private void assertStructure(String ciphertext) throws IOException {
if (ciphertext.startsWith("{") && ciphertext.endsWith("}")) {
ciphertext = ciphertext.substring(1, ciphertext.length() - 1);
}
Base64Encoder decoder = new Base64Encoder();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
decoder.decode(ciphertext, baos);
byte[] res = baos.toByteArray();
assertEquals(8, res[0]);
}