code: public static OutputStream encrypt(OutputStream outputStream, byte[] key) {
          checkNotNull(outputStream);
          checkNotNull(key);
          AESFastEngine aesEngine = new AESFastEngine();
          PaddedBufferedBlockCipher cipher =
                  new PaddedBufferedBlockCipher(aesEngine, new PKCS7Padding());
          cipher.init(true, new KeyParameter(key));
          return new CipherOutputStream(outputStream, cipher);
      }
docs: AES/ECB/PKCS5Padding Encryption
  
  @param outputStream output stream to be encrypted
  @param key          valid AES key sizes are 128, 192, or 256 bits (16, 24, or 32 bytes).
  @return encrypted output stream