hostage/src/de/tudarmstadt/informatik/hostage/protocol/SSH.java

package de.tudarmstadt.informatik.hostage.protocol;

import java.io.IOException;
import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;

import de.tudarmstadt.informatik.hostage.commons.HelperUtils;
import de.tudarmstadt.informatik.hostage.ssh.crypto.KeyMaterial;
import de.tudarmstadt.informatik.hostage.ssh.crypto.PEMDecoder;
import de.tudarmstadt.informatik.hostage.ssh.crypto.cipher.CBCMode;
import de.tudarmstadt.informatik.hostage.ssh.crypto.cipher.DESede;
import de.tudarmstadt.informatik.hostage.ssh.crypto.dh.DhExchange;
import de.tudarmstadt.informatik.hostage.ssh.crypto.digest.MAC;
import de.tudarmstadt.informatik.hostage.ssh.signature.DSAPrivateKey;
import de.tudarmstadt.informatik.hostage.ssh.signature.DSASHA1Verify;
import de.tudarmstadt.informatik.hostage.ssh.signature.DSASignature;
import de.tudarmstadt.informatik.hostage.ssh.util.TypesReader;
import de.tudarmstadt.informatik.hostage.ssh.util.TypesWriter;
import de.tudarmstadt.informatik.hostage.wrapper.Packet;

/**
 * SSH protocol. Implementation of RFC documents 4250, 4251, 4252, 4253, 4254.
 * It can handle the following requests: Server Protocol, Key Exchange Init,
 * Diffie-Hellman Key Exchange Init, New Keys, Service Request, Connection
 * Request, Channel Open Request, Channel Request.
 * 
 * @author Wulf Pfeiffer
 */
public class SSH implements Protocol {
	/**
	 * Represents the states of the protocol.
	 */
	private enum STATE {
		NONE, SERVER_VERSION, CLIENT_VERSION, KEX_INIT, NEW_KEYS, USERAUTH, CONNECTION, CHANNEL, TERMINAL_CMD, TERMINAL_ENTER, CLOSED
	}

	/**
	 * Denotes in which state the protocol is right now.
	 */
	private STATE state = STATE.NONE;
	private boolean useEncryption = false;

	// version stuff
	private String[][][] possibleSshTypes = {
			{ { "3." }, { "4", "5", "6", "7", "8", "9" } },
			{ { "4." }, { "0", "1", "2", "3", "4", "5", "6", "7", "9" } },
			{ { "5." }, { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" } },
			{ { "6." }, { "0", "1", "2", "3", "4" } } };

	private String initSshType() {
		SecureRandom rnd = new SecureRandom();
		int majorVersion = rnd.nextInt(possibleSshTypes.length);
		return "OpenSSH_"
				+ possibleSshTypes[majorVersion][0][0]
				+ possibleSshTypes[majorVersion][1][rnd
						.nextInt(possibleSshTypes[majorVersion][1].length)];
	}

	// server infos
	private static final String serverVersion = "SSH-2.0-";
	private String serverType = initSshType();
	private String serverName = HelperUtils.getRandomString(16, false);
	private int packetNumber = 0;
	private int recipientChannel;
	private String userName;
	private String terminalPrefix;
	private StringBuffer command = new StringBuffer();
	private SecureRandom random = new SecureRandom();

	// SSH Parameters for Kex etc.
	private byte[] V_S = (serverVersion + serverType).getBytes();
	private byte[] V_C;
	private byte[] I_S;
	private byte[] I_C;
	private byte[] e;
	private BigInteger f;
	private byte[] h;
	private BigInteger k;
	private byte[] K_S;
	private byte[] signature;

	// allowed algorithms for kexinit
	private static final String KEX_ALG = "diffie-hellman-group1-sha1";
	private static final String SERVER_ALG = "ssh-dss";
	private static final String ENCRYPT_ALG_C = "3des-cbc";
	private static final String ENCRYPT_ALG_S = "3des-cbc";
	private static final String MAC_ALG_C = "hmac-sha1";
	private static final String MAC_ALG_S = "hmac-sha1";
	private static final String COMP_ALG_C = "none";
	private static final String COMP_ALG_S = "none";

	private int cipherBlockSize = 16;

	// for en- and decryption
	private DESede desEncryption;
	private DESede desDecryption;
	private CBCMode cbcEncryption;
	private CBCMode cbcDecryption;
	private MAC macEncryption;
	// private MAC macDec;

