justified slot: - * Let `previous_epoch_justified_attestations = [a for a in current_epoch_attestations + previous_epoch_attestations if a.data.justified_slot == state.previous_justified_slot]`. + * Let `previous_epoch_justified_attestations = [a for a in current_epoch_attestations + previous_epoch_attestations if a.data.justified_epoch == state.previous_justified_epoch]`. * Let `previous_epoch_justified_attester_indices` be the union of the validator index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in previous_epoch_justified_attestations]`. * Let `previous_epoch_justified_attesting_balance = sum([get_effective_balance(state, i) for i in previous_epoch_justified_attester_indices])`. * Validators justifying the epoch boundary block at the start of the previous epoch: - * Let `previous_epoch_boundary_attestations = [a for a in previous_epoch_justified_attestations if a.data.epoch_boundary_root == get_block_root(state, state.slot - 2 * EPOCH_LENGTH)]`. + * Let `previous_epoch_boundary_attestations = [a for a in previous_epoch_justified_attestations if a.data.epoch_boundary_root == get_block_root(state, get_epoch_start_slot(previous_epoch))]`. * Let `previous_epoch_boundary_attester_indices` be the union of the validator index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in previous_epoch_boundary_attestations]`. * Let `previous_epoch_boundary_attesting_balance = sum([get_effective_balance(state, i) for i in previous_epoch_boundary_attester_indices])`. * Validators attesting to the expected beacon chain head during the previous epoch: @@ -1595,9 +1737,9 @@ All [validators](#dfn-validator): * Let `previous_epoch_head_attester_indices` be the union of the validator index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in previous_epoch_head_attestations]`. * Let `previous_epoch_head_attesting_balance = sum([get_effective_balance(state, i) for i in previous_epoch_head_attester_indices])`. -**Note**: `previous_epoch_boundary_attesting_balance` balance might be marginally different than `current_epoch_boundary_attesting_balance` during the previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety. +**Note**: `previous_total_balance` and `previous_epoch_boundary_attesting_balance` balance might be marginally different than the actual balances during previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety. -For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`, compute: +For every `slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch))`, let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`, compute: * Let `shard_block_root` be `state.latest_crosslinks[shard].shard_block_root` * Let `attesting_validator_indices(crosslink_committee, shard_block_root)` be the union of the [validator](#dfn-validator) index sets given by `[get_attestation_participants(state, a.data, a.aggregation_bitfield) for a in current_epoch_attestations + previous_epoch_attestations if a.data.shard == shard and a.data.shard_block_root == shard_block_root]`. @@ -1611,56 +1753,64 @@ Define the following helpers to process attestation inclusion rewards and inclus * Let `inclusion_slot(state, index) = a.slot_included` for the attestation `a` where `index` is in `get_attestation_participants(state, a.data, a.aggregation_bitfield)`. If multiple attestations are applicable, the attestation with lowest `slot_included` is considered. * Let `inclusion_distance(state, index) = a.slot_included - a.data.slot` where `a` is the above attestation. -### Eth1 data +#### Eth1 data -If `state.slot % ETH1_DATA_VOTING_PERIOD == 0`: +If `next_epoch % ETH1_DATA_VOTING_PERIOD == 0`: -* Set `state.latest_eth1_data = eth1_data_vote.eth1_data` if `eth1_data_vote.vote_count * 2 > ETH1_DATA_VOTING_PERIOD` for some `eth1_data_vote` in `state.eth1_data_votes`. +* If `eth1_data_vote.vote_count * 2 > ETH1_DATA_VOTING_PERIOD * EPOCH_LENGTH` for some `eth1_data_vote` in `state.eth1_data_votes` (ie. more than half the votes in this voting period were for that value), set `state.latest_eth1_data = eth1_data_vote.eth1_data`. * Set `state.eth1_data_votes = []`. -### Justification +#### Justification -* Set `state.previous_justified_slot = state.justified_slot`. -* Set `state.justification_bitfield = (state.justification_bitfield * 2) % 2**64`. -* Set `state.justification_bitfield |= 2` and `state.justified_slot = state.slot - 2 * EPOCH_LENGTH` if `3 * previous_epoch_boundary_attesting_balance >= 2 * total_balance`. -* Set `state.justification_bitfield |= 1` and `state.justified_slot = state.slot - 1 * EPOCH_LENGTH` if `3 * current_epoch_boundary_attesting_balance >= 2 * total_balance`. +First, update