/*
 * "@(#)GssServer.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 
 * RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR 
 * ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE 
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 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF 
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 * 
 * You acknowledge that Software is not designed, licensed or 
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 */

import org.ietf.jgss.*;
import java.io.*;
import java.net.Socket;
import java.net.ServerSocket;
import java.security.*;
import java.util.Date;

/**
 * A sample server application that uses JGSS to do mutual authentication
 * with a client using Kerberos as the underlying mechanism. It then
 * exchanges data securely with the client.
 *
 * Every message exchanged with the client 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 wrap token to the server.
 *    3. server sends a wrap token back to the client.
 *
 * Start GssServer first before starting GssClient.
 *
 * Usage:  java <options> GssServer
 *
 * Example: java -Djava.security.auth.login.config=jaas-krb5.conf \
 *               GssServer
 *
 * Add -Djava.security.krb5.conf=krb5.conf to specify application-specific
 * Kerberos configuration (different from operating system's Kerberos
 * configuration).
 */

public class GssServer  {
    private static final int PORT = 4567;
    private static final boolean verbose = false;
    private static final int LOOP_LIMIT = 1;
    private static int loopCount = 0;
    
    public static void main(String[] args) throws Exception {

	PrivilegedExceptionAction action = new GssServerAction(PORT);

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

    static class GssServerAction implements PrivilegedExceptionAction {
	private int localPort;

	GssServerAction(int port) {
	    this.localPort = port;
	}

	public Object run() throws Exception {
    
	    ServerSocket ss = new ServerSocket(localPort);

	    // Get own Kerberos credentials for accepting connection
	    GSSManager manager = GSSManager.getInstance();
	    Oid krb5Mechanism = new Oid("1.2.840.113554.1.2.2");
	    GSSCredential serverCreds = manager.createCredential(null,
                                             GSSCredential.DEFAULT_LIFETIME,
                                             krb5Mechanism,
                                             GSSCredential.ACCEPT_ONLY);
	    while (loopCount++ < LOOP_LIMIT) {

		System.out.println("Waiting for incoming connection...");

		Socket socket = ss.accept();
		DataInputStream inStream = 
		    new DataInputStream(socket.getInputStream());

		DataOutputStream outStream = 
		    new DataOutputStream(socket.getOutputStream());

		System.out.println("Got connection from client " +
		    socket.getInetAddress());
	
	        /*
	         * Create a GSSContext to receive the incoming request 
	         * from the client. Use null for the server credentials 
	         * passed in. This tells the underlying mechanism
	         * to use whatever credentials it has available that
	         * can be used to accept this connection.
	         */

		GSSContext context = manager.createContext(
		    (GSSCredential)serverCreds);

		// Do the context establishment loop
		
		byte[] token = null;
	   
		while (!context.isEstablished()) {
		
		    if (verbose) {
			System.out.println("Reading ..."); 
		    }
		    token = new byte[inStream.readInt()];
		
		    if (verbose) {
			System.out.println("Will read input token of size " +
			    token.length + " for processing by acceptSecContext");
		    }
		    inStream.readFully(token);
	
		    if (token.length == 0) {
			if (verbose) {
			    System.out.println("skipping zero length token");
			}
			continue;
		    }	
		    if (verbose) {
			System.out.println("Token = " + getHexBytes(token));
			System.out.println("acceptSecContext.."); 
		    }
		    token = context.acceptSecContext(token, 0, token.length);
		
		    // Send a token to the peer if one was generated by
		    // acceptSecContext
		    if (token != null) {
			if (verbose) {
			    System.out.println("Will send token of size " +
				token.length + " from acceptSecContext.");
			}

			outStream.writeInt(token.length);
			outStream.write(token);
			outStream.flush();
		    }
		}
	    
		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!");
	    
	        /*
	         * Create a MessageProp which unwrap will use to return 
	         * information such as the Quality-of-Protection that was 
	         * applied to the wrapped token, whether or not it was 
	         * encrypted, etc. Since the initial MessageProp values
	         * are ignored, just set them to the defaults of 0 and false.
	         */
		MessageProp prop = new MessageProp(0, false);

		/* 
	         * Read the token. This uses the same token byte array 
	         * as that used during context establishment.
	         */
		token = new byte[inStream.readInt()];
		if (verbose) {
		    System.out.println("Will read token of size " + token.length);
		}
		inStream.readFully(token);
	    
		byte[] input = context.unwrap(token, 0, token.length, prop);
		String str = new String(input, "UTF-8");

		System.out.println("Received data \"" +
		    str + "\" of length " + str.length());
	    
		System.out.println("Confidentiality applied: " +
		    prop.getPrivacy());
	
		/*
	         * Now generate reply that is the concatenation of the
		 * incoming string with the current time.
	         */
	    
	        /*
	         * First reset the QOP of the MessageProp to 0
	         * to ensure the default Quality-of-Protection
	         * is applied.
	         */
		prop.setQOP(0);

		String now = new Date().toString();
		byte[] nowBytes = now.getBytes("UTF-8");
		int len = input.length + 1 + nowBytes.length;
		byte[] reply = new byte[len];
		System.arraycopy(input, 0, reply, 0, input.length);
		reply[input.length] = ' ';
		System.arraycopy(nowBytes, 0, reply, input.length+1, 
		    nowBytes.length);
	    
		System.out.println("Sending: " + new String(reply, "UTF-8"));
		token = context.wrap(reply, 0, reply.length, prop);
	    
		outStream.writeInt(token.length);
		outStream.write(token);
		outStream.flush();

		System.out.println("Closing connection with client " +
		    socket.getInetAddress());
		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);
    }
}