	// dsa private key
	private static final char[] dsaPem = ("-----BEGIN DSA PRIVATE KEY-----\n"
			+ "MIIBugIBAAKBgQCDZ9R2vfCPwjv5vKF1igIv9drrZ7G0dhMkGT9AZTjgI34Qm4w0\n"
			+ "0iWeCqO7SmqiaMIjbRIm91MeDed4ObAq4sAkqRE/2P4mTbzFx5KhEczRRiDoqQBX\n"
			+ "xYa0yWKJpeZ94SGM6DEPuBTxKo0T4uMjbq2FzHL2FXT1/WoNCmRU6gFSiwIVAMK4\n"
			+ "Epz3JiwDUbkSpLOjIqtEhJmVAoGAL6zlXRI4Q8iwvSDh0vDf1j9a5Aaaq+93LTjK\n"
			+ "SwL4nvUWBl2Aa0vqu05ZS5rOD1I+/naLMg0fNgFJRhA03sl+12MI3a2HXJWXRSdj\n"
			+ "m1Vq9cUXqiYrX6+iGfEaA/y9UO4ZPF6if6eLypXB8VuqjtjDCiMMsM6+qQki7L71\n"
			+ "yN4M75ICgYAcFXUhN2zRug3JvwmGxW8gMgHquSiBnbx1582KGh2B/ukE/kOrbKYD\n"
			+ "HUkBzolcm4x1Odq5apowlriFxY6zMQP615plIK4x9NaU6dvc/HoTkjzT5EYSMN39\n"
			+ "eAGufJ0jrtIpKL4lP8o8yrAHfmbR7bjecWc0viTH0+OWlyVsex/bZAIUEKn310Li\n"
			+ "v62Zs4hlDvhwvx8MQ+A=\n" + "-----END DSA PRIVATE KEY-----")
			.toCharArray();

	@Override
	public int getPort() {
		return 22;
	}

	@Override
	public TALK_FIRST whoTalksFirst() {
		return TALK_FIRST.CLIENT;
	}

	@Override
	public List<Packet> processMessage(Packet requestPacket) {
		List<Packet> responsePackets = new ArrayList<Packet>();
		byte[] request = null;
		if (requestPacket != null) {
			request = requestPacket.getBytes();
			if (useEncryption) {
				request = decryptBytes(request);
			}
		}
		switch (state) {
		case NONE:
			extractType(request);
			responsePackets.add(new Packet(serverVersion + serverType + "\r\n",
					toString()));
			state = STATE.SERVER_VERSION;
			break;
		case SERVER_VERSION:
			extractPayload(request);
			responsePackets.add(kexInit());
			state = STATE.CLIENT_VERSION;
			break;
		case CLIENT_VERSION:
			extractPubKey(request);
			responsePackets.add(dhKexReply());
			state = STATE.KEX_INIT;
			break;
		case KEX_INIT:
			responsePackets.add(newKeys());
			useEncryption = true;
			state = STATE.NEW_KEYS;
			break;
		case NEW_KEYS:
			responsePackets.add(serviceReply(request));
			state = STATE.USERAUTH;
			break;
		case USERAUTH:
			responsePackets.add(connectionReply(request));
			state = STATE.CONNECTION;
			break;
		case CONNECTION:
			responsePackets.add(channelOpenReply(request));
			state = STATE.CHANNEL;
			break;
		case CHANNEL:
			responsePackets.add(channelSuccessReply(request));
			responsePackets.add(terminalPrefix());
			state = STATE.TERMINAL_CMD;
			break;
		case TERMINAL_CMD:
			responsePackets.add(terminalReply(request));
			break;
		case CLOSED:
			break;
		default:
			state = STATE.CLOSED;
			break;
		}

		return responsePackets;
	}

	@Override
	public boolean isClosed() {
		return (state == STATE.CLOSED);
	}

	@Override
	public boolean isSecure() {
		return false;
	}

	@Override
	public String toString() {
		return "SSH";
	}

	/**
	 * Wraps the packets with packet length and padding.
	 * 
	 * @param response
	 *            content that is wrapped.
	 * @return wrapped packet.
	 */
	private Packet wrapPacket(byte[] response) {
		// 4 byte packet length, 1 byte padding length, payload length
		int packetLength = 5 + response.length;
		int paddingLengthCBS = cipherBlockSize
				- (packetLength % cipherBlockSize);
		int paddingLength8 = 8 - (packetLength % 8);
		int paddingLength = paddingLengthCBS > paddingLength8 ? paddingLengthCBS
				: paddingLength8;
		if (paddingLength < 4)
			paddingLength += cipherBlockSize;
		// add padding string length to packet length
		packetLength = packetLength + paddingLength - 4;