the justification bitfield: -Set `state.finalized_slot = state.previous_justified_slot` if any of the following are true: +* Let `new_justified_epoch = state.justified_epoch`. +* Set `state.justification_bitfield = state.justification_bitfield << 1`. +* Set `state.justification_bitfield |= 2` and `new_justified_epoch = previous_epoch` if `3 * previous_epoch_boundary_attesting_balance >= 2 * previous_total_balance`. +* Set `state.justification_bitfield |= 1` and `new_justified_epoch = current_epoch` if `3 * current_epoch_boundary_attesting_balance >= 2 * current_total_balance`. -* `state.previous_justified_slot == state.slot - 2 * EPOCH_LENGTH and state.justification_bitfield % 4 == 3` -* `state.previous_justified_slot == state.slot - 3 * EPOCH_LENGTH and state.justification_bitfield % 8 == 7` -* `state.previous_justified_slot == state.slot - 4 * EPOCH_LENGTH and state.justification_bitfield % 16 in (15, 14)` +Next, update last finalized epoch if possible: -### Crosslinks +* Set `state.finalized_epoch = state.previous_justified_epoch` if `(state.justification_bitfield >> 1) % 8 == 0b111 and state.previous_justified_epoch == previous_epoch - 2`. +* Set `state.finalized_epoch = state.previous_justified_epoch` if `(state.justification_bitfield >> 1) % 4 == 0b11 and state.previous_justified_epoch == previous_epoch - 1`. +* Set `state.finalized_epoch = state.justified_epoch` if `(state.justification_bitfield >> 0) % 8 == 0b111 and state.justified_epoch == previous_epoch - 1`. +* Set `state.finalized_epoch = state.justified_epoch` if `(state.justification_bitfield >> 0) % 4 == 0b11 and state.justified_epoch == previous_epoch`. -For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`, compute: +Finally, update the following: -* Set `state.latest_crosslinks[shard] = Crosslink(slot=state.slot, shard_block_root=winning_root(crosslink_committee))` if `3 * total_attesting_balance(crosslink_committee) >= 2 * total_balance(crosslink_committee)`. +* Set `state.previous_justified_epoch = state.justified_epoch`. +* Set `state.justified_epoch = new_justified_epoch`. -### Rewards and penalties +#### Crosslinks + +For every `slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch))`, let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`, compute: + +* Set `state.latest_crosslinks[shard] = Crosslink(epoch=current_epoch, shard_block_root=winning_root(crosslink_committee))` if `3 * total_attesting_balance(crosslink_committee) >= 2 * total_balance(crosslink_committee)`. + +#### Rewards and penalties First, we define some additional helpers: -* Let `base_reward_quotient = integer_squareroot(total_balance) // BASE_REWARD_QUOTIENT`. +* Let `base_reward_quotient = integer_squareroot(previous_total_balance) // BASE_REWARD_QUOTIENT`. * Let `base_reward(state, index) = get_effective_balance(state, index) // base_reward_quotient // 5` for any validator with the given `index`. * Let `inactivity_penalty(state, index, epochs_since_finality) = base_reward(state, index) + get_effective_balance(state, index) * epochs_since_finality // INACTIVITY_PENALTY_QUOTIENT // 2` for any validator with the given `index`. -#### Justification and finalization +##### Justification and finalization Note: When applying penalties in the following balance recalculations implementers should make sure the `uint64` does not underflow. -* Let `epochs_since_finality = (state.slot - state.finalized_slot) // EPOCH_LENGTH`. +* Let `epochs_since_finality = next_epoch - state.finalized_epoch`. Case 1: `epochs_since_finality <= 4`: * Expected FFG source: - * Any [validator](#dfn-validator) `index` in `previous_epoch_justified_attester_indices` gains `base_reward(state, index) * previous_epoch_justified_attesting_balance // total_balance`. + * Any [validator](#dfn-validator) `index` in `previous_epoch_justified_attester_indices` gains `base_reward(state, index) * previous_epoch_justified_attesting_balance // previous_total_balance`. * Any [active validator](#dfn-active-validator) `v` not in `previous_epoch_justified_attester_indices` loses `base_reward(state, index)`. * Expected FFG target: - * Any [validator](#dfn-validator) `index` in `previous_epoch_boundary_attester_indices` gains `base_reward(state, index) * previous_epoch_boundary_attesting_balance // total_balance`. + * Any [validator](#dfn-validator) `index` in `previous_epoch_boundary_attester_indices` gains `base_reward(state, index) * previous_epoch_boundary_attesting_balance // previous_total_balance`. * Any [active validator](#dfn-active-validator) `index` not in `previous_epoch_boundary_attester_indices` loses `base_reward(state, index)`. * Expected beacon