Cryptography expert (C++ and C# Developer)

Technique: C++ C# .NET Framework 4.0 Visual Studio 2012 Task: I need a c++ dll which has an encryption and decryption method. The method should be very complex. I think about a combination of several encryption methods. This dll has to be integrated in a c# software. From this c# software a string (see below) will send to the encryption-method and the return value is a encrypted string. From this c# software a encrypted string will send to the decryption-method and the return value is the decrypted (original) string. Sample for the original string: "<Name>Tom Miller</Name><City>London</City><Country>United Kingdom</Country>"