<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_identity_document(current_block: dict, uid: str, salt: str, password: str) -> Identity: """ Get an Identity document :param current_block: Current block data :param uid: Unique IDentifier :param salt: Passphrase of the account :param password: Password of the account :rtype: Identity """


    # get current block BlockStamp
    timestamp = BlockUID(current_block['number'], current_block['hash'])

    # create keys from credentials
    key = SigningKey.from_credentials(salt, password)

    # create identity document
    identity = Identity(
        version=10,
        currency=current_block['currency'],
        pubkey=key.pubkey,
        uid=uid,
        ts=timestamp,
        signature=None
    )

    # sign document
    identity.sign([key])

    return identity