/*
 * "@(#)GssSpNegoClient.java	1.1	05/06/15 SMI"
 *
 * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following 
 * conditions are met:
 * 
 * -Redistributions of source code must retain the above copyright  
 * notice, this  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduct the above copyright 
 * notice, this list of conditions and the following disclaimer in 
 * the documentation and/or other materials provided with the 
 * distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of 
 * contributors may be used to endorse or promote products derived 
 * from this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any 
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND 
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY 
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY 
 * DAMAGES OR LIABILITIES  SUFFERED BY LICENSEE AS A RESULT OF  OR 
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 */

import org.ietf.jgss.*;
import java.net.Socket;
import java.io.IOException;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.security.*;
import javax.security.auth.login.LoginException;

/**
 * A sample client application that uses JGSS to do mutual authentication
 * with a server using Kerberos as the underlying mechanism. It then
 * exchanges data securely with the server.
 *
 * Every message sent to the server includes a 4-byte application-level 
 * header that contains the big-endian integer value for the number
 * of bytes that will follow as part of the JGSS token.
 *
 * The protocol is:
 *    1.  Context establishment loop:
 *         a. client sends init sec context token to server
 *         b. server sends accept sec context token to client
 *         ....
 *    2. client sends a wrapped token to the server.
 *    3. server sends a wrapped token back to the client for the application
 *
 * Start GssServer first before starting GssClient.
 *
 * Usage:  java <options> GssSpNegoClient <service> <serverName>
 *
 * Example: java -Djava.security.auth.login.config=jaas-krb5.conf \
 *               GssSpNegoClient host machine.imc.org
 *
 * Add -Djava.security.krb5.conf=krb5.conf to specify application-specific
 * Kerberos configuration (different from operating system's Kerberos
 * configuration).
 */

public class GssSpNegoClient {
    private static final int PORT = 4567;
    private static final boolean verbose = false;

    public static void main(String[] args) throws Exception {

	// Obtain the command-line arguments and parse the server's principal
	
	if (args.length < 2) {
	    System.err.println(
		"Usage: java <options> GssSpNegoClient <service> <serverName>");
	    System.exit(-1);
	}

	String serverPrinc = args[0] + "/" + args[1];

	PrivilegedExceptionAction action =
	    new GssClientAction(serverPrinc, args[1], PORT);

	Jaas.loginAndAction("client", action);
    }

    static class GssClientAction implements PrivilegedExceptionAction {
	private String serverPrinc;
	private String hostName;
	private int port;

	GssClientAction(String serverPrinc, String hostName, int port) {
	    this.serverPrinc = serverPrinc;
	    this.hostName = hostName;
	    this.port = port;
	}

	public Object run() throws Exception {
	    Socket socket = new Socket(hostName, port);
	    DataInputStream inStream = 
		new DataInputStream(socket.getInputStream());
	    DataOutputStream outStream = 
		new DataOutputStream(socket.getOutputStream());

	    System.out.println("Connected to address " +
		socket.getInetAddress());

	    /*
	     * This Oid is used to represent the SPNEGO GSS-API
	     * mechanism. It is defined in RFC 2478. We will use this Oid
	     * whenever we need to indicate to the GSS-API that it must
	     * use SPNEGO for some purpose.
	     */
	    Oid spnegoOid = new Oid("1.3.6.1.5.5.2");

	    GSSManager manager = GSSManager.getInstance();

	    /*
	     * Create a GSSName out of the server's name. 
	     */
	    GSSName serverName = manager.createName(serverPrinc, 
		GSSName.NT_HOSTBASED_SERVICE, spnegoOid);