		byte[] packetLen = ByteBuffer.allocate(4).putInt(packetLength).array();
		byte[] paddingLen = { (byte) paddingLength };
		byte[] paddingString = HelperUtils.randomBytes(paddingLength);
		byte[] wrappedResponse = HelperUtils.concat(packetLen, paddingLen,
				response, paddingString);
		if (useEncryption) {
			byte[] mac = createMac(wrappedResponse);
			byte[] responseEnc = encryptBytes(wrappedResponse);
			wrappedResponse = HelperUtils.concat(responseEnc, mac);
		}
		packetNumber++;

		return new Packet(wrappedResponse, toString());
	}

	/**
	 * Encrypts a request with triple DES.
	 * 
	 * @param request
	 *            that is encrypted.
	 * @return encrypted request.
	 */
	private byte[] encryptBytes(byte[] bytes) {
		byte[] responseEncrypted = new byte[bytes.length];
		for (int i = 0; i < bytes.length; i += 8) {
			cbcEncryption.transformBlock(bytes, i, responseEncrypted, i);
		}
		return responseEncrypted;
	}

	/**
	 * Decrypts a request with triple DES.
	 * 
	 * @param request
	 *            that is decrypted.
	 * @return decrypted request.
	 */
	private byte[] decryptBytes(byte[] request) {
		byte[] decryptedRequest = new byte[request.length
				- ((request.length % 8 == 0) ? 0 : 20)];
		for (int i = 0; i < decryptedRequest.length; i += 8) {
			cbcDecryption.transformBlock(request, i, decryptedRequest, i);
		}
		return decryptedRequest;
	}

	/**
	 * Creates the SHA1 Mac with the given bytes.
	 * 
	 * @param bytes
	 *            that are used for the Mac.
	 * @return Mac.
	 */
	private byte[] createMac(byte[] bytes) {
		byte[] mac = new byte[20];
		macEncryption.initMac(packetNumber);
		macEncryption.update(bytes, 0, bytes.length);
		macEncryption.getMac(mac, 0);
		return mac;
	}

	/**
	 * Builds the Kex Init packet that contains all the allowed algorithms by
	 * the server.
	 * 
	 * @return Kex Init packet.
	 */
	private Packet kexInit() {
		TypesWriter tw = new TypesWriter();
		tw.writeByte(0x14);
		// cookie
		tw.writeBytes(HelperUtils.randomBytes(16));
		tw.writeString(KEX_ALG);
		tw.writeString(SERVER_ALG);
		tw.writeString(ENCRYPT_ALG_C);
		tw.writeString(ENCRYPT_ALG_S);
		tw.writeString(MAC_ALG_C);
		tw.writeString(MAC_ALG_S);
		tw.writeString(COMP_ALG_C);
		tw.writeString(COMP_ALG_S);
		// language client to server
		tw.writeBytes(new byte[] { 0x00, 0x00, 0x00, 0x00 });
		// language server to client
		tw.writeBytes(new byte[] { 0x00, 0x00, 0x00, 0x00 });
		// no guess from server
		tw.writeByte(0x00);
		// reserved
		tw.writeBytes(new byte[] { 0x00, 0x00, 0x00, 0x00 });
		byte[] response = tw.getBytes();
		I_S = response;

		return wrapPacket(response);
	}

	/**
	 * Builds the Diffie-Hellman Kex Reply, containing the host key,f and the
	 * signature.
	 * 
	 * @return Diffie-Hellman Kex Reply packet.
	 */
	private Packet dhKexReply() {
		byte[] response = null;
		try {
			DhExchange dhx = new DhExchange();
			dhx.serverInit(1, random);
			dhx.setE(new BigInteger(e));
			f = dhx.getF();
			DSAPrivateKey dsa = (DSAPrivateKey) PEMDecoder.decode(dsaPem, null);
			K_S = DSASHA1Verify.encodeSSHDSAPublicKey(dsa.getPublicKey());
			h = dhx.calculateH(V_C, V_S, I_C, I_S, K_S);
			k = dhx.getK();
			DSASignature ds = DSASHA1Verify.generateSignature(h, dsa, random);
			signature = DSASHA1Verify.encodeSSHDSASignature(ds);
			TypesWriter tw = new TypesWriter();
			tw.writeByte(31);
			tw.writeString(K_S, 0, K_S.length);
			tw.writeMPInt(f);
			tw.writeString(signature, 0, signature.length);
			response = tw.getBytes();

