LegacyFields

Standard EVM transaction fields

Standard EVM transaction fields used in metadata construction.

Overview

LegacyFields is a subset of standard Ethereum transaction parameters used when constructing TxSeismicMetadata for AAD (Additional Authenticated Data) in AES-GCM encryption.

Definition

@dataclass(frozen=True)
class LegacyFields:
    """Standard EVM transaction fields used in metadata construction.

    Attributes:
        chain_id: Numeric chain identifier.
        nonce: Sender's transaction count.
        to: Recipient address, or None for contract creation.
        value: Amount of wei to transfer.
    """
    chain_id: int
    nonce: int
    to: ChecksumAddress | None
    value: int

Fields

Field	Type	Description
chain_id	int	Numeric chain identifier (e.g., 5124 for Seismic testnet)
nonce	int	Sender's transaction count
to	ChecksumAddress | None	Recipient address, or None for contract creation
value	int	Amount of wei to transfer

Examples

Manual Construction

from seismic_web3 import LegacyFields

legacy = LegacyFields(
    chain_id=5124,
    nonce=42,
    to="0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
    value=1_000_000_000_000_000_000,  # 1 ETH in wei
)

Contract Creation

from seismic_web3 import LegacyFields

# For contract deployment, set to=None
legacy = LegacyFields(
    chain_id=5124,
    nonce=0,
    to=None,  # Contract creation
    value=0,  # No ETH sent
)

Use in TxSeismicMetadata

from seismic_web3 import TxSeismicMetadata, LegacyFields, SeismicElements

metadata = TxSeismicMetadata(
    sender="0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
    legacy_fields=LegacyFields(
        chain_id=5124,
        nonce=42,
        to="0x1234567890123456789012345678901234567890",
        value=1_000_000_000_000_000_000,
    ),
    seismic_elements=SeismicElements(...),
)

Extract from Wallet Client

# SDK automatically extracts these fields
from seismic_web3 import create_wallet_client, SEISMIC_TESTNET, PrivateKey

w3 = create_wallet_client(
    rpc_url="https://gcp-1.seismictest.net/rpc",
    chain=SEISMIC_TESTNET,
    account=PrivateKey(...),
)

# SDK uses chain_id from config
chain_id = w3.eth.chain_id

# SDK fetches nonce automatically
nonce = w3.eth.get_transaction_count(w3.eth.default_account)

Field Details

chain_id

The numeric chain identifier prevents cross-chain replay attacks:

• 5124 - Seismic testnet

• 31337 - Seismic local (sanvil)

nonce

The sender's transaction count ensures:

• Ordered execution - Transactions execute in sequence

• Replay protection - Can't reuse old transactions

• Fetched automatically - SDK calls eth_getTransactionCount

to

The recipient address:

• Checksummed address - EIP-55 format (mixed case)

• None - For contract creation transactions

• Must be valid - Invalid addresses cause transaction failure

value

Amount of native currency to transfer:

• In wei - Smallest unit (1 ETH = 10^18 wei)

• Can be 0 - For pure function calls

• Integer only - No fractional wei

Properties

• Immutable - Cannot be modified after construction (frozen=True)

• Type-safe - All fields are validated at construction

• Subset of full transaction - Excludes gas, gasPrice, data

Why Called "Legacy"?

These are the standard EVM fields that exist in all Ethereum transaction types:

• Present in Legacy (pre-EIP-2718) transactions

• Present in EIP-2930 (Type 1) transactions

• Present in EIP-1559 (Type 2) transactions

• Present in Seismic (Type 0x4a) transactions

The name emphasizes these fields are unchanged from traditional Ethereum transactions, unlike the new SeismicElements fields.

Notes

• Used exclusively in TxSeismicMetadata

• Part of the AAD (Additional Authenticated Data) for AES-GCM encryption

• Automatically extracted by the SDK from wallet and chain config

• Does not include gas, gasPrice, or data fields (those are in UnsignedSeismicTx)

See Also

• TxSeismicMetadata - Uses LegacyFields

• SeismicElements - Seismic-specific fields (contrast)

• UnsignedSeismicTx - Full transaction structure