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diff --git a/hdcp/diff_network.v b/hdcp/diff_network.v
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+//////////////////////////////////////////////////////////////////////////////
+// Copyright (c) 2011, Andrew "bunnie" Huang
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, 
+// are permitted provided that the following conditions are met:
+//
+//  * Redistributions of source code must retain the above copyright notice, 
+//    this list of conditions and the following disclaimer.
+//  * Redistributions in binary form must reproduce the above copyright notice, 
+//    this list of conditions and the following disclaimer in the documentation and/or 
+//    other materials provided with the distribution.
+//
+//    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
+//    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 
+//    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
+//    SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
+//    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
+//    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
+//    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
+//    WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+//    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
+//    POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////////
+
+module diff_network (
+		     input wire [6:0]   i,
+		     output wire [6:0]  o,
+		     input wire [6:0]   k
+		     );
+
+   assign o[0] = k[0] ^      ^ i[1] ^ i[2] ^ i[3] ^ i[4] ^ i[5] ^ i[6];
+   assign o[1] = k[1] ^ i[0] ^      ^ i[2] ^ i[3] ^ i[4] ^ i[5] ^ i[6];
+   assign o[2] = k[2] ^ i[0] ^ i[1] ^      ^ i[3] ^ i[4] ^ i[5] ^ i[6];
+   assign o[3] = k[3] ^ i[0] ^ i[1] ^ i[2] ^      ^ i[4] ^ i[5] ^ i[6];
+   assign o[4] = k[4] ^ i[0] ^ i[1] ^ i[2] ^ i[3] ^      ^ i[5] ^ i[6];
+   assign o[5] = k[5] ^ i[0] ^ i[1] ^ i[2] ^ i[3] ^ i[4] ^      ^ i[6];
+   assign o[6] = k[6] ^ i[0] ^ i[1] ^ i[2] ^ i[3] ^ i[4] ^ i[5] ^ i[6];
+   
+endmodule // diff_network