/** RC4 encryption type identifier */
    int RC4_ENC_TYPE = 23;
    /** RC4 algorithm name */
    String RC4_ALGORITHM = "ARCFOUR";
    /** HMAC algorithm name */
    String HMAC_ALGORITHM = "HmacMD5";
    /** Size of confounder in bytes */
    int CONFOUNDER_SIZE = 8;
    /** Size of checksum in bytes */
    int CHECKSUM_SIZE = 16;

        assertEquals(23, KerberosConstants.RC4_ENC_TYPE, "RC4_ENC_TYPE should have the correct value.");
        assertEquals("HmacMD5", KerberosConstants.HMAC_ALGORITHM, "HMAC_ALGORITHM should have the correct value.");
    }

     */
    public static byte[] calculateMacArcfourHMACMD5(int keyusage, Key key, byte[] data) throws GeneralSecurityException {
        int ms_usage = mapArcfourMD5KeyUsage(keyusage);
        Mac mac = Mac.getInstance("HmacMD5");
        MessageDigest md = MessageDigest.getInstance("MD5");
        mac.init(key);
        byte[] dk = mac.doFinal(MD5_CONSTANT);
        try {
            // little endian