diff --git a/rfb/SSecurityVncAuth.cxx b/rfb/SSecurityVncAuth.cxx
new file mode 100644
index 0000000..532d1a6
--- /dev/null
+++ b/rfb/SSecurityVncAuth.cxx
@@ -0,0 +1,83 @@
+/* Copyright (C) 2002-2003 RealVNC Ltd.  All Rights Reserved.
+ *    
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+//
+// SSecurityVncAuth
+//
+
+#include <rfb/SSecurityVncAuth.h>
+#include <rdr/RandomStream.h>
+#include <rfb/SConnection.h>
+#include <rfb/vncAuth.h>
+#include <rfb/Configuration.h>
+#include <rfb/LogWriter.h>
+#include <rfb/util.h>
+#include <string.h>
+#include <stdio.h>
+
+using namespace rfb;
+
+static LogWriter vlog("VncAuth");
+
+
+SSecurityVncAuth::SSecurityVncAuth(VncAuthPasswdGetter* pg_)
+  : sentChallenge(false), responsePos(0), pg(pg_)
+{
+}
+
+bool SSecurityVncAuth::processMsg(SConnection* sc, bool* done)
+{
+  *done = false;
+  rdr::InStream* is = sc->getInStream();
+  rdr::OutStream* os = sc->getOutStream();
+
+  if (!sentChallenge) {
+    rdr::RandomStream rs;
+    rs.readBytes(challenge, vncAuthChallengeSize);
+    os->writeBytes(challenge, vncAuthChallengeSize);
+    os->flush();
+    sentChallenge = true;
+    return true;
+  }
+
+  if (responsePos >= vncAuthChallengeSize) return false;
+  while (is->checkNoWait(1) && responsePos < vncAuthChallengeSize) {
+    response[responsePos++] = is->readU8();
+  }
+
+  if (responsePos < vncAuthChallengeSize) return true;
+
+  CharArray passwd(pg->getVncAuthPasswd());
+
+  // Beyond this point, there is no more VNCAuth protocol to perform.
+  *done = true;
+
+  if (!passwd.buf) {
+    failureMessage_.buf = strDup("No password configured for VNC Auth");
+    vlog.error(failureMessage_.buf);
+    return false;
+  }
+
+  vncAuthEncryptChallenge(challenge, passwd.buf);
+  memset(passwd.buf, 0, strlen(passwd.buf));
+
+  if (memcmp(challenge, response, vncAuthChallengeSize) != 0) {
+    return false;
+  }
+
+  return true;
+}