Add attribution for RFC 3492

THIRD-PARTY-NOTICES

@@ -0,0 +1,38 @@
+.NET Core uses third-party libraries or other resources that may be
+distributed under licenses different than the .NET Core software.
+
+In the event that we accidentally failed to list a required notice, please
+bring it to our attention. Post an issue or email us:
+
+           dotnet@microsoft.com
+
+The attached notices are provided for information only.
+
+License notice for RFC 3492
+---------------------------
+
+Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+This document and translations of it may be copied and furnished to
+others, and derivative works that comment on or otherwise explain it
+or assist in its implementation may be prepared, copied, published
+and distributed, in whole or in part, without restriction of any
+kind, provided that the above copyright notice and this paragraph are
+included on all such copies and derivative works.  However, this
+document itself may not be modified in any way, such as by removing
+the copyright notice or references to the Internet Society or other
+Internet organizations, except as needed for the purpose of
+developing Internet standards in which case the procedures for
+copyrights defined in the Internet Standards process must be
+followed, or as required to translate it into languages other than
+English.
+
+The limited permissions granted above are perpetual and will not be
+revoked by the Internet Society or its successors or assigns.
+
+This document and the information contained herein is provided on an
+"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

src/mscorlib/src/System/Globalization/IdnMapping.cs

@@ -24,6 +24,38 @@
 //  RFC 3491 - Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)
 //  RFC 3492 - Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)
 //
+
+/*
+
+The punycode implementation is based on the sample code in RFC 3492
+        
+Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+This document and translations of it may be copied and furnished to
+others, and derivative works that comment on or otherwise explain it
+or assist in its implementation may be prepared, copied, published
+and distributed, in whole or in part, without restriction of any
+kind, provided that the above copyright notice and this paragraph are
+included on all such copies and derivative works.  However, this
+document itself may not be modified in any way, such as by removing
+the copyright notice or references to the Internet Society or other
+Internet organizations, except as needed for the purpose of
+developing Internet standards in which case the procedures for
+copyrights defined in the Internet Standards process must be
+followed, or as required to translate it into languages other than
+English.
+
+The limited permissions granted above are perpetual and will not be
+revoked by the Internet Society or its successors or assigns.
+
+This document and the information contained herein is provided on an
+"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+*/
+
 namespace System.Globalization
 {
     using System;