	    /*
	     * Create a GSSContext for mutual authentication with the
	     * server.
	     *    - serverName is the GSSName that represents the server.
	     *    - krb5Oid is the Oid that represents the mechanism to
	     *      use. The client chooses the mechanism to use.
	     *    - null is passed in for client credentials
	     *    - DEFAULT_LIFETIME lets the mechanism decide how long the
	     *      context can remain valid.
	     * Note: Passing in null for the credentials asks GSS-API to
	     * use the default credentials. This means that the mechanism
	     * will look among the credentials stored in the current Subject
	     * to find the right kind of credentials that it needs.
	     */
	    GSSContext context = manager.createContext(serverName,
		spnegoOid,
		null,
		GSSContext.DEFAULT_LIFETIME);

	    // Set the desired optional features on the context. The client
	    // chooses these options.

	    context.requestMutualAuth(true);  // Mutual authentication
	    context.requestConf(true);  // Will use confidentiality later
	    context.requestInteg(true); // Will use integrity later

	    // Do the context eastablishment loop

	    byte[] token = new byte[0];

	    while (!context.isEstablished()) {

		// token is ignored on the first call
		token = context.initSecContext(token, 0, token.length);

		// Send a token to the server if one was generated by
		// initSecContext
		if (token != null) {
		    if (verbose) {
			System.out.println("Will send token of size " +
			    token.length + " from initSecContext.");
			System.out.println("writing token = " +
			    getHexBytes(token));
		    }

		    outStream.writeInt(token.length);
		    outStream.write(token);
		    outStream.flush();
		}

		// If the client is done with context establishment
		// then there will be no more tokens to read in this loop
		if (!context.isEstablished()) {
		    token = new byte[inStream.readInt()];
		    if (verbose) {
			System.out.println("reading token = " +
			    getHexBytes(token));
			System.out.println("Will read input token of size " +
			    token.length + " for processing by initSecContext");
		    }
		    inStream.readFully(token);
		}
	    }
	
	    System.out.println("Context Established! ");
	    System.out.println("Client principal is " + context.getSrcName());
	    System.out.println("Server principal is " + context.getTargName());

	    /*
	     * If mutual authentication did not take place, then only the
	     * client was authenticated to the server. Otherwise, both
	     * client and server were authenticated to each other.
	     */
	    if (context.getMutualAuthState())
		System.out.println("Mutual authentication took place!");

	    byte[] messageBytes = "Hello There!".getBytes("UTF-8");
	
	    /*
	     * The first MessageProp argument is 0 to request
	     * the default Quality-of-Protection.
	     * The second argument is true to request
	     * privacy (encryption of the message).
	     */
	    MessageProp prop =  new MessageProp(0, true);

	    /*
	     * Encrypt the data and send it across. Integrity protection
	     * is always applied, irrespective of confidentiality
	     * (i.e., encryption).
	     * You can use the same token (byte array) as that used when 
	     * establishing the context.
	     */

	    System.out.println("Sending message: " + 
		new String(messageBytes, "UTF-8"));
	    token = context.wrap(messageBytes, 0, messageBytes.length, prop);
	    outStream.writeInt(token.length);
	    outStream.write(token);
	    outStream.flush();

	    /*
	     * Now we will allow the server to decrypt the message,
	     * append a time/date on it, and send then it back.
	     */

	    token = new byte[inStream.readInt()];
	    System.out.println("Will read token of size " + token.length);
	    inStream.readFully(token);
	    byte[] replyBytes = context.unwrap(token, 0, token.length, prop);
	
	    System.out.println("Received message: " + 
		new String(replyBytes, "UTF-8"));

	    System.out.println("Done.");
	    context.dispose();
	    socket.close();

	    return null;
	}
    }
    
    private static final String getHexBytes(byte[] bytes, int pos, int len) {

	StringBuffer sb = new StringBuffer();
	for (int i = pos; i < (pos+len); i++) {
	
	    int b1 = (bytes[i]>>4) & 0x0f;
	    int b2 = bytes[i] & 0x0f;

	    sb.append(Integer.toHexString(b1));
	    sb.append(Integer.toHexString(b2));
	    sb.append(' ');
	}
	return sb.toString();
    }

    private static final String getHexBytes(byte[] bytes) {
	return getHexBytes(bytes, 0, bytes.length);
    }
}