package de.tudarmstadt.informatik.hostage.protocol;

import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.PublicKey;
import java.security.Signature;
import java.security.interfaces.DSAPublicKey;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import javax.crypto.KeyAgreement;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHPublicKeySpec;
import de.tudarmstadt.informatik.hostage.commons.HelperUtils;
import de.tudarmstadt.informatik.hostage.wrapper.ByteArray;

/**
 * SSH protocol.
 * @author Wulf Pfeiffer
 */
public final class SSH implements Protocol<ByteArray> {
	/**
	 * Represents the states of the protocol.
	 */
	private enum STATE {
		NONE,
		SERVER_VERSION,
		CLIENT_VERSION,
		KEX_INIT,
		CLOSED
	}
	
	/**
	 * Denotes in which state the protocol is right now.
	 */
	private STATE connectionState = STATE.NONE;
	
	private String serverVersion = "SSH-2.0-";
	private String serverType = "OpenSSH_6.0p1 Debian-4";
		
	//Diffie-Hellman-Group-1 p and g
	private final byte[] p = {
            (byte)0x00,
            (byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,
            (byte)0xC9,(byte)0x0F,(byte)0xDA,(byte)0xA2,(byte)0x21,(byte)0x68,(byte)0xC2,(byte)0x34,
            (byte)0xC4,(byte)0xC6,(byte)0x62,(byte)0x8B,(byte)0x80,(byte)0xDC,(byte)0x1C,(byte)0xD1,
            (byte)0x29,(byte)0x02,(byte)0x4E,(byte)0x08,(byte)0x8A,(byte)0x67,(byte)0xCC,(byte)0x74,
            (byte)0x02,(byte)0x0B,(byte)0xBE,(byte)0xA6,(byte)0x3B,(byte)0x13,(byte)0x9B,(byte)0x22,
            (byte)0x51,(byte)0x4A,(byte)0x08,(byte)0x79,(byte)0x8E,(byte)0x34,(byte)0x04,(byte)0xDD,
            (byte)0xEF,(byte)0x95,(byte)0x19,(byte)0xB3,(byte)0xCD,(byte)0x3A,(byte)0x43,(byte)0x1B,
            (byte)0x30,(byte)0x2B,(byte)0x0A,(byte)0x6D,(byte)0xF2,(byte)0x5F,(byte)0x14,(byte)0x37,
            (byte)0x4F,(byte)0xE1,(byte)0x35,(byte)0x6D,(byte)0x6D,(byte)0x51,(byte)0xC2,(byte)0x45,
            (byte)0xE4,(byte)0x85,(byte)0xB5,(byte)0x76,(byte)0x62,(byte)0x5E,(byte)0x7E,(byte)0xC6,
            (byte)0xF4,(byte)0x4C,(byte)0x42,(byte)0xE9,(byte)0xA6,(byte)0x37,(byte)0xED,(byte)0x6B,
            (byte)0x0B,(byte)0xFF,(byte)0x5C,(byte)0xB6,(byte)0xF4,(byte)0x06,(byte)0xB7,(byte)0xED,
            (byte)0xEE,(byte)0x38,(byte)0x6B,(byte)0xFB,(byte)0x5A,(byte)0x89,(byte)0x9F,(byte)0xA5,
            (byte)0xAE,(byte)0x9F,(byte)0x24,(byte)0x11,(byte)0x7C,(byte)0x4B,(byte)0x1F,(byte)0xE6,
            (byte)0x49,(byte)0x28,(byte)0x66,(byte)0x51,(byte)0xEC,(byte)0xE6,(byte)0x53,(byte)0x81,
            (byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF
      };
	private final byte[] g = {0x02};
	
	//SSH Parameters for Kex etc.
    private byte[] V_S = serverType.getBytes();
    private byte[] V_C;
    private byte[] I_S;
    private byte[] I_C;
    private byte[] e;
    private byte[] f;
    private byte[] k;
    private byte[] h;
    private byte[] K_S;
    private byte[] sig;

    //Keys for signature
    private KeyPair dsa;
			
