# SeismicSecurityParams

Optional overrides for the SDK's default security parameters when creating shielded transactions. All fields default to `None`.

## Definition

```python
@dataclass(frozen=True)
class SeismicSecurityParams:
    blocks_window: int | None = None
    encryption_nonce: EncryptionNonce | None = None
    recent_block_hash: Bytes32 | None = None
    expires_at_block: int | None = None
```

## Fields

| Field               | Type                                                                                   | Default           | Description                             |
| ------------------- | -------------------------------------------------------------------------------------- | ----------------- | --------------------------------------- |
| `blocks_window`     | `int \| None`                                                                          | `None` → 100      | Number of blocks before the tx expires  |
| `encryption_nonce`  | [`EncryptionNonce`](/clients/python/api-reference/types/encryption-nonce.md) `\| None` | `None` → random   | Explicit AES-GCM nonce                  |
| `recent_block_hash` | [`Bytes32`](/clients/python/api-reference/types/bytes32.md) `\| None`                  | `None` → latest   | Explicit block hash for freshness proof |
| `expires_at_block`  | `int \| None`                                                                          | `None` → computed | Explicit expiry block number            |

## Example

```python
from seismic_web3 import SeismicSecurityParams

# Transaction expires in 200 blocks instead of default 100
security_params = SeismicSecurityParams(blocks_window=200)

result = await contract.write.transfer(
    recipient,
    amount,
    security_params=security_params,
)
```

## Field relationships

* If both `blocks_window` and `expires_at_block` are provided, `expires_at_block` takes precedence
* If neither is provided, defaults to `current_block + 100`

## See Also

* [SeismicElements](/clients/python/api-reference/transaction-types/seismic-elements.md) — constructed from these params
* [EncryptionNonce](/clients/python/api-reference/types/encryption-nonce.md) — type for `encryption_nonce`
* [Bytes32](/clients/python/api-reference/types/bytes32.md) — type for `recent_block_hash`


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