Ethereum Specification

Introduction

Entry point for the Ethereum specification.

Module Contents

Classes

BlockChain

History and current state of the block chain.

Functions

apply_fork

Transforms the state from the previous hard fork (old) into the block

get_last_256_block_hashes

Obtain the list of hashes of the previous 256 blocks in order of

state_transition

Attempts to apply a block to an existing block chain.

validate_header

Verifies a block header.

generate_header_hash_for_pow

Generate rlp hash of the header which is to be used for Proof-of-Work

validate_proof_of_work

Validates the Proof of Work constraints.

apply_body

Executes a block.

validate_ommers

Validates the ommers mentioned in the block.

pay_rewards

Pay rewards to the block miner as well as the ommers miners.

process_transaction

Execute a transaction against the provided environment.

validate_transaction

Verifies a transaction.

calculate_intrinsic_cost

Calculates the gas that is charged before execution is started.

recover_sender

Extracts the sender address from a transaction.

signing_hash_pre155

Compute the hash of a transaction used in a legacy (pre EIP 155) signature.

signing_hash_155

Compute the hash of a transaction used in a EIP 155 signature.

compute_header_hash

Computes the hash of a block header.

check_gas_limit

Validates the gas limit for a block.

calculate_block_difficulty

Computes difficulty of a block using its header and parent header.

Attributes

BLOCK_REWARD

GAS_LIMIT_ADJUSTMENT_FACTOR

GAS_LIMIT_MINIMUM

MINIMUM_DIFFICULTY

MAX_OMMER_DEPTH

BOMB_DELAY_BLOCKS

EMPTY_OMMER_HASH

Module Details

BLOCK_REWARD

BLOCK_REWARD
BLOCK_REWARD = U256(5U256(3 * 10**18)

GAS_LIMIT_ADJUSTMENT_FACTOR

GAS_LIMIT_ADJUSTMENT_FACTOR
GAS_LIMIT_ADJUSTMENT_FACTOR = 1024

GAS_LIMIT_MINIMUM

GAS_LIMIT_MINIMUM
GAS_LIMIT_MINIMUM = 5000

MINIMUM_DIFFICULTY

MINIMUM_DIFFICULTY
MINIMUM_DIFFICULTY = Uint(131072)

MAX_OMMER_DEPTH

MAX_OMMER_DEPTH
MAX_OMMER_DEPTH = 6

BOMB_DELAY_BLOCKS

BOMB_DELAY_BLOCKS
BOMB_DELAY_BLOCKS = 3000000

EMPTY_OMMER_HASH

EMPTY_OMMER_HASH
EMPTY_OMMER_HASH = keccak256(rlp.encode([]))

BlockChain

History and current state of the block chain.

class BlockChain
blocks :List[ethereum.spurious_dragon.eth_types.Block]:List[ethereum.byzantium.eth_types.Block]
state :ethereum.spurious_dragon.state.State:ethereum.byzantium.state.State
chain_id :ethereum.base_types.Uint64

apply_fork

apply_fork(old)

Transforms the state from the previous hard fork (old) into the block chain object for this hard fork and returns it.

When forks need to implement an irregular state transition, this function is used to handle the irregularity. See the DAO Fork for an example.

Parameters

old – Previous block chain object.

Returns

new – Upgraded block chain object for this hard fork.

Return type

BlockChain

def apply_fork(old: BlockChain) -> BlockChain:
    return old

get_last_256_block_hashes

get_last_256_block_hashes(chain)

Obtain the list of hashes of the previous 256 blocks in order of increasing block number.

This function will return less hashes for the first 256 blocks.

The BLOCKHASH opcode needs to access the latest hashes on the chain, therefore this function retrieves them.

Parameters

chain – History and current state.

Returns

recent_block_hashes – Hashes of the recent 256 blocks in order of increasing block number.

Return type

List[Hash32]

def get_last_256_block_hashes(chain: BlockChain) -> List[Hash32]:
    recent_blocks = chain.blocks[-255:]
    # TODO: This function has not been tested rigorously
    if len(recent_blocks) == 0:
        return []

    recent_block_hashes = []

    for block in recent_blocks:
        prev_block_hash = block.header.parent_hash
        recent_block_hashes.append(prev_block_hash)

    # We are computing the hash only for the most recent block and not for
    # the rest of the blocks as they have successors which have the hash of
    # the current block as parent hash.
    most_recent_block_hash = keccak256(rlp.encode(recent_blocks[-1].header))
    recent_block_hashes.append(most_recent_block_hash)

    return recent_block_hashes

state_transition

state_transition(chain, block)

Attempts to apply a block to an existing block chain.

