docs: @Restricted(NoExternalUse.class) // TODO pending ApI
      public Cipher decrypt(byte[] iv) {
          try {
              Cipher cipher = Secret.getCipher(ALGORITHM);
              cipher.init(Cipher.DECRYPT_MODE, getKey(), new IvParameterSpec(iv));
              return cipher;
          } catch (GeneralSecurityException e) {
              throw new AssertionError(e);
          }
      }