			// init for decryption and encryption
			// KeyMaterial: alg, h, k, keylength, blocklength, maclength,
			// keylength, blocklength, maclength
			KeyMaterial km = KeyMaterial.create("SHA1", h, k, h, 24, 8, 20, 24,
					8, 20);
			desEncryption = new DESede();
			desDecryption = new DESede();
			desEncryption.init(true, km.enc_key_server_to_client);
			desDecryption.init(false, km.enc_key_client_to_server);
			cbcEncryption = new CBCMode(desEncryption,
					km.initial_iv_server_to_client, true);
			cbcDecryption = new CBCMode(desDecryption,
					km.initial_iv_client_to_server, false);
			macEncryption = new MAC("hmac-sha1",
					km.integrity_key_server_to_client);
		} catch (Exception e) {
			e.printStackTrace();
		}

		return wrapPacket(response);
	}

	/**
	 * New Keys response.
	 * 
	 * @return New Keys response.
	 */
	private Packet newKeys() {
		byte[] msgCode = { 0x15 };
		return wrapPacket(msgCode);
	}

	/**
	 * Service ssh-userauth reply.
	 * 
	 * @param request
	 *            from the client.
	 * @return Service reply.
	 */
	private Packet serviceReply(byte[] request) {
		byte[] message;
		// if newkeys request is included in the same packet remove it
		if (request[5] == 0x15) {
			message = new byte[request.length - 16];
			System.arraycopy(request, 16, message, 0, request.length - 16);
		} else {
			message = request;
		}
		if (message[5] != 0x05
				&& !(HelperUtils.byteToStr(message).contains("ssh-userauth"))) {
			// disconnect because its not servicerequest ssh-userauth
			return disconnectReply(7);
		}
		TypesWriter tw = new TypesWriter();
		tw.writeByte(0x06);
		tw.writeString("ssh-userauth");
		return wrapPacket(tw.getBytes());
	}

	/**
	 * Userauth ssh-connection reply.
	 * 
	 * @param request
	 *            from the client.
	 * @return ssh-connection reply.
	 */
	private Packet connectionReply(byte[] request) {
		if (request[5] != 0x32
				&& !(HelperUtils.byteToStr(request).contains("ssh-connection"))) {
			// disconnect because its not servicerequest ssh-connect
			return disconnectReply(14);
		}
		try {
			TypesReader tr = new TypesReader(request, 6);
			userName = tr.readString();
			terminalPrefix = "[" + userName + "@" + serverName + " ~]$ ";
		} catch (IOException e) {
			e.printStackTrace();
		}
		byte[] msgcode = { 0x34 };
		return wrapPacket(msgcode);
	}

	/**
	 * Channel Open Reply.
	 * 
	 * @param request
	 *            from client.
	 * @return Channel Open Reply.
	 */
	private Packet channelOpenReply(byte[] request) {
		if (!(HelperUtils.byteToStr(request).contains("session"))) {
			// if contains "session" ok else disc
			return disconnectReply(2);
		}
		TypesReader tr = new TypesReader(request, 6);
		TypesWriter tw = new TypesWriter();
		try {
			tr.readString();
			recipientChannel = tr.readUINT32();
			int senderChannel = recipientChannel;
			int initialWindowSize = tr.readUINT32();
			int maximumPacketSize = tr.readUINT32();

			// msgcode
			tw.writeByte(0x5b);
			tw.writeUINT32(recipientChannel);
			tw.writeUINT32(senderChannel);
			tw.writeUINT32(initialWindowSize);
			tw.writeUINT32(maximumPacketSize);
		} catch (IOException e) {
			e.printStackTrace();
		}

		return wrapPacket(tw.getBytes());
	}

	/**
	 * Channel Success Reply.
	 * 
	 * @param request
	 *            from client.
	 * @return Channel Success Reply.
	 */
	private Packet channelSuccessReply(byte[] request) {
		if (!(HelperUtils.byteToStr(request)).contains("pty-req")) {
			return disconnectReply(2);
		}
		TypesWriter tw = new TypesWriter();
		// msgcode
		tw.writeByte(0x63);
		tw.writeUINT32(recipientChannel);

