--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/com/trilead/ssh2/crypto/dh/DhGroupExchange.java	Thu May 22 10:41:19 2014 -0700
@@ -0,0 +1,107 @@
+
+package com.trilead.ssh2.crypto.dh;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import com.trilead.ssh2.DHGexParameters;
+import com.trilead.ssh2.crypto.digest.HashForSSH2Types;
+
+
+/**
+ * DhGroupExchange.
+ *
+ * @author Christian Plattner, plattner@trilead.com
+ * @version $Id: DhGroupExchange.java,v 1.1 2007/10/15 12:49:57 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(String hashAlgo, byte[] clientversion, byte[] serverversion,
+                             byte[] clientKexPayload, byte[] serverKexPayload, byte[] hostKey, DHGexParameters para) {
+        HashForSSH2Types hash = new HashForSSH2Types(hashAlgo);
+        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();
+    }
+}