// Create new Mac instance for thread safety without blocking other operations
            Mac mac;
            try {
                mac = createMacInstance();
            } catch (GeneralSecurityException e) {
                log.error("Failed to create Mac instance for signing", e);
                throw new RuntimeException("Failed to create Mac instance", e);
            }

        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
            md.update((byte) (ms_usage & 0xFF));

        System.arraycopy(name.getBytes("US-ASCII"), 0, src, srcIndex + 13, 16);
        src[srcIndex + 28] = 0x00; // hex code
        src[srcIndex + 29] = 0x04; // flags
        // MAC address (6 bytes)
        byte[] mac = new byte[6];
        System.arraycopy(mac, 0, src, srcIndex + 31, 6);
        // Stats (6 bytes)
        byte[] stats = new byte[6];
        System.arraycopy(stats, 0, src, srcIndex + 37, 6);

    /**
     * Retrieves the MAC address of the remote network interface. Samba returns all zeros.
     *
     * @param tc
     *            context to use
     *
     * @return the MAC address as an array of six bytes
     * @throws UnknownHostException
     *             if the host cannot be resolved to
     *             determine the MAC address.
     */

    private int updates;
    private int signSequence;

    /**
     * Constructs a new signing digest with the specified MAC signing key.
     *
     * @param macSigningKey the MAC signing key for message authentication
     * @param bypass whether to bypass MAC signing
     * @throws SmbException if MD5 algorithm is not available
     */

        // Using a key with a known value for reproducibility
        SecretKeySpec key = new SecretKeySpec(new byte[16], "ARCFOUR");
        byte[] mac = PacMac.calculateMacArcfourHMACMD5(3, key, TEST_DATA);
        assertNotNull(mac);
        assertEquals(16, mac.length);

        // Test with a different key usage
        byte[] mac2 = PacMac.calculateMacArcfourHMACMD5(9, key, TEST_DATA);
        assertNotNull(mac2);

 * message integrity and authenticity using MAC (Message Authentication Code) algorithms.
 *
 * @author mbechler
 */
public interface SMBSigningDigest {

    /**
     * Performs MAC signing of the SMB. This is done as follows.
     * The signature field of the SMB is overwritten with the sequence number;
     * The MD5 digest of the MAC signing key + the entire SMB is taken;

        final byte[] seqBytes = new byte[4];
        SMBUtil.writeInt4(seqNum, seqBytes, 0);

        final MessageDigest mac = Crypto.getHMACT64(sk);
        mac.update(seqBytes); // sequence
        mac.update(data); // data
        final byte[] dgst = mac.digest();
        byte[] trunc = new byte[8];
        System.arraycopy(dgst, 0, trunc, 0, 8);

        if (log.isDebugEnabled()) {

            Mac mac = Mac.getInstance("HmacSHA256");
            mac.init(new SecretKeySpec(sessionKey, "HmacSHA256"));

            // Zero signature field for calculation
            Arrays.fill(data, SIGNATURE_OFFSET, SIGNATURE_OFFSET + SIGNATURE_LENGTH, (byte) 0);
            mac.update(data, 0, data.length);
            byte[] validSig = mac.doFinal();

        Key macKey = new SecretKeySpec(key.clone(), KerberosConstants.HMAC_ALGORITHM);
        Mac mac = Mac.getInstance(KerberosConstants.HMAC_ALGORITHM);
        mac.init(macKey);
        return mac.doFinal(data);
    }

    /**
     * Returns the user's Kerberos realm.
     *
     * @return the user realm
     */
    public String getUserRealm() {