diff --git a/rfb/SSecurity.h b/rfb/SSecurity.h
new file mode 100644
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+++ b/rfb/SSecurity.h
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+/* 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.
+ */
+//
+// SSecurity - class on the server 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 client until either it returns false, indicating authentication/security
+// failure, or it returns with done set to true, to indicate success.
+//
+// processMsg() must never block (or at least must never block until the client
+// has been authenticated) - this is to prevent denial of service attacks.
+// Note that the first time processMsg() is called, there is no guarantee that
+// there is any data to read from the SConnection's InStream, but subsequent
+// calls guarantee there is at least one byte which can be read without
+// blocking.
+//
+// getType() should return the secType value corresponding to the SSecurity
+// implementation.
+//
+// failureMessage_.buf can be set to a string which will be passed to the client
+// if processMsg returns false, to indicate the reason for the failure.
+
+#ifndef __RFB_SSECURITY_H__
+#define __RFB_SSECURITY_H__
+
+#include <rfb/util.h>
+
+namespace rfb {
+
+  class SConnection;
+
+  class SSecurity {
+  public:
+    virtual ~SSecurity() {}
+    virtual bool processMsg(SConnection* sc, bool* done)=0;
+    virtual void destroy() { delete this; }
+    virtual int getType() const = 0;
+
+    // getUserName() gets the name of the user attempting authentication.  The
+    // storage is owned by the SSecurity object, so a copy must be taken if
+    // necessary.  Null may be returned to indicate that there is no user name
+    // for this security type.
+    virtual const char* getUserName() const = 0;
+
+    virtual const char* failureMessage() {return failureMessage_.buf;}
+  protected:
+    CharArray failureMessage_;
+  };
+
+  // SSecurityFactory creates new SSecurity instances for
+  // particular security types.
+  // The instances must be destroyed by calling destroy()
+  // on them when done.
+  class SSecurityFactory {
+  public:
+    virtual ~SSecurityFactory() {}
+    virtual SSecurity* getSSecurity(int secType, bool noAuth=false)=0;
+  };
+
+}
+#endif