    //allowed algorithms for kexinit
	private String kex_alg = "diffie-hellman-group1-sha1";
	private String server_alg = "ssh-dss";
	private String encrypt_alg_c = "aes128-ctr";
	private String encrypt_alg_s = "aes128-ctr";
	private String mac_alg_c = "hmac-sha1";
	private String mac_alg_s = "hmac-sha1";
	private String comp_alg_c = "none";
	private String comp_alg_s = "none";
	
	private int cipherBlockSize = 16;
	
	/** Denotes in which state the protocol is right now */
	private STATE state = STATE.NONE;
	
	private byte[] lastMessage;

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

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

	@Override
	public List<ByteArray> processMessage(ByteArray message) {
		if(message != null)
			lastMessage = message.get();
		List<ByteArray> response = new ArrayList<ByteArray>();
		byte[] request = null;
		if(message != null) request = message.get();
		
		switch(connectionState) {
		case NONE:			
			response.add(new ByteArray(serverVersion + serverType + "\r\n"));
			connectionState = STATE.SERVER_VERSION;
			break;
		case SERVER_VERSION:
			extractType(request);
			extractCookie(request);
			response.add(new ByteArray(kexInit()));
			connectionState = STATE.CLIENT_VERSION;
			break;
		case CLIENT_VERSION:
			extractPubKey(request);
			response.add(new ByteArray(dhKexReply()));
			//FIXME signature in dhKexReply is wrong, don't know why
			response.add(new ByteArray(newKeys()));
			connectionState = STATE.KEX_INIT;
			break;
		case KEX_INIT:
			connectionState = STATE.CLOSED;
			break;
		case CLOSED:
			break;
		default:
			connectionState = STATE.CLOSED;
			break;
		}
		
		return response;
	}

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

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

	@Override
	public Class<ByteArray> getType() {
		return ByteArray.class;
	}

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

	/**
	 * Wraps the packets with packet length and padding.
	 * @param packet content that is wrapped.
	 * @return wrapped packet.
	 */
	private byte[] wrapPacket(byte[] packet) {
		int packetLength = 5 + packet.length; 	//4 byte packet length, 1 byte padding length, payload length
		int paddingLengthCBS = cipherBlockSize - (packetLength % cipherBlockSize);
		int paddingLength8 = 8 - (packetLength % 8);
		int paddingLength = paddingLengthCBS > paddingLength8 ? paddingLengthCBS : paddingLength8;
		if(paddingLength < 4) paddingLength += cipherBlockSize;
		packetLength = packetLength + paddingLength - 4;					//add padding string length to packet length
		
		byte[] packetLen = ByteBuffer.allocate(4).putInt(packetLength).array();
		byte[] paddingLen = {(byte) paddingLength};
		byte[] paddingString = new byte[paddingLength];
		for(int i = 0; i < paddingLength; i++) {
			paddingString[i] = 0x00;
		}
		return HelperUtils.concat(packetLen, paddingLen, packet, paddingString);
	}
	
	/**
	 * Builds the Kex Init packet that contains all the allowed algorithms by the server.
	 * @return Kex Init packet.
	 */
	private byte[] kexInit() {
		byte[] msgCode = {0x14};
		I_S = randomBytes(16);
		byte[] kexLength = ByteBuffer.allocate(4).putInt(kex_alg.getBytes().length).array();
		byte[] serverLength = ByteBuffer.allocate(4).putInt(server_alg.getBytes().length).array();
		byte[] encrypt_c_Length = ByteBuffer.allocate(4).putInt(encrypt_alg_c.getBytes().length).array();
		byte[] encrypt_s_Length = ByteBuffer.allocate(4).putInt(encrypt_alg_s.getBytes().length).array();
		byte[] mac_c_Length = ByteBuffer.allocate(4).putInt(mac_alg_c.getBytes().length).array();
		byte[] mac_s_Length = ByteBuffer.allocate(4).putInt(mac_alg_s.getBytes().length).array();
		byte[] comp_c_Length = ByteBuffer.allocate(4).putInt(comp_alg_c.getBytes().length).array();
		byte[] comp_s_Length = ByteBuffer.allocate(4).putInt(comp_alg_s.getBytes().length).array();
		byte[] language_c_s = {0x00, 0x00, 0x00, 0x00};
		byte[] language_s_c = {0x00, 0x00, 0x00, 0x00};
		byte[] kexFirsPckt = {0x00};
		byte[] reserved = {0x00, 0x00, 0x00, 0x00};	
		
		byte[] response = HelperUtils.concat(msgCode, I_S, kexLength, kex_alg.getBytes(), serverLength, server_alg.getBytes(),
							encrypt_c_Length, encrypt_alg_c.getBytes(), encrypt_s_Length, encrypt_alg_s.getBytes(), mac_c_Length, mac_alg_c.getBytes(),
							mac_s_Length, mac_alg_s.getBytes(), comp_c_Length, comp_alg_c.getBytes(), comp_s_Length, comp_alg_s.getBytes(),
							language_c_s, language_s_c, kexFirsPckt, reserved);
		return wrapPacket(response);
	}
	