chain head: - * Any [validator](#dfn-validator) `index` in `previous_epoch_head_attester_indices` gains `base_reward(state, index) * previous_epoch_head_attesting_balance // total_balance)`. + * Any [validator](#dfn-validator) `index` in `previous_epoch_head_attester_indices` gains `base_reward(state, index) * previous_epoch_head_attesting_balance // previous_total_balance)`. * Any [active validator](#dfn-active-validator) `index` not in `previous_epoch_head_attester_indices` loses `base_reward(state, index)`. * Inclusion distance: * Any [validator](#dfn-validator) `index` in `previous_epoch_attester_indices` gains `base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY // inclusion_distance(state, index)` @@ -1670,21 +1820,23 @@ Case 2: `epochs_since_finality > 4`: * Any [active validator](#dfn-active-validator) `index` not in `previous_epoch_justified_attester_indices`, loses `inactivity_penalty(state, index, epochs_since_finality)`. * Any [active validator](#dfn-active-validator) `index` not in `previous_epoch_boundary_attester_indices`, loses `inactivity_penalty(state, index, epochs_since_finality)`. * Any [active validator](#dfn-active-validator) `index` not in `previous_epoch_head_attester_indices`, loses `base_reward(state, index)`. -* Any [active_validator](#dfn-active-validator) `index` with `validator.penalized_slot <= state.slot`, loses `2 * inactivity_penalty(state, index, epochs_since_finality) + base_reward(state, index)`. +* Any [active_validator](#dfn-active-validator) `index` with `validator.penalized_epoch <= current_epoch`, loses `2 * inactivity_penalty(state, index, epochs_since_finality) + base_reward(state, index)`. * Any [validator](#dfn-validator) `index` in `previous_epoch_attester_indices` loses `base_reward(state, index) - base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY // inclusion_distance(state, index)` -#### Attestation inclusion +##### Attestation inclusion For each `index` in `previous_epoch_attester_indices`, we determine the proposer `proposer_index = get_beacon_proposer_index(state, inclusion_slot(state, index))` and set `state.validator_balances[proposer_index] += base_reward(state, index) // INCLUDER_REWARD_QUOTIENT`. -#### Crosslinks +##### Crosslinks -For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot - EPOCH_LENGTH)`, let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`, compute: +For every `slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(current_epoch))`: -* If `index in attesting_validators(crosslink_committee)`, `state.validator_balances[index] += base_reward(state, index) * total_attesting_balance(crosslink_committee) // total_balance(crosslink_committee))`. -* If `index not in attesting_validators(crosslink_committee)`, `state.validator_balances[index] -= base_reward(state, index)`. +* Let `crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)`. +* For every `(crosslink_committee, shard)` in `crosslink_committees_at_slot`: + * If `index in attesting_validators(crosslink_committee)`, `state.validator_balances[index] += base_reward(state, index) * total_attesting_balance(crosslink_committee) // total_balance(crosslink_committee))`. + * If `index not in attesting_validators(crosslink_committee)`, `state.validator_balances[index] -= base_reward(state, index)`. -### Ejections +#### Ejections * Run `process_ejections(state)`. @@ -1694,24 +1846,24 @@ def process_ejections(state: BeaconState) -> None: Iterate through the validator registry and eject active validators with balance below ``EJECTION_BALANCE``. """ - for index in get_active_validator_indices(state.validator_registry, state.slot): + for index in get_active_validator_indices(state.validator_registry, current_epoch(state)): if state.validator_balances[index] < EJECTION_BALANCE: exit_validator(state, index) ``` -### Validator registry and shuffling seed data +#### Validator registry and shuffling seed data First, update the following: -* Set `state.previous_epoch_calculation_slot = state.current_epoch_calculation_slot` -* Set `state.previous_epoch_start_shard = state.current_epoch_start_shard` -* Set `state.previous_epoch_seed = state.current_epoch_seed` -* Set `state.latest_index_roots[epoch % LATEST_INDEX_ROOTS_LENGTH] = hash_tree_root(get_active_validator_indices(state, state.slot))` +* Set `state.previous_calculation_epoch = state.current_calculation_epoch`. +* Set `state.previous_epoch_start_shard = state.current_epoch_start_shard`. +* Set `state.previous_epoch_seed = state.current_epoch_seed`. +* Set `state.latest_index_roots[next_epoch % LATEST_INDEX_ROOTS_LENGTH] = hash_tree_root(get_active_validator_indices(state, next_epoch))`. If