diff --git a/common/rfb/CSecurity.h b/common/rfb/CSecurity.h
new file mode 100644
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--- /dev/null
+++ b/common/rfb/CSecurity.h
@@ -0,0 +1,52 @@
+/* Copyright (C) 2002-2005 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.
+ */
+//
+// CSecurity - class on the client side for handling security handshaking.  A
+// derived class for a particular security type overrides the processMsg()
+// method.
+
+// processMsg() is called first when the security type has been decided on, and
+// will keep being called whenever there is data to read from the server.  It
+// should return false when it needs more data, or true when the security
+// handshaking is over and we are now waiting for the SecurityResult message
+// from the server.  In the event of failure a suitable exception should be
+// thrown.
+//
+// Note that the first time processMsg() is called, there is no guarantee that
+// there is any data to read from the CConnection's InStream, but subsequent
+// calls guarantee there is at least one byte which can be read without
+// blocking.
+//
+// description is a string describing the level of encryption applied to the
+// session, or null if no encryption will be used.
+
+#ifndef __RFB_CSECURITY_H__
+#define __RFB_CSECURITY_H__
+
+namespace rfb {
+  class CConnection;
+  class CSecurity {
+  public:
+    virtual ~CSecurity() {}
+    virtual bool processMsg(CConnection* cc)=0;
+    virtual void destroy() { delete this; }
+    virtual int getType() const = 0;
+    virtual const char* description() const = 0;
+  };
+}
+#endif