code: public byte[] sign(byte[] bytes) {
  		try {
  			Mac mac = Mac.getInstance(algorithm);
  			mac.init(key);
  			return mac.doFinal(bytes);
  		}
  		catch (GeneralSecurityException e) {
  			throw new RuntimeException(e);
  		}
  	}
docs: val keyLength = key.getEncoded.length * 8