# sign\_seismic\_tx\_eip712

Sign and serialize a Seismic transaction using EIP-712 typed data hashing. This is the primary signing function for `message_version == 2` transactions.

## Signature

```python
def sign_seismic_tx_eip712(
    tx: UnsignedSeismicTx,
    private_key: PrivateKey,
) -> HexBytes
```

## Parameters

| Parameter     | Type                                                                                                                   | Required | Description                                                           |
| ------------- | ---------------------------------------------------------------------------------------------------------------------- | -------- | --------------------------------------------------------------------- |
| `tx`          | [`UnsignedSeismicTx`](https://docs.seismic.systems/clients/python/api-reference/transaction-types/unsigned-seismic-tx) | Yes      | The unsigned Seismic transaction (should have `message_version == 2`) |
| `private_key` | [`PrivateKey`](https://docs.seismic.systems/clients/python/api-reference/types/private-key)                            | Yes      | 32-byte secp256k1 private key                                         |

## Returns

| Type       | Description                                                                            |
| ---------- | -------------------------------------------------------------------------------------- |
| `HexBytes` | Full signed transaction bytes (`0x4a` prefix + RLP) ready for `eth_sendRawTransaction` |

## Steps

1. Compute [`eip712_signing_hash(tx)`](https://docs.seismic.systems/clients/python/api-reference/eip712/eip712-signing-hash)
2. Sign with `eth_keys.PrivateKey.sign_msg_hash()`
3. Serialize with `serialize_signed(tx, sig)` — same RLP as raw signing

The RLP serialization is identical to raw signing mode; only the ECDSA message hash differs. The Seismic node checks `message_version` to determine which verification path to use.

## EIP-712 vs raw signing

| Aspect             | EIP-712 (`message_version=2`)  | Raw (`message_version=0`) |
| ------------------ | ------------------------------ | ------------------------- |
| **Signing hash**   | Structured EIP-712 hash        | RLP hash of unsigned tx   |
| **Wallet support** | Better UX (structured display) | Generic message signing   |
| **RLP output**     | Identical                      | Identical                 |
| **Verification**   | Node uses EIP-712 path         | Node uses raw path        |

## Example

```python
from seismic_web3 import sign_seismic_tx_eip712

signed_tx = sign_seismic_tx_eip712(unsigned_tx, private_key)
tx_hash = w3.eth.send_raw_transaction(signed_tx)
```

## Warnings

* The function does not enforce `message_version == 2`; callers should set it appropriately
* Ensure `expires_at_block` hasn't passed before broadcasting

## See Also

* [eip712\_signing\_hash](https://docs.seismic.systems/clients/python/api-reference/eip712/eip712-signing-hash) — computes the signing hash
* [build\_seismic\_typed\_data](https://docs.seismic.systems/clients/python/api-reference/eip712/build-seismic-typed-data) — build typed data dict for external signers
* [UnsignedSeismicTx](https://docs.seismic.systems/clients/python/api-reference/transaction-types/unsigned-seismic-tx) — input transaction type
* [PrivateKey](https://docs.seismic.systems/clients/python/api-reference/types/private-key) — signing key type