	/**
	 * Builds the Diffie-Hellman Kex Reply, containing the host key,f and the signature.
	 * @return Diffie-Hellman Kex Reply packet.
	 */
	private byte[] dhKexReply() {
		generateDHKeys();
		generateHostKey();
		generateSha1Hash();
		generateSignature();
		byte[] msgCode = {0x1f};
		byte[] hostKeyLength = ByteBuffer.allocate(4).putInt(K_S.length).array();
				byte[] fDHLength = ByteBuffer.allocate(4).putInt(f.length).array();
		byte[] signatureLength = ByteBuffer.allocate(4).putInt(sig.length).array();
		byte[] server_algLength = ByteBuffer.allocate(4).putInt(server_alg.getBytes().length).array();
		byte[] payloadLength = ByteBuffer.allocate(4).putInt(server_algLength.length + signatureLength.length + sig.length + server_alg.getBytes().length).array();
		byte[] response = HelperUtils.concat(msgCode, hostKeyLength,  K_S,
									fDHLength, f, payloadLength, server_algLength, server_alg.getBytes(), signatureLength, sig);
		return wrapPacket(response);
	}
	
	/**
	 * New Keys response.
	 * @return New Keys response.
	 */
	private byte[] newKeys() {
		byte[] msgCode = {0x15};
		return wrapPacket(msgCode);
	}
	
	/**
	 * Generates the required Diffie-Hellman keys with p and g from Oakley Group 1.
	 */
	private void generateDHKeys() {	
		try {
			KeyPairGenerator myKpairGen = KeyPairGenerator.getInstance("DH");
			KeyAgreement myKeyAgree = KeyAgreement.getInstance("DH");
			BigInteger p = new BigInteger(this.p);
			BigInteger g = new BigInteger(this.g);
			BigInteger e = new BigInteger(this.e);
			
            DHParameterSpec dhParamSpec = new DHParameterSpec(p, g);
            myKpairGen.initialize(dhParamSpec);
            KeyPair myKpair = myKpairGen.generateKeyPair();
            myKeyAgree.init(myKpair.getPrivate());
            BigInteger f = ((DHPublicKey) (myKpair.getPublic())).getY();
            this.f = f.toByteArray();
            
            KeyFactory myKeyFac = KeyFactory.getInstance("DH");
            DHPublicKeySpec keySpec = new DHPublicKeySpec(e, p, g);
            PublicKey yourPubKey = myKeyFac.generatePublic(keySpec);
            myKeyAgree.doPhase(yourPubKey, true);
            byte[] mySharedSecret = myKeyAgree.generateSecret();
            k = mySharedSecret;
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * Generates the Host Key based on the DSA algorithm
	 */
	private void generateHostKey() {
        try {
            KeyPairGenerator generator = KeyPairGenerator.getInstance("DSA");
            dsa = generator.generateKeyPair();
            
            byte[] string = "ssh-dss".getBytes();
            byte[] stringLength = ByteBuffer.allocate(4).putInt(string.length).array();
            
            byte[] p = ((DSAPublicKey) dsa.getPublic()).getParams().getP().toByteArray();
            if(p[0] != 0x00) p = HelperUtils.concat(new byte[]{0x00}, p);
            byte[] pLength = ByteBuffer.allocate(4).putInt(p.length).array();
            
            byte[] q = ((DSAPublicKey) dsa.getPublic()).getParams().getQ().toByteArray();
            if(q[0] != 0x00) q = HelperUtils.concat(new byte[]{0x00}, q);
            byte[] qLength = ByteBuffer.allocate(4).putInt(q.length).array();
            
            byte[] g = ((DSAPublicKey) dsa.getPublic()).getParams().getG().toByteArray();
            if(g[0] != 0x00) g = HelperUtils.concat(new byte[]{0x00}, g);
            byte[] gLength = ByteBuffer.allocate(4).putInt(g.length).array();
            
            byte[] y = ((DSAPublicKey) dsa.getPublic()).getY().toByteArray();
            if(y[0] != 0x00) y = HelperUtils.concat(new byte[]{0x00}, y);
            byte[] yLength = ByteBuffer.allocate(4).putInt(y.length).array();
            