All parts of the block’s contents need to be verified before being added to the chain. Blocks are verified by ensuring that the contents of the block make logical sense with the contents of the parent block. The information in the block’s header must also match the corresponding information in the block.

To implement Ethereum, in theory clients are only required to store the most recent 255 blocks of the chain since as far as execution is concerned, only those blocks are accessed. Practically, however, clients should store more blocks to handle reorgs.

Parameters
  • chain – History and current state.

  • block – Block to apply to chain.

def state_transition(chain: BlockChain, block: Block) -> None:
    parent_header = chain.blocks[-1].header
    validate_header(block.header, parent_header)
    validate_ommers(block.ommers, block.header, chain)
    (
        gas_used,
        transactions_root,
        receipt_root,
        block_logs_bloom,
        state,
    ) = apply_body(
        chain.state,
        get_last_256_block_hashes(chain),
        block.header.coinbase,
        block.header.number,
        block.header.gas_limit,
        block.header.timestamp,
        block.header.difficulty,
        block.transactions,
        block.ommers,
        chain.chain_id,
    )
    ensure(gas_used == block.header.gas_used, InvalidBlock)
    ensure(transactions_root == block.header.transactions_root, InvalidBlock)
    ensure(state_root(state) == block.header.state_root, InvalidBlock)
    ensure(receipt_root == block.header.receipt_root, InvalidBlock)
    ensure(block_logs_bloom == block.header.bloom, InvalidBlock)

    chain.blocks.append(block)
    if len(chain.blocks) > 255:
        # Real clients have to store more blocks to deal with reorgs, but the
        # protocol only requires the last 255
        chain.blocks = chain.blocks[-255:]

validate_header

validate_header(header, parent_header)

Verifies a block header.

In order to consider a block’s header valid, the logic for the quantities in the header should match the logic for the block itself. For example the header timestamp should be greater than the block’s parent timestamp because the block was created after the parent block. Additionally, the block’s number should be directly folowing the parent block’s number since it is the next block in the sequence.

Parameters
  • header – Header to check for correctness.

  • parent_header – Parent Header of the header to check for correctness

def validate_header(header: Header, parent_header: Header) -> None:
    parent_has_ommers = parent_header.ommers_hash != EMPTY_OMMER_HASH
    ensure(header.timestamp > parent_header.timestamp, InvalidBlock)
    ensure(header.number == parent_header.number + 1, InvalidBlock)
    ensure(
        check_gas_limit(header.gas_limit, parent_header.gas_limit),
        InvalidBlock,
    )
    ensure(len(header.extra_data) <= 32, InvalidBlock)

    block_difficulty = calculate_block_difficulty(
        header.number,
        header.timestamp,
        parent_header.timestamp,
        parent_header.difficulty,
    parent_has_ommers,
    )
    ensure(header.difficulty == block_difficulty, InvalidBlock)

    block_parent_hash = keccak256(rlp.encode(parent_header))
    ensure(header.parent_hash == block_parent_hash, InvalidBlock)

    validate_proof_of_work(header)

generate_header_hash_for_pow

generate_header_hash_for_pow(header)

Generate rlp hash of the header which is to be used for Proof-of-Work verification.

In other words, the PoW artefacts mix_digest and nonce are ignored while calculating this hash.

A particular PoW is valid for a single hash, that hash is computed by this function. The nonce and mix_digest are omitted from this hash because they are being changed by miners in their search for a sufficient proof-of-work.

Parameters

header – The header object for which the hash is to be generated.

Returns

hash – The PoW valid rlp hash of the passed in header.

Return type

Hash32

def generate_header_hash_for_pow(header: Header) -> Hash32:
    header_data_without_pow_artefacts = [
        header.parent_hash,
        header.ommers_hash,
        header.coinbase,
        header.state_root,
        header.transactions_root,
        header.receipt_root,
        header.bloom,
        header.difficulty,
        header.number,
        header.gas_limit,
        header.gas_used,
        header.timestamp,
        header.extra_data,
    ]

    return rlp.rlp_hash(header_data_without_pow_artefacts)

validate_proof_of_work

validate_proof_of_work(header)

Validates the Proof of Work constraints.

