'Extract a crypto_meta dict from a header.
:param header_name: name of header that may have crypto_meta
:return: A dict containing crypto_meta items
:raises EncryptionException: if an error occurs while parsing the
crypto meta'

def get_crypto_meta(self, header_name):

    crypto_meta_json = self._response_header_value(header_name)
    if (crypto_meta_json is None):
        return None
    crypto_meta = load_crypto_meta(crypto_meta_json)
    self.crypto.check_crypto_meta(crypto_meta)
    return crypto_meta
