--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ch/ethz/ssh2/crypto/dh/DhGroupExchange.java	Fri Jul 18 11:21:46 2014 -0700
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2006-2011 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.DHGexParameters;
+import ch.ethz.ssh2.crypto.digest.HashForSSH2Types;
+
+/**
+ * DhGroupExchange.
+ *
+ * @author Christian Plattner
+ * @version 2.50, 03/15/10
+ */
+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) throws IOException {
+        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();
+    }
+}