package ch.ethz.ssh2.crypto.dh;
import java.math.BigInteger;
import java.security.SecureRandom;
import ch.ethz.ssh2.DHGexParameters;
import ch.ethz.ssh2.crypto.digest.HashForSSH2Types;
/**
* DhGroupExchange.
*
* @author Christian Plattner, plattner@inf.ethz.ch
* @version $Id: DhGroupExchange.java,v 1.6 2006/09/20 12:51:37 cplattne Exp $
*/
public class DhGroupExchange
{
/* Given by the standard */
private BigInteger p;
private BigInteger g;
/* Client public and private */
private BigInteger e;
private BigInteger x;
/* Server public */
private BigInteger f;
/* Shared secret */
private BigInteger k;
public DhGroupExchange(BigInteger p, BigInteger g)
{
this.p = p;
this.g = g;
}
public void init(SecureRandom rnd)
{
k = null;
x = new BigInteger(p.bitLength() - 1, rnd);
e = g.modPow(x, p);
}
/**
* @return Returns the e.
*/
public BigInteger getE()
{
if (e == null)
throw new IllegalStateException("Not initialized!");
return e;
}
/**
* @return Returns the shared secret k.
*/
public BigInteger getK()
{
if (k == null)
throw new IllegalStateException("Shared secret not yet known, need f first!");
return k;
}
/**
* Sets f and calculates the shared secret.
*/
public void setF(BigInteger f)
{
if (e == null)
throw new IllegalStateException("Not initialized!");
BigInteger zero = BigInteger.valueOf(0);
if (zero.compareTo(f) >= 0 || p.compareTo(f) <= 0)
throw new IllegalArgumentException("Invalid f specified!");
this.f = f;
this.k = f.modPow(x, p);
}
public byte[] calculateH(byte[] clientversion, byte[] serverversion, byte[] clientKexPayload,
byte[] serverKexPayload, byte[] hostKey, DHGexParameters para)
{
HashForSSH2Types hash = new HashForSSH2Types("SHA1");
hash.updateByteString(clientversion);
hash.updateByteString(serverversion);
hash.updateByteString(clientKexPayload);
hash.updateByteString(serverKexPayload);
hash.updateByteString(hostKey);
if (para.getMin_group_len() > 0)
hash.updateUINT32(para.getMin_group_len());
hash.updateUINT32(para.getPref_group_len());
if (para.getMax_group_len() > 0)
hash.updateUINT32(para.getMax_group_len());
hash.updateBigInt(p);
hash.updateBigInt(g);
hash.updateBigInt(e);
hash.updateBigInt(f);
hash.updateBigInt(k);
return hash.getDigest();
}
}