code: public Packer useHMAC(final String hMacAlg, final String passphrase) throws NoSuchAlgorithmException,
  			InvalidKeyException {
  		hMac = Mac.getInstance(hMacAlg); // "HmacSHA256"
  		hMac.init(new SecretKeySpec(passphrase.getBytes(charsetUTF8), hMacAlg));
  		return this;
  	}
docs: Sets the usage of Hash-MAC for authentication (default no)
  
  @param hMacAlg
  HMAC algorithm (HmacSHA1, HmacSHA256,...)
  @param passphrase
  shared secret
  @return
  
  @throws NoSuchAlgorithmException
  @throws InvalidKeyException
  
  @see {@link javax.crypto.Mac#getInstance(String)}
  @see <a
  href="http://docs.oracle.com/javase/6/docs/technotes/guides/security/SunProviders.html#SunJCEProvider">JCE
  Provider</a>