How to use the libnacl.secret.SecretBox function in libnacl

def secretbox_encrypt(data, **kwargs):
    '''
    Encrypt data using a secret key generated from `nacl.keygen`.
    The same secret key can be used to decrypt the data using `nacl.secretbox_decrypt`.

    CLI Examples:

    .. code-block:: bash

        salt-run nacl.secretbox_encrypt datatoenc
        salt-call --local nacl.secretbox_encrypt datatoenc sk_file=/etc/salt/pki/master/nacl
        salt-call --local nacl.secretbox_encrypt datatoenc sk='YmFkcGFzcwo='
    '''
    sk = _get_sk(**kwargs)
    b = libnacl.secret.SecretBox(sk)
    return base64.b64encode(b.encrypt(data))

def generate_symmetric_key():
    """
    Generate a random key for symmetric encryption.

    :return:
    """
    box = libnacl.secret.SecretBox()
    return box.sk

'''
    Decrypt data that was encrypted using `nacl.secretbox_encrypt` using the secret key
    that was generated from `nacl.keygen`.

    CLI Examples:

    .. code-block:: bash

        salt-call nacl.secretbox_decrypt pEXHQM6cuaF7A=
        salt-call --local nacl.secretbox_decrypt data='pEXHQM6cuaF7A=' sk_file=/etc/salt/pki/master/nacl
        salt-call --local nacl.secretbox_decrypt data='pEXHQM6cuaF7A=' sk='YmFkcGFzcwo='
    '''
    if data is None:
        return None
    key = _get_sk(**kwargs)
    b = libnacl.secret.SecretBox(key=key)
    return b.decrypt(base64.b64decode(data))

:param val: the value to encrypt
    :param secretKey: Optional key, if provided should be either in hex or bytes
    :return: Tuple of the encrypted value and secret key encoded in hex
    """

    if isinstance(val, str):
        val = val.encode("utf-8")
    if secretKey:
        if isHex(secretKey):
            secretKey = bytes(bytearray.fromhex(secretKey))
        elif not isinstance(secretKey, bytes):
            error("Secret key must be either in hex or bytes")
        box = libnacl.secret.SecretBox(secretKey)
    else:
        box = libnacl.secret.SecretBox()

    return box.encrypt(val).hex(), box.sk.hex()

def _sk_encrypt(key, data, nonce=None):
    """
    Encrypt data by using secret-key encryption.

    Arguments:
        - `key`: A secret key.
        - `data`: Data (bytes).
        - `nonce`: A predefined nonce.

    Return a tuple of bytes containing the nonce and the encrypted
    data.
    """
    # Assemble and encrypt the payload
    box = libnacl.secret.SecretBox(key=key)
    # Note: Workaround for libnacl which lacks `pack_nonce` option
    # (see: https://github.com/saltstack/libnacl/pull/61)
    # return box.encrypt(data, nonce=nonce, pack_nonce=False)
    data = box.encrypt(data, nonce=nonce)
    nonce_length = libnacl.crypto_secretbox_NONCEBYTES
    return data[:nonce_length], data[nonce_length:]