the following are satisfied: -* `state.finalized_slot > state.validator_registry_update_slot` -* `state.latest_crosslinks[shard].slot > state.validator_registry_update_slot` for every shard number `shard` in `[(state.current_epoch_start_shard + i) % SHARD_COUNT for i in range(get_current_epoch_committee_count_per_slot(state) * EPOCH_LENGTH)]` (that is, for every shard in the current committees) +* `state.finalized_epoch > state.validator_registry_update_epoch` +* `state.latest_crosslinks[shard].epoch > state.validator_registry_update_epoch` for every shard number `shard` in `[(state.current_epoch_start_shard + i) % SHARD_COUNT for i in range(get_current_epoch_committee_count(state))]` (that is, for every shard in the current committees) update the validator registry and associated fields by running @@ -1721,8 +1873,9 @@ def update_validator_registry(state: BeaconState) -> None: Update validator registry. Note that this function mutates ``state``. """ + current_epoch = get_current_epoch(state) # The active validators - active_validator_indices = get_active_validator_indices(state.validator_registry, state.slot) + active_validator_indices = get_active_validator_indices(state.validator_registry, current_epoch) # The total effective balance of active validators total_balance = sum([get_effective_balance(state, i) for i in active_validator_indices]) @@ -1735,7 +1888,7 @@ def update_validator_registry(state: BeaconState) -> None: # Activate validators within the allowable balance churn balance_churn = 0 for index, validator in enumerate(state.validator_registry): - if validator.activation_slot > entry_exit_effect_slot(state.slot) and state.validator_balances[index] >= MAX_DEPOSIT_AMOUNT: + if validator.activation_epoch > get_entry_exit_effect_epoch(current_epoch) and state.validator_balances[index] >= MAX_DEPOSIT_AMOUNT: # Check the balance churn would be within the allowance balance_churn += get_effective_balance(state, index) if balance_churn > max_balance_churn: @@ -1747,7 +1900,7 @@ def update_validator_registry(state: BeaconState) -> None: # Exit validators within the allowable balance churn balance_churn = 0 for index, validator in enumerate(state.validator_registry): - if validator.exit_slot > entry_exit_effect_slot(state.slot) and validator.status_flags & INITIATED_EXIT: + if validator.exit_epoch > get_entry_exit_effect_epoch(current_epoch) and validator.status_flags & INITIATED_EXIT: # Check the balance churn would be within the allowance balance_churn += get_effective_balance(state, index) if balance_churn > max_balance_churn: @@ -1756,21 +1909,21 @@ def update_validator_registry(state: BeaconState) -> None: # Exit validator exit_validator(state, index) - state.validator_registry_update_slot = state.slot + state.validator_registry_update_epoch = current_epoch ``` and perform the following updates: -* Set `state.current_epoch_calculation_slot = state.slot` -* Set `state.current_epoch_start_shard = (state.current_epoch_start_shard + get_current_epoch_committee_count_per_slot(state) * EPOCH_LENGTH) % SHARD_COUNT` -* Set `state.current_epoch_seed = hash(get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD) + get_active_index_root(state, state.current_epoch_calculation_slot))` +* Set `state.current_calculation_epoch = next_epoch` +* Set `state.current_epoch_start_shard = (state.current_epoch_start_shard + get_current_epoch_committee_count(state)) % SHARD_COUNT` +* Set `state.current_epoch_seed = generate_seed(state, state.current_calculation_epoch)` If a validator registry update does _not_ happen do the following: -* Let `epochs_since_last_registry_change = (state.slot - state.validator_registry_update_slot) // EPOCH_LENGTH`. -* If `epochs_since_last_registry_change` is an exact power of 2: - * Set `state.current_epoch_calculation_slot = state.slot`. - * Set `state.current_epoch_seed = hash(get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD) + get_active_index_root(state, state.current_epoch_calculation_slot))`. +* Let `epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch`. +* If `epochs_since_last_registry_update` is an exact power of 2: + * Set `state.current_calculation_epoch = next_epoch`. + * Set `state.current_epoch_seed = generate_seed(state, state.current_calculation_epoch)` * _Note_ that `state.current_epoch_start_shard` is left unchanged. **Invariant**: the active index root that is hashed into the shuffling seed actually is the `hash_tree_root` of the validator set that is used for that epoch. @@ -1779,14 +1932,15 @@ Regardless of whether or not a validator set change happens, run the following: ```python def