/*
 * Copyright (c) 2006-2013 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */
package ch.ethz.ssh2.crypto.dh;

import java.io.IOException;
import java.math.BigInteger;
import java.security.SecureRandom;

import ch.ethz.ssh2.crypto.digest.HashForSSH2Types;
import ch.ethz.ssh2.log.Logger;
import ch.ethz.ssh2.util.StringEncoder;

/**
 * @author Christian Plattner
 * @version $Id: DhExchange.java 152 2014-04-28 11:02:23Z dkocher@sudo.ch $
 */
public class DhExchange {
    private static final Logger log = Logger.getLogger(DhExchange.class);

	/* Given by the standard */

    static final BigInteger p1, p14;
    static final BigInteger g;

    BigInteger p;

	/* Client public and private */

    BigInteger e;
    BigInteger x;

	/* Server public and private */

    BigInteger f;
    BigInteger y;

	/* Shared secret */

    BigInteger k;

    static {
        final String p1_string = "17976931348623159077083915679378745319786029604875"
                + "60117064444236841971802161585193689478337958649255415021805654859805036464"
                + "40548199239100050792877003355816639229553136239076508735759914822574862575"
                + "00742530207744771258955095793777842444242661733472762929938766870920560605"
                + "0270810842907692932019128194467627007";

        final String p14_string = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129"
                + "024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0"
                + "A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB"
                + "6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A"
                + "163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208"
                + "552BB9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36C"
                + "E3BE39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF69558171"
                + "83995497CEA956AE515D2261898FA051015728E5A8AACAA68FFFFFFFFFFFFFFFF";

        p1 = new BigInteger(p1_string);
        p14 = new BigInteger(p14_string, 16);
        g = new BigInteger("2");
    }

    public DhExchange() {
    }

    public void clientInit(int group, SecureRandom rnd) {
        k = null;

        if(group == 1) {
            p = p1;
        }
        else if(group == 14) {
            p = p14;
        }
        else {
            throw new IllegalArgumentException("Unknown DH group " + group);
        }

        while(true) {
            x = new BigInteger(p.bitLength() - 1, rnd);
            if(x.compareTo(BigInteger.ONE) > 0) {
                break;
            }
        }

        e = g.modPow(x, p);
    }

    public void serverInit(int group, SecureRandom rnd) {
        k = null;

        if(group == 1) {
            p = p1;
        }
        else if(group == 14) {
            p = p14;
        }
        else {
            throw new IllegalArgumentException("Unknown DH group " + group);
        }

        y = new BigInteger(p.bitLength() - 1, rnd);

        f = g.modPow(y, p);
    }

    /**
     * @return Returns the e.
     * @throws IllegalStateException
     */
    public BigInteger getE() {
        if(e == null) {
            throw new IllegalStateException("DhDsaExchange not initialized!");
        }

        return e;
    }

    /**
     * @return Returns the f.
     * @throws IllegalStateException
     */
    public BigInteger getF() {
        if(f == null) {
            throw new IllegalStateException("DhDsaExchange not initialized!");
        }

        return f;
    }

    /**
     * @return Returns the shared secret k.
     * @throws IllegalStateException
     */
    public BigInteger getK() {
        if(k == null) {
            throw new IllegalStateException("Shared secret not yet known, need f first!");
        }

        return k;
    }

    /**
     * @param f
     */
    public void setF(BigInteger f) {
        if(e == null) {
            throw new IllegalStateException("DhDsaExchange not initialized!");
        }

        if(BigInteger.ZERO.compareTo(f) >= 0 || p.compareTo(f) <= 0) {
            throw new IllegalArgumentException("Invalid f specified!");
        }

        this.f = f;
        this.k = f.modPow(x, p);
    }

    /**
     * @param e
     */
    public void setE(BigInteger e) {
        if(f == null) {
            throw new IllegalStateException("DhDsaExchange not initialized!");
        }

        if(BigInteger.ZERO.compareTo(e) >= 0 || p.compareTo(e) <= 0) {
            throw new IllegalArgumentException("Invalid e specified!");
        }

        this.e = e;
        this.k = e.modPow(y, p);
    }

    public byte[] calculateH(byte[] clientversion, byte[] serverversion, byte[] clientKexPayload,
                             byte[] serverKexPayload, byte[] hostKey) throws IOException {
        HashForSSH2Types hash = new HashForSSH2Types("SHA1");

        if(log.isInfoEnabled()) {
            log.info("Client: '" + StringEncoder.GetString(clientversion) + "'");
            log.info("Server: '" + StringEncoder.GetString(serverversion) + "'");
        }

        hash.updateByteString(clientversion);
        hash.updateByteString(serverversion);
        hash.updateByteString(clientKexPayload);
        hash.updateByteString(serverKexPayload);
        hash.updateByteString(hostKey);
        hash.updateBigInt(e);
        hash.updateBigInt(f);
        hash.updateBigInt(k);

        return hash.getDigest();
    }
}