private byte[] getHMAC(byte[] message) {

        try {
            return getMacInstance(mode, key).doFinal(message);
        }
        catch (InvalidKeyException e) {

            // As the key is verified during construction of the TOTPGenerator,
            // this should never happen
            throw new IllegalStateException("Provided key became invalid after "
                    + "passing validation.", e);

        }

    }
private byte [ ] getHMAC ( byte [ ] message ) { try { return getMacInstance ( mode , key ) . doFinal ( message ) ; } catch ( InvalidKeyException e ) { throw new IllegalStateException ( "Provided key became invalid after " + "passing validation." , e ) ; } }
Calculates the HMAC for the given message using the key and algorithm
provided when this TOTPGenerator was created.

@param message
The message to calculate the HMAC of.

@return
The HMAC of the given message.