In order to verify that a miner’s proof-of-work is valid for a block, a mix-digest and result are calculated using the hashimoto_light hash function. The mix digest is a hash of the header and the nonce that is passed through and it confirms whether or not proof-of-work was done on the correct block. The result is the actual hash value of the block.

Parameters

header – Header of interest.

def validate_proof_of_work(header: Header) -> None:
    header_hash = generate_header_hash_for_pow(header)
    # TODO: Memoize this somewhere and read from that data instead of
    # calculating cache for every block validation.
    cache = generate_cache(header.number)
    mix_digest, result = hashimoto_light(
        header_hash, header.nonce, cache, dataset_size(header.number)
    )

    ensure(mix_digest == header.mix_digest, InvalidBlock)
    ensure(
        Uint.from_be_bytes(result) <= (U256_CEIL_VALUE // header.difficulty),
        InvalidBlock,
    )

apply_body

apply_body(state, block_hashes, coinbase, block_number, block_gas_limit, block_time, block_difficulty, transactions, ommers, chain_id)

Executes a block.

Many of the contents of a block are stored in data structures called tries. There is a transactions trie which is similar to a ledger of the transactions stored in the current block. There is also a receipts trie which stores the results of executing a transaction, like the post state and gas used. This function creates and executes the block that is to be added to the chain.

Parameters
  • state – Current account state.

  • block_hashes – List of hashes of the previous 256 blocks in the order of increasing block number.

  • coinbase – Address of account which receives block reward and transaction fees.

  • block_number – Position of the block within the chain.

  • block_gas_limit – Initial amount of gas available for execution in this block.

  • block_time – Time the block was produced, measured in seconds since the epoch.

  • block_difficulty – Difficulty of the block.

  • transactions – Transactions included in the block.

  • ommers – Headers of ancestor blocks which are not direct parents (formerly uncles.)

  • chain_id – ID of the executing chain.

Returns

  • gas_available (ethereum.base_types.Uint) – Remaining gas after all transactions have been executed.

  • transactions_root (ethereum.eth_types.Root) – Trie root of all the transactions in the block.

  • receipt_root (ethereum.eth_types.Root) – Trie root of all the receipts in the block.

  • block_logs_bloom (Bloom) – Logs bloom of all the logs included in all the transactions of the block.

  • state (ethereum.eth_types.State) – State after all transactions have been executed.

def apply_body(
    state: State,
    block_hashes: List[Hash32],
    coinbase: Address,
    block_number: Uint,
    block_gas_limit: Uint,
    block_time: U256,
    block_difficulty: Uint,
    transactions: Tuple[Transaction, ...],
    ommers: Tuple[Header, ...],
    chain_id: Uint64,
) -> Tuple[Uint, Root, Root, Bloom, State]:
    gas_available = block_gas_limit
    transactions_trie: Trie[Bytes, Optional[Transaction]] = Trie(
        secured=False, default=None
    )
    receipts_trie: Trie[Bytes, Optional[Receipt]] = Trie(
        secured=False, default=None
    )
    block_logs: Tuple[Log, ...] = ()

    for i, tx in enumerate(transactions):
        trie_set(transactions_trie, rlp.encode(Uint(i)), tx)

        ensure(tx.gas <= gas_available, InvalidBlock)
        sender_address = recover_sender(chain_id, tx)

        env = vm.Environment(
            caller=sender_address,
            origin=sender_address,
            block_hashes=block_hashes,
            coinbase=coinbase,
            number=block_number,
            gas_limit=block_gas_limit,
            gas_price=tx.gas_price,
            time=block_time,
            difficulty=block_difficulty,
            state=state,
        )

        gas_used, logs, has_erred = process_transaction(env, tx)
        gas_available -= gas_used

        trie_set(
            receipts_trie,
            rlp.encode(Uint(i)),
            Receipt(
                succeeded=not has_erred,
                cumulative_gas_used=(block_gas_limit - gas_available),
                bloom=logs_bloom(logs),
                logs=logs,
            ),
        )
        block_logs += logs pay_rewards(state, block_number, coinbase, ommers)

    gas_remaining = process_transaction(env, tx)block_gas_limit -
        gas_available -= gas_used