process_penalties_and_exits(state: BeaconState) -> None: + current_epoch = get_current_epoch(state) # The active validators - active_validator_indices = get_active_validator_indices(state.validator_registry, state.slot) + active_validator_indices = get_active_validator_indices(state.validator_registry, current_epoch) # The total effective balance of active validators total_balance = sum([get_effective_balance(state, i) for i in active_validator_indices]) for index, validator in enumerate(state.validator_registry): - if (state.slot // EPOCH_LENGTH) == (validator.penalized_slot // EPOCH_LENGTH) + LATEST_PENALIZED_EXIT_LENGTH // 2: - e = (state.slot // EPOCH_LENGTH) % LATEST_PENALIZED_EXIT_LENGTH + if current_epoch == validator.penalized_epoch + LATEST_PENALIZED_EXIT_LENGTH // 2: + e = current_epoch % LATEST_PENALIZED_EXIT_LENGTH total_at_start = state.latest_penalized_balances[(e + 1) % LATEST_PENALIZED_EXIT_LENGTH] total_at_end = state.latest_penalized_balances[e] total_penalties = total_at_end - total_at_start @@ -1795,11 +1949,11 @@ def process_penalties_and_exits(state: BeaconState) -> None: def eligible(index): validator = state.validator_registry[index] - if validator.penalized_slot <= state.slot: - PENALIZED_WITHDRAWAL_TIME = LATEST_PENALIZED_EXIT_LENGTH * EPOCH_LENGTH // 2 - return state.slot >= validator.penalized_slot + PENALIZED_WITHDRAWAL_TIME + if validator.penalized_epoch <= current_epoch: + penalized_withdrawal_epochs = LATEST_PENALIZED_EXIT_LENGTH // 2 + return current_epoch >= validator.penalized_epoch + penalized_withdrawal_epochs else: - return state.slot >= validator.exit_slot + MIN_VALIDATOR_WITHDRAWAL_TIME + return current_epoch >= validator.exit_epoch + MIN_VALIDATOR_WITHDRAWAL_EPOCHS all_indices = list(range(len(state.validator_registry))) eligible_indices = filter(eligible, all_indices) @@ -1812,13 +1966,13 @@ def process_penalties_and_exits(state: BeaconState) -> None: break ``` -### Final updates +#### Final updates -* Let `epoch = state.slot // EPOCH_LENGTH`. -* Set `state.latest_penalized_balances[(epoch+1) % LATEST_PENALIZED_EXIT_LENGTH] = state.latest_penalized_balances[epoch % LATEST_PENALIZED_EXIT_LENGTH]`. -* Remove any `attestation` in `state.latest_attestations` such that `attestation.data.slot < state.slot - EPOCH_LENGTH`. +* Set `state.latest_penalized_balances[(next_epoch) % LATEST_PENALIZED_EXIT_LENGTH] = state.latest_penalized_balances[current_epoch % LATEST_PENALIZED_EXIT_LENGTH]`. +* Set `state.latest_randao_mixes[next_epoch % LATEST_RANDAO_MIXES_LENGTH] = get_randao_mix(state, current_epoch)`. +* Remove any `attestation` in `state.latest_attestations` such that `slot_to_epoch(attestation.data.slot) < current_epoch`. -## State root processing +### State root verification Verify `block.state_root == hash_tree_root(state)` if there exists a `block` for the slot being processed. diff --git a/specs/simple-serialize.md b/specs/simple-serialize.md index 150c71b62..13cc47299 100644 --- a/specs/simple-serialize.md +++ b/specs/simple-serialize.md @@ -143,11 +143,8 @@ Lists are a collection of elements of the same homogeneous type. |:--------------------------------------------|:----------------------------| | Length of serialized list fits into 4 bytes | ``len(serialized) < 2**32`` | -1. Get the number of raw bytes to serialize: it is ``len(list) * sizeof(element)``. - * Encode that as a `4-byte` **little endian** `uint32`. -2. Append the elements in a packed manner. - -* *Note on efficiency*: consider using a container that does not need to iterate over all elements to get its length. For example Python lists, C++ vectors or Rust Vec. +1. Serialize all list elements individually and concatenate them. +2. Prefix the concatenation with its length encoded as a `4-byte` **little-endian** unsigned integer. **Example in Python** diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md index 29ec0c7e0..83ebb5751 100644 --- a/specs/validator/0_beacon-chain-validator.md +++ b/specs/validator/0_beacon-chain-validator.md @@ -158,12 +158,12 @@ _Note_: To calculate `state_root`, the validator should first run the state tran ##### Randao reveal -Set `block.randao_reveal = reveal_signature` where `reveal_signature` is defined as: +Set `block.randao_reveal = epoch_signature` where `epoch_signature` is defined as: ```python -reveal_signature = bls_sign( +epoch_signature = bls_sign( privkey=validator.privkey, # privkey store locally, not in state - message=int_to_bytes32(validator.proposer_slots + 1), + message=int_to_bytes32(block.slot // EPOCH_LENGTH), domain=get_domain( fork_data, # `fork_data` is the fork_data at the slot `block.slot` block.slot,