		return wrapPacket(tw.getBytes());
	}

	/**
	 * Returns the terminal prefix for the client.
	 * 
	 * @return terminal prefix.
	 */
	private Packet terminalPrefix() {
		TypesWriter tw = new TypesWriter();
		tw.writeByte(0x5e);
		tw.writeUINT32(recipientChannel);
		tw.writeString(terminalPrefix);

		return wrapPacket(tw.getBytes());
	}

	/**
	 * Computes the reply for the client input.
	 * 
	 * @param request
	 *            client input.
	 * @return input reply.
	 */
	private Packet terminalReply(byte[] request) {
		TypesReader tr = new TypesReader(request, 6);
		String message = "";
		try {
			tr.readUINT32();
			message = tr.readString();
			if (message.contains("\r")) {
				if (command.toString().contains("exit")) {
					state = STATE.CLOSED;
					return disconnectReply(2);
				}
				message = "\r\nbash: " + command + " :command not found\r\n"
						+ terminalPrefix;
				command = new StringBuffer();
			} else if (message.contains(new String(new char[] { '\u007F' }))
					&& command.length() > 0) {
				command = command
						.delete(command.length() - 1, command.length());
			} else {
				command.append(message);
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
		TypesWriter tw = new TypesWriter();
		// msgcode
		tw.writeByte(0x5e);
		tw.writeUINT32(recipientChannel);
		tw.writeString(message);
		return wrapPacket(tw.getBytes());
	}

	/**
	 * Disconnect Reply using the given number as reason code.
	 * 
	 * @param reasonCode
	 *            for disconnect reply. Must be between 1 and 15, default is 2.
	 * @return Disconnect Reply.
	 */
	private Packet disconnectReply(int reasonCode) {
		TypesWriter tw = new TypesWriter();
		tw.writeByte(0x01);
		switch (reasonCode) {
		case 1:
			tw.writeUINT32(1);
			tw.writeString("SSH_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT");
			break;
		case 7:
			tw.writeUINT32(7);
			tw.writeString("SSH_DISCONNECT_SERVICE_NOT_AVAILABLE");
			break;
		case 14:
			tw.writeUINT32(14);
			tw.writeString("SSH_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE");
			break;
		default:
			tw.writeUINT32(2);
			tw.writeString("SSH_DISCONNECT_PROTOCOL_ERROR");
			break;
		}
		return wrapPacket(tw.getBytes());
	}

	/**
	 * Extracts the type of the client
	 * 
	 * @param request
	 *            containing the clients type
	 */
	private void extractType(byte[] request) {
		int length = 0;
		for (int i = 0; i < request.length; i++, length++) {
			// find the end of the type: '\r'
			if (request[i] == 0x0d)
				break;
		}
		V_C = new byte[length];
		System.arraycopy(request, 0, V_C, 0, length);
	}

	/**
	 * Extracts the payload of a packet and writes it in I_C.
	 * 
	 * @param request
	 *            packet of which the payload is extracted.
	 */
	private void extractPayload(byte[] request) {
		int position = 0;
		if (request[5] != 0x14) {
			position = 1;
			for (int i = 0; i < request.length; i++, position++) {
				if (request[i] == 0x0a)
					break;
			}
		}
		int packetLength = byteToInt(new byte[] { request[position],
				request[1 + position], request[2 + position],
				request[3 + position] });
		int paddingLength = byteToInt(new byte[] { request[4 + position] });
		byte[] payload = new byte[packetLength - paddingLength - 1];
		for (int i = 5; i < packetLength - paddingLength - 1; i++) {
			payload[i - 5] = request[i + position];
		}
		I_C = payload;
	}

	/**
	 * Extracts the public key from the DH Kex Request
	 * 
	 * @param request
	 *            containing the clients public key
	 */
	private void extractPubKey(byte[] request) {
		e = new byte[byteToInt(new byte[] { request[6], request[7], request[8],
				request[9] })];
		for (int i = 0; i < e.length; i++) {
			e[i] = request[i + 10];
		}
	}

	/**
	 * Converts a byte[] to int
	 * 
	 * @param bytes
	 *            that are converted
	 * @return converted byte[] as int
	 */
	private static int byteToInt(byte[] bytes) {
		int convertedInteger = 0;
		for (int i = 0; i < bytes.length; i++) {
			convertedInteger <<= 8;
			convertedInteger |= bytes[i] & 0xFF;
		}
		return convertedInteger;
	}

}