* Returns the effective user session key.
     * 
     * @param challenge The server challenge.
     * @return A <code>byte[]</code> containing the effective user session key,
     * used in SMB MAC signing and NTLMSSP signing and sealing.
     */
    public byte[] getUserSessionKey(byte[] challenge) {
        if (hashesExternal) return null;
        byte[] key = new byte[16];
        try {

            this.writeSizeFile = Math.min(th.getConfig().getSendBufferSize() - 70, 0xFFFF - 70);
        }
        else {
            log.debug("No support or SMB signing is enabled, not enabling large writes");
            this.writeSizeFile = this.writeSize;
        }

        if ( log.isDebugEnabled() ) {
            log.debug("Negotiated file write size is " + this.writeSizeFile);

            this.negotiatedFlags2 &= 0xFFFF ^ SmbConstants.FLAGS2_SECURITY_REQUIRE_SIGNATURES;
        }

        if ( log.isDebugEnabled() ) {
            log.debug(
                "Signing " + ( ( this.negotiatedFlags2 & SmbConstants.FLAGS2_SECURITY_SIGNATURES ) != 0 ? "enabled " : "not-enabled " )

            if (SmbTransport.log.level >= 3)
                SmbTransport.log.println(
                    "Default credentials (jcifs.smb1.smb1.client.username/password)" +
                    " not specified. SMB signing may not work propertly." +
                    "  Skipping DC interrogation." );
        } else {
            SmbSession ssn = trans.getSmbSession( NtlmPasswordAuthentication.DEFAULT );

            log.flush();
        }
        updates = 0;

        return b;
    }

    /**
     * Performs MAC signing of the SMB.  This is done as follows.
     * The signature field of the SMB is overwritted with the sequence number;
     * The MD5 digest of the MAC signing key + the entire SMB is taken;
     * The first 8 bytes of this are placed in the signature field.
     *
     * @param data The data.

    /**
     * Indicates datagram authentication.
     */
    public static final int NTLMSSP_NEGOTIATE_DATAGRAM_STYLE = 0x00000040;

    /**
     * Indicates that the LAN Manager session key should be used for
     * signing and sealing authenticated communication.
     */
    public static final int NTLMSSP_NEGOTIATE_LM_KEY = 0x00000080;

    /**
     * ??? According to spec this is a reserved bit and must be set to zero
     */

     * @return the maximum buffer size reported by the server
     * @throws CIFSException
     */
    int getMaximumBufferSize () throws CIFSException;


    /**
     * @return whether the session uses SMB signing
     * @throws CIFSException
     * @throws SmbException
     */
    boolean areSignaturesActive () throws CIFSException;


    /**
     * Internal/testing use only
     * 
     * @return attached session

    public int getSecurityMode () {
        return this.securityMode;
    }


    @Override
    public boolean isSigningEnforced () {
        return ( getSecurityMode() & Smb2Constants.SMB2_NEGOTIATE_SIGNING_REQUIRED ) != 0;
    }


    /**
     * @return the capabilities
     */
    public int getCapabilities () {
        return this.capabilities;
    }


    /**

            if ( !tf.hasDefaultCredentials() ) {
                trans.ensureConnected();
                log.warn(
                    "Default credentials (jcifs.smb.client.username/password)" + " not specified. SMB signing may not work propertly."
                            + "  Skipping DC interrogation.");
            }
            else {

    @Override
    public boolean isMICAvailable () {
        return !this.auth.isGuest() && this.signKey != null && this.verifyKey != null;
    }


    @Override
    public byte[] calculateMIC ( byte[] data ) throws CIFSException {
        byte[] sk = this.signKey;
        if ( sk == null ) {
            throw new CIFSException("Signing is not initialized");
        }

        int seqNum = this.signSequence.getAndIncrement();