        trie_set(
            receipts_trie,
            rlp.encode(Uint(i)),
            Receipt(
                post_state=state_root(state),
                cumulative_gas_used=(block_gas_limit - gas_available),
                bloom=logs_bloom(logs),
                logs=logs,
            ),
        )
        block_logs += logs

    pay_rewards(state, block_number, coinbase, ommers)

    gas_remaining = block_gas_limit - gas_available

    block_logs_bloom = logs_bloom(block_logs)

    return (
        gas_remaining,
        root(transactions_trie),
        root(receipts_trie),
        block_logs_bloom,
        state,
    )

validate_ommers

validate_ommers(ommers, block_header, chain)

Validates the ommers mentioned in the block.

An ommer block is a block that wasn’t canonically added to the blockchain because it wasn’t validated as fast as the canonical block but was mined at the same time.

To be considered valid, the ommers must adhere to the rules defined in the Ethereum protocol. The maximum amount of ommers is 2 per block and there cannot be duplicate ommers in a block. Many of the other ommer contraints are listed in the in-line comments of this function.

Parameters
  • ommers – List of ommers mentioned in the current block.

  • block_header – The header of current block.

  • chain – History and current state.

def validate_ommers(
    ommers: Tuple[Header, ...], block_header: Header, chain: BlockChain
) -> None:
    block_hash = rlp.rlp_hash(block_header)

    ensure(rlp.rlp_hash(ommers) == block_header.ommers_hash, InvalidBlock)

    if len(ommers) == 0:
        # Nothing to validate
        return

    # Check that each ommer satisfies the constraints of a header
    for ommer in ommers:
        ensure(1 <= ommer.number < block_header.number, InvalidBlock)
        ommer_parent_header = chain.blocks[
            -(block_header.number - ommer.number) - 1
        ].header
        validate_header(ommer, ommer_parent_header)

    # Check that there can be only at most 2 ommers for a block.
    ensure(len(ommers) <= 2, InvalidBlock)

    ommers_hashes = [rlp.rlp_hash(ommer) for ommer in ommers]
    # Check that there are no duplicates in the ommers of current block
    ensure(len(ommers_hashes) == len(set(ommers_hashes)), InvalidBlock)

    recent_canonical_blocks = chain.blocks[-(MAX_OMMER_DEPTH + 1) :]
    recent_canonical_block_hashes = {
        rlp.rlp_hash(block.header) for block in recent_canonical_blocks
    }
    recent_ommers_hashes: Set[Hash32] = set()
    for block in recent_canonical_blocks:
        recent_ommers_hashes = recent_ommers_hashes.union(
            {rlp.rlp_hash(ommer) for ommer in block.ommers}
        )

    for ommer_index, ommer in enumerate(ommers):
        ommer_hash = ommers_hashes[ommer_index]
        # The current block shouldn't be the ommer
        ensure(ommer_hash != block_hash, InvalidBlock)

        # Ommer shouldn't be one of the recent canonical blocks
        ensure(ommer_hash not in recent_canonical_block_hashes, InvalidBlock)

        # Ommer shouldn't be one of the uncles mentioned in the recent
        # canonical blocks
        ensure(ommer_hash not in recent_ommers_hashes, InvalidBlock)

        # Ommer age with respect to the current block. For example, an age of
        # 1 indicates that the ommer is a sibling of previous block.
        ommer_age = block_header.number - ommer.number
        ensure(1 <= ommer_age <= MAX_OMMER_DEPTH, InvalidBlock)

        ensure(
            ommer.parent_hash in recent_canonical_block_hashes, InvalidBlock
        )
        ensure(ommer.parent_hash != block_header.parent_hash, InvalidBlock)

pay_rewards

pay_rewards(state, block_number, coinbase, ommers)

Pay rewards to the block miner as well as the ommers miners.

The miner of the canonical block is rewarded with the predetermined block reward, BLOCK_REWARD, plus a variable award based off of the number of ommer blocks that were mined around the same time, and included in the canonical block’s header. An ommer block is a block that wasn’t added to the canonical blockchain because it wasn’t validated as fast as the accepted block but was mined at the same time. Although not all blocks that are mined are added to the canonical chain, miners are still paid a reward for their efforts. This reward is called an ommer reward and is calculated based on the number associated with the ommer block that they mined.

Parameters
  • state – Current account state.

