# compute\_deposit\_data\_root

Compute the 32-byte deposit data root hash (SHA-256 SSZ hash tree root) for validator deposits. This value must be passed as the `deposit_data_root` parameter when calling `deposit()`.

## Signature

```python
def compute_deposit_data_root(
    *,
    node_pubkey: bytes,
    consensus_pubkey: bytes,
    withdrawal_credentials: bytes,
    node_signature: bytes,
    consensus_signature: bytes,
    amount_gwei: int,
) -> bytes
```

All parameters are keyword-only.

## Parameters

| Parameter                | Type    | Bytes | Description                                                                                                       |
| ------------------------ | ------- | ----- | ----------------------------------------------------------------------------------------------------------------- |
| `node_pubkey`            | `bytes` | 32    | ED25519 public key for node identity                                                                              |
| `consensus_pubkey`       | `bytes` | 48    | BLS12-381 public key for consensus                                                                                |
| `withdrawal_credentials` | `bytes` | 32    | Use [`make_withdrawal_credentials`](https://docs.seismic.systems/clients/python/abis/make-withdrawal-credentials) |
| `node_signature`         | `bytes` | 64    | ED25519 signature over deposit data                                                                               |
| `consensus_signature`    | `bytes` | 96    | BLS12-381 signature over deposit data                                                                             |
| `amount_gwei`            | `int`   | —     | Deposit amount in gwei (e.g. `32 * 1000000000`)                                                                   |

## Returns

`bytes` — 32-byte deposit data root hash.

Raises `ValueError` if any byte-length parameter has the wrong size.

## How It Works

The function computes the SSZ hash tree root, mirroring the on-chain verification in `DepositContract.sol`:

```
pubkey_root         = SHA256(node_pubkey + SHA256(consensus_pubkey + pad_16))
signature_root      = SHA256(SHA256(node_sig) + SHA256(SHA256(con_sig[:64]) + SHA256(con_sig[64:] + pad_32)))
deposit_data_root   = SHA256(SHA256(pubkey_root + withdrawal_credentials) + SHA256(amount_le8 + pad_24 + signature_root))
```

Where `amount_le8` is the gwei value encoded as 8-byte little-endian, and `pad_N` extends data to chunk boundaries.

## Example

```python
from seismic_web3 import compute_deposit_data_root, make_withdrawal_credentials

withdrawal_credentials = make_withdrawal_credentials(
    "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266"
)

root = compute_deposit_data_root(
    node_pubkey=bytes(32),
    consensus_pubkey=bytes(48),
    withdrawal_credentials=withdrawal_credentials,
    node_signature=bytes(64),
    consensus_signature=bytes(96),
    amount_gwei=32 * 1000000000,
)

print(root.hex())  # 32-byte hex string
```

## See Also

* [make\_withdrawal\_credentials](https://docs.seismic.systems/clients/python/abis/make-withdrawal-credentials) — Build the `withdrawal_credentials` input
* [Deposit Contract](https://docs.seismic.systems/clients/python/abis/deposit-contract) — ABI, address, and deposit requirements
* [deposit](https://docs.seismic.systems/clients/python/namespaces/methods/deposit) — Namespace method for making deposits