            K_S = HelperUtils.concat(stringLength, string, pLength, p, qLength, q, gLength, g, yLength, y);       		
        } catch (Exception e) {
        	e.printStackTrace();
        }
	}
	
	/**
	 * Generates the SHA-1 Hash from several values
	 */
	private void generateSha1Hash() {
		try {
			MessageDigest sha = MessageDigest.getInstance("SHA-1");
			sha.update(V_C);
			sha.update(V_S);
			sha.update(I_C);
			sha.update(I_S);
			sha.update(K_S);
			sha.update(e);
			sha.update(f);
			sha.update(k);
			h = sha.digest();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * Generates the signature of the hash using DSA algorithm with SHA-1
	 */
	private void generateSignature() {	
		//FIXME something is wrong with this signature.. maybe one of the used components is generated wrong?! 
		try {
			Signature sig = Signature.getInstance("SHA1withDSA");
            sig.initVerify(dsa.getPublic());
            sig.initSign(dsa.getPrivate());
            sig.update(h);
            this.sig = extractSignature(sig.sign());
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * Extracts the type of the client
	 * @param request containing the clients type
	 */
	private void extractType(byte[] request) {
		int length = 0;
		for(int i = 8; i < request.length; i++, length++) { 	//start at 8 because "SSH-2.0-" is not part of type
			if(request[i] == 0x0d) break;			//find the end of the type: '\r'
		}
		V_C = new byte[length];
		System.arraycopy(request, 8, V_C, 0, length);
	}
	
	/**
	 * Extracts the cookie from the Kex Init client request 
	 * @param request containing the clients cookie
	 */
	private void extractCookie(byte[] request) {
		int pos = 0;
		if(request[5] != 0x14) {	//if type packet is in front of kex init
			pos = 1;				//start behind the end of type message
			for(int i = 0; i < request.length; i++, pos++) {
				if(request[i] == 0x0a) break;		//find end of type message: '\n'
			}
		}
		I_C = new byte[16];
		System.arraycopy(request, 6+pos, I_C, 0, 16); //srcLen: headersize+position after type packet
	}
	
	/**
	 * 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 ret = 0;
		  for (int i=0; i < bytes.length; i++) {
		    ret <<= 8;
		    ret |= bytes[i] & 0xFF;
		  }
		  return ret;
	}
	
	/**
	 * Generates a random byte[] of a specified size
	 * @param size of the byte[]
	 * @return random byte[]
	 */
	private byte[] randomBytes(int size) {
		byte[] bytes = new byte[size];
		Random rdm = new Random();
		rdm.nextBytes(bytes);
		return bytes;		
	}

	/**
	 * Extracts r and s from a DSA-signature
	 * @param signature 
	 * @return r and s as byte[]
	 */
	private byte[] extractSignature(byte[] signature) {
        //{ r INTEGER, s INTEGER }
        int length = 0;
        int index = 3;
        length = signature[index++] & 0xff;
        byte[] r = new byte[length];
        System.arraycopy(signature, index, r, 0, r.length);
        index = index + length + 1;
        length = signature[index++] & 0xff;
        byte[] s = new byte[length];
        System.arraycopy(signature, index, s, 0, s.length);
        byte[] result = new byte[40];
        // result must be 40 bytes, but length of r and s may not be 20 bytes
        System.arraycopy(r,
                         (r.length > 20) ? 1 : 0,
                         result,
                         (r.length > 20) ? 0 : 20 - r.length,
                         (r.length > 20) ? 20 : r.length);
        System.arraycopy(s,
                         (s.length > 20) ? 1 : 0,
                         result,
                         (s.length > 20) ? 20 : 40 - s.length,
                         (s.length > 20) ? 20 : s.length);
        return result;
    }

}