  • block_number – Position of the block within the chain.

  • coinbase – Address of account which receives block reward and transaction fees.

  • ommers – List of ommers mentioned in the current block.

def pay_rewards(
    state: State,
    block_number: Uint,
    coinbase: Address,
    ommers: Tuple[Header, ...],
) -> None:
    miner_reward = BLOCK_REWARD + (len(ommers) * (BLOCK_REWARD // 32))
    create_ether(state, coinbase, miner_reward)

    for ommer in ommers:
        # Ommer age with respect to the current block.
        ommer_age = U256(block_number - ommer.number)
        ommer_miner_reward = ((8 - ommer_age) * BLOCK_REWARD) // 8
        create_ether(state, ommer.coinbase, ommer_miner_reward)

process_transaction

process_transaction(env, tx)

Execute a transaction against the provided environment.

This function processes the actions needed to execute a transaction. It decrements the sender’s account after calculating the gas fee and refunds them the proper amount after execution. Calling contracts, deploying code, and incrementing nonces are all examples of actions that happen within this function or from a call made within this function.

Accounts that are marked for deletion are processed and destroyed after execution.

Parameters
  • env – Environment for the Ethereum Virtual Machine.

  • tx – Transaction to execute.

Returns

  • gas_left (ethereum.base_types.U256) – Remaining gas after execution.

  • logs (Tuple[ethereum.eth_types.Log, …]) – Logs generated during execution.

def process_transaction(
    env: vm.Environment, tx: Transaction
) -> Tuple[U256, Tuple[Log, ...]]:...], bool]:
    ensure(validate_transaction(tx), InvalidBlock)

    sender = env.origin
    sender_account = get_account(env.state, sender)
    gas_fee = tx.gas * tx.gas_price
    ensure(sender_account.nonce == tx.nonce, InvalidBlock)
    ensure(sender_account.balance >= gas_fee + tx.value, InvalidBlock)
    ensure(sender_account.code == bytearray(), InvalidBlock)

    gas = tx.gas - calculate_intrinsic_cost(tx)
    increment_nonce(env.state, sender)
    sender_balance_after_gas_fee = sender_account.balance - gas_fee
    set_account_balance(env.state, sender, sender_balance_after_gas_fee)

    message = prepare_message(
        sender,
        tx.to,
        tx.value,
        tx.data,
        gas,
        env,
    )

    output = process_message_call(message, env)

    gas_used = tx.gas - output.gas_left
    gas_refund = min(gas_used // 2, output.refund_counter)
    gas_refund_amount = (output.gas_left + gas_refund) * tx.gas_price
    transaction_fee = (tx.gas - output.gas_left - gas_refund) * tx.gas_price
    total_gas_used = gas_used - gas_refund

    # refund gas
    sender_balance_after_refund = (
        get_account(env.state, sender).balance + gas_refund_amount
    )
    set_account_balance(env.state, sender, sender_balance_after_refund)

    # transfer miner fees
    coinbase_balance_after_mining_fee = (
        get_account(env.state, env.coinbase).balance + transaction_fee
    )
    if coinbase_balance_after_mining_fee != 0:
        set_account_balance(
            env.state, env.coinbase, coinbase_balance_after_mining_fee
        )
    elif account_exists_and_is_empty(env.state, env.coinbase):
        destroy_account(env.state, env.coinbase)

    for address in output.accounts_to_delete:
        destroy_account(env.state, address)

    for address in output.touched_accounts:
        if account_exists_and_is_empty(env.state, address):
            destroy_account(env.state, address)

    return total_gas_used, output.logsoutput.logs, output.has_erred

validate_transaction

validate_transaction(tx)

Verifies a transaction.

The gas in a transaction gets used to pay for the intrinsic cost of operations, therefore if there is insufficient gas then it would not be possible to execute a transaction and it will be declared invalid.

Additionally, the nonce of a transaction must not equal or exceed the limit defined in EIP-2681. In practice, defining the limit as 2**64-1 has no impact because sending 2**64-1 transactions is improbable. It’s not strictly impossible though, 2**64-1 transactions is the entire capacity of the Ethereum blockchain at 2022 gas limits for a little over 22 years.

Parameters

tx – Transaction to validate.

Returns

verified – True if the transaction can be executed, or False otherwise.

