code: public byte[] encrypt(final byte[] iv, final byte[] message) throws RuntimeException {
  
          AEADParameters aeadParams = new AEADParameters(
                  new KeyParameter(key), TAG_LENGTH,
                  iv,
                  authData);
  
          cipher.init(true, aeadParams);
          byte[] cipherText = newBuffer(cipher.getOutputSize(message.length));
          int outputOffset = cipher.processBytes(message, 0, message.length, cipherText, 0);
  
          try {
              cipher.doFinal(cipherText, outputOffset);
          } catch (InvalidCipherTextException e) {
              throw new RuntimeException("Error: ", e);
          }
  
          return cipherText;
      }
docs: Given the iv, encrypt the provided data
  
  @param iv      initialization vector
  @param message data to be encrypted
  @return byte array with the cipher text
  @throws RuntimeException