code: public static byte[] randomBytes(int n) {
          byte[] buffer = new byte[n];
          if (RandomUtils.secureRandom == null) {
              try {
                  RandomUtils.secureRandom = SecureRandom.getInstance(ALGORITHM);
              } catch (NoSuchAlgorithmException e) {
                  e.printStackTrace();
              }
          }
          RandomUtils.secureRandom.nextBytes(buffer);
          return buffer;
      }
docs: Generates a number random bytes specified by the user
  
  @return byte array representation of random bytes