Return type

bool

def validate_transaction(tx: Transaction) -> bool:
    return calculate_intrinsic_cost(tx) <= tx.gas and tx.nonce < 2**64 - 1

calculate_intrinsic_cost

calculate_intrinsic_cost(tx)

Calculates the gas that is charged before execution is started.

The intrinsic cost of the transaction is charged before execution has begun. Functions/operations in the EVM cost money to execute so this intrinsic cost is for the operations that need to be paid for as part of the transaction. Data transfer, for example, is part of this intrinsic cost. It costs ether to send data over the wire and that ether is accounted for in the intrinsic cost calculated in this function. This intrinsic cost must be calculated and paid for before execution in order for all operations to be implemented.

Parameters

tx – Transaction to compute the intrinsic cost of.

Returns

verified – The intrinsic cost of the transaction.

Return type

ethereum.base_types.Uint

def calculate_intrinsic_cost(tx: Transaction) -> Uint:
    data_cost = 0

    for byte in tx.data:
        if byte == 0:
            data_cost += TX_DATA_COST_PER_ZERO
        else:
            data_cost += TX_DATA_COST_PER_NON_ZERO

    if tx.to == Bytes0(b""):
        create_cost = TX_CREATE_COST
    else:
        create_cost = 0

    return Uint(TX_BASE_COST + data_cost + create_cost)

recover_sender

recover_sender(chain_id, tx)

Extracts the sender address from a transaction.

The v, r, and s values are the three parts that make up the signature of a transaction. In order to recover the sender of a transaction the two components needed are the signature (v, r, and s) and the signing hash of the transaction. The sender’s public key can be obtained with these two values and therefore the sender address can be retrieved.

Parameters
  • tx – Transaction of interest.

  • chain_id – ID of the executing chain.

Returns

sender – The address of the account that signed the transaction.

Return type

ethereum.eth_types.Address

def recover_sender(chain_id: Uint64, tx: Transaction) -> Address:
    v, r, s = tx.v, tx.r, tx.s

    ensure(0 < r and r < SECP256K1N, InvalidBlock)
    ensure(0 < s and s <= SECP256K1N // 2, InvalidBlock)

    if v == 27 or v == 28:
        public_key = secp256k1_recover(r, s, v - 27, signing_hash_pre155(tx))
    else:
        ensure(v == 35 + chain_id * 2 or v == 36 + chain_id * 2, InvalidBlock)
        public_key = secp256k1_recover(
            r, s, v - 35 - chain_id * 2, signing_hash_155(tx)
        )
    return Address(keccak256(public_key)[12:32])

signing_hash_pre155

signing_hash_pre155(tx)

Compute the hash of a transaction used in a legacy (pre EIP 155) signature.

Parameters

tx – Transaction of interest.

Returns

hash – Hash of the transaction.

Return type

ethereum.eth_types.Hash32

def signing_hash_pre155(tx: Transaction) -> Hash32:
    return keccak256(
        rlp.encode(
            (
                tx.nonce,
                tx.gas_price,
                tx.gas,
                tx.to,
                tx.value,
                tx.data,
            )
        )
    )

signing_hash_155

signing_hash_155(tx)

Compute the hash of a transaction used in a EIP 155 signature.

Parameters

tx – Transaction of interest.

Returns

hash – Hash of the transaction.

Return type

ethereum.eth_types.Hash32

def signing_hash_155(tx: Transaction) -> Hash32:
    return keccak256(
        rlp.encode(
            (
                tx.nonce,
                tx.gas_price,
                tx.gas,
                tx.to,
                tx.value,
                tx.data,
                Uint(1),
                Uint(0),
                Uint(0),
            )
        )
    )

compute_header_hash

compute_header_hash(header)

Computes the hash of a block header.

The header hash of a block is the canonical hash that is used to refer to a specific block and completely distinguishes a block from another.

keccak256 is a function that produces a 256 bit hash of any input. It also takes in any number of bytes as an input and produces a single hash for them. A hash is a completely unique output for a single input. So an input corresponds to one unique hash that can be used to identify the input exactly.

Prior to using the keccak256 hash function, the header must be encoded using the Recursive-Length Prefix. See Recursive Length Prefix (RLP) Encoding. RLP encoding the header converts it into a space-efficient format that allows for easy transfer of data between nodes. The purpose of RLP is to encode arbitrarily nested arrays of binary data, and RLP is the primary encoding method used to serialize objects in Ethereum’s execution layer. The only purpose of RLP is to encode structure; encoding specific data types (e.g. strings, floats) is left up to higher-order protocols.

Parameters

header – Header of interest.

Returns

hash – Hash of the header.

Return type

ethereum.eth_types.Hash32

def compute_header_hash(header: Header) -> Hash32:
    return keccak256(rlp.encode(header))

check_gas_limit

check_gas_limit(gas_limit, parent_gas_limit)

Validates the gas limit for a block.

The bounds of the gas limit, max_adjustment_delta, is set as the quotient of the parent block’s gas limit and the GAS_LIMIT_ADJUSTMENT_FACTOR. Therefore, if the gas limit that is passed through as a parameter is greater than or equal to the sum of the parent’s gas and the adjustment delta then the limit for gas is too high and fails this function’s check. Similarly, if the limit is less than or equal to the difference of the parent’s gas and the adjustment delta or the predefined GAS_LIMIT_MINIMUM then this function’s check fails because the gas limit doesn’t allow for a sufficient or reasonable amount of gas to be used on a block.

Parameters
  • gas_limit – Gas limit to validate.

  • parent_gas_limit – Gas limit of the parent block.

Returns

check – True if gas limit constraints are satisfied, False otherwise.

Return type

bool

def check_gas_limit(gas_limit: Uint, parent_gas_limit: Uint) -> bool:
    max_adjustment_delta = parent_gas_limit // GAS_LIMIT_ADJUSTMENT_FACTOR
    if gas_limit >= parent_gas_limit + max_adjustment_delta:
        return False
    if gas_limit <= parent_gas_limit - max_adjustment_delta:
        return False
    if gas_limit < GAS_LIMIT_MINIMUM:
        return False

    return True

calculate_block_difficulty

calculate_block_difficulty(block_number, block_timestamp, parent_timestamp, parent_difficulty, parent_has_ommers)

Computes difficulty of a block using its header and parent header.

The difficulty is determined by the time the block was created after its parent. The offset is calculated using the parent block’s difficulty, parent_difficulty, and the timestamp between blocks. This offset is then added to the parent difficulty and is stored as the difficulty variable. If the time between the block and its parent is too short, the offset will result in a positive number thus making the sum of parent_difficulty and offset to be a greater value in order to avoid mass forking. But, if the time is long enough, then the offset results in a negative value making the block less difficult than its parent.

The base standard for a block’s difficulty is the predefined value set for the genesis block since it has no parent. So, a block can’t be less difficult than the genesis block, therefore each block’s difficulty is set to the maximum value between the calculated difficulty and the GENESIS_DIFFICULTY.

Parameters
  • block_number – Block number of the block.

  • block_timestamp – Timestamp of the block.

  • parent_timestamp – Timestamp of the parent block.

  • parent_difficulty – difficulty of the parent block.

  • parent_has_ommers – does the parent have ommers.

Returns

difficulty – Computed difficulty for a block.

Return type

ethereum.base_types.Uint

def calculate_block_difficulty(
    block_number: Uint,
    block_timestamp: U256,
    parent_timestamp: U256,
    parent_difficulty: Uint,
parent_has_ommers: bool,
) -> Uint:
    offset = (
        int(parent_difficulty)
        // 2048
        * max(1max(
            (2 if parent_has_ommers else 1) - int(block_timestamp - parent_timestamp) // 10, -99)9,
            -99,
    )
    )
    difficulty = int(parent_difficulty) + offset
    # Historical Note: The difficulty bomb was not present in Ethereum at the
    # start of Frontier, but was added shortly after launch. However since the
    # bomb has no effect prior to block 200000 we pretend it existed from
    # genesis.
    # See https://github.com/ethereum/go-ethereum/pull/1588
    num_bomb_periods = (int(block_number)((int(block_number) - BOMB_DELAY_BLOCKS) // 100000) - 2
    if num_bomb_periods >= 0:
        difficulty += 2**num_bomb_periods

    # Some clients raise the difficulty to `MINIMUM_DIFFICULTY` prior to adding
    # the bomb. This bug does not matter because the difficulty is always much
    # greater than `MINIMUM_DIFFICULTY` on Mainnet.
    return Uint(max(difficulty, MINIMUM_DIFFICULTY))