def keyczar_symmetric_decrypt(decrypt_key, ciphertext):
    """
    Decrypt the given crypto text into plain text. Returns the original
    string input. Note that we first convert the string to hex notation
    and then decrypt. This is reverse of the encrypt operation.

    :param decrypt_key: Symmetric AES key to use for decryption.
    :type decrypt_key: :class:`keyczar.keys.AESKey`

    :param crypto: Crypto text to be decrypted.
    :type crypto: ``str``

    :rtype: ``str``
    """
    from keyczar.keys import AesKey as KeyczarAesKey  # pylint: disable=import-error
    from keyczar.keys import HmacKey as KeyczarHmacKey  # pylint: disable=import-error
    from keyczar.keyinfo import GetMode  # pylint: disable=import-error

    decrypt_key = KeyczarAesKey(
        decrypt_key.aes_key_string,
        KeyczarHmacKey(decrypt_key.hmac_key_string, decrypt_key.hmac_key_size),
        decrypt_key.size,
        GetMode(decrypt_key.mode),
    )

    return decrypt_key.Decrypt(binascii.unhexlify(ciphertext))

    Decrypt the given crypto text into plain text. Returns the original
    string input. Note that we first convert the string to hex notation
    and then decrypt. This is reverse of the encrypt operation.

    :param decrypt_key: Symmetric AES key to use for decryption.
    :type decrypt_key: :class:`keyczar.keys.AESKey`

    :param crypto: Crypto text to be decrypted.
    :type crypto: ``str``

    :rtype: ``str``
    
st2common